A Manual on Dental Metallurgy.
Content
UNIVERSITY
of
GLASGOW
James Ireland
Memorial Library
III
I mill
nil Mil llllinilllill"!
m ""I""
301140 08961511
Glasgow University Library
A MAI^UAL
ON
DENTAL METALLURGY
BY
ERNEST
A.
SMITH
ASSOCIATE OP THE ROYAL SCHOOL OP MINES,
LONDON FELLOW OF THE
CHEMICAL SOCIETr AND OP THE SOCIETr OF
CHEMICAL INDUSTRY
LATE ASSISTANT INSTRUCTOR IN METALLURGY,
;
•
'
ROYAL COLLEGE
OF SCIENCE, LONDON
SECOND EDITION
LONDON
&
J.
7
CHURCHILL
A.
GEEAT MARL130K0UGH STREET
1903
J
PREFACE.
The
present manual
syllabus
of
dental
is
based largely upon the new
metallurgy,
1897,
issued
by the
Eoyal College of Surgeons of England, and is
primarily
designed for the nse of students preparing
for. their
examination.
In
the
preparation
of
the
manual
I
have also
endeavoured to place in the hands of dental
students
an outline of the scientific principles involved
in the
extraction of the metals from their ores,
their physical
properties,
and their application
the dentist.
Attention
to the requirements of
has been drawn to the fact
"that metallurgy has not received hitherto
its
due
share of attention at the hands of the
dental student,
and of
its
importance to him there can be no doubt. "
While the properties
of all the metals
*
which have any
application, directly or indirectly, in the
dental labora-
tory have
been dealt with, special consideration has
been given to those most frequently used
by dentists.
*
Howard Mummery,
delivered
at
London, 1897.
Esq., M.K.C.S., L.D.S.
In an Address
the Trize Distribution, National Denial
Hospitnl.
PREFACE.
IV
Full descriptions of metallurgical processes are out
of place in a text-book of dental metallurgy,
be sought in metallurgical text-books.
and must
Only such con-
densed outlines, therefore, have been given as are
methods by which the
sufficient to explain briefly the
metals are obtained in a state suitable for industrial
purposes.
An
elementary knowledge of chemistry and
physics on the part of
my
readers has been taken for
granted.
Although
student a
have endeavoured to present to the
I
condensed
and
succinct
account of the
physical properties of the metals and their chief alloys,
it
a
must be borne
in
mind that the mere reading
of
text-book will never give the student a practical
knowledge
It is only
of these properties.
by handling
the metals and their alloys, and subjecting them to
various mechanical tests, that he can become acquainted
with the
toughness, hardness,
qualities of the metals
observation, for
and know,
I
and other
as a result of his
what purposes each
Acting upon this principle
two
fusibility,
is
own
best suited.
have divided the book into
parts.
Part
I.
properties
dental
contains a brief sketch of the metals, their
and
alloys, their special application in
laboratory,
and other
details
the
required in the
syllabus of the Royal College of Surgeons.
In this
portion of the book special attention has been given to
the preparation and properties of alloys for amalgams,
as this subject
now
occupies a conspicuous place in
V
PREFACE.
denttil practice.
is
extensive,
be done
;
Although the literature on
much
it is
this subject
experimental work yet remains to
hoped, however, that the matter given in
the present work will prepare the student for a fuller
comprehension of the subject.
Part
II.
consists of a series of simple experiments
which can be readily performed, thus enabling the
student to acquire a practical knowledge
perties of the raetals
and their
()f
the pro-
alloys.
I have omitted all chemical equations
and detailed
descriptions of the chemistry of the metallurgical processes
for
extracting
the metals,
confining
myself
merely to a short mention of them in a few general
remarks at the commencement of the various chapters.
The author
cordially
kindly rendered by Mr.
acknowledges the assistance
Oswald E. Smith and Mr.
A. Jarman in executing some of the drawings, and by
Mr. F,
J.
Padgett in reading the proof'-sheets.
His
thanks are also due to Messrs. Claurlius Ash and Co. for
the loan of several blocks.
E. A. S.
RoYAi, College of Sciesce, London.
PREFACE TO SECOND EDITION.
A SECOND edition o£ this volume having become necessary,
the opportunity has been
taken to correct the few-
typographical and other errors of the
to completely revise
The additions
will
first
and
and amplify the work.
be found principally in the chapter
on the physical properties of the metals.
illustrations
edition,
have also been introduced.
Several
new
Great advances
have been made in the study of the structure of metals
and
of alloys during the past five years,
has been
made
to these in the
new
and reference
edition.
In revising the work several valuable suggestions have
been offered by Mr. A. McWilliam, A.R.S.M., especially
with regard to iron and
steel,
and these the author
gratefully acknowledges.
The chapter on iron and
steel has
been rewritten and
brought up to date.
The Author hopes that
this edition
may meet
with
the same cordial reception as that which was accorded
to the first edition.
E. A. S.
Assay
Oi-'Kice,
Sheffield.
1
i
-
CONTENTS.
PAET
I.
INTRODUCTION
CHAPTER
I.
PHYSICAL PROPERTIES OP THE Uy^TALS.
......
.............
LUSTHE AND COLOUR
TASTE
DENSITY
HARDNESS
MALLEABILITY
BRITTLENESS
.
.
.
.
J
9
...........
...........
...........
'
.
.
.
'
.
.
lO
12
13
FLOW UNDER PRESSURE
I4
DUCTILITY
TENACITY
ELASTICITY
75
FUSIBILITY
.
.
.
.
•
,
•
.
.
.
.
EFFECT OF COLD
FRACTURE
CRYSTALLINE CHARACTER
MICRO-STRUCTURE
CONDUCTIVITY OF HEAT AND OF ELECTRICITY
CAPACITY FOR HEAT
EXPANSION BY HEAT
.
CIlANflE OK VOLU.ME
.
.
.
.
.
.
.
,
16
I7
18
19
20
20
....
ON SOLIDIFICATION
24
25
27
28
29
<iALVANIt VCTION
3O
CHAPTER
II.
ACTION OF CERTAIN AGEXTS ON METALS.
33
Hl'LPHURETTED IIVDROOF.N
,-3
X
CONTENTS.
PA.6E
WATER
ACID.S
34
— NITRIC
34
HVDBOCIILORlf
34
suLpnuRic
ACETIC
ALKALIES
EFFECT OF EXPOSURE IN THE .MOUTH
SOLVENTS FOR METALS
34
35
.
•
•
35
35
3^
CHAPTER
III.
ALLOYS.
37
DEFINITION
PIIVSICAL PROPERTirS
41
PREPARATION
ALLOYS FOR DIES AND COUNTER-DIES
FUSIBLE METALS
PREPARATION OP FUSIBLE METALS
DETERMINATION OF MELTING-POINT OF FUSIBLE ALLOY
SOLDERS
PRKPAUATION OF SOLDERS
.
.
.
.
.
.
.
•
•
CHAPTER
•
•
43
44
SO
51
.
52
55-
,
55.
IV.
THEORY AND VARIETIES OF BLOWPIPES.
57
58
THEORY OF BLOWPIPE FLA.ME
MOUTH BLOWPIPES
BELLOWS BLOWPIPES
BLOWING APPARATUS
OXY-HYDROGEN BLOWPIPE
61
63
64
.
CHAPTER
V.
FLUXES.
MELTING APPLIANCES, FURNACES, AND
MELTING APPLIANCES
65
68
CRUCIBLES
FORMS OF FURNACES
69
.
MUFFLE FURNACE
INGOT-MOULDS
ROLLING lNOOT.«
WIRE-DRAWING
75
76
.
•
78
.
CONTENTS.
XI
P.VGR
FLDXES
79'
TIIEORV Of SOLDEKINCi
80
HOFT SOLDEUlNli
83.
CHAPTER VI
GOLD.
occunnENCE
PBEPARATIOX
PARTING HOLD FROM SILVER
PREPARATION OF PURE GOLD
PROPERTIES OF GOLD
'
.
.
85
85
86
87
.
88;
.
USE FOR DENTAL PURPOSES.
EFFECT OF IMPURITIES ON PROPF.RTIKS OP GOLD
BRITTLE GOLD
GOLD FOILS
PRECIPITATED AND SPONGY GOLD
.
...
CRYSTAL GOLD
ASSAY OF GOLD
ASSAY BY' TIJE TQUCHSTONE.
.
.
100
....
CARAT AND FINENESS
GOLD PI,ATE
PREPARATION OF GOLP PLATE
GOLD SOLDERS
PREPARATION OF GOLD SOLDERS
TO ASCERTAIN THE CARAT FINENESS OF A GIVEN LLLOY
TO REDUCE GOLD TO A REQUIRED CARAT
TO RAISE GOLD TO A HIGHER CARAT
COLOURING OF GOLD
.
....
.
...
.
'CILDINO
.
.
I02-
103
loS
106
109
no
113
113
114
"5
116
116
RECOVERY OF GOLD FROM SCRAP
PURIFICATION OF SWEEP OR LEMEL
PURPLK-OF-CASSIUS
91
96-
99'
DETECTION AJfD ESTIMATION OF GOLD, IN ALLOYs'
ALLOYS. OF GOLD
.
90.
90
98
,
.
89:
118
119.
.
121
CHAPTER
VII.
MERCUUY.
OrCURRE.NCE
PKRPARATION
123
.
PROPERTIES
'SB FCP. DENTAL PURPOSES
123
124
12
c;
CONTENTS.
Xll
PAGE
TESTING THE PURITY OF MERCURY
PURIFICATION OP MERCURY
VERMILION AND DETECTION OF IMPURITIES THEREIN
•
.
.
.
•
•
.
.
^^5
126
.128
130
AMALUAMS
.
.
.
•
CHAPTER
VIII.
DENTAL AMALGAMS.
140
•GENERAL CONSIDERATIONS AN O PROPERTIES
•COMPOSITION
146
EFFECT OF DIFFERENT METALS
CHANGE OF VOLUME
METHODS OF TESTING CHANCE OF VOLUME
ALTERATION OF SHAPE
•CHANGE OF COLOUR
.
.
•
.
.
.
•
.
.
•
•
148
149
•
•
154
LEAKAGE
EDGE-STRENGTH
THE MOUTH
POSSIBLE ACTION ON OTHER METALS
PERMANENCE
IN
^54
•
155
.
IN THF.
IIOUTH
156
AGEING
158
liUANTITV OF MERCURY NEEDED
MIXIN<i
156
AMALGAMS
.
.
,
•
PREPARATION OF ALLOYS FOR DENTAL
•QUALITATIVE E.XAMINATION
•
AMA
AM S
161
163
DENTAL COPPER AMALGAMS
CHAPTER
159
160
IX.
SILVEK.
166
OCCURRENCE
PREPARATION
.
.
166
•
•
.
.
•
•
167
PROPERTIES
USES FOR DENTAL PURPOSES
PREPARATION OF PURE SILVER
PRECIPITATED SILVER
ALLOYS OF SILVER
.
•
.
•
169
.
169
171
171
.
DENTAL ALLOY'
.
174
176
SILVER SOLDERS
PREPARATION OF SILVER SOLDERS
ASSAY BY CUPBLLATION
WET ASSAY OF SILVER
ELECTRO-PLATING
RECOVERY OF SILVER FROM SCRAPS
.
177
178
181
181
182
CONTENTS.
CHAPTER
xiii
X.
PLATINUM AND IRIDIUM.
PAGE
......
..........
PLATINUM
OCCURRENCE AND PREPARATION
183.
183
PROPERTIES
USE IN DENTAL LABORATORY
BRITTLE PLATINUM
184
PLATINUM FOIL
PLATINUM BLACK
SPONGY PLATINUM
DETECTION OP PLATINUM IN ALLOYS
ESTIMATION OF PLATINUM IN ALLOYS
ALLOYS OF PLATINUM
185
.........
..........
.........
........
............
.........
.........
IRIDIUM
PROPERTIES
ALLOYS OF IRIDIUM
USE IN DENTISTRY
CHAPTER
185.
185.
186
187
187
188
189
191
191
I92
I92:
XI.
PALLADIUM.
.......
...........
........
.........
.........
OCCURRENCE AND PREPARATION
PROPERTIES
USE FOR DENTAL PURPOSES
PALLADIU.M PRECIPITATE
ALLOYS OF PALLADIUM
CHAPTER
193
193
I95
195
I95.
XII.
ZINC.
OCCURRENCE
PREPAn.VTION
...........
...........
.........
..........
...........
..........
..........
PROPERTIES
USE FOR DENTAL PURPOSES
ZINC DIES
I97
197
198
I99
199
200
PURIFICATION OP ZINC
COMPOUNDS OF ZINC
20I
O.XV-CIILORIDE
203
O.W-PIIOSPIIATE
0.\Y-SULPII.VTE
ALLOYS OF ZINC
204
205
205
CONTENTS.
XIV
CHAPTER XIIL
LEAD.
PAGE
OCCinRENCK
208
PBEl'ARATION
PROPERTIES
2°^
209
•
2IO
USE rOR DENTAL PURPOSES
ALLOYS OF LEAB
2IO
CHAPTER
XIV.
TIN.
OCCURRENCE
PREPARATION
213
PROPERTIES
214
USES IN
213
DENTAL LAHOHATOliV
215
TIN-FOIL
216
TIN-PLATE
ALLOYS OP TIN
DETECTION OF TIN IN ALLOYS
216
2l6
21?
.
CHAPTER XV.
COPPEK.
OCCURRENCE
PREPARATION
PROPERTIES
^^9
EFFECT OF IMPURITIES ON COPPER
USE IN DENTAL LABORATORY
220
^^9
221
ALLOYS
CHAPTER
XVI.
CADMIUM.
224
OCCURRF.NCE
.
PREPARATION
.
.
USE
ITS
FOIl DENTAL PURl'OSUS
ADVANTAGES AND UI8ADVANTA0ES
224
224
PROPERTIES
225
IN
ALLOYS AND AMAI.CA.MS
225
CONTENTS.
CHAPTER
XV
XVII.
BISMUTH.
OCCL'UUENCE
yilEPARATION
PROPERTIES
227
227
USE FOR DENTAL PURPOSES
ALI.OVS OF
........
BISMUTH
228
229
229
CHAPTER
XVIII.
ANTIMONY.
•OCCURRENCE
....
...........
...........
.........
PREPARATION
PROPERTIES
USE FOR DENTAL PURPOSES
ALLOVS OF ANTIMONY
231
23I
231
232
232
CHAPTER XIX.
IKON.
...........
...........
............
...........
...........
•OCCURRENCE
CAST IRON
234
234
"WROUGHT IRON
STEEL
PREPARATION
235
236
PROPERTIES
•EFFECT OF IMPURITIES ON IKON
IIARDENINO AND TEMPERING
.......
ANNEALING
BURNING OF IRON AND STEEI
237
238
239
24Q
342
242
CHAPTER XX.
ALUMINIUM.
•OCCURRENCE AND PREPARATION
PROPERTIES
USES FOR DENTAL PURPOSES
244
ALUMINIUM PLATE FOR DENTUUEH
CASTING ALUMINIUM FOR DENTURES
245
246
243
245
CONTENTS.
XVI
SOLDERS FOR ALUMINIDM
ALUMINIUM BRONZE
SOLDERS FOR ALUMINIUM BUONZK
ALLOYS OP ALUMINIUM
247
.......
248
249249.
CHAPTER XXI.
NICKEL.
OCCURRENCE
PREPARATION
PROPERTIES
USE IN THE DENTAL LABORATORY
ALLOYS OF NICKEL
^S'^
252
^5-
GBRMAN SILVER
-5^
NICKEL PLATING
^54
PART
II.
EXPERIMENTS RELATING TO
COLD
.
SILVER
MERCURY
PLATINUM
TIN
ZINC
LEAD
.
.
COPPER
CADMIUM
BISMUTH
ANTIMONY
IRON AND STEE
ALUMINIUM
NICKEL
EXPERIMENTS WITH THE BLOWPIPE FLAME
APPENDIX
INDEX
A MANUAL ON
DEKTAL METALLUEGY.
PART
I.
INTRODUCTION.
When
only a few of the metals were
divided into two classes,
viz.
known they were
—noble or precious metals
and base metals.
Noble Metals.— Those having a very
feeble affinity
for oxygen,
which renders them incapable of rusting or
tarnishing by oxidation in the air at common tempera-
tures or on heating.
Base Metals.— Those which
lustre or are oxidised at
lose
their
metallic
an ordinary temperature or by
heating.
The term " noble
" or
" precious
" is
applied to gold,
and platinum (and some of the rarer metals found
in combination with platinum), as none of these metals
silver,
rust
or oxidise at the ordinary temperature or on
heating; on the contrary, the oxides of these metals cease
to exist
on heating, the metal being set free and the
oxygen given off". Mercury is also included sometimes
as one of the noble metals.
Thus it will be seen that
A
DENTAL METALLURGY.
2
the
number
of
noble metals
so-called
is
very small
so-called base metals.
in comparison with that of the
Metals.—
Occurrence and Distribution of
distributed
sparingly
The majority of the metals are
rare occurrence and
nature, and some are only of
little
m
are ot
practical importance.
occur
a few of the metals
majority
uncombined state, the
Native Metals.-Only
in nature in the free or
combination with oxygen,
being generally found in
Those
element.
sulphur or some other non-metallic
are gold, silver, copper,
that occur in the metallic state
mercury, bismutb
platinum (and its allied rarer metals),
stated
Lead and zinc are also
iron.
antimony and
to have been found
in the
uncombined
state,
but their
occurrence requires confirmation.
occur
Ores.-As above stated, metals usually
non-metals formmg a series
nature in combination with
Native
as mdcdlifa'cym .nm.r«/s.
of bodies known
included under this heading.
metals are also generally
which contain a metal
Those mineral substances
as to admit
in such association
sufficient quantity and
extraction
advantageously treated for the
of their being
of
known as ores. The proportion
of that metal are
vary
a mineral an oi;e will
xnetal necessary to constitute
the
mineral and the value of
with the nature of the
mineral
to subject the
It is usually necessary
metal.
mechanical preparation to
which contains the metal to
mineral matter or " gangue_
free it from the valueless
Metallurgy is
associated.
with which it is invariably
preparmetals from their ores and
the art of extracting
manufacturei
uses of the artisan and
ing them for the
em-
m
m
Methods
of
Extraction—The
processes
metals from
their ores
ployed for extracting
i.he
may
INTRODUCTION.
be divided iuto two classes,
Wet
viz.
2
—Dry
processes and
processes.
Dry Processes.—Those
which are conducted in
furnaces, or their equivalent, at a relatively
high temperature.
The operation of extj-acting
metals from
their
by fusion
ores
in
a
furnace with suitable fluxes
is
known
as smelting.
The metallurgical operaconducted at a high
temperature require the use
tions
of furnaces
built or lined
with some material capable
of
withstanding
excessive
heat and the wearing action
of the materials with which
it
comes in contact.
Wet
Processes.
Those in which the metal
is extracted by a suitable
solvent after being, in
cases, first
some
converted into a
more readily soluble compound.
Metallurgical
naces.— The
of
furnaces
Fur-
various forms
Fig.
I.
employed are
conveniently divided into (i.) Blast
furnaces (ii ) Reverberatory furnaces
(iii.) Muffle furnaces
and (iv )
Crucible furnaces.
;
;
;
Blast Furnace (Fig. i)._The
construction
the modern blast furnace varies
much
(i.)
and the proportion of
of
as to shape, size
its
parts,
accoi'ding
to
the
DENTAL METALLURGY.
4
fuel
em-
and of the
nature of the ore to be smelted
essentially ot a
For iron smelting it consists
ployed.
feet high),
chamber or " stack " (about 80
vertical
m
ing.
and formed as illustrated
by
top
the
admitted at
The charge of ore and fuel is
arrangement, which closes
means of the cup and cone
hot blast is forced through
the furnace, and a powerful
" placed round the base of the
"
small pipes or tuyeres
off at intervals
The molten metal is drawn
circular in section,
i.
furnace.
Fig.
2.
the "slag,
as
it
base, while
from a tap-hole at the
an open^
at intervals through
accumulates, is tapped off
W known
" slag hole."
as the
are
The waste gase
furnace through a side
Ub
drawn off at the top of the
for heating P-P-^;^
and subsequently utilised
used
in section,
furnaces, rectangular
smelting.
lead and copper
(ii )
are largely
Reverberatory Furnace
furnace,
a horLontal
(Fig.
fJfor
2)—This
is
"consisting
--^^^l^^^^^^
the
^^^^^
chimney at
one end, a stack or
narts-a
material
the two, on which the
^e
and ^a bed between
_^
other nnd
^
^^^^
^^^^^
C
fireplace at
l^^^X
" fire-bridge,"
called the
and both are
INTRODUCTION.
covered by an arched roof.
On
5
the sides of the bed are
openings through which the ore
may be
stirred
when
necessary.
The flame
to the
downwards or rGverheratcd
spread over the bed, whence the name
stack
on the ore
is
in its course
from the
fireplace
reflected
reverheratonj furnace." *
(iii.)
istic of
Muffle Furnaces.—The
these furnaces
does not
come
is
essential character-
that the material being heated
into contact either with the fuel or the
products of combustion.
The furnaces
are
made
in
many
forms according to the purpose for which they are to
be used.
As a type, the assay furnace on p.
75 may
be taken.
Crucible Furnaces.— Furnaces of this class
are chiefly used for melting metals and alloys.
They
consist essentially of a closed fire-brick chamber with
(iv.)
fire
bars at the bottom, and a small flue at the top.
is usually fitted with a door by means
of
The ashpit
which the draught
on
p.
73
is
is
regulated.
The laboratory furnace
a type of this class.
Useful Metals.— Although
a large number of
metals are known, about twenty-one only of these are
of any considerable industrial importance, viz.
Alimiiiiiuni.
Copper.
Antiiiioiiy.
Gold.
Platiniiiii.
A rufi/iir.
Iron.
Putassiuiii.
Bi.smiith.
Lead.
Silver.
f'lidwiuiii.
Miiijiirfiiiuii.
Nickel.
Snd'iHiii.
(lirnniinni.
Aid IIIJII ItfKC.
Tin.
Ciiliall.
Mercury.
Zinc.
Of
these, only about thirteen (those printed in Eoman
type) are employed in the metallic state for industi-ial
*
l'er(;y,
" Mebilliiruy," vol.
i.
p.
45.
DENTAL METALLURGY.
6
purposes or in the dental laboratory. Of those printed
in the metallic
in italics a few are used to a small extent
while their various compounds are extensively
for other
used in the arts as colouring pigments, or
purdental
The application of metals to
purposes.
origin, as " gold
poses cannot be regarded as of recent
fixing artifiwas employed in Eome for the purposes of
centuries before the Christian
cial teeth more than three
Tables makes exception
era, and a law of the Twelve
it to be buried
with regard to such gold, permitting
state,
*
with the dead."
*
C'ic.
do Leg.,
ii.
24
.
" Metallurgy," Phillips, p.
2.
CHAPTER
I.
PHYSICAL PROPERTIES OF THE
METALS.
Although
the division of the elements into metals and
non-metals does not admit of exact definition, yet the
metals as a class possess certain generic properties
which the non-metals either do not possess at
all
or
exhibit only in a very slight degree.
All
with the single exception of mercnry
metals,
(a liquid), are solid at the ordinary
temperature they
high power of reflecting light
they are
opaque except in the thinnest possible films, in which
possess
;
a
;
state they allow light to pass
they are better conductors of heat and of electricity than the non-metals, and,
;
have higher densities than these, and
with few exceptions, malleable and ductile. The
metals diffisr widely from each other both in their
as a rule, they
are,
physical
and in their chemical properties, and are
accordingly adapted for different uses.
The most important physical properties possessed by
the various metals, rendering them fit for purposes
which could not be
are as follows
fulfilled
by non-metallic substances,
:
Lustre and Colour.— One
teristic properties
of the
possessed by metals
is
most characthat of a high
DENTAL METALLURGY.
8
power whereby a peculiar
reflective
appearance
is
presented,
known
briglit glittering
as the metallic lustre.
in a state of fine division the metals frequently
When
appear in the form of black or grey powders, and the
be
metallic lustre is not noticeable, but it can readily
subobserved when the powder is rubbed with a hard
stance, such as polished steel or agate.
The peculiar lustre characteristic of metals
is,
how-
as certain
ever, not wholly confined to these substances,
some of the non-metals exhibit a closely
compounds and
an example.
Although the light reflected from polished surfaces
similar lustre
gi-aphite
is
;
nearly white, yet frequently there is
best seen when the
a slight tinge of colour, which is
the metallic surface.
is repeatedly reflected from
most metals
of
is
light
other metals
Thus, whilst tin, silver, platinum and
appear alike
have a nearly pure white colour, and
distinct
equally polished, lead and zinc have a
'
when
and bismuth a slightly
bluish shade, iron a greyish hue,
brownish
tint.
from a gold surface,
tint is deepened to a
the characteristic pale yellow
by looking
orange-red, which may be readily seen
When
light is repeatedly reflected
full
obliquely into an
internally.
by
empty metal
The red colour
vessel
which
is
gilded
of copper is also deepened,
reflection, to a bright scarlet.
thin leaves are
Certain metals in the form of very
transmitted light
transparent, and when viewed by
metals
different to those possessed by the
possess colours
light and
Thus, gold-leaf transmits green
transmitted light.
silver-leaf appears blue by
to the
of the metals when applied
in mass.
Taste.—A few
tongue
"
le"ave a peculiar
metallic" taste, which
is
pro-
PHYSICAL PROPERTIES OF THE METALS.
9
bably due to the action of the saliva.
Copper possesses
a characteristic faint nauseous taste.
Zinc also has a
slight metallic taste.
The majority of the metals, however, are tasteless when pure.
Specific Gravity or Density of a metal
may
be defined as the weight of a certain
bulk of such
metal as compared with the same bulk of
water.
All metals are lighter when molten
than when in the
solid state, with the exception of
bismuth, which attains
its maximum density just before
solidifying (see
p. 30).
The density
of a metal
dependent on the intimacy
of the contact between the molecules,
and is influenced
by the purity of the metal, by the mechanical
treatment, by the temperature of casting, and
by the rate
is
of cooling.*
The density of a metal is increased by mechanical
treatment, such as hammering,
wire-drawing or rolling.
Thus the density of platinum in the
cast state
which
increased to 21.45 by hammering.
Alteration of temperature also affects this
as
is
21.21,
is
expansion
is
Advantage
is
property,
caused by increase of temperature
a given bulk of metal will
therefore weigh less at a
higher temperature than at a lower one.
•
sometimes taken of this property of
density in extracting metals from their ores.
The extraction of platinum and gold are
examples.
The
following table contains the principal
metals, arranged
according to their densities, referred to
water at its
maximum density at 4° C. (39° P.). To facilitate comparison the densities compared with
aluminium, the
lightest of the common metals,
is also given in the
second column.
*
Roberts-Austen, " riitroductiuii to MetalUirgy,"
|).
14
DENTAL METALLURGY.
lO
Specific Gravity op Metals.*
i.
=
H
"c3
Water
1
B
0
11
<.
Heaviest.
Iridium
Platinum
Gold
Mercury,
.
.
22.4
21.5
19.4
8.0
14.4
54
13.6
12.0
5-1
-39°"C.,
/
Mercury, liquid
Lead
8.9
8.7
.
Nickel
Iron
Tin
Zinc »
.
solid, )
Palliidiuiii
7-3
Copper
Cadmiuiu
.
1.4
10.5
1
.
Silver
Bismuth
9.8
4-5
4.2
.
Antimony
Aluminium
.
3-3
8.5
3-3
3-2
7.8
2.9
7-3
6.9
6.8
2.7
2.7
2.6
2.2
I.O
Liglilcst.
3-9
3-7
substance
the resistance offered by a
of another substance.
to the penetrating action
between the degrees
Great differences are observable
metals in common use
of hardness of the various
admit of being scratched with
Hardness
Lead
is
so soft as to
is
can only be scratched by
the finger-nail, while others
The hardness of metals is imvery hard substances.
applications to mdustnal
portant in considering their
manufacture of jewellery
purposes gold used in the
with
is invariably alloyed
and for coining into money
pure
copper, to harden it, as
some other metal, such as
which
resist the attrition to
aold would be too soft to
Gold used
jewellery are exposed.
;
coins
*
is
and
The
articles of
specific gravity of a
metal
the metal.
the specific gravity of
is
determined by
first
weighing
PHYSICAL PROPERTIES OF
for artificial dentures
also
is
TFIE METALS.
I
I
hardened by the addition
of other metals for similar reasons.
The property of hardness is one of importance in selecting a metal for dies to be nsed in swaging metal plates, as
a die must be sufficiently hard to stand the necessary force
applied to it in stamping up the plate to the required
shape without becoming deformed to anymaterial extent.
It is partly on this account that zinc has been selected as
a suitable metal for dies, as it possesses hardness as well
as
most of the other properties necessary for a
On
die.
the other hand, preference
is usually given to
lead in the formation of a counter-die, mainly on account
of its greater softness, this property in a counter being
of practical importance.
The hardness
of metals diminishes with
an increase
The following table gives the relative
hardness of the more important metals compared with
the hardness of the diamond as loo.
To facilitate comparison, the hardness of the metals
when compared with lead, the softest metal in common
of temperature.
use, is also inserted.
Hardness ov Metals.
H
1
•M
o
12
too.
II
Diamond
5"
—
(-1
Diniiiond
Nickel
Tron
.
Copper
Palladium
I'latiniim
Zinc
Antiniony
.
.
.
lOO.O
46.8
45-6
45-2
41.6
36.8
35-8
33-8
6.3
Silver
2-5
Gold
Bismuth
2.4
2.4
2.2
2.0
1.9
1.8
.
Aluuiiniuni
.
(Jadniiiini
Tin
Lead
.
.
.
32-9
32-5
30.2
27-5
25.2
21.6
18.9
1.8
1-7
t.6
'•.S
1.4
1
.2
I.O
DENTAL METALLURGY.
12
The hardness
of metals
may be approximately
ascer-
tained by cutting them with a good steel knife.
Malleability is the property of permanently ex-
tending in
or rolling,
by pressure, as by hammering
without rupture. Most metals possess this
all
directions
property in a greater or
less
degree.
Gold
is
the
into
most malleable metal, and may be hammered
each grain of
leaves ^ swirott of an inch in thickness,
which
inches.
will cover a surface of fifty-six square
be extended to a greater
square inches,
extent and made to cover ninety-eight
silver the leaves
but on account of the lower density of
are thicker than those of gold.
of an
Iron has been beaten into leaves ^W^h
One
grain of silver
inch in thickness.
may
Malleability
is
often affected
by
when present in very
the presence of impurities, even
of ^lyW^h part of
small quantities. Thus the addition
gold quite brittle and
lead or of bismuth would render
are
the malleability of many metals
:
similar efEects on
metals.
produced by small admixtures of other
impaired when
malleability of nearly all metals is
The
long-continued hammering or
they are subjected to
may be restored by «n7^6a/^«^/,
rolling, but this property
metal to a uniform red
which consists in heating the
rapidly or
slowly-
either
heat and allowing it to cool
for
In some cases, as with copper
nsually the latter.
cooled
the metal be
example, it is immaterial whether
It is on
process.
or slowly in the annealing
rapidly
the malleability, by hamaccount of this impairing of
have to
plates for artificial dentures
mering
&c., that
during the process of swaging
be frequently annealed
them more pliable. The molecules
in order to render
positions by
forced into unnatural
of the metals are
PHYSICAL PBOPERTIES OF THE METALS.
M
hammering,
&c., and require occasional annealing or
softening by heat to bring them back again to their
normal condition. The relative malleability of metals
is determined by the degrees of
thinness of the sheets
that can be
irithout
produced by hammering or
by rolling
The more impo]-tant metals are
arranged according to their malleability in the
following table
annealing.
Oedeb op Malleability.
Most.
Mdllmblc.
1.
Gold.
JO.
2.
Silver.
ii_ ii-OQ
3.
Aluminium.
12.
Nickel.
4.
Copper.
13
Mercury
Zinc.
5-
(frozen).
Least Malleable.
6.
Platinum.
7.
Palladium.
^-
Lead.
9.
Cadmium.
Bismuth
Antimony
^
15.
16.
Iridium
J
14.
Brittleness.— When the metals
and have a tendency
leability,
hirittle.
are void of mal-
to fly to pieces
hammered or rolled, they are said to be brittle.
Antimony and bismuth are characteristic
metals at
all
when
brittle
temperatures.
Some metals which are very malleable at one temperature are brittle at another.
Zinc, for example, is
brittle
at ordinary temperatures,
between
but when heated to
100° and 150° C. (2 r 2^-302° F.)
it
becomes
malleable and can readily be rolled into thin
sheets,
whilst at 200° C. (392° F.) and upwards
it
again
becomes
and can easily be powdered in a morOther metals which are malleable at ordinary
temperatures become brittle when heated to a temperabrittle
tar.
ture just below their melting-points
and aluminium are examples.
;
lead, tin, copper,
DENTAL METALLURGY.
14
lead
Bearing in mind these properties of zinc and
be taken in the
at elevated temperatures, care should
metal
of dies and counter-dies for swaging
preparation
remove them
plates to
not allow them to
fall
carefiilly
when
from the moulds, and
hot, otherwise the dies
may
be broken owing to their brittleness.
Flow of Metals.— " When a malleable metal
mechanical processes such as rolling,
is extended by
hammering,
stamping,
ticles of
&c.,
a
true
flow of the par-
the metal occurs, analogous
m
all
respects
exerted
The pressure
fluids.
to the flow of viscous
transmitted in the
upon the surface of the metal is
interior of the
particle to particle,
mass from
direction
to produce ^ flow in the
is least."
and tends
where the resistance
*
like
,.n
^
fl
solid metals flow
application of this fact, that
importance in industrial
viscous fluids, is of great
art
and the production
1
The
by
rolling,
punching, &c.,
by the artificer.
from a single sheet
The manufacture of jelly-moulds,
the striking of a com
copper or other metal, and
when
of the metal
of
forms
of various complicated
entirely depends on the flow
are
suitably guided
the metal,
instances of this property,
into the sunken
pressure, being made to flow
familiar
under
fracturing, thus producmg
portions of the die without
The flow of metals is of much
a true impression.
laboratory, as it is this
importance in the dental
swaging metal plates for
made to flow by
dentures, the metal being
conform to all parts of
it may accurately
property which
artificial
is utilised in
force, so that
» h^,p1 "
vol
!rr395
Metals
").
C'
11
22
•
0" C-'Sn
Kobe.'ts-Aiisteu, Pruc. Hoy. Lid.
Fluids and .olid
I'-oi-'tieB Common to
and
PHYSICAL PROPERTIES- OF THE METALS.
the die.
less
1
which enables seamcrowns to be struck in one piece from the sheet
It is also this jiroperty
metal.
Ductility is the property of permanently extending by traction, as in wire-drawing, and is closely
allied
to malleability.
sarily malleable,
in the
exact
All ductile
but they are
ratio of
their
metals are neces-
not
necessarily ductile
Thus iron
malleability.
very ductile, and may be drawn out into very fine
wire
but it cannot be hammered or rolled out into
such thin sheets as some other less ductile metals.
is
;
Tin and
lead are
fairly malleable
are not sufficiently ductile to be
wires.
Wire
drawn
they
into very fine
manufactured by passing a cylindrical rod
through a steel plate known as a draw-fjlatc,
is
of metal
which
metals, but
pierced with a series of conical holes gradually
diminishing in diameter (see p. 78). It is generally
necessary to anneal the wire from time to time (see
is
otherwise it becomes hard and more or less liable
break after having passed through a certain number
of holes.
In certain cases, however, the annealing is
p. 12),
to
reduced to a minimum, in which case the
to be hard-clrmun.
"wire is said
The following metals are arranged according
ductility
to their
:
OnDER OF
DUCTXIilTY.
Maul DKclilr.
1-
*'^olf'-
2-
^'l^'cr.
8.
Cndniiiiin.
3.
Platinum.
g.
Aluminium.
4-
Ii'»n.
5.
Nicitol.
6.
Copper.
7.
.
,0.
I'illliulium.
Zinc.
II.
12.
Lead.
Least
J)iiclilc.
DENTAL METALLURGY.
i6
Tenacity
the property a metal possesses of re-
is
sisting fracture
when subjected
to a tensile or stretch-
one of the most important properties
their apof the malleable metals in connection with
With an increase
plication to industrial purposes.
This
ing force.
is
a
tenacity of
the
temperature
of
metal
is
usually
metals is
diminished. The relative tenacity of different
exactly
determined by taking bars of pure metals and of
one end and
the same diameter, fixing them firmly at
gradually
applying weights at the other, the load being
each bar is
increased until the utmost tveight which
been exactly
capable of suspending without breaking has
determined.
tenacity in tons per sq. in. of the
following
metals in the cast state is given in the
The approximate
common
table
Order of Tenacity.
Tous per
Tons per
Most Tenacious.
f Steel,
„
2.
3.
4.
5.
special
.
ordinary
Nickel
Iron, wrouglit
Platinum
Iron, cast
6. Silver
7.
8.
10.
Aluminium
38
20-26
11.
Zinc
3-0
12.
Cadmium
2-5
18.0
13.
Tin
2.0
S-15
14.
lO.O
15.
8.5
16.
Bismuth
Antimony
Lead
.
.
Copper
aold
As
25-65
6.7
.
•
.
.
.
.
6.9
.
.
.
Palladium
go-loo
.
.
sq. in.
sq. in.
9.
7-0
the tensile strength of metals
.
.
.
1.2
I.O
I.O
.
Least Tenacious.
is
very gi-eatly
afi^ected
temperatiire,
their purity, structure, and
must not be
given in tables of tenacity
bv variations in
the values
regarded as constants.
increased when metals
The tenacity is usually greatly
rolling,
mechanical treatment, such as
are hardened by
Thus, when copper is
&c.
hammering, wire-drawing,
PHYSICAL PROPERTIES OF THE METALS.
worked, the tenacity
1
may
be raised to over 18 tons per
Annealing will usnally reduce the tenacity to
that of the cast metal.
sq. in.
The
ratio in
which each metal possesses the properties
of malleability,
ductility
from the following
table,
and tenacity may be seen
in which the numbers repre-
sent the order given in the preceding tables
Metiils.
Gold
.
Silver
.
jMiiUeiibilitv.
6
2
.
Copper
Tin
3
9
4
6
5
Platinum
Palladium
Lead
Cadmium
1
1
7
7
8
3
7
12
8
10
10
4
2
5
I
12
14
9
13
14
15
Antimcinv
Elasticity
8
5
->
II
(l'ro>!en)
4
6
9
10
.
Mercury
Bismuth
Tenacity.
I
Aluminium
Zinc
Iron
Nickel
Buctilit}-.
:
12
13
the power a substance possesses
of
resuming its original form after the removal
of the
force which has produced a change in
that form.
The
good
is
elasticity varies considerably in difPerent
steel possesses it to a very high
metals
;
degree, but lead
scarcely exhibits a trace of this quality.
Within recent years advantage has been taken
of the
elasticity or " springiness " of
various metals, more especially of "pianoforte wire," for
regulating the teeth.
The elasticity of metals is also utilised
in matrices,
and is a matter of importance in
clasps employed as
a means of retaining partial
dentures in the
mouth.
DENTAL METALLURGY.
jg
hammering,
The operations of wire-drawing, rolling,
of metals,
&c generally increase the elasticity
annealing generally diminishes it.
gentle
very little elasticity, but by
whilst
Gold wire possesses
hammermg
this
may
made " springy." In this
be increased and the wire
employed for regulating purposes
state it is sometimes
keeps its colour better and
place of steel wire, as it
in
a
as pianoforte wire has
does not blacken the teeth,
its applicaso universal
tendency to do but it is not
elasticity
be used where great
bility, as it can only
often
The elasticity of a metal is
is not necessary.
with another metal (see
developed by combination
m
;
^
property of metals
this
itere Is^a^mit, however, to
their
incapable of regaining
beyond which they are
This point is known as
break.
original form, or even
the
liviit
of elasticity.
Fusibility
-AH
metals
t
when heated
•
iii
^.w
sufficiently
reqmred
state, but the temperatures
pass into the liquid
considerably.
to melt them differ
tenrpera39° C, but above this
Mercury is solid at
therefore always
liquid form, and is
ture it assumes the
Some metals are readily
-
ordinary temperatures.
and a few
heat, while platinum
ed below or at a red
by the highest attammetals can only be melted
,a
flame or the electric arc^
reat of the oxyhydrogen
^
considered as easily
Metals are usually
bright red heat
temperatures below a very
they melt at
melting above that point
lOOO^ C and those
or refractory.
«^ difficult of fusion
the high temperadifficult to judge
fluid at
t
Te
oZZ
Itt somewhat
.
terms commonly
melt metals from the
tures required to
red
degrees of heat, such as
ndicate different
used t
PHYSICAL rnOPERTIES OF THE METALS.
heat, white heat, &c.
but some idea of these temperabe gaiued by regarding a bright domestic
as bright red heat about 900° 0.
(1652° F.).
;
may
tures
fire
1
The following
a convenient practical classification
is
of the metals, founded on their degrees
of fusibility
Melting-points
oi'
Metals.*
Cent.
Mercury
-
Tin
+
.
Bismuth
Fusible at or below a red
heat
at
naces
Cadmium
320°
608°
325°
617°
.
.
Aluminium
temperatures Antimony
Silver
bright red heat Copper
white heat
Gold
Fusible only at the high
"1 Palladi um
est
temperature
at "
iNickel
tained
in
furnaces
Iron
bright white heat
j
Fusible only by the oxy-i
hydrogen flame or the 1^1**'""'"
:
.
415°
779°
625°
1157°
632°
1170°
960°
1760°
1050°
1922°
1061°
1942°
.
to
1500°
2732°
1600°
2912°
1600°
2912°
1775°
2500°
4532°
|'
:
,
electric arc
449
514
Lead
'-Zinc
and
38.2°
268°
Fusible above a red heat
easily attained in fur
l'"ahr.
39°
212°
,
J
3227°
Some metals, such as zinc, cadmium, and
antimony,
are readily converted into
vapour when heated, and all'
metals can be volatilised by the
use of either the oxyhydrogen flame or the electric arc.
Effect of Cold.— It has been pointed
out by Dewar f
when metals are exposed to the very
low tempera-
that
ture of
- 180^^
C, the tenacity
instance, the strength of steel
is
greatly increased.
and of German
For
silver is
nearly doubled at this low
temperature.
In some cases brittleness is
produced by exposure to
*
"Introduction
to
Metallurgy": Roberts- Austen
t Lecture before the Uoyal Institution, Loudon,
lcS9^.
DENTAL METALLURGY.
20
cold
thus, ingots of tin,
:
a Kussian winter,
fell
Fracture.—The
when exposed
to the rigour of
into powder.
appearance of the fractured sur-
as giving in many
face of a metal is of importance
or impurity of the
instances an indication of the purity
pure zinc
Thus the fracture of an ingot of
metal.
set at various
presents bright crystalline surfaces
the frequent impurity
angles, while the presence of
of black specks on the
iron is indicated by a number
and the duller and greyer
faces of the cleavage planes
fracture depends
appearance of the fracture. The
metal and partly on the
partly on the nature of the
manner in which solidification occurred.
relation to the fracThe following terms are used in
appearances can only be
ture of metals, but these
thoroughly learned by practice
satisfactorily
:
and
bismuth are chaGrystalline.-Zinc, antimony and
racteristic examples.
the
a,^amdar.-(Dmr^ from the last only m
As in grey forge pig-iron
size of the crystals.)
Fihrous.-^^oodi
wrought-iron
smaller
broken
partly
by
bending double.
nicking with a chisel and
backwards and forwards
^^^jty.— Tough copper bent
breaks presents a silky lustre.
of commerce,
CWz.m«a7-.-0bserved in^the grain tin
until
at
it
resembles
GonMcd
common
starch.)
'
or Vitreous.-(Glass-like.)
zinc
certain alloys such as
Crystalline
2,
copper
i
Character. -Much
Presented by
(Percy.)
attention
has
constituyears to the molecular
been given in recent
When the molecules of a substance
tion of metals.
regular manner
certain definite and
are arranged in a
cry^aU^^e. When growth
substance is said to be
Te
PHYSICAL PROPERTIES OF THE METALS.
in this
manner has been
free
2
1
and nninterrnpted, geo-
metrical forms are developed externally, characterised
by the constancy of the angles between similar faces in
all individuals of the same species {e.g.,
the same metal).
These definite forms are called crystals and the
substance exhibiting them is said to be crystallised.
If, as
mass of a cooling metal, the boundaries of the
individuals are the result of their mutual
interference
in the
Fig. 3.— Pure Gold.
Magnified 42 diameters.
the definite external forms cannot be
developed
;
but,
on examining the polished and etched surface of
the
metal the same regular internal arrangement is
seen
as
to
exist,
each individual
the mass
is
is still
spoken of as a crystal and
said to be crystalline.
Thus, Fig. 2, is taken from a micrograph *
of the
polished surface of a section of pure gold
etched with
* Taken by Mr. McWilliain
from tlie original sections kindly lent
by Prof. Arnold, Slieffield see
/'J,if/ini-rrim/, P'ebniiiry
:
7,
1896.
DENTAL METALLURGY.
22
aqua regia aud sliows the
by
crystals of the metal
their lines of interference.
Fig.
bounded
4 represents the
with
appearance of a similar section of gold alloyed
It will be noticed that the
0.2 per cent, of copper.
mass of the
copper had apparently remained in the
seen between the two
crystals as no difference can be
crystals, and the
structures excepting the size of the
cent, of copper.
Fig. 4.— Gold alloyed with 0.2 per
Magnified 42 diameters.
metal in the mass
ductile as before.
is
practically as malleable
still
Fig.
5,
and
however, shows the appeargo d
of a similar section of
ance under the microscope
and here the bright
containing 0.2 per cent, of lead,
they are
gold are seen as before, but
yellow crystals of
BOW
separated by thin
substance.
This latter
alloy of gold
and
and
crystallised
lead,
from
avails
is
of a brownish-coloured
a very fusible
and
brittle
and the gold having solidihed
was
centres while this alloy
PHYSICAL PROPERTIES OF THE METALS.
2T,
liquid, the still
thoroughly malleable crystals of gold
are surrounded by au envelope of brittle alloy, and
thus the whole mass
is
individual crystals are
tion of this sample
of the grains
quite brittle.
still
thoroughly malleable, a por-
was pounded in a mortar, and one
was beaten as thin as ordinary
Gold with 0.2 per cent, of
*"IG. 5.
To show that the
—Gold
silver (an
gold-leaf.
element of
hio-h
alloyed with 0.2 per cent, of lena
Magiiitied 42 dianietei-s.
melting-point) has a structure similar to that shown in
Fig. 4, while gold with 0.2 per cent, of tellurium (an
element of low melting-point) is similar to Fig.
5.
In the case of metals showing a fibrous or a silky
fracture the crystals have clung together and drawn out
into the thread-like forms seen on the
ruptured portion,
while in those showing a "crystalline" fracture the
crystals have not
drawn out and the rupture has taken
place along planes of weakness, sometimes
apparently
DENTAL METALLURGY.
24
along crystal junctions, and sometimes as true cleavage, and hence the crystalline appearance of the
fracture.
All metals under favourable conditions
tained in the form of definite crystals.
particularly gold, silver, and copper
may be obMany metals
— occur
—
lised in nature,
and are found most frequently
crystal-
as cubes
Metals usually crystallise on solidification
In order to crystallise a metal artificially
after melting.
a
quantity of it
it is sometimes sufiicient to melt a
or octahedra.
m
solidified, to
crucible, and, as soon as it has partially
possible
the crust on the surface, and as rapidly as
break
very
pour out what remains liquid. By this means
may be
beautiful crystals of bismuth (rhombohedral)
obtained.
To produce
this effect with the less fusible
necessary.
metals larger masses and slower cooling are
condensed
Crystals are also obtained when metals are
electrofrom the state of vapour or are deposited by the
former
the
In
decomposition of metallic solutions.
lytic
case the
more
yield crystals
volatile metals, such as zinc
somewhat
and cadmium,
readily.
crystals
yield
In the latter case nearly all the metals
currents
when deposited from their solution by electric
of feeble intensity.
happens that one metal may be
placing a strip
precipitated in the form of crystals by
In this way
its salts.
of another metal in a solution of
Tree )
lead (known as the "Lead
It also frequently
feathery crystals of
are deposited
when
a piece of zinc
is
placed
of lead acetate.
Micro- Structure.*—Much
*
For
m a sol iition
.
attention
is
now
de-
Stu.ly of
Iloberts-Austen, " Intrc.d,u.ti,.,> to
fuller details, see
Metallurgy."
PHYSICAL PROPERTIES OF THE METALS.
25
voted to the study of the structure of metals and
alloys
by the aid of the microscope, a method of investigation instituted by Dr. H. C. Sorby in 1
864.
As the sections of metals, however thin, are opaque,
they must be viewed by reflected light.
For this purpose it is essential that the surface should
be perfectly smooth, and this is effected by careful
grinding on emery and polishing with rouge. In
most
cases the structure of the metal or alloy is not
shown by
polisliing only, and must be made evident
by physical
or chemical processes which produce different
effects
upon the different constituents.
These processes vary with the nature of the metals
concerned. The carefully polished specimen is usually
submitted to the action of a suitable reagent
(such
as very dilute nitric acid) in order
to develop the
structure.
A
microscope fitted with powers varying from
30 to
350 diameters, and provided with special accessories
for
good
perpendicular
illumination,
generally
is
employed.
By
this
information
method
of
investigation
much
metals, alloys,
gained as to the structure of
and amalgams. For example, the micro-
scopical examination of the gold alloys
has
to
valuable
has been
show why the
done much
qualities of gold are greatly modified
by the addition of very small quantities
of certain
metals fas described on
p. 22).
In the author's opinion much of our future
knowledge
respecting the structure of dental amalgams
will have
to be gained by the aid of the microscope.
Conductivity of Heat and of Electricity.—
The superior power
of conducting heat
and
electricity
DENTAL METALLURGY.
26
is
one of the most prominent characters possessed by
The metals
the metals.
are the best conductors of heat
the solid bodies, but the power
being highest
of transmission varies very considerably,
brittle metalsin silver and copper, and lowest in the
and
among
electricity
bismuth and antimony.
power that
It is on account of their conducting
They are good
feel cold to the touch.
metals always
conductors, and therefore carry
away rapidly the heat
m
they are
from the part of the body with which
contact.
The order
heat
will
of conducting
power of the metals
for
the same, as
for dedricity is comparatively
which the
appear from the following table,* in
and
conductivity of silver
is
assumed
to
be lOO at
o'
C.
Conducting I'ower of Metals.
luir KIn-li-ii-ll !!
/(.( Iloiit.
100.0
oo.o
Silver
73-6
97.8
53-2
Copper
Gold
31-3
65-5
Aliiininiiiiii
Aliiniiniuni
Zinc
28.1
Zinc
20.
Cadmium
15.2
Iron
II.
Platinum
Silver
I
Copper
Gold
.
.
Ciubnium
Tin
Iron
Nickel
.
.
Mercury
Tin
(1
inid)
I3-S
76.7
.
29.6
.
14.6
.
14.4
.
12.9
Nicki'l
Lead
8.4
Antimony
Antimony
4.0
Bisuiutli
1.8
Mercury
Bismuth
.
Platinum
12.
.
8.4
8-5
Lead
14.S
.
Palladium
Palliidiinn
24.4
.
.
.
.
3-6
1.8
1.4
the electrical conrelative values obtained for
(juite
one temperature are not
dactivity of metals at
The
* Beckert, "
Eisenhuttenkunde,"
p. 6.
PHYSIOAL PROPERTIES OF THE METALS.
the same
ductivity
27
those obtaiued at another, as the concHviinuIu'd by a rise of temperature, but
as
is
not always at the same rate in each case.
Capacity for Heat, or Specific Heat.— Equal
weights of different metals require different amounts
of heat to raise them from the same to a higher
given
temperature.
The amount of heat necessary to raise
one part by weight of water from 0° C. to
1°
C. being
amount of heat required respectively to
the same weight of the following metals from
I,
the
to 1° G. will
be as follows
Specific
raise
o' C.
:
Heat of Metals.*
Aluminium
0.2143
Tin
Iron
0.1138
Antimony
0.0508
Nickel
0.1086
Zinc
0-0955
Mercury
Platinum
Gold
Lead
Bismuth
0.0333
0.0324
.
.
Copper
0.0952
Palladiinn
0-0593
Silver
0.0570
Cadniiiim
0.0562
.
.
0.0324
.
0.0314
0.0308
0.0567
.
From the above
table it will be seen that the
capacity for heat of the metals is very
variable.
If
small balls of equal weights of the different
metals are
exposed for the same length of time to exactly
the
same temperature and then withdrawn simultaneously
and placed upon a thin cake of wax, it will
be observed
that the metals having the greatest
capacity for heat,
such as iron, will
much
more
"melt"
rapidly than
their
way through the wax
those
having
a
smaller
capacity for heat, such as bismuth.
The
specific
temperature and
heat
is
their fusing-point.
increases with an elevation
greater
Any
* Kegnniilt, "
as the
action,
of
metals approach
such as hammering,
Courn filCnientairc,"
ii.
28.
DENTAL METALLURGY.
28
which increases the density of a metal, diminishes its
capacity for heat, but it regains its original value
after the metal has been again heated.
heat of
It is important to consider the capacity for
metals used for artificial dentures, as in the mouth they
frequently to
are exposed to varying temperatirres and
hot liquids.
The comparatively high specific heat of palladium,
this
combined with its low conducting power, makes
properties
metal suitable for artificial dentures, as these
plate
gold
would prevent the sudden chill felt with a
similar manner
on drinking a cold liquid, and also in a
liquids. It is
would assist in preventing scalding with hot
advantageously
be
quite probable that palladium would
high price did
in prosthetic dentistry if its
exclude it from the dental laboratory.
employed
not
for heat of aluminium,
combined
would render that metal
also very
The great capacity
with
its
lightness,
its other properties
suitable for dental plates, provided
did not
make
it
unsuitable.
when
Expansion by Heat.— Metals expand
generally in a degree
heated, and, within certain limits,
in temperature.
nearly proportionate to the increase
also in dentistry, it is
In many industrial arts, and
amount of eximportant to ascertain the exact
very
pansion
which
temperature
diff-erent
metals undergo
when
their
is raised.
represent the
the following table
own length, of a bar of the
extension, in parts of its
the
in temperature from
given metal during a rise
boiling-point of
(32° F.) to the
The
figures
Lezing-point
water,
100^^ C.
in
C.
(212° F.):
PHYSICAL PROPERTIES OP THE METALS.
29
Expansion op Metals by Heat.
(r rentes/
Cadmium
Jixpaiisioii.
.
Lead
Zinc
0.00306
=
0.00292
=
= ^l-j
=
= ^hs
=
= -FF?
= ^»
0.00291
.
Aluminium
0.00231
Tin
0.00223
.
Silver
0-00193
Copper
Bismuth
0.00167
.
0.00162
The above
coefficient of
^ij^
Gold
Nickel
0.00145
0.00127
Iron (malleable)
0.00122
Palladium
0.001 17
Iron (cast)
0.00107
Antimony
0.00105
Platinum
0.00089
table indicates
jsr
—
1
1
Least Expansion.
the
linear
increase or
expansion— that is, the increase
Most substances, however, expand
linear
in one direction.
equally in each direction, and the cubical
may be taken
_
—
expansion
as approximately three times the above
fractions.
Change of Volume on Solidification.— All
metals undergo a change of volume when they
pass
from^ the fluid to the solid state.
With the exception
of bismuth, which expands, all metals
contract on
solidification.
This change of volume is a matter of
great practical importance not only in the arts
but in
many branches
of dentistry.
It is one of the most important properties to be considered in the
selection of
a metal for the production of dies for
swaging
metal
plates, as the successful adaptation of
the plate
to a large extent upon the die being
depends
an accurate representation of the precise form of the mouth.
Owing to
this general property of contraction
it is impossible to
obtain a metal which will give an exact
reproduction of
the mouth.
The unavoidable shrinkage, however,
is
partially or wholly
compensated for by the ex])ans'ion
of the plaster model employed, and the
yielding condition of the soft tissues of the
mouth.
Although the
DENTAL METALLURGY.
30
somewhat greater than that of
other metals, it is almost universally employed for the
production of dies, as it possesses most of the other
properties necessary for this purpose (see p. 44). The
contraction of zinc
is
contraction of metals
is
often considerably diminished
by being alloyed with other metals.
The following table gives the percentage of change
the
in volume of metals on passing from the liquid to
cold solid state
*
:
Change op Volume on
Bismuth
•
.
.
Solidification.
increase of volume
2.30
1.02
decrease
Iron (cast)
Mercuryt
4-85
Tin
Copper
6.76
7.10
9-93
II. 10
Lead
Zinc
1
Silver
1.20
Other metals in common use, such as gold and
solidification,
aluminium, undergo change of volume on
the latter case
the contraction being considerable in
;
but the exact amount
of contraction of metals has only
been determined in a few
Galvanic Action.
—When
two dissimilar metals
which
in a fluid, the chemical action of
and
energetic on one than on the other,
immersed
are
more
is
cases.
current is
then brought into contact, a feeble electric
analogous
produced known as galvanic action, which is
heating the junction of a
to the result obtained on
antimony.
thermo-couple, such as bismuth and
and a steel
tongue,
silver coin be placed on the
If a
pen
*
t
or iron
nail
under the tongue, and the
Roberts and Wriglitson, Proe.
Grumnach,
Pln/.^: Sor., 5, 1884, PP-
Chem.-Zelt., 1901, 25 [84], p. 9i9-
edges
97-104-
PHYSICAL PROPERTIES OP THE METALS.
brought into contact, a feeble electric current is produced, giving rise to a peculiar bitter taste known
as
a galvanic taste.
This galvanic action is sometimes
experienced
when
mouth, where
different metals are in contact in the
they are continually bathed in the oral
The amount of action
fluids.
states of saliva
dition,
action.
;
infinitesimal in healthy
but in acid, or other unhealthy con-
a very efficient
Many
is
exciting fluid
is
in
constant
known in which galvanic
action has been experienced with combination fillings
instances are
and amalgam, the gold being found subsequently
corroded at the line of junction of the two metals.
In
one case the action resulted from a pin on an
u^jper
of gold
gold
plate striking an
amalgam
filling in
the lower
jaw.*
Seeing that electrical
when
efiects are
always exhibited
different metals are in contact
and moistened by
exciting fluids, and that the wider apart metals
are in
their positive and negative character the
greater will
be the action developed, the selection of amalgam
and
metals for use in the mouth ought to be
carefully
considered and the contact of metals of wide
electrical
differences avoided.
The following
list gives the principal metals,
arranged
according to their usual relative electrical
position to
each other in most lifjiiids.
Commencing with the most elcdro-ner/ntivc and passdown to the most clectro-x)osif,ivc, they
ing regularly
.
have the following order
Negatuk.
— Gold,
:
platinum,
palladium, antimony,
bismuth, lead, nickel, iron, tin,
cadmium, zinc, aluminium,
l'(j,srnvK.
mercury,
silver, coj)per,
—
*
Mr.
iriuiihy, .Invni.
of
J!ril.
Drnl.
.l.v.vor..
vol. xviii. p. 300, 1S97.
32
DENTAL METALLURGY.
In this series each metal is usually nccjative to
those below it, and positive to all those above
all
it;
consequently none are absolutely positive or negative.
The above series can only be regarded, however, as a
with
general arrangement, as the order varies slightly
may be
every different liquid in which the metals
immersed.
CHAPTER
II.
ACTION OF CERTAIN AGENTS ON
METALS.
Air,
—With one or two
go no change in dry
aii-,
exceptions, the metals under-
and are not sensibly altered
in
moist air at ordinary temperatures, those most readily
acted upon being copper, lead, zinc and iron.
In moist
air, in
the presence of carbonic acid, copper becomes
coated with a green layer of carbonate called verdigris.
Lead and zinc are also acted upon, the surfaces of
these metals becoming coated with a greyish-white film.
Iron is readily oxidised, forming a brown coating known
as
riost.
When
heated, the metals are
more readily oxidised
than at the ordinary temperature.
ordinary conditions retains
siderable time, but
its
Thus, tin under
bright surface for a con-
when heated
it is
quickly tarnished.
Sulphuretted Hydrogen.— In
the presence of
sulphuretted hydrogen certain metals are tarnished or
blackened owing to the formation of sulphides.
Silver
and copper are readily blackened, while
also tarnished.
coated with a
tin and lead are
The surface of cadmium becomes slowly
yellow film of cadmium sulphide.
Sul-
phuretted hydrogen has very
other metals.
little
or no action on the
C
DENTAL METALLURGY.
34
Water.
action
— Perfectly
pure water
on the metals.
When
lias
practically
dissolved
no
oxygen and
carbonic acid are present as in ordinary water, copper,
with the
lead, iron and zinc are gradually corroded
formation of a coating of an oxide or of a carbonate of
surface
the metal, which in some cases protects the
from further corrosion.
Acids.
With the exception
of gold, platinum and
all
iridium (and other metals of the platinum group),
upon by
the metals are dissolved or more or less acted
Gold and platinum are not soluble in any single
gold), but are
acid (except selenic, which dissolves
nitro-hydrosoluble in some mixtures of acids, such as
acids.
chloric (aqua regia).
Nitric
Acid.—Tin and antimony
are converted into
other metals,
oxides by the action of nitric acid all
the acid and
with the exceptions quoted, are soluble in
some being readily soluble in the stroug
;
form
nitrates,
attacked by the dilute
acid, while others are more easily
majority of
This acid is the best solvent for the
acid!
the metals.
acid has no action on gold,
little action
platinum, iridium and mercury, and very
It dissolves the
lead, copper and bismuth.
HydrocMoric
on
^cwL—This
silver,
according to the
other metals with more or less facility,
strength of acid used, forming chlorides.
sulphuric acid
Sulplmnc ^cirf.— Boiling concentrated
lead sulphate and
converts lead and antimony into
antimony sulphate respectively.
are
silver, aluminium and mercury
Bismuth,
zinc,
are not
by concentrated sulphuric acid, but
slightly affected by the
acted upon or are only very
dissolved
dilute acid.
All other
common
metals, with the excep-
ACTION OF CERTAIN AGENTS ON METALS.
35
of
tiou
platinum,
gold,
iridium
and palladium, are
soluble in this acid, whether strong or dilute.
Acetic Acid.
— Lead
is
rapidly attacked, and copper
slowly acted upon, by acetic acid (vinegar)
acid has little or
Alkalies.
;
is
but this
no action on the other metals.
— Comparatively
few of the metals are
acted upon by alkaline solutions
;
aluminium, however,
readily dissolved in solutions of caustic potash or o£
soda.
Zinc, lead, cadmium and tin are also slowly
is
attacked by solutions of the alkalies. Alkaline chlorides
convert metallic silver into its chloride, which is dissolved in an excess of the alkaline solution.
slowly dissolves copper.
Exposure in the Mouth.— All
Effect of
metals,
with the exception of
palladium, are
the month.
the
affinity
Ammonia
more or
less
gold,
platinum
the
and
acted upon by exposure in
Copper, silver and cadmium, on account of
which they possess for sulphur, are the
metals most readily acted upon
when exposed in the
mouth, owing to the presence of sulphuretted hydrogen.
Carbonic acid, which is always present, acts with
greater
facility
metals,
while aluminium
on zinc and lead than
alkaline fluids of the mouth.
action
upon other
by the
some cases
readily attacked
is
Although
in
slow in
healthy states of saliva, yet the
presence of vegetable acids in articles of food, such
as fruit,
is
and
of drugs
as
of sulphuretted hydrogen,
niedicine,
greatly
and
facilitate
tlie
the
taking
action,
causing the metals to become black in a comparatively
short period.
The
action
is
also facilitated
when two
metals are in contact in presence of the acid fluids,
thus giving rise to galvanic action (see
Soluble
p. 30).
salts
which
are
injurious
to
health
are
sometimes
DENTAL METALIJJRGY.
36
produced by the action of the
saliva.
The
effect
metals possessing a strong affinity for sulphur
on
may be
modified in a few instances by the admixture of other
Thus, the addition of platinum to silver tends
metals.
to
minimise the
On
sulphur.
affinity
which the
latter possesses for
the other hand, the necessary admixture
of other metals
may
accelerate the action.
Gold in a
pure state retains its colour in the mouth, but when
alloyed with copper it becomes more or less tarnished,
according to the quantity of base metal present.
Solvents for Metals.
—The principal solvents used
to eifect the solution of metals are nitric, hydrochloric,
sulphuric, and nitro-hydrochloric acid (aqua regia). This
when required
last is prepared,
only,
by mixing one part
parts of
of concentrated nitric acid with three to four
concentrated hydrochloric acid. This mixture evolves
chlorine,
The
which attacks the metal and
following
table
contains
solvents for the different metals
Autiniony
Bismuth"
Cadmium
Copper
QqIiJ
Iron
.
list
of
the
:
.
.
.
•
Hydrochloric acid.
Nitro-hydrochloric acid.
Nitric acid.
.
Do.
•
.
.
•
.
.
Do.
Nitro-hydrochloric acid.
.
.
Nitric acid (dilute *) or hydrochloric
acid.
Lead
.
Mercury
jsficliel
Nitric acid.
.
Nitric or nitro-hydrochloric acid.
Do.
Nitric acid
.
.
.
f^ilver
.
rpi,,
.
(liot).
Nitro-hydrocliloric acid.
.
Nitric acid (dilute).
Hydrochloric acid (when heated).
•
.
.
*
•
.
.
Palladium
Platinum
best
Soh-cmt.
Metiil.
AlumiiiiMiii
effects its solution.
a
Hydrochloric or siilphuric acid.
.
Dilute acid
=
equal parts of acid and water.
CHAPTER
III.
ALLOYS.
Most
to
metals are capable of uniting with one another
form a
class
of bodies
termed alloys, in which
the physical properties are sometimes quite different
from those of the constituent metals. Alloys, however,
being composed of metals, will possess all the physical
and chemical characteristics common to metals they
;
have the metallic Instre, are more or less ductile, malleable, elastic,
and sonorous, and are good conductors of
While retaining, however, these
heat and of electricity.
characteristics, the bodies
produced are frequently so
modified in some of their properties that they often do
not resemble either of the constituents and may consequently be regarded as
istics
new
metals, having character-
peculiar to themselves.
The
most generally useful are frequently those
whose constituents are most dissimilar in character.
alloys
By means
of alloys, therefore, the
number
of useful
metals
is multiplied, as it were, and usefulness sometimes given to such as are separately of little value.
Comparatively few of the metals possess properties
such as render them suitable to be employed alone, but
most of them have important applications in the form
of alloys.
Pure gold possesses many good qualities,
DENTAL METALLURGY.
^8
seldom used alone, as it is too soft to resist wear
and tear copper is therefore added to harden it as
Bismuth and antimony have
well as lower its cost.
comlittle application in an uucombined state, but in
bination with other metals they form a series of alloys
dental
of much value, several of which are used in the
from
predict
It is not always possible to
laboratory.
but
is
;
the properties of the various metals employed what
from given
will be the character of an alloy formed
proportions of each.
Thus,
it
might be supposed that
gold and lead, which are both very malleable metals,
would produce a malleable alloy but, although these
obmetals unite readily in all proportions, the alloys
;
utility
tained are in some cases very brittle and without
in the arts.
one
Metals differ in respect to their affinity for
equal facility
another, and do not therefore alloy with
and iron, but the
is difficult to unite silver
;
thus,
it
former combines readily with gold, copper, or
The
much
^
received
subject of the constitution of alloys has
progress
attention within recent years, and great
has been
made
alloys with that
it
lead.
metallic
in connecting the behaviour of
As the result of research
of solutions.
that alloys
has become more and more evident
may
(i) Those which
be divided into two main classes:*
constituent metal?, and
are merely solutipns of the
contain compounds in solution, for
(2) those which
as true chemical comw'hile few alloys are regarded
compounds
solution
pounds, most series of alloys hold in
are disposed to attribute
to which some experimenters
definite chemical formula.
*
ll,,be.-ts-A.>sten,
1897.
'Alloys"; (^uiU.r Lectures, Ho.Mcty
.,r
Arts,
ALLOYS.
As
compounds
these
molten mass of metals,
separate
them
39
dissolve in all proportions in the
it is
very
difficult to satisfactorily-
for examination.
Although metals may be mixed in the fused state,
it by no means follows that they will remain in admixture if they are allowed to cool slowly, or sometimes
even rapidly.
and zinc be thoroughly mixed
and slowly cooled in a deep mould,
If lead
in the molten state,
the two metals separate almost completely
being lighter,
rises to
at the bottom.
the zinc,
;
the top, leaving the heavier metal
With other metals there
is
sometimes
a tendency, on solidification, for one of the constituents
to
become concentrated
in the middle or at the surface
of the mass, thus giving a casting
homogeneous.
It is
now
which
not perfectly
is
well established that most of
the possible associations of any two metals have more
than one point of
solidification,
and do not
pure water does, at a single point.
many
There
" freeze," as
is,
however,
one particular association of
the two metals which is more fusible than the rest
in
series of alloys
of the alloys of the series.
eutedic alloy, and
tion, that
is,
it
This alloy
is
called the
possesses a single point of solidifica-
when the
sharply as a whole at
eutectic alloy
a given
is
cooled
temperature.
it
sets
Many
two metals contain an eutectic alloy
and consequently have two points of solidification.
As a molten mass of alloy cools down it begins to
solidify at a certain point, but the eutectic alloy on
account of its low solidifying-point remains fluid, and
entangled in the portion which has set, until the tem-
associations
perature
alloy, at
of
falls
to the solidifying-] )oint of the eutectic
which temperature
completed.
There
is,
solidification of the
therefore, in
many
cases
mass
is
abundant
DENTAL METALLURGY.
40
opportunity in the interval between the
initial
point of
and that of the eutectic for
the mass to arrange itself in a peculiar way which
frequently results in a want of uniformity of the mass.
solidification of the alloy
A
the
striking instance of this
alloys of the
is
afforded in the case of
silver-copper series,
all
of
which,
except the eutectic alloy, exhibit divergencies in comThe eutectic alloy of the series contains 71.8
position.
preper cent, of silver and solidifies at 778° 0. The
standard
sence of the eutectic has been detected in
per cent, of silver) and in several other
members of the series, and consequently these alloys
silver (92.5
have two points of
solidification.
case of standard silver, the initial solidify883° C.
ing-point of which has been ascertained to be
to
begins
it
As a molten mass of this alloy cools down
To take the
but the eutectic alloy remains fluid,
until the
and entangled in the portion which has set,
the
temperature falls to 778° C, at which temperature
solidify at 883" 0.,
the interval
mass sets sharply as a whole. During
is ample
between these two solidifying-points there
a peculiar
opportunity for the mass to arrange itself in
the mass.
way, hence the want of iiniformity of
The
eutectic alloy in this
and in several other
series
composition corresponding
of alloys occurs exactly at a
has led to the conclusion,
to a definite formula, and this
alloys are chemical
as previously stated, that eutectic
compounds.
is, however,
The exact composition of the eutectic
The most recent experiments
difficult to determine.
eutectic alloys does
have shown that the composition of
with simple atomic propornot in general correspond
metals, and this fact, and the
tions of the component
A.LLOYS.
theory of the subject, point to the conclusion that the
eutectic alloy
is
not generally a compound, and hence
Further research, however,
should not have a formula.
is
necessary before any definite conclusion on this point
can be generally accepted.
The tendency
of the con-
known
as liqucdmi,
stituents to separate on cooling is
and
is
a matter of importance
industrial purposes, as for
difes,
in"
casting alloys
for
In some instances
&c.
where liquation has taken place a more homogeneous
alloy may be obtained by breaking up the ingot and
remelting (see also
p.
175).
Physical Properties of Alloys.
Colour.
—The
strongly coloured
copper and gold, are very
much
metals, such
as
modified in tint by
alloying with metals of light colour, such. as aluminium,
Thus, when 5 per cent, of aluminium
added to copper the resulting alloy has a beautiful
silver
is
and
tin.
golden-yellow colour, and zinc
when added
in certain proportions acts in a similar
colour of gold
is
is
The
manner.
modified by the addition of only one-
twentieth part of
when gold
The colours
to copper
silver,
and
it
alloyed with half
is
entirely destroyed
its
weight of
silver.
of alloys, however, are not always dependent on those of the separate metals.
For example,
when
of
thirty -nine parts of gold are
aluminium
an
ijitensely
obtained.
Antimony,
weight of
copper
also,
added
to eleven parts
ruby-coloured
when
alloy
is
fused with an equal
produces a violet
alloy
known
as
" regnlns of Venus."
Density.
the mean of
—
'I'he specific
gravity of an alloy
is
rarely
the densities of the constituent metals,
DENTAL METALLURGY.
42
When
being sometimes greater and sometimes less..
has
contraction
the density is increased it shows that
occurred, and chemical combination has probably taken
place between the constituents.
When
c.qmnsion takes
place by the union of the metals, the density will be
below that calculated from the densities of the constituents.
Fusibility.
—In
nearly
all
of an alloy is lower than the
cases the melting-point
mean
melting-point of the
conconstituent metals, and in some instances it is
either of its
siderably lower than the melting-point of
constituents.
bismuth with one part of
temperature of
lead and one part of tin melts at a
An
alloy of
two parts
of
melting-point of
93° C. (200° F.), whilst the lowest
232° C. (449' F-)the constituent metals is that of tin,
the
By the addition of a small quantity of cadmium
melting-point
reduced
is
to
65° C.
(150° F.) (see
Fusible Metals, p. 51).
expansion of alloys is
of
the ratio of the relative volumes
Expansion by Heat.— The
approximately
in
the constituent metals.
Specific
the
mean
capacity for heat of alloys is
which
specific heats of the metals
Heat.— The
of the
compose them.
Conductivity for Heat and for Electricity.—
to
an alloy are found in some cases
powers of the combe the mean of the conducting
have apparently no
ponent metals, and in others to
mean.
relation whatever to such
the
Alloys are generally harder than
These properties
in
Hardness.—
mean hardness
*
of
the constituent metals.*
Calvert and Johnson, PhU.
4tli series, xvii. p.
This
114
is
ALLOYS.
43
especially noticeable in the silver-platinum alloy
as
"Dental Alloy
" (see
p. 174).
contrary, the hardness
lated, tin-zinc alloys
is
known
In some cases, on the
slightly less
than that calcu-
being examples.
Malleability and Ductility.
—These
properties
and sometimes completely deThe brittleness produced
stroyed by alloying metals.
by the addition of lead to gold has already been menare usually diminished
tioned.
Action of Solvents.
alloys
is
— The
sometimes very different from their action on
the constituent metals alone.
uble in nitric acid, but
alloyed with
much
much
is
gold
it is
Thus, platinum
is
insol-
dissolved in this acid
when
silver; silver also
when
alloyed with
not affected by nitric acid, but
completely soluble
excess.
action of solvents on
when present
it
is
in the alloy in large
Generally speaking, however, alloys are readily
soluble in the acids which are solvents of
the con-
stituent metals.
Preparation of Alloys.
adopted to effect the union of
is,
method ordinarily
metals is by fusion
that
—
melting them together, usually in a graphite crucible.
To do
of
— The
this successfully, however, requires a
the properties
Sometimes the
of
the various
metals
knowledge
employed.
mixed
and melted
together, but in other cases one of the metals is melted
first and the others subsequently added to it, sometimes
in the fluid state, but more often in the solid.
A little
charcoal powder should be placed on the surface of the
charge to prevent oxidation, and the lifjiiid metal
constituents are
should be carefully stiiTed with an
ii'on
or fireclay rod
and in sach a manner as to secure
most complete intermixture without liability to in jure it
after each addition,
DENTAL METALLURGY.
44
The molten
an oxidisiag atmosphere.
alloy should be poured at the lowest possible temperaby exposure
to.
ture consistent with the
proper degree of
liqiiidity,
excessive heating always being avoided.
—There
Alloys for Dies and Counter-Dies.
are certain properties which
metallic die
it is
indispensable that a
and counter-die should possess in order
fully the requirements of the dentist.
to
These
answer
may be summarised as follows
hard to resist aiiy
1. A die should be sufficiently
necessary force applied to it in stamping the plate
during swaging without suffering any material change
in the form of
its face.
It should not to
2.
any material extent contract in
the act of cooling.
It should be fusible at a
3.
should not be brittle,
4. It
low temperature.
but should be sufficiently
hammer
cohesive to resist the repeated blows of a heavy
these
without cracking. No metal possesses perfectly
hardness, non-contractibility, fusibility
or two
cohesiveness, although metals possessing one
properties
and
of
of these are readily obtainable.
Much
pended
time and thought have therefore
in the effort to discover
some
alloy
been ex-
which
shall
referred to,
possess more fully the several properties
of metals
but although a large number of combinations
these^ are
of
have been suggested, comparatively few
a die it is
In selecting an alloy to serve as
used.
nature of some
necessary to bear in miad that the
melting, and that their
is changed by repeated
alloys
Thus, an
altered.
physical properties are materially
answer the requirements of a die for a time,
alloy
may
but
very
much
deteriorate
by constant
use.
Some
ALLOYS.
when they
alloys also,
tend to " liquate
" or
solidify
45
from a
state of fusion,
even separate into two distinct
which may
layers of different composition, a property
prove fatal to the
the bottom layer will
die, as
fill
up
the deeper portion of the mould representing the most
prominent part of the
and may be
and
soft
totally
purpose of swaging.
unfit for the
The
die,
most frequently employed for
alloys
counter-dies are as follows
Type Metal. — The
:
better qualities of
this alloy
antimony
consist of three parts of lead with one part of
and one part of
tin.
In different proportions, however,
sometimes with
these metals,
dies or
the
addition of small
quantities of copper and other metals, form
different
grades of type metal (see also p. 211).
This alloy is sometimes used for dies and
less fre-
quently
for
"when used
adding to
counter-dies.
as a counter to a zinc die it
it
states *
Richardson
is
an equal quantity of lead
;
that
improved by
may
it
also
be used in the form of a die in connection with a lead
counter after rough stamping with a zinc die."
Type
metal
is
considerably harder than lead, but a
little
softer
and gives sharp castings. It melts more
readily than zinc, being more fusible than the average
than
zinc,
and the contraction
than one-half that of zinc.
It is somewhat
and therefore needs very careful handling when
fusibility of the constituent metals,
is
less
brittle,
used as a
with the
die.
air
When
lead,
melted in contact
even when
taken, thus the composition
after repeated melting.
*
is
the antimony and tin are oxidised
more readily than the
is
the alloy
When
is
all
much
precaution
very liable to alter
preparing this alloy the
" Mecliiiiiicnl Dentistry," 1S94 edit.
p.
124.
DENTAL METALLURGY.
46
lead
and
then the anti-
tin are first melted together,
added, a layer of charcoal being used to prevent
Excessive heating must be avoided.
oxidation.
mony
Babbitt's Metal,— This
part,
antimouy two
and
parts,
is
an alloy of copper one
tin six parts
;
the propor-
however, vary considerably with different makers.
"iThe melting-point of this alloy is lower than that of
zinc and somewhat higher than that of lead, so that
tions,
counter-dies of the latter metal can be readily
The alloy contracts but
it with proper care."
solidification
brittle,
brittle
and
and is nearly as hard
as zinc, btit
It is
needs care in using.
by the addition
more
of
made
to
little
on
somewhat
rendered
less
tin.
The following proportions of the above metals are
recommended by Fletcher for dental purposes Copper
one part, antimony two parts, tin twenty-four parts.
:
This alloy melts at a little lower temperature than the
is
above, and on account of the larger quantity of tin it
somewhat less brittle than Babbitt's metal of the proportion given above.
Haskell recommends the following alloy for dental
Copper one, antimony two, tin eight. " This
work
:
alloy is nearly as
hard as zinc and has
less shrinkage.
used to finish the swaging of a plate after being
As this alloy
nearly completed on the zinc model.
fuses at a lower temperature than lead, it is necessary
It
is
forms a constituent,
such as lead five, tin one. The die should also be quite
before
cold and covered with a quantity of whiting
to have a counter-die in
inserting
it
tin
in the molten metal."*
Babbitt's metal
is
copper with half the
*
which
best prepared by
tin,
first
melcing the
then adding the antimony and
H. Rose, Brit. Jimm. of Unit. Sc.
1895,
P-
53i-
ALLOYS.
the remainder of
finally
the
tin,
47
stirring well after
each addition and then casting into suitable moulds.
Charcoal powder should be thrown on to the surface
of the metal to prevent oxidation.
to waste
and
alter in
This alloy
is liable
composition by repeated melting.
—
Spence's " Metal." This is not, strictly speaking,
an alloy, but a compound obtained by dissolving metallic
The sulphides of iron,
sulphides in melted sulphur.
lead,
antimony and zinc are usually employed in vary-
ing proportions according to the quality of the product
desired,
which
depend upon the use for
will naturally
The Spence's "metal" usually
employed for dies is " sulphide of iron," made by
melting iron with excess of sulphur. The compound
which
it
is
designed.
melts at i6o° C. (320° F.), expands slightly on cooling
and gives very good castings it is hard although somewhat brittle, and needs care in handling. This " metal "
should be melted in a fireclay crucible and not in an
;
By
iron ladle.
remelting, loss of sulphur
is
invariably
occasioned and the composition of the mass altered.
Alloys of Zinc and
Tin.— These
alloys
are
frequently employed in casting dies for swaging plates,
and are best prepared by melting the zinc and then
adding the tin. According to Richardson, an alloy
suitable for dental purj)oses,
consisting of zinc four
one part, " fuses at a lower temperature, contracts less on cooling, and has less surface hardness
than zinc. This alloy is also more rigid than zinc and
parts, tin
less brittle."
Fletcher
two
and
It
parts,
recommends the following proportions
tin one part, and states that all alloys of
:
zinc
zinc
tin are superior to zinc alone for dies.
may
be remarked, however, that in casting alloys
DENTAL METALLURGY.
48
which zinc predominates there is a
tendency for the metals to separate at the bottom of the
mould, and this tendency increases as the proportion of
of zinc
and
tin in
tin decreases.
The waste
in melting is greater
when
zinc
is
in
All the alloys of zinc and tin give sharp
excess.
and on this account are largely employed for
casting ornamental objects (see also p. 206).
Alloys of Tin and Antimony. Alloys of these
Eichardson gives
metals have also been used for dies.
the following proportions tin five parts, antimony one
castings,
—
:
This alloy has a low melting-point, contracts
but slightly on cooling, is harder than tin, and suffiIt is, however, readily oxidised on
ciently cohesive.
part.
melting, and should be poured as soon as thoroughly
Alloys of tin and antimony are harder than
molten.
tin but less malleable,
brittle
greater
is
and the tendency
the
as
proportion
of
become
antimony
to
increases (see also p. 2 7).
1
Brass.—"
dies, brass,
Before the introduction of zinc for dental
an alloy of copper and
this purpose.
It is generally
zinc,
composed
was used
for
of two-thirds
copper and one-third zinc a small percentage of lead
being sometimes added when used for dental purposes.
;
Brass
may be melted and poured
to ensure
good results
it is
the same as zinc, but
as well to have a good
head
This can be
of metal for the die to contract from.
of sand on
full
effected by placing another casting ring
bell-shaped
the one containing the model, and catting a
comes
cavity in the upper ring, tapering down until it
back of the plaster model. The model is then
removed and the upper ring adjusted to the lower, and
brass can
securely cemented to it by sand the melted
to the
;
ALLOYS.
49
then be poured through the opening on to the sand im-
and when hard and the casting removed and
cooled the bell-shaped piece of brass may be sawn off.
It must be mentioned that the sand impression should
be smoked, and a good carbon surface produced on it
by burning resin. This greatly improves the surface of
pression,
the casting."*
Other Alloys for Dies.
lead with
tin,
—A
of
series
alloys of
bismuth and antimony, having compara-
and possessing other properties
necessary for a die, are given by Austen in a paper on
His results are embodied in the followmetallic dies.f
ing table, in which zinc is introduced for the purposes
tively low melting-points
of comparison.
Alloy.s for Dies.
I
Lead.
Tin.
BisAntimutli. mony.
Zinc.
Contrac-
Haivl-
BHttlc-
tion.
ness.
ness.
.00133
.00200
.00066
.00266
.00566
.00500
2.7
00433
1.4
2.8
McItiiii;'-i)oiiit.
200° F.
200°
250°
300°
320°
340°
420°
440°
779°
93° C.
93°
121°
139°
160°
171°
216°
227°
415°
2-5
2-3
1-7
1.9
2.2
•00633
.01366
I
In the above table the hardness of zinc
is
taken as
and the brittleness as five those alloys having a
hardness below five being malleable, and those above
Kve being more brittle than zinc.
one,
;
*
K. Rose,
t
Am.
/////. .Itmni.
Jimnt.
nf Dciil
11/ Drill. Sr.^
.
Sr., 1895,
xx.wiii.
vol. vi. p. 367.
D
p.
530.
DENTAL METALLURGY.
50
Fusible Metals.
This
uame
is
given to a series of alloys which melt at
very low temperatures, and consist chiefly of tin, lead
and bismuth, with occasionally the addition of cadmium
Many of the alloys obtained by the
and mercury.
union of these metals, in different proportions, melt at
far
a temperature below the boiling-point of water and
below the melting-point of the most fusible metal
entering into their composition.
Tin and bismuth both have low melting-points and
they readily combine in all proportions when fused
together, the resulting alloys being more fusible than
either of the metals taken separately.
very small quantity of bismuth imparts to tin more
hardness, but the alloys become brittle as the pro-
A
portion of bismuth increases.
Alloys of
tin,
bismuth
and lead are more fusible than those containing only
these
two of these metals. It is difficult to obtain
as there is
alloys in a perfectly homogeneous state,
somewhat at the
a tendency for the lead to separate
bottom
of the
mass while solidifying from
a state of
are rapidly tarnished in the air, and
above
more so in boiling water. The alloys of the
addition
the
metals are rendered still more fusible by
readily
being
alloys
of cadmium, some of the resulting
fusion.
They
melted in boiling water.
Cadmium, however, does not
render the alloys so britle as bismuth.
The
following
melting-points of a
table
shows
number
the
composition and
of " fusible metals "
:
1
1
ALLOYS.
51
Fusible Metals.
Hi till"! 11 1
-Li
1
11
nil oy
po \vi t z
4
Wood
s
ulloy
1;
8
Fusible
Jl
Fusible
c
0
3
J
2
I
2
4
2
8
2
10
2
,,
s'
2
8
„
3
,
e
)i
51
)I
1'
!)
i»
:)
n
11
2
3
I
I
3
2
S
I
'3
I
167°
170°
175°
187°
197°
197°
200°
202°
203°
310°
320°
I
I
I
I
I
2
3
2
I
4
4
12
12
IS
I
4
Mi,'ltinf4'-l)0iut.
145° F.
150°
160°
8
lOi
,
CtHliiiiuiii.
1
2
Diilton's.
Newton's
4
3
Fusible
Onion's
Ucll
Lb
Lend.
J
2
0
16
8
ii
Tin.
331°
338°
341°
352°
392°
16
All the fusible alloys are brittle and expand on cool-
ing and are
all more or less
Preparation. Fusible
hard.
—
melting the
are
alloys
prepared
constituents together under a
charcoal and well stirring with a stick of hard
before pouring.
Mercury
is
of one-sixteenth of its
alloy " a
new
alloy
temperature of the
is
formed which
body.
still
Thus, by the addition
weight of mercury to
human
wood
sometimes added to
further lower the melting-point.
by
layer of
"
Darcefs
is fusible at the
The addition
of one
two parts of mercury to "Newton's alloy" also produces a very fusible alloy, and any of the fusible
metals may be rendered more fusible by the addition
of mercury.
The mercury is added after the other
to
metals are perfectly melted.
DENTAL METALLURGY.
52
Uses in the Dental Laboratory.— In
tbe
dental laboratory fusible metals are mainly used for
"fusible plugs" to vulcanisers, the composition of the
alloys being such that the plugs will
"blow
out,"
when the temperature exceeds about 350°
i.e.
melt,
F. or 177" C.
Fusible metals have been used in crowu, bridge, and
vulcanite work, and novel methods have been introduced
for accomplishing in a simple
manner many kinds
dental work with fusible metals.
of
In a very interesting
paper read before the Britiah Dental Association in 1891,
E. P. Lennox of Cambridge drew attention to a number
work.
of uses for these alloys in connection with bridge
Mellotte has introduced the following fusible metal
for
crown and bridge work
:
bismuth
8, tin 5,
lead 3.*
This alloy melts at 100° 0. (212° F.) and expands on
It is harder than tin, but not so hard as
solidification.
For obtaining accurate models with
zinc, and is brittle.
metal he uses a compound of potter's clay
and glycerine known as " moldine," which retains its
it stiffens, however, with constant
plasticity for months
this fusible
:
use,
little
but
may be made
plastic
by moistening with a
glycerine.
Determination of Melting-point of Fusible
Alloys.— A very simple method for determining the
the
melting-point of a fusible alloy consists in melting
burner.
Bunsen
alloy in a porcelain crucible over a
thoroughly melted the flame is removed and a
thermometer held carefully in the molten mass.
When
The temperature
at
which
solidification takes place is
be readily ascertained, as the mercury
stationary for
thread of the thermometer will remain
The
some considerable time when this point is reached.
noted
;
this can
* Efisip:, "
Dental Metallurgy," 1893,
p. 263,
ALLOYS.
53
thermometer, which becomes embedded in the
alloy, is removed by agaiu melting the alloy.
When
due precaution
is
taken there
is
solidified
no risk of
breaking the thermometer, but it is very necessary to
avoid excessive heating of the alloy.
Another method
quantity of the alloy
is
This
of a delicate
the stem
attached to
is
small
placed in a glass test-tube,
and the open end closed with a cork.
tube
A
illustrated in Fig. 6.
is
thermometer just above the bulb by binding
it with thread or fine wire or by means of a
small rubber ring slipped over the larger end
of the
thermometer stem.
The thermometer
and tube are placed in a glass vessel containing water and the vessel gently heated until
the alloy melts the lamp is then removed and
the temperature at which the alloy solidifies
The
accurately noted by the thermometer.
;
mean temperature obtained from
will give
process
several observations
the melting-point of the alloy.
of
heating
During the
should be constantly
the water
For determining the melting-points of alloys
which melt at a temperature a little above that of the
agitated.
boiling-point of water, a liquid with a higher boilingpoint,
such as
glycerine,
may
with
advantage
be
employed instead of water. The alloys should be previously melted and cast on a flat surface in order to obtain
This should be broken up and a small
a thin sheet.
portion only used for determining the melting-point.
The melting-points of alloys which are not sufficiently
fusible to test by the above methods may be approximately determined by placing a fragment of metal of
known melting-point
in
the
locality
of the piece of
DENTAL METALLURGY.
54
and carefully subjecting them to a
uniform heat before the blowpipe, or by other means.
Thus, a small piece of bismuth (melting at 514° F.)
alloy to be tested
may melt
placed beside the alloy
before the alloy
fused, though a piece of lead (melting at 617° F.)
is
may
remain unmelted at the fusing-point of the alloy.
It follows, therefore, thab the temperature at which the
alloy melts
must be between 514° and 617°
Withing recent years very
F.
precise determinations of
the melting-points of metals and of alloys have been
made by means
of pyrometers.
almost universally adopted
when
a junction of
electrical
is
The instrument now
based on the fact that,
two dissimilar metals
equilibrium of the system
the measurement of the
difference
is
is
heated, the
disturbed,
and
of potential thus
produced affords a means of estimating the temperature
In its latest form the instrument conof the junction.*
sists of a thermo-couple of two wires, one of platinum
and the other of platinum alloyed with 10 per cent, of
rhodium, simply twisted at the ends, and connected
with a dead-beat galvanometer usually of the suspendedcoil type. An autographic recorder is used in connection
with the thermo-couple whereby a photographic curve,
of the cooling of a mass of metal or of alloy, is
registeied.
The pyrometer
j
is
unction to certain
calibrated by exposing the thermo-
known
temperatures, such as the
solidifying-points of salts or of readily fusible metals.
a mass of metal passes from the solid to the fluid
state, the temperature remains constant for a short
As
period, hence there
*
For
is
no
a description of tliis
difficulty in
recognising the
pyrometer, see "Introduction to Study
of Metallurgy," Roberts-Austen.
—
ALLOYS.
55
meltiug- or the solidifying-points. By means of this
instrument much vahiable information respecting the
molecular constitution of alloys has been obtained.
Solders.
This term
is
given to alloys used in joining metallic
by fusing them upon the surfaces when in
contact and allowing them to coSl, thus obtaining a
more or less firm joint at the point of juncture.
The alloys used must be necessarily more fusible than
the metal or metals to be united and must possess the
property of flowing readily. They must also consist of
surfaces
metals which possess a strong affinity for the substances
Solders should, if possible, be
to be soldered together.
of the same colour as the metals to be joined, and should
not discolour or undergo decomposition with age.
Solders for dental purposes must also be capable of
resisting the action of the fluids of the
a solder has a high melting-point
heat— it is said to be " hard."
meltiug-point
is
fusible metal, or
i.e.
mouth.
at or
When
above a red
When, however, the
lowered by the addition of an easily
by the addition
of a greater
amount
the more fusible constituents of the alloy, the solder
The term "soft solder"
said to be "easy" or soft.
of
is
is
usually applied to the alloys of tin and lead used for
soldering (see p. 211).
Each metal
kind of solder
requires, to a certain extent, a particular
;
the alloys most suitable as solders are
described under the different metals.
Preparation of Solders,— In making
solders
great care must be taken to secure uniformity of comThey are prepared in the same manner as
position.
other alloys by melting the constituent metals under a
DENTAL METALLURGY.
56
layer of
powdered charcoal and well
stirring the molten
mass before pouring. The metals used must be free
from impurity, and may with advantage be employed
in a " granulated " state.
form
Many
of powder, obtained by
solders are used in the
filing the ingot of alloy;
and gold solders are usually
but
silver
and
" soft solders " are generally sold in sticks.
rolled into sheets
CHAPTER
IV.
THEORY AND VARIETIES OF
BLOWPIPES.
—
The blowpipe is an
Theory of the Bloiopipe Flame.
instrument which is nsecl to direct a stream of air
lamp or coal-gas flame in order to produce a
more intense heat. The introduction of the air within
the flame at once destroys its luminosity for the same
into a
reason that the luminosity of the gas-flame
in the
Bunsen burner
—
viz.
that
with a proper proportion of air
oxygen of the
body
ing
a
it
is
when gas
destroyed
is
mixed
before being burnt the
burns the whole of the carbon in the
air
of the flame,
mak-
non-luminous.
In
well-formed blowpipe
may
flame two parts
distiugaished
Jlame, which
:
is
be
the inner
a.
blue and
and around this
an almost colourless
pointed,
known as the outer
The inner flame
Jlame.
Fig.
7.
flame
reducinfj Jlame, as
it
(Fig. 7, h)
is
often called the
contains excess of carbon, and
is
therefore capable of deoxidising or reducing substances.
The outer flame
(Fig. 7, a) is
known
as the oxidviing
DENTAL METALLURGY.
58
as
flame,
contains excess of oxygen and
it
readily
changes metals into their oxides. The reducing flame
is best obtained by placing the blowpipe nozzle in the
edge of the flame; whilst the oxidising flame
duced,
when the
nozzle
is ptished.
much
is
pro-
further into the
flame and a stronger blast employed.
important in soldering operations to bear in
It is
mind the
properties of the
two flames,
as the object to
be soldered would become unnecessarily
oxidising
flame were
"
dirty " if the
owing to the excessive
used,
oxidation of the base metals present.
Mo^dh Blowpipes. Blowpipes should be
—
either brass or
German
made
of
silver, as these alloys are poor
The simplest form of blowpipe
a plain metal tube, 200-240 mm. long
conductors of heat.
consists of
(8 to
10 inches), larger at
the
end applied
to
the
mouth, and tapering gradually to a point at its other
The tube is curved for convenience in
extremity.
directing the blast to the desired spot (see Fig. 8).
The aperture of the blowpipe nozzle should be quite
circular
and not too
This
large.
adjustment in new blowpipes.
should be slightly
the aperture
;
hammered
When
of the nozzle
be enlarged by thrust-
until a perfectly circular
continued for a long period
the tube and is liable to be
a steady flame
moisture collects in
it,
The end
over, in order to contract
this should again
ing a large pin through
opening is produced.
generally requires
is
THEORY AND VARIETIES OF BLOWPIPES.
59
expelled by the pressure of the air, causing disturbances
To avoid this a hollow chamber is somein the flame.
midway
times constructed about
hold any moisture that
may
in the instrument to
mouth
escape from the
(Fig- 9).
.
Another form of blowpipe for overcoming this diffiIt consists
culty is supplied by Letcher, of Truro.
Fig.
9.
brass tube fitting into a small chamber, which
collects and retains the moisture, and the bottom of
of a
which
is
movable, so that
it
can be taken
off
and the
moisture shaken out at the end of the operation (see
Fig. 10).
Hot-Blast Month £lotu2}ipe.— Fletcher, of Warrington,
has introduced a new form of blowpipe for obtaining
temperatures beyond those attainable
with
ordinary
blowpipes.
The
shown
hot-blast
in Fig.
1
1
.
mouth blowpipe, as it is termed, is
The improvement consists in coiling
Via.
II.
the end of the tube into a light spiral over the point
l^y this arrangement the air becomes
of the jet.
DENTAL METALLURGY.
6o
coil
takes
up the heat which would otherwise be wasted.
The
may
con-
heated iu passing thvongh the tube, as the
moisture
also
which
collect in the
tube
is
verted into steam.
It
is
claimed that by the
much higher temperatures
use of this instrument
are reached than is possible
with the ordinary blowpipe, and- that with the same
amount of blowing a larger amount of work is accomplished, while, if a high temperature
the labour of blowing
The operation
is
not required,
redu.ced in proportion.
blowing
of
is
is
not
always
readily
acquired, but usually a few days' practice removes
the difficulty at
first
all
experienced in producing a con-
tinuous steady blast, and
when once produced
it
may
be continued for a considerable time without fatiguing
even the muscles of the cheeks. The operation is
mouth with air, expanding
the cheeks, and then keeping up a steady pressure
commenced by
filling
the
respiration being allowed to go
with the muscles
on as usual through the nose. To avoid tiring the
muscles of the lips by continual blowing, the trumpet
;
mouthpiece, shown in Fig. lO, which is merely pressed
The
against the open mouth, has been recommended.
curvature of the mouthpiece should, however, correspond
to that of the
mouth and
fit
comfortably, otherwise
it
lips
will require to be pressed very forcibly against the
With this form
in order to prevent the escape of air.
of
mouthpiece an uninterrupted blast may be kept up
fatigue to
for a long period without causing the least
the muscles of the lips.
The length of the blowpipe
(8 inches), but, as
which the flame
it is
is
is
usually about 200
mm.
important that the object upon
directed should be seen distinctly,
1
THEORY AND VARIETIES OF BLOWPIPES.
6
operator
the length must be adapted to the eye of the
short-sighted persons require a short blowpipe, whilst
;
for the long-sighted a longer
one
is
necessary.
Blowpipes.— Ma.ny of the
Bellows
operations
con-
ducted in the dental laboratory require the application
with the
of a higher temperature than that obtainable
mouth blowpipe. In order to effect this, special blowpipe burners are employed, while the necessary blast
obtained by means of a suitable blower.
A
form of burner commonly employed
The burner
in Fig. 12.
is capable of being ad-
angle,
directed
at
any
and when neces-
sary can
in
represented
that the flame
justed so
can be
is
is
be firmly fixed
position by
means
of
at the base.
wing nut
The jet of this blowpipe
a
is
of
removable, so that jets
any
size
as desired.
is
so
can be fitted
The tap
arranged
will turn the
lever
that
light
leave a small pilot
Fig.
12.
it
when pushed backward, and
light when drawn forward, thus
out
avoiding the necessity of relighting for each operation.
The burner is mounted on a heavy bi'ass stand to make
it
perfectly steady
Oinen's
when
Bloiopi'pe is
in use.
also
very frequently used.
It
two peparate brass tubes arranged as shown
inin Fig. 13, thus making the gas and air supplies
Each tube is fitted with an india-rubber
dependent.
consists of
valve,
on which the thumb or fingers are placed in
DENTAL METALLURGY.
62
order to regulate the gas and
ment the blowpipe flame
is
pipe for
many
By
this arrange-
under perfect control.
Fig.
Automatic Blowpipe.
air.
13.
—-A very convenient
purposes in the dental
hand blow-
laboratory
Fletcher's automatic blowpipe, shown in Fig. 14.
is
is
This
a very manageable and effective instrument and
is
capable of producing very high temperatures, and the
intensity of the heat
may be
Fig.
graduated at
will.
The
14.
blowpipe is held in the hand and is provided with taps
as shown, which are under perfect control, so that
the supply of both gas and air can be readily regulated.
Complete mastery over the character of the flame can
be gained after a few minutes' practice. When burning
at full power the blowpipe consumes about ten cubic
feet of gas per hour.
Other forms of automatic blowpipes well adapted for
dental purposes have also been designed by Fletcher.
For soldering operations in
Hot-Blast Blovpipe.
which pure gold is used, as in continuous-gum work,
—
and other operations requiring
a greater intensity of
heat than that furnished with ordinary gas blowpipes,
THEORY AND VARIETIES OF BLOWPIPES.
63
Fletcher's hot-blast blowpipe is sometimes used (Fig. 15).
This blowpipe is so constructed that the air-pipe is
around the gas-pipe
and both are heated by an
independent Bunsen burner,
the gas siipply to which is
coiled
regulated
By
this
by a separate
simple device
the
claimed that
the apparatus
that
of
is
an
tap.
it
is
power
of
about double
ordinary
gas
Fig.
15.
blowpipe.
The advantage of the hot blast is only apparent
when a pointed flame is required having a high temperature
;
under these conditions
platinum wire
may be
The blowpipe
is
it
is
stated
that
thm
fused.
also supplied
with a bench light
attached for convenience in working.
Blowing Apparatus.— The blast necessary for the
production of the flame
with gas blowpipes is obtained by means of a footblower, connected with the
burner by a flexible rubber tube.
s..
A
1^^^
form
Fig.
16.
simple
of
and compact
bellows
for
the
purpose is shown in Fig.
With this apparatus
16.
a
obtained which is
continuous, equable supply of air is
A disc
operator.
completely under the control of the
bellows,
of rubber is fitted beneath the
under the pressure of the
air,
which expands
while the bellows are
m
DENTAL METALLURGY.
64
motion, forming a reservoir which holds the
and
air
thus affords a veiy compact, powerful, and effective
arrangement.
The bellows
are
mounted on
a stand,
thus reducing the risk of injury to the disc, and fitted
with a step for the foot, so that they can be used with
ease,
whether the operator
is
standing or seated.
Oxyhydrogen Blowpipe. — Blowpipes
now
are
dental purposes in which the
means
of compressed oxygen
by
blast is obtained
The blowpipes are very similar in
instead of by air.
specially designed for
construction to those previously described for use with
air blast.
The oxygen
is
supplied from a cylinder of the com-
with
a
regulator for controlling the pressure of gas, as this
is
pressed gas.
The cylinder should be
fitted
more satisfactory than a fine adjustment valve. When
oxygen is not readily obtainable, nitrous oxide may be
employed, but
is
not so suitable as
it
gives rise to a less
steady flame.
Oxy hydrogen blowpipes
are
now being more
exten-
sively used in the dental laboratory than formerly, as
they are well adapted to certain classes of work the
heat obtained, however, is very intense, and care must
;
be exercised in using them.
CHAPTER
V.
MELTING APPLIANCES, FURNACES,
AND FLUXES.
Simple Ingot-Mould.
— When
it
is
required to
melt a small quantity o£ gold or silver, tlie simplest
form of apparatus for the purpose is that shown in
Fig.
follows
A
It
17.
is
very
easily
and
quickly
made
as
:
block of compressed charcoal or carbon
is
carefully
cut in halves lengthways with a saw, in order to obtain
Fig.
17.
two thin slabs, which are rubbed together until perA circular cavity
fectly smooth surfaces are obtained.
cut in one of the slabs for the reception of the metal
At the other end of the slab an ingotto be melted.
is
mould
made
is
carefully carved, the size
and shape of which
to suit the requirements of the case.
A
is
gutter or
then cut to connect the two cavities, after
which the other slab is cut in halves and one half ])laced
over the ingot-mould and secured in position by means
groove
is
DENTAL METALLURGY.
66
of thin iron or copper wire.
The metal
to he melted
is
placed in the cavity and the blowpipe-flame directed
and when thoroughly fluid the charcoal is tilted
so that the molten metal will run into the ingot-mould
upon
it,
prepared for
It is necessary that the charcoal should
it.
be perfectly dry before
use, as the presence of moisture
from the mould.
will cause the projection of the metal
This simple and convenient apparatus
employed
in the dental laboratory
and
is
also
frequently
by jewellers
when only small quantities of metal have to be melted.
similar form of combined melting appliance and
A
ingot-mould made of asbestos
is
obtainable at the dental
depots.
The author has made many
red Windsor brick, which is
and is easily cut and shaped.
Melting Scrap.— When
similar
moulds out of
suitable for
soft
the purpose
melting gold
scrap
for
to prevent
the dental laboratory care should be taken
containing
the admixture of old plates, backings, &c.,
quality, as
portions of solder and scrap of doubtful
and give a
these would lower the standard of the gold
plate of inferior carat to that required.
neglect scrap
this account it is usually safer to
On
and filings
containing solder, and melt only clippings
to prevent
taken
from new plate. Care must also be
the introduction of
impure
filings
:
lead
fragments of dental-alloy or of
is
specially injurious, as
it
renders
the gold brittle and useless.
Melting Apparatus.— A
very convenient and
embodying the same prinuseful form of apparatus,
above, has been devised by
ciples as those described
ingots of gold and silver
Fletcher for quickly obtaining
the
It is shown
without the use of a furnace.
m
MELTING APPLIANCES.
accompanyiug Fig.
18.
A
67
represents a moulded carbon
ii'on side-plate, which
B is an iron ingot-mould
which slide on each other, to
block, siip])Orted in posit on
by an
acts as a shallow crucible.
constructed in two parts,
admit of ingots of any width being cast. By this
arrangement the mould serves for both plate and wire.
Fin.
The apparatus
18.
mounted on a rocking stand for convenience in tilting.
The metal to be melted is placed
in the shallow crucible and the flame of the blowpipe
is
When
adjusted.
apparatus
the
is tilted in
sound ingot
may
metal
order to
is
fill
melted
the
the ingot-mould.
be obtained in a few minutes
use of this simple apparatus.
whole
A
by the
The metal should be
thoroughly molten before being run into the mould,
but excessive heating should be avoided.
The ingot-mould
lieat
of
the flame
is
;
made
it
sufliiciently
hot by the waste
should, however, be
oiled,
or
coated with lampblack by holding the inner surfaces
DENTAL METALLURGY.
68
over the flame of an oil-lamp or gas-jet before using.
When very bulky scrap is to be melted it should be run
into a
mass
placed
in
in a
the
moulded carbon block before being
The melting appliance as
crucible.
usually supplied for dental purposes
ducing ingots of about
3 ozs.
larger size
of
capable of pro-
is
Similar appliances of
may be
producing 20
obtained capable
oz. ingots,
but these
require a half-inch gas supply and a
good blower.
These simple melting appliances
are not adapted to large
of
metal
;
crucibles
are,
quantities
therefore,
usually employed for this purpose.
—
Crucibles. These are made of
fireclay and of graphite (plumbago)
and are of various shapes and sizes
to suit the requirements of the case.
A
dental purposes
is
convenient form of crucible for
shown
in Fig.
Earthen crucibles are made
1
9.
of fireclay
mixed with
fireclay,
other infusible materials, such as sand or burnt
which raw clay
in order to counteract the tendency
The materials
possesses of shrinking when heated.
on heating,
thus mixed with the clay expand slightly
the clay.
and therefore act in an opposite manner to
a
resisting
of
Crucibles of these materials are capable
high temperature without softening.
of varying
Graphite or plumbago crucibles are made
powdered graphite
proportions of fireclay mixed with
Good plumbago crucibles withstand
or with coke dust.
temperature without cracking,
the greatest changes of
by the
relractory and the least corroded
are highly
MELTING AiTLJANOES.
of metallic oxides.
action
Tliey
are,
69
therefore, very
suitable to the requirements of the dental laboratory, as
with due care they
may
be used
many
times in succes-
very important befoi-e using these crucibles
to subject them to a careful preliminary annealing by
sion.
It is
placing them in a
warm
place in an inverted position,
otherwise they will split
when suddenly
The
shown in
heated.
crucibles are usually provided with covers, as
Fig. 19.
and
Gold
plumbago
its
alloys
crucibles,
inside with a
little
particles of metal
When
should
melted in good
be
which when new should be rubbed
charcoal powder, to prevent any
adhering to the sides of the pot.
earthen crucibles are employed for the purpose
they should be glazed inside with a thin coating of
borax.
This is done by placing a small quantity of
borax in the crucible and exposing
ture until the borax
is
it
to a high tempera-
The crucible is
the tongs and carefully
perfectly liquid.
then removed, held firmly in
rotated in an inclined position in order to allow the
molten borax to flow over the entire surface.
When thus glazed the crucible may be
inverted position until ready for use.
By
left in
this
an
means
the pores of the crucible are closed and the retention
of globules of metal during pouring
is
prevented.
—
of Furnaces. Melting operations may
be conducted in any form of fire or furnace in which
Forms
a sufficiently high temperature can be obtained.
The
fire
of an ordinary cooking-stove
is
often
em-
ployed where gas is available, however, the operation
may he more effectually accomplished in a suitable gas
;
furnace, such as those invented by Fletcher, which are
very compact, convenient and effective.
These furnaces
DENTAL METALLURGY.
yo
are easily attended to, and
work can be
them in a very cleanly manner.
The choice of furnace to be used
will
carried ou with
depend
chiefly
on the degree of heat to be obtained, but the following
furnaces will be found perfectly adapted to the require-
ments of the mechanical dentist.
Injector Gas Furnace.
— Fig.
Fletcher's injector gas furnace.
20
represents
The furnace
is
con-
structed of a special refractory material, which is a bad
conductor of heat and very light. It is enclosed by
bands of hoop iron and contains an interior space
Fig.
20.
of
sufficiently large to take crucibles with a capacity
the size
six ounces to twelve pounds, according to
of the furnace.
The necessary temperature
is
obtained
by injecting a mixture of air and gas into the furnace
the
by means of a special burner, constructed on
obtained
principle of the Bunsen burner, the blast being
by a suitable blower, such as that described on p. 63.
the
The burner is provided with a screw check, so that
Extremely high
supply of air can be easily adjusted.
furnaces,
temperatures can be obtained with these
melted
half-pounds of cast iron being completely
twelve minutes, but for rapid working
of gas is
and for high temperatures a free supply
in seven
requix'ed.
to
MELTINU AITLIANCES.
A
thin layer of silver-sand
is
7^
usually placed on the
bottom of the furnace to prevent crucibles adhering
when a white heat is employed.
These furnaces need a special gas supply, varying
from three-eighths to five-eighths inch pipe, and the
india-rubber tubing used for the connections must be
smooth inside, the tubing made on wire not being
suitable.
supply
The burner
to get very hot if the gas
is liable
is insuflicient.
To adjust a new furnace
to its highest power, put the
nozzle of the burner tightly up against tbe hole in the
Fig. 21.
side of the furnace casing, turn
light the gas in the furnace,
on the
full
gas supply,
and commence blowing,
before putting on the cover of the furnace, with the
air- way full
open.
when the cover
If,
i-eplaced, the
is
flame comes out of the hole in the cover about two
inches, the adjustment
is
correct.
If the flame is longer, enlarge the hole in the air -jet
until the proper flame is obtained, or reduce the gas
supply.
Before stopping the blower, draw the burner
back from the hole.
Concentric -Jet
recently
introduced
Gas Furnace.
a
new
series
—
of
h'letclier
haa
concentric-jet
furnaces, which are designed to supersede the injector
These furnaces (Fig. 2i)
furnaces above described.
DENTAL METALLURGY.
72
are very similar
to
the injector furnaces, with the
exception of the burnei-, which
to
avoid any
cutting
is
specially constructed
action or " cold spot " on the
crucible.
no wire gauze in the burner to get choked
or damaged, and the power is limited only by the air
pressure and the gas supply available it is also so conTJie burner and
structed that it cannot light back.
furnace are mounted on an iron stand, so that the former
There
is
;
cannot get displaced when in
Fig.
use.
The furnaces
are
22.
supplied in four sizes with a capacity of from four
superior to the
to twelve pounds, and are in every way
ordinary form of injector furnaces for use in the dental
laboratory, where high temperatures and rapid working
are required.
Injector Oil Furnace.
—When
gas
is
not ob-
lamp
tainable the injector furnace can be fitted with a
a
oil,
for burning ordinary kerosene or petroleum
burner having
been designed by Fletcher for this
purpose.
must be
In using this the wick-holder of the lamp
placed
The
The
close
against the hole in the furnace casing.
blast is supplied
oil
by means
furnace (Fig. 22)
is,
of a blower as before.
however,
iuferioi- in
power
MELTING APPLIANCES.
to the furnaces supplied
wilh gas, but with a
management
experience in
73
little
a half-pound of cast iron
can be melted in about twelve minutes, starting
cold.
Furnace for Coke.
Melting
venient and portable furnace for
—A
very
all
con-
melting operations
where a suitable supply of gas
is
not available
trated
Fig.
in
that illus-
is
made by
23,
Morgan and Co.,
London. The furnace
Battersea,
structed
of
is
con-
suitably
fireclay,
bound with hoop iron, and is
made in two parts for convenience in cleaning and repairing. The necessary draught
is obtained by fixing an iron
tube chimney to the socket a,
and is regulated by means of
the small door
very
d.
convenient
damper,
chimney
for
draught.
An
The
in
iron
a
also
have
a
the iron
regulating
poker
is
Fig. 2^.
the
grate, /,
which
of the furnace,
introducing
is
to
fitted
g,
It
is
fitted at
the
bottom
kept free from clinker by
through
the
stokiug-door
crucibles are introduced through the door h
e.
and
placed on a small fireclay stand resting on the grate.
The fuel usually employed is coke, vvbich should be
broken to
])ieces
the si/e of an egg and well packed
round the sides of the crucible, but not over
furnaces are
made
in
several
sizes to hold
with a capacity of from four to thirty pounds.
it.
The
crucibles
DENTAL METALLURGY.
74
Ladle Furnace.
—Fletcher
has devised
a
new
and substantial form of ladle furnace (Fig. 24) for
melting zinc and lead, which is well adapted for the
dental laboratory.
The furnace
Fig.
is
seven
24.
heated by a special highremovable, and can therefore be
inches in diameter, and
power burner, which
will take ladles
is
used for boiling water and other purposes. The body
and lid are arranged to admit the handles of different-
sized ladles at various heights, to enable
kept perfectly
them
to be
level.
Ladles. The ladles used with these furnaces are
shown in Fig. 25. In order to insure perfect steadiness
fitted with a slide
in pouring, the handles are
]iiished to
and
is,
the cool end while the metal
therefore, always cold.
The
is
which
is
being heated,
ladles are
made
and with mallewith cast-iron bowls for melting lead
MELTING APPLIANCES.
75
able iron bowls for zinc, the handle being so constructed
new bowl can be fixed in a few minutes.
Muffle Furnace, The mufiie furnaces used
that a
—
metallurgical
silver are
poses
;
for
laboratory
assay of
the
in the
gold and
very similar to those nsed for dental pur-
the muffles, however, are
the former case.
The
somewhat larger
in
special feature of this class of
furnace consists in the device for isolating the materials
Fig. 26.
operated upon from both the fuel and the products of
combustion.
The muffle proper
shaped thus
surrounded by the flame on
number
all
chamber
a fireclay
in section, closed at
fixed in the furnace in such a
pei'forated with a
is
one end, and
manner that
The
sides.
of holes or slits
it
can be
sides
ai-e
through which
drawn, the muffle furnace being used chiefly
for operations requiring the passage of a current of
air, as in the processes of cupellation and scorification
the air
is
mentioned under Hilver Assays.
Gas Muffle Furnace.
recently
—A
invented by Fletcher
gas
is
muffle
shown
in
furnace
Fig.
26.
76
DENTAL METALLURGY.
This furnace has been designed specially for gold and
silver assays, and ranks among the best of its kind for
this purpose.
It is
designed to give the best results
and the
uniform from end to end,
at the lowest ordinary day pressure of gas,
temperature of the muffle is
and can be adjusted to any extent.
The
muffle
parts, so that
is
closed
can be
two
extra supply of air is needed.
an
partially opened when
A thin layer of bone ash should be spread over the
by a door arranged
in
it
bottom of the muffle to protect it in case of accident.
A muffle furnace fired by coke somewhat similar
is
in construction to the furnace described on p. 73
and
Morgan
also made by Messrs.
Co.,
and
will
be found useful for
purposes when
assaying
cannot be obtained.
Ingot-Moulds.
coal-gas
— Metals which
are to be rolled into plate are cast
moulds which give a flat ingot
suitable for passing through the
The ingot-mould usually emrolls.
into
shown in
Pio- 07. It is made of cast iron, in two
should
parts, for convenience in removing the ingot, and
compensate
be slightly concave on the inner surfaces, to
ployed for this purpose
is
middle than at
for the greater shrinkage of gold in the
edges of the ingot. Before pouring, the moulds
the
with a
should be moderately heated and rubbed over
by
well-oiled rag, or coated with a deposit of carbon
flauie.
holding the inner surfaces over a gas or oil
Moulds are
also
frequently
rubbed
with
blacklead
must be taken
powder, but when this is
from the mould before
to remove all excess powder
used care
—
.
MELTING APPLIANCES.
the
pouring
Ingot-moulds
metcal.
77
formed
of
soap-
stone are also employed for casting purposes and are
As the metals for dental purposes
preferred by some.
require to be in the form of plate or wire, the ingot is
subjected to rolling, &c., to fit it for the purpose
required.
Rolling, or Laminating.
This
is
accomplished
by passing the ingot rebetween
two
peatedly
cylindrical
Many
polished
highly
strong,
steel
different
rollers.
forms of
flatting mill are used for
this purpose, that
being frequently
in Fig. 28
These are so
employed.
constructed
the
justing
shown
that
by ad-
screws
the
may be brought
rollers
closer together every time
the ingot is passed through
It
is
very
keep the
rollers perfectly
by
parallel
important to
very
careful
Fig.
28.
adjustment of the screws,
otherwise the metal will twist and become unmanageable.
As metals become hardened by
rolling, the ingot
should be frequently annealed during the process.
rollers for the pui'poses of
The
the dentist should be from
three to four inches in length.
Thickness of Plate.
is
of attenuation
determined by a gauge-plate,
sometimes circular in shape and sometimes
obtained by rolling
which
—The degree
is
DENTAL METALLURGY.
78
shown
oblong, as
strument
which
is
in Fig.
29.
The edge
provided with a series of
gradually diminish in size
of the
slits
in-
as shown,
and are indexed by
corresj)ond to regular fixed standards,
numbers which
which vary for the different countries. In order to
determine when the plate has been rolled
sufficiently thin it is repeatedly tested by
the gauge during the operation of rolling.
Wire -Drawing. Thick wire or thin
—
metal rods
])assing
may
be drawn into finer wire by
them through
a draw-plate, which
consists of an oblong piece of steel pierced
with a series of conical holes which graOn a small
dually diminish in diameter.
scaio,
strips of
of
metal
rolling, or
wire
off
by
is
readily obtained
by cutting
the rolled sheet in the direction
casting the metal into a thin rod,
and passing it into one of the
holes of the draw-plate, which is firmly held in the
jaws of a vice. The rod is then forcibly pulled through
slightly pointing one end,
the hole by means of a pajr of drawing tongs or pliers,
and the process repeated with smaller holes in succes-
wire of the desired size is obtained. The
or
holes in the draw-plate should be filled with grease
fat to facilitate the operation.
the wire from
It is generally necessary to anneal
sion, until
time to time during the operation, otherwise
it
becomes
after
hard and more or less liable to crack or break,
holes.
having passed through a certain number of
Draw-plates are
also constructed for
round, square, and other forms of wire.
obtaining half-
MELTING APPLIANCES.
79
Fluxes.
—A
added when melting metals and smelting ores, for the purpose of combining with the infusible substances present or formed
Bcjinition.
flux is a substance
fusible
body thus formed
When
air the
The
render them fusible.
during the operation to
termed a
is
slag.
metals or alloys are melted in contact with
oxygen
and converts
flnx is added
fusible slag,
acts on the surface of the
into
it
it
will
oxide
;
molten metal
however, a suitable
if,
combine with the oxide to form a
which protects the surface of the metal
"In many
from further oxidation.
melting of metals
it is
cases of
simple
desirable to remove base metals,
often
it is then
which are present as impurities
advisable to add an oxidising flnx, in order first to
;
oxidise
the
impurities, in
which
state
they readily
combine with other fluxes to form a liquid
is
for this reason that nitre is
impure gold (see
p.
90).
The
in the dental laboratory is borax,
slag."
It
added when melting
chief
which
flux
is
employed
principally
used for soldering purposes, but also used occasionally
when melting
metals.
—
Borm: (Sodium horatc). This substance fuses readily
and is very fluid when in the molten state. In the
crystallised or hydrated form it contains nearly half its
weight of water, which is driven off on heating, causing
When sti'ongly heated it
it to swell up considerably.
fuses into a clear white glass
known
as horax glass.
The
inconvenience sometimes experienced by the swelling
up
of the hydrated borax
fused borax.
may be
avoided by the use of
The commercial material
adulterated with
common
salt
and alum.
is
frequently
DENTAL METALLURGY.
8o
Ammoniuiii Chloride, commonly called Sal-ammoniac,
Several metals when
is also frequently used as a flux.
in a molten state decompose this substance, forming
Advantage
metallic chlorides and liberating ammonia.
frequently taken of this property in purifying gold
and also for purifying zinc which has become impure
is
by frequent melting (see pp. 91 and 200).
A mixture of sal-ammoniac and charcoal is sometimes
employed instead
Sodium
of the former alone.
Chloride, or
common
salt,
is
employed as a
flux in melting operations, as it preserves the substance
beneath from the action of the atmosphere and thus
prevents oxidation. It is also used to moderate the
violent
action of substances such as nitre, which cause
It is for this reason that it is included in
ebullition.
It
the charge for refining " lemel "—given on p. 120.
very
is
and
melts at a red heat in an open crucible
fluid
when
molten.
Potassium Nitrate, also called Nitre and Saltpetre.
agent,
This substance is largely used as an oxidising
yields a large
as it is decomposed on heating and
volume
of oxygen.
It is specially useful
ing gold contaminated with
when
melt-
small quantities of base
metals.
employed to prevent
Flour and resin are
oxidation when melting metals.
Charcoal
Poioder
is
largely
purpose.
also frequently used for the
Soldering.
regarded as a
of soldering is rightly
with
mechanical dentistry, but as it deals
The process
branch of
the
the melting of metals and
use of
fluxes, a
few
MELTING ArPLlANCES.
may be
notes on these points
8l
considered as coming
within the scope of dental metallurgy.
Soldering
is
the process by which two or more pieces
of metal are united
by means of a fusible alloy termed a
" solder " (see p. 55).
It
is
chiefly confined in the dental
laboratory to the use of gold solders, although occasionally " soft soldering" is
is
found useful for several purposes.
In order to facilitate the soldering operation a " flnx
employed, which is usually borax.
"
When
the various parts to be united are heated the
surfaces become " darkened " by a thin coating of oxide,
owing
to the oxidation of the base metals present.
however, borax
is
employed
dissolve the metallic oxides
as a flux
it
which form, and
If,
readily
will
also protect
metal from further oxidation by excluding the
oxygen of the atmosphere. The flux is prepared by
taking a lump of borax and rubbing it on a slab of
the
ground
glass, or porcelain,
wdth clean water, until
attains the consistency of cream, after
to the surfaces to be united
brush.
A
which
by means
saturated solution of borax
for soldering, the piece to be
with solution where the solder
it is
it
applied
of a camel's-hair
may also be
used
soldered being painted
is
wanted
to flow.
The conditions necessary for successful soldering are:
1.
A
2.
Contact of
3.
Avoidance of excess of solder.
Exposure of a clean, bright surface in
over which solder is to flow.
4.
solder which flows freely.
all
the parts to be united.
jjlaces
A
gradual and uniform distribution of heat.
As previously stated, the solders used should be more
5.
fusible than the metals to be united, should
when
fused,
and should possess a strong
How readily
affinity for
I'-
the
DENTAL METALLURGY.
82
metals to be joined, in order that
it
may run
into every
The
part of the joint and thus effect a perfect union.
colour of the
solder
should correspond as nearly as
possible to that of the plate on which
the solder
is
to be exposed
it
is
used.
As
to the action of the fluids
of the mouth, in order that it may resist this action as
far as possible it should be as high in quality as the
plate will admit, without risk of melting the latter
during
i\\e
fuduii of the solder.
form
in
inch)
an
of thin plate (about 0.75 mm. (yVth of
thickness), which is cut up into pieces varying in
size, depending on the extent of the surfaces to be
Solders
for dental purposes should be in the
united.
Very thin plate
is
objectionable, as
it
exposes a larger
surface of base mecal to oxidation, and consequently
retards the flow of the solder and thus tends to weaken
the joint.
When
solder
is
used in the form of
flliugs
mixed with borax of the consistency of cream
form a paste, which is then applied to the parts to
it is first
to
The quantity of
be reduced to the minimum,
have to be removed in the
be united.
excess of solder
place on cooling
teeth.
is
is
solder used should always
as all superfluous portions
finishing process.
When
used the contraction which takes
liable to cause the fracture of the
Care should also be taken to avoid the use of
excess of flux.
oxidising flame should be avoided in all soldering
operations, as this makes the surfaces of the metals
An
unnecessarily " dirty," and renders it diflicult to obtain
It is also necessary that cleanliness be
a clean joint.
to be
observed and care taken to prevent the surfaces
this
as
plaster-of-Paris,
soldered from contact with
—
MELTING APPLIANCES.
substance, on account of
83
iufusibility, greatly inter-
its
feres with the perfect union of the parts.
distribution of heat
The gradual and uniform
great importance in
failure
to
give
all
of
is
soldering operations, and the
proper attention to these points
frequently the cause of
much
is
delay and want of success.
The temperature should be raised gradually
at
first,
to
prevent the displacement of pieces of solder by the
The heating
swelling up of the borax used as a flux.
process for an artificial denture should also be conducted
gradually, as a sudden elevation of temperature will
cause displacement of the plaster owing to the too
rapid expulsion of moisture and will tend to cause the
fracture of the porcelain teeth.
In soldering a large piece of work the flame should
be carefully directed until all parts are uniformly
heated to the
required
temperature, and
then
the
blowpipe-flame directed to the solder and parts to be
united.
The process
of soldering is a delicate oj)eration to
accomplish successfully, and needs to be undertaken
with care and patience.
With
a little practice,
how-
ever, the difficulties at first experienced are soon over-
come, and neat aud successful joints obtained.
—
Soft Soldering. The method of soldering by
means of the blowpipe is known as " hard soldering";
but when
points
The
tin
soft,
solders
i.e.
those with very low melting-
— are used, the process
is
termed "soft soldering."
solders used for this process are usually alloys of
aud lead
" softest " or
in varying proportions (see
\).
21
1),
the
most fusible being those containing the
largest proportion of tin, this being the more fusible
These solders are cast into the form of
constituent.
/
DENTAL METALLURGY.
84
thin,
naiTOW
strips.
The fusion
surfaces to be united
is
of the solder on the
usually effected by
means
" soldering iron," instead of the blowpipe as in
soldering.
employed
sists of a
of a
hard
The blowpipe, however, is in some
The soldering-iron conspecially shaped piece of copper, known as the
cases
for soft soldering.
"bit," which
fixed in a
is
attached to an iron stem and securely
wooden handle.
In soft soldering a flux
and
which is designated " soft soldering fluid " is used,
made by dissolving
consists of a solution of zinc chloride,
a small quantity of zinc in dilute hydrochloric acid.
This solution
is
employed instead
of borax to dissolve
oxides or prevent oxidation of the surfaces to be united,
and
When
also to assist the " flow " of the solder.
surfaces have been prepared the solder
is
the
melted and
applied to the work by means of the soldering-iron. A
novel application of " soft soldering " to dental pur-
poses has been introduced by Mr. Baldwin * in connection with the repairing of bridges and crowns, the
The process
porcelain facings of which are broken.
consists in soldering a " backed " tooth to the preexisting "back," the
new
faces being attached with
For this purpose
a small clockmaker's soldering-iron is necessary, and
soft solder
by soldering in
the mouth.
in easy cases a fine quality of ordinary soft solder
used, while for
more
diflacult cases,
such as
crowns, a solder with lower melting-point
is
Eichmond
is
required,
which contains bismuth
and mercury, in addition to tin and lead, being very
that
known
as "pearl solder,"
suitable for the purpose.
*
Dental Epcuril, i8g6,
vol. xvi. p. 489.
;
CHAPTER
VI.
GOLD.
SYMBOL, An
Occurrence.
(Aiiruni).
— Gold
ATOMIC WEIGHT,
occurs
197.
distributed
very widely
and almost invariably in the metallic state,
the native metal being found disseminated in veins in
some of the oldest rocks. Formerly the most important
deposits were the alluvial deposits, resulting from the
in nature,
disintegration of the ancient gold-bearing rocks by the
atmosphere and running
waters.
The gold occurs in this gravel or sand
detritus in rounded masses, and also in the form of
the masses when of any considerfine grains or dust
able size being termed " nuggets," some of which have
weathering action of
the
;
been found weighing as much as from a few pounds to
two cwt.
Native gold invariably contains more or
less silver
while copper and iron are also frequently present in
The purest specimens of native gold
The Californian
contain about 99 per cent, of gold.
small quantities.
89 per cent., and the
Australian from 96 to 97 per cent, of pure gold.
Preparation. In order to extract the gold from
native
gold
averages
87
to
—
alluvial deposits
The
advantage
auriferous earth
is
is
taken of
washed
in a
its
high density.
" cradle "
or
pnu
DENTAL METALLURGY.
86
whereby the light particles of
rock are carried away, and the greater portion of the
inetallic grains remains at the bottom of the washing
apparatus, from which it is collected and melted into
in a stream of water,
bars.
Gold
is
extracted from auriferous rocks by stamping
the rock to coarse poWder, then causing the powder to
flow; by means of a stream of water, over inclihed
copper plates, the surfaces of which have been amalga^
mated i:e. covered with a layer of mercury. The gold
particles adhere to the mercury, with which they
amalgamate, while the finely crushed rock
The gold amalgam thus obtained
away.
removed, placed in a
off,
retort,
is
is
and the mercury
washed
carefully
distilled
leaving the gold behind.
Another method adopted very
years
treat
and
with a dilute solution of potassium cyanide, which
The gold solution is then
dissolves out the gold.
is
it
readily
largely within recent
to place the crushed ore in large tanks,
run into boxes containing shavings of metallic
zinc,
the precipitate is then
which precipitates the gold
collected, washed, dried and melted into bars.
Parting Gold from Silver.— Gold when ex;
tracted from its ores contains silver, and is frequently
impure and brittle, owing to the presence of small
quantities
of
base
metals.
In order,
therefoi-e,
to
fit
separate these and render the gold malleable and
be
and this may
for use it has to be refined or parted,
efiected either
by
a dry or
wet method.
Miller's Proem.— This dry method, which
is
frequently
crucible,
employed, consists in melting the gold in a
of
current
a
glazed internally with borax, and passing
by means of a
chlorine gas into the molten metal
87
OOLD.
fireclay
tube passing through the
lid of
the crucible.
and other impurities are converted into
partly volachlorides and rise to the surface aud are
The
silver
When
tilised.
is
the operation
allowed to cool, aud
still
molten
when
silver chloride is
is
complete, the crucible
the gold has solidified the
poured
The gold
off.
is
cleaned from adhering chloride, aud then remelted and
cast.
Parting with Acid.
— Gold
is
also purified
from
copper, &c., by the wet process, termed "quart aIn this case the gold is melted with
tion or ])arting."
from two to three times its own weight of silver, the
silver,
molten alloy thus produced being poured into water in
order to
granulate
it.
The granules
are
carefully
acid,
collected, and then boiled with strong- sulphuric
whereby the silver and copper are converted into
sulphates which dissolve in hot water, and the gold is
The
left behind in a pure state as a brown powder.
gold powder
is
washed, dried and then melted and cast
into bars.
obtained by placing sheets of
copper in the solution, which precipitates the silver in
The
silver is readily
the metallic state.
Nitric acid
is
sometimes employed for parting instead
of sulphuric acid.
necessary to have the proportion of silver to
about three to one, otherwise the silver would
It is
gold
only be dissolved from the surface of the alloy, the
large proportion aud density of the gold present i)re-
venting the action of the acid throughout the mass
and the complete removal of the silver when the pro})ortion is less.
Preparation of Pure Gold.
— Gold
of
extreme
88
DENTAL METALLURGY.
purity cannot be obtained by parting alone
therefore, gold
required of absolute puritj^
is
when,
;
it
must be
specially prepared.
Chemicall}'
pure gold
is
parted or standard gold in
the excess of
The gold
by dissolving
prepared
nitro-hydrochloric
acid being driven
chloride thus obtained
is
off
acid,
by evaporation.
dissolved in a large
quantity of water and left at rest for about twenty-four
hours to enable any precipitate of silver chloride to
subside.
The
clear
liquid
then carefully removed
is
from the deposited silvei- chloride by means of a syphon,
and the gold is jarecipitated by passing a current of
gaseous sulphur dioxide through the solution, or by the
addition of oxalic acid or other precipitating agent (see
p. 96).
The gold
precipitate
repeatedly with dilute acid,
obtained
is
washed
then with ammonia and
melted in a crucible with a
potassium bisulphate and borax and poured into
water, after which
little
so
it
is
an ingot-mould.
a small quantity of
If
platinum
is
present in the
gold treated, alcohol and potassium chloride must be
added
to precipitate
it
before diluting the gold chloride
with water.
Properties.
—Gold has a characteristic yellow colour,
but very thin leaves of the metal are translucent and
appear green by transmitted light. It possesses a brilGold is
liant lustre and is susceptible of a high polish.
one of the heaviest metals, its specific gravity being 19.4.
between that of aluminium and silver.
In malleability (see p. 12) and in ductility gold exceeds
a wire
all other metals, its ductility being such that
can be drawn so fine that 500 feet weigh only one
Its
hardness
grain.
lies
89
GOLID.
It is a
electricity,
though
inferior to silver.
It is
good conductor of heat and of
in these respects
it
much
is
welded together in the cold by
It is tenacious, though
the application of pressure.
inferior in this respect to iron, copper, platinum and
also capable of being
the purest gold obtainable having a tenacity of 7
tons per square inch and an elongation of nearly 31
silver,
per cent.
Gold
is
not acted upon by atmospheric
ordinary temperatures or
is it
when
air,
strongly heated
either at
;
neither
tarnished by exposure to the action of sulphuretted
hydrogen.
Gold
is
not acted upon by any single acid
(except selenic), but
it
acid mixture such as
which
evolves
is
dissolved
by chlorine or an
nitro-hydrochloric (aqua regia),
Selenic
chlorine.
acid,
even when
moderately concentrated, has no effect upon gold in
the cold, but the
concentrated
acid
when used hot
(230°-300'' C.) dissolves the gold, forming gold selenate.*
Alkaline solutions have no action on the metal.
and contracts consider"
and though practically a " fixed
It melts at 1061° C. (1942°
ably on solidification,
metal
It
it
may be
will
¥.),
slightly volatilised at a very intense heat.
thus
be seen
that
gold possesses, in an
eminent degree, those general properties which render
it peculiarly fit for the purposes to which it is applied
in dental practice.
Use for Dental Purposes. — On
account of
its
untarnishable nature, gold has long been employed in
In the pure state it is used in
form
the
of foil, as a filling for teeth and for other
purposes.
In combination with copper and silver it is
largely employed for the base of artificial dentures.
the dental laboratory.
*
Liriilicr.
Jdvni. Aiiirr.
Chriii. Sor. 1902.
24 [4]. 354-355.
DENTAL METALLURGY.
90
Effect of Impurities on the Properties of
Gold.— The malleability and ductility of gold are mateiuHueuced by the presence of only small proportions of other metals, such as tin, lead, zinc, antimony, &c.
Gold alloys readily with Und, but a very small quantity
rially
of this metal
and
is
sufficient to
impair the
ductility of gold, rendering
it
malleability
quite brittle, and
generally useless for any of the purposes to which gold
even -.,^t\\ part of lead renders standard
is applied
;
gold
brittle
Having regard
and
destroys
its
working
properties.
to this influence of small proportions of
a
lead on gold, care should be taken, after annealing
coming
gold plate, to prevent the plate while hot from
metal
this
contact with any particles of lead, as
into
would at once be diffused into the plate and probably
quite unfit for further treatment.
Antimony is particularly destructive to the mallea-
render
it
per cent, renders gold quite brittle,
impair its
while quantities not exceeding .05 per cent,
bility of
gold;
.5
malleability.
Bismuth
making
Zinc
alloys with
gold,
hard and brittle.
and Tin both form
and
is
highly injurious,
it
alloys
with
gold,
the
gold more or less
presence of these metals making the
brittle.
become
liable to
In the dental laboratory gold is very
and other
contaminated with particles of lead, zinc,
When, therefore, the gold scrap, &c., is to be
metals.
use, care should be
reconverted into proper form for
as practicable from
taken to prevent the gold as far
metals.
becoming contaminated with base
impure and brittle
Brittle Gold.— Gold which is
little borax in a
may be refined by melting it with a
GOLD.
crucible,
sium
ing
91
and adding a small quantity of nitre (potas-
The
nitrate).
effect
nitre exercises a powerlul oxidis-
on the base metals
in
tbe gold, and the
resulting oxides form a liquid --^lag" with the borax;
sometimes sprinkled on the surface
of the molten gold to remove the lead and tin after
Sal-ammoniac
skimming
Gold
is
the slag;
ofi'
Foils.
— For the manufacture! of
industrial purposes the gold
silver aJid
gold-leaf for
usually alloyed with
is
copper, according to the colour required
the finished leaf
but gold
;
ill
for dental purposes is
foil
beaten from pure gold, on account of its superior welding power, which enables it to be pressed more readily
into a compact form.
The metal
is first
melted and cast into small ingots,
which are thinned by hammering, and then rolled
until a ribbon is produced having a thickness of about
^jiyth of an inch
;
the gold requiring frequent anneal-
The ribbon
ing during this operation.
is
then cut into
pieces one inch square, weighing about six grains, about
150 of which are interleaved with sheets of vellum or
parchment and the whole made into a packet. The
" cutch " thus produced is beaten with a hammer nntil
it has become extended to about four inches square or
sixteen
times
intended for
beyond
the
filling
original
area.
If
teeth the beating
is
the sheets are
not continued
this stage.
For application in the
arts,
however, the beating
is
frec|uently continued until the thickness of the leaves
is
about iTaoVoo^h of an inch.
sheets are cut into four, and ])iled
For this purpose the
again between sheets
of goldbeater's skin, thus forming a " shoder."
beating
is
The
then carried on for some time, after which
DENTAL METALLURGY.
92
the sheets are again cut up into squares, rearranged
as before,
forming a " mould," and the operation of
beating repeated for about two hours until the leaves
have acquired the degree of tenuity required for the
purposes to which they are to be applied.
Prom
the
finished leaves thus produced squares of about three
inches are cut from the central portions by a piece of
bamboo sharpened to a cutting edge. These are then
piled in a book made of soft paper rubbed over with
red ochre or red chalk to prevent adhesion, twentyMechafive leaves being usually placed in each book.
power has in recent years been substituted for
During the earlier
manual labour in gold-beating.
stages of the process the blows are directed mainly
nical
towards the centre, which causes cracks and rents near
the edges of the leaves these cracks, however, become
;
closed up again subsequently, the edges of the cracks
welding together perfectly, so that the finished leaves
exhibit no trace of them.
filling teeth is
Gold for
degrees of thickness, the
according
of
which
60 grains
to
is
the tveiglit
beaten into
foils of
varying
being generally numbered
size
of the sheet, the standard
foils
Each book of foil contains
gold, and the number of the foal
four inches.
ounce) of
indicates the weight of each full sheet.
would contain
three
20 sheets, e^ch four inches square and weighing
sheets,
1
2
a book of No. 5 foil would contain
grains
book
grains;
five
weighiug
inches square, each
For example, a book
of
No.
3
foils
;
four
grains in
10 sheets, four inches square, each six
upwards
weight, and so on. Foils ranging from No. 32
prepared by folding a
are usually employed and are
equivalent to
sheet of No. 4 foil, so that it becomes
No.
6,
GOLD.
93
and then folding it again to make it as thick
as No. 16 foil, and then again to make it equal to
No. 32 foil. When heavier foils are needed several
No. 8
foil,
sheets can be folded together.
Although the foils are generally prepared by beating, yet some of the heavier numbers, averaging from
No. 20 to No. 60, are produced by rolling, and these
are sometimes used instead of thin foils folded to the
required thickness, as they are extremely cohesive and
may be
advantageously employed in extensive contour
operations. The heavier foils, however, are not
worked and considerable practice is required
so easily
in using
them.
The advantages claimed
teeth are that
which
it is
fillings are
for
gold as
a
filling for
able to withstand the attrition to
exposed and that
it
retains its shape,
and, therefore, forms a practically watertight plug
;
it
has no preservative action, however, upon the tooth
substances.
Cohesive and Non-Cohesive Gold.
two
—There are
varieties of gold-foil used in dentistry,
cohesive
and
non-cohesive.
known
as
In the cohesive variety the
characteristic welding property of pure gold
is
each piece of gold-foil introduced into the
utilised,
cavity of
the tooth being carefully welded to the others already
in
position,
principally
by means
of
pluggers
and
mallets, thus consolidating the gold.
In the non-cohesive variety uniou does not take
place between the pieces of gold introduced into the
made to retain
mechanically by wedging and intimately
cavity,
the
the gold
pieces
cavity.
very
being
tightly
between
the
its
position
interlacing
walls
of
the
DENTAL METALLURGY.
94
The
between these varieties of
difference
gold-foil
brought about by a slight alteration in the method
Non-cohesive gold is so prepared
of manufacture.
that there is no possibility of one piece sticking to
is
This appears to be attained by subjecting
the leaves of foil to the influence of certain gases, such
Graham has shown * that when pure
as ammonia gas.
another.
heated
gold
is
ing
gases,
it
has the power of occluding or absorb-
and
notably hydrogen
nitrogen.
"The
hydrogen occluded by gold is sensible, but
most
does not exceed 0.48 of its volume. Probably the
amount
of
gases
interesting point connected with the occlusion of
by gold is presented by the fact tha,t the metal retains
It
0.2 of its volume of nitrogen."
retention
of
which
nitrogen
property of gold.
A
is,
destroys
no doubt, the
the
cohesive
pellet of cohesive gold
made non-cohesive by exposing it
may be
to the atmosphere, or,
more expeditiously, by submitting it to the action
ammonia gas. " If non-cohesive gold is annealed
will
often be noticed that a vapour
then
it
becomes, as a
are a few
so slightly
rule,
is
given
thoroughly cohesive.
off,
of
it
and
There
of non-cohesive gold which become
cohesive on being annealed that this does
makes
These
non-cohesively.
not prevent their being worked
changed
slightly
is only
foils, the character of which
non-cohesive
are often spoken of as 'true
by annealing,
demands
They can be worked cohesively, but it
gold.'
gives
that
is
What it
special care and manipulation.
them
some
this particular
property
is
a trade
secret.
In
probably due to a very slight admixthese true non-cohesive foils,
ture of another metal
cases
it is
;
* Percy's " Metallurgy." vol.
Koberts-Austeu.
i.
p.
by
35; experiments recorded
GOLD.
95
however, seem also to have been subjected to the action
of some vapour, for, as above mentioned, they are not
so absolutely non-cohesive
when annealed, and heating
them causes a vapour to be given off just as with other
makes of non-cohesive gold."* "In using cohesive
gold, care should be taken to avoid touching it with the
destroy
its
grease,
moisture,
hands, since
and exposure
Though
cohesiveness.
foils
are
to
air
sold
as
always best to pass them througli the
flame before working, in order to anneal them and
restore their cohesiveness, and for this purpose a spirit
cohesive,
it
is
lamp should be
A
used.
owing
later to failure,
Bunsen burner
leads sooner or
to the impurities contained in
In annealing, care should be taken not to
overheat the gold, since many varieties become harsh
when exposed to a high temperature. Good cohesive
gold can be annealed to a dull red-heat without becoming
the gas.
The annealing
harsh." f
foil
upon a sheet
is
of mica,
best effected by placing the
which
is
held over the flame
of a spirit lamp.
diversity of opinion exists with regard to the
Much
relative values of the
two
varieties of foil, the advantages
claimed by the advocates of each variety being briefly
as follows
:
For Cohedve
compact
filling,
—That
makes a harder and more
although taking longer to work. That
Foil.
it
adapts itself to the walls of the cavity as well as noncohesive foil.
That in any case exposed to mastica-
it
tion the filling remains
smoother and the edges stand
better.
For Noii-CohcHirr
*
't
Foil.
— That
liUingH are
Grayston, JJcnlal Jtccord, 1896, vol. xvi.
Snuilo
and Colyur,
much more
p. 105.
" Diseiisus oi Teutli," p. 193.
DENTAL METALLURGY.
96
rapidly made, as larger pieces can be used.
adaptation to the walls of the cavity
is
That the
better than with
cohesive gold, thus the preservation of the tooth
That
it
is
better.
can be more thoroughly burnished to the edges
on account of the greater softness which it possesses.
With due care either variety is capable of affording
good results a combination of the two varieties, however, is extremely iiseful and often employed, the
advocates of this combined method claiming that a
;
better joint
cohesive
is
obtained at the cervical edge than with
foil.
Cohesive
foil is
the variety most generally employed,
the gold being consolidated by hand pressure or by
means
of a series of blows struck
by a hand,
electric,
automatic, pneumatic, or engine mallet.
Precipitated and
may be
Spongy Gold. — Metallic
gold
precipitated from a solution of gold chloride in
the form of fine powder, in scales, in a more or less
spongy condition, according to
the nature of the precipitating agent employed, and
also on the strength of the solution and mode of
The gold chloride solution is prepared by
operating.
crystallised state, or in a
dissolving metallic gold in aqua regia as described in
the preparation of pure gold (p. 87).
Owing to the facility with which gold chloride
duced to the metallic
reagents
The
phurous
may
state, a large
most frequently employed are
oxalic acid, and ferrous sulphate.
By Sulphurous Acid.
sul-
—-When an excess of sulphurous
added to a hot solution of gold chloride the gold
precipitated in the form of a brown powder which is
acid
is
of different
be used for precipitating the gold.
reagents
acid,
number
is re-
is
more or
less scaly.
GOLD.
By
O.mlic Acid.
—This
acid
97
is
a vety useful precipi-
tant aud will give gold of several forms, from sponge-
masses to the different crystalline or powdery forms,
according to the strength and temperature of the gold
solution.
Its action, however, is somewhat slower than
like
other precipitants
that of
and the solution requires
heating.
The
crystallised oxalic acid is dissolved in water
and
then added to the gold solution, when carbonic acid gas
is evolved, owing to the decomposition of the acid, and
the gold
By
is
precipitated.
Ferrous Sulphate.
tallic gold, either at
in the form
of
—This reagent
precipitates
me-
once or on heating the solution,
a very finely divided
brown powder.
powder is suspended appears
dark blue by transmitted light aud reddish and turbid
The solution is poured off" after subby reflected light.
sidence has taken place, and the precipitate is washed
first with a little dilute hydrochloric acid and subsequently with water, and then dried.
By other Precipitating Agents. The majority of the
common metals will precijoitate metallic gold from a
The
liquid in
which the
fine
—
solution of the chloride.
Many
metal.
organic substances also readily precipitate the
Thus,
when
a solution of gold chloride
with sugar the gold
is
thrown down
first
is
boiled
as a light
red precipitate, which afterwards darkens in colour.
As sugar
is
similar to oxalic acid in its action, the pre-
cipitation is capable of regulation,
gold
may be
obtained.
"
Lamm's
and various forms of
so-called
'
shredded
somewhat extensively used by dentists for filling
teeth during 1867 and 1868, was produced by the addi-
gold,'
tion of sugar or
gum
arabic to an acid solution of gold."
DENTAL METALLURGY.
98
When
precipitated from
its solutions,
gold assumes a
on being rubbed with a piece
of polished steel, or other hard substance, it readily
assumes its characteristic colour and metallic aspect.
dark-brown
colour, but
and finely divided gold are capable of
being welded and united into a solid mass by the appli-
Precipitated
cation of pressure.
The various forms of sponge and crystal gold used by
dentists are frequently prepared by precipitation, but
other methods are also adopted.
Crystal Gold. When an electric current of
—
through a solution of gold
chloride in which a plate of pure gold forming the
anode is suspended, and a platinum plate, forming the
cathode, the solution is decomposed and the gold defeeble intensity is passed
posited on the platinum plate in the form of crystals,
which vary in size according to the strength of the
solution and intensity of the current.
As the
solution loses gold
by deposition
of the metal,
replenished from the suspended gold plate, which
gradually dissolved. The crystal gold thus formed is
it is
is
generally very pure
and
is
;
then ready for
it is
collected,
washed and
dried,
use.
The beautiful spongy form of gold known as "Watts'
It is a cohesive
Crystal Gold" is produced in this way.
gold,
A
and must be used strictly as such.
an
crystallised form of gold is also obtained when
slowly heated until the whole of the
amalgam
of gold
mercury
is
mass
required, the
is
is
expelled.
When, however, a
amalgam is first
light
spongy
treated with
mercury. The
then heated
aggregate of crystals thus obtained is
thus leaving the gold
to expel the remaining mercury,
of
nitric acid to dissolve out the excess
GOLD.
spongy mass, having a
light
a
as
99
hiptrous
In-ight
appearance.
Assay
of Gold.
— Alloys of gold are usually assayed
by1st.
them with
Alloying
silver
by the process of
cnpellation (see Silver Assay, p. 178).
2nd. Parting the gold from the silver by
means
of
acid.
For this purpose about
grains) of the alloy
is
|-
to
i
gramme (10
to
20
and wrapped
carefully v?eighed
in a piece of lead-foil with pure silver equal in
weight
to 2^ times the quantity of gold assumed to be present
in the
This
weight of alloy taken for assay.
is
then subjected to cupellation, by which means
the lead and copper are oxidised and absorbed by the
and gold remain behind as an
The gold-silver bead is removed
cupel, while the silver
alloy
and
on the cupel.
an oblong
rolled out to
after
which
The
it is
spiral or
glass flask,
and
strip
about 2 inches long,
annealed and coiled into a
"
cornet," as
it is
termed,
spiral.
is
placed in a
" parted "
nitric acid for about
1
5
by heating it, first with dilute
minutes and then with stronger
by which means the silver is dissolved out,
leaving the metallic gold as a brown residue.
The acid is poured off" and the gold washed \vith
water, after which it is dried and then placed in a small
annealed " in a red-hot muffle for a short
crucible, and
time, when the gold acquires the usual yellow colour,
nitric acid,
with a considerable shrinkage in bulk.
The gold
is
allowed to cool, then carefully weighed
and the percentage
of gold present in the alloy calcu-
lated from the weight thus obtained.
After ))arting, the gold retains a very small quantity
DENTAL METALLURGY.
TOO
of silver, so that
when very
great accuracy
is
required a
system of working with " checks " is adopted. In this
case an amount of pure gold (approximately equal
to that in the assay) is very accurately weighed and
alloyed with the necessary quantity of other metals,
in order that the check
may correspond
in composition
then treated simultaneously with the assay and exactly in the same way.
the
If the gold left after parting the cornet from
to the alloy to be assayed.
It is
weighs more than the pure gold taken, the
gold
excess weight is deducted from the weight of the
obtained from the assay of th ? alloy and, conversely,
" check "
;
if it
weighs
less
the deficiency
Assay by the
is
added.
Touchstone.
— This
method
determining the fineness of a gold alloy conbe tested on a small
sists in rubbing the alloy to
resembling slate,
block of hard, smooth, dark stone,
appearance and
called a tonclidone, and comparing the
with those made
colour of the streak thus produced
prepared alloys
series of small bars of carefully
of
by
a
of
definite
composition,
known
as
"touch-needles"
of
and 31). The effect of the action of a drop
regia on these streaks
nitric acid and of dilute aqua
will
the streak from the less pure alloy
is also noted
(Figs. 30
;
production of a
be more readily acted upon, with the
the proportion
more or less green colour, according to
Several series of touch-needles are
alloys of gold and
usually employed, consisting of
gold, silver and copper,
copper, gold and silver, and
of copper present.
the alloys being
made
either
to correspond to legal
the proportion of gold
standards or in series in which
For the sake of
carats or half-carats.
increases
by
are frequently soldered
convenience, the touch-needles
GOLD.
lOI
to the points of a star-shaped piece of metal, as
shown
in Fig. 31.
The vahiation
made by determining
of an alloy is
to
which of the touch-needles the streak it produces most
In order to get correctly the
nearly corresponds.
the alloy to be
streak of
metal should
first
be slightly
have been made
the
tested, the
filed
surface of
away, as this
the
may
than the bulk of
somewhat
by boiling with acid to remove the base
alloy
richer
Fig. 31.
Fig. 30.
or inferior metal
from the surface, as
"
in the " colouring
process used by goldsmiths (see p. 116).
The touchstone is generally used for the approximate
assay of small articles of jewellery, which
it
would be
necessary to destroy in order to obtain samples for a
correct assay
;
it is
also of use to the assayer in deter-
mining the approximate fineness of gold bullion but it
cannot be relied upon for very accurate assay, although
;
it
yields sufficiently useful results for a preliminary test,
and for some purposes is sufficiently exact. It requires,
" The trial
however, a sharp and very practised eye.
is more sensitive for alloys below 750 fine (18 carat)
than for higher standards.
The amount
of
gold in
between 700 and 800 fine (17 to 20 carat) can
be determined correct to 5 parts per 1000." *
alloys
*
T. K. Jlose, " MBtiilhirgy of Gold,"
[i.
459.
DENTAL METALLURGY.
I02
Detection and Estimation of Gold in Alloys.
— Alloys for dental
amalgams are mainly composed of
small quantities of gold and
which
tin
platinum, and sometimes other metals, are added.
-
and
silver, to
—
Detection of Gold. The presence of gold in these
alloys may be detected by treating a small quantity of
the alloy with nitric acid,
undissolved.
As
alloys, it will
acid
when the gold
remain
invariably present in dental
tin is
converted
be
will
by the
into oxide
nitric
and remain with the gold, forming a purple residue
(pu.rple-of-Oassius).
If gold is absent the residue will
be white (metastannic
The
acid).
following are the usual
obtaining a solution in aqua regia
Stannous Chloride containing a
tests
for
gold
after
:
little
stannic chloride
a very characteristic test for gold, giving a beautiful
purple precipitate (purple-of-Cassius), even in solutions
is
containing extremely small quantities of gold.
Ff.rrous SidjyJiatc is also a delicate test, producing
either at once or
on heating the solution a very
divided precipitate of gold
:
the liquid usually appears
by transmitted light, and
turbid by reflected light.
bluish
Sid2)liurettecl
is
always reddish and
Hydrogen gives a brown or black pre-
cipitate of gold sulphide.
Estimation
finely
of
Gold.
—When
tin
is
absent,
the
residue of gold obtained after treatment of a definite
weight of the alloy with nitric acid may be filtered off"
and then heated
to redness
and weighed.
"
" purple-of-Cassins
If tin is present the residue of
caustic potash, which
is filtered off and then fused with
combines with the
tin,
forming a compound (stannate
leaving the gold as
of potash) readily soluble in water,
GOLD.
This
a fine powder.
is
103
collected on a
filter,
then washed,
heated to redness and weighed.
The gold
by
in
amalgam
submitting a
also be
quantity to
small
under Silver,
described
may
alloys
scorification, as
then cupelling and
180,
p.
determined
parting the gold-silver bead with nitric acid in the
ordinary
way
from one-tenth per cent,
in these alloys usually varies
to about 5 per cent.
Alloys of Gold.
— Gold
almost any of the metals,
constituting
The gold present
as previously described.
its
is
its
capable of uniting with
alloys with other metals
most important
uses,
as pure gold is
too soft for application alone.
Gold and Copper,
gether in
all
proportions
—These
when
metals alloy well
fused.
maximum
the hardness of gold, the
to-
Copper increases
degree of hardness
being attained when the copper constitutes one-eighth
The yellow colour of gold is deepened by
of the alloy.
the presence of copper, and when much cop]3er is preThe
sent the alloys become tarnished on exposure.
malleability of these alloys
of gold
if
pure copper
ceed 10 to 12 per cent.
is
scarcely inferior to that
employed, and does not ex-
is
Alloys of gold and copper are
more fusible than pure gold.
The gold coinage of this country
is
made from
22-carat gold, or 916.6 parts of gold to 83.3 parts of
copper, the alloying metal being copper.
termed standard gold (see
An
This alloy
is
p. 105).
and copper of i8-carat standard is
very largely employed for jewelleiy.
Gold and Silver. These metals unite iu all
alloy of gold
—
proportions
when melted
together, the resulting alloys
being paler in colour than pure gold, the presence of
DENTAL METALLUEGY.
I04
oue-twentietli part of silver being sufficient to modify
the colour of gold.
the
alloys
With 27
have a green
to 30 per cent, of silver
but when the silver
tint,
exceeds 50 per cent, the alloys are nearly white. The
effect of silver is to give hardness to the gold without
impairing
more
its
elastic,
and to make it tougher and
the same time sensibly reducing
malleability,
while at
the melting-point.
Gold-silver alloys do not oxidise on exposure to
air,
but are more or less tarnished in the presence of sulphuretted hydrogen.
Gold, Silver, and Copper.
—These
are largely used by jewellers and
by
three metals
dentists for the
production of alloys, v/hich are tougher, more malleable
and more ductile than when copper alone is used as
the alloying metal.
Alloys of these metals, in varying proportions, are
no).
Platinum. These metals unite by
used as gold solders (see
Gold and
p.
—
fusion, but require a high temperature to effect their
combination, in consequence of the high melting-point
The effect of platinum on gold is to
of platinum.
produce alloys which are ductile and
elastic,
but
its
presence makes the colour of gold paler.
Gold and Mercury.— These metals have a great
affinity
for one
another, even
at
ordinary tempera-
Gold-Amalgam, p. 1 34). If a piece of gold
penetrated
is rubbed with mercury it is immediately
and becomes exceedingly brittle care should therefore
be taken to prevent globules of mercury coming into
tures (see
;
contact with gold plate in the dental laboratory.
Gold and Tin.— These metals form alloys which
gold.
are usually brittle and of a paler colour than
GOLD.
Carat and Fineness. —Gold
in
pure
a
but
state,
is
almost
is
never emploj^ed
universally
with a certain j^roportion of copper or of
made
being
alloys
up
definite
to
alloyed
the
silver,
proportions
or
" standards."
Pure gold
fineness
is
described as 24 carats fine, and the
gold,
of
or
proportion in the
its
therefore expressed by stating the
number
alloy, is
of carats
pure gold present in 24 carats of the
The English gold coinage, or standard gold,
(or parts) of
alloy.
consisting of an alloy of 22 parts of gold with 2 parts
of copper, is accordingly described as 22 carats fine.
i8-carat gold
is
an alloy consisting of 18 parts of
gold and 6 parts of copper.
copper
is
In some cases part of the
substituted by silver
thus,
;
the
standard
frequently employed by goldsmiths, though of 22 carats
fine,
contains in the 24 carats 22 of gold with
copper and
metal
for
i
may be
i
of
In special cases the alloying
of silver.
platinum, as in 17-carat gold plate used
bands in dental work.
In England at the present time
exist for gold ware, viz.
18,
15,
12,
17,
and
The
made
16 carat, while
swivels 13-carat gold
is
;
Gold plate and wire
standards of 22, 20,
to
for
gold
springs
and
employed.
fineness of gold is also frequently expressed in
decimals, in which case pure gold
fine.
standards
22-carat, or standard gold
and 9-carat gold.
for dental purposes are
18,
—
five legal
The English standard
would therefore be g 16.6
fine,
is
described as lOOO
for gold coin,
22 carat,
and would contain
this
number of parts of fine gold in lOOO parts of alloy.
The standard of the American, German, and French
gold coinage
is
21.6 carats or 900
fine.
rhe relation
DENTAL METALLURGY.
io6
of the carat to decimals
is
shown
in
following
the
table
Decimal.
Cavat.
Pure gold
English gold coin
24
22
American
21 6
,,
1000
916.6
900
834
750
709
667
62s
542
20
Dentist's gold
18
17
16
IS
13
12
1
— Pure
seldom employed in
the dental laboratory, on account of its softness and
In order to obtain the degree of hardness,
flexibility.
Gold Plate.
gold
is
strength, and elasticity necessary to enable
it
to resist
the wear and strain to which an artiBcial denture is
invariably exposed in the mouth, the gold for dental
purposes
alloyed with other metals.
is
These important properties are usually conferred
upon the gold by the addition of copper or of silver, or
both; or by copper, silver and platinum. Varying
proportions of copper and silver are most generally
gold
employed, but
bands,
&c.,
gold which
not,
is
it
as
that
used for
platinum in
The quahty of
the mouth should
additional elasticity.
to be introduced into
a rule,
as
such
sometimes alloyed with
is
order to give
plate,
be
less
than
18 carat fine or
much
Gold of low standard is much more
proportion of
readily tarnished, owing to the larger
to the
communicates
copper and silver present, and
above 20
mouth
a
carat.
disagreeable
metallic taste,
while
gold of
:
GOLD.
107
high standard will generally be found too soft and
yielding and
not capable of resisting the strain put
upon it during mastication.
Higher grades of gold plate intended
for dental
purposes may, however, have the requisite amount of
and strength conferred upon them by the
addition of a small quantity of platinum.
Gold plate
rigidity
suitable
as
base
a
for
dentures
artificial
may
be
*
the
prepared according to the following formulaa
proportions
relative
;
the various metals added to
of
the pure gold or to the standard gold may, however,
be varied to suit the requirements of the manipulator.
The approximate
preparation
quantities are also given for the
gold plate from
of
English standard gold (coin)
is
the
formulas
when
used, (22 carats fine)
instead of pure gold
Gold Plate.
18
carats fine.
lUvts
Piii-e
gold
Copper
Silver
ihvts. ops.
Standard gold
Copper
18
4
Silver
.
Gold Plate.
Silver
9
2
O
20 carats fine.
(Iwts. grs.
20
.
IS
2
.
(Iwls.
Pure gold
Copper
19
Standard gold
21
19
o
5
2
o
'
.
2
Coppei-
2
Silver
Gold Plate.
22
.
carats fine.
(twts. ni-s.
Pure gold
.
(!opper
*
O
O
I
SilviMI'iMtiniini
22
.
O
o
iS
Kichardaon, "Mechanical Dentistry," 7th edit, 1898,
6
p, Si,
DENTAL METALLURGY.
io8
The addition
amount
of a small
of platinum to high
carat gold, as in the last formula, furnishes an alloy
in
rich
gold, while, as
previously stated,
to the plate a suitable degree of stiffness
and
imparts
it
and
elasticity
does not destroy the characteristic colour of line
gold nor materially impair
its susceptibility
of receiving
The richness of colour of the gold plate
however, more or less impaired as the quantity of
a high polish.
is,
platinum
increased.
is
Gold plate 20 or 21 carats fine, in which the alloying
metals are copper and platinum, is frequently used by
dentists on account of its greater strength and power
of resisting the chemical action
mouth.
With
reference
platinum, Essig remarks*
strength and stiffness a
plate
and
may
of the fluids of the
gold
to
that
much
containing
plates
"owing
to its increased
thinner and lighter
be employed without the additional labour
cost of doubling the plate at
what would be weak
points in partial cases composed of ordinary
or
20-carat gold."
An
objection urged
1
8-,
19-,
against the
employment of gold plate containing platinum is the
increased difficulty of swaging a plate of the alloy so
that
it shall
the die.
perfectly conform to
all
the depressions of
Essig having invariably found,
when the
any considerable percentage of platinum, that the ordinary method of swaging between
zinc and lead was not effective, has for more than
alloy contained
twenty years employed zinc for counter dies as well
for dies, thus entirely overcoming any difficulty
as
in
swaging.
Gold plate and wire used in making bands and
clasps should contain a little platinum in order to
* Essig, "
Dental Metallurgy," 1893,
p. 139.
;
GOLD.
it
tootli.
17-carat
embrace
firmly
to
elastic
sufficiently
render
109
with platinum
gold alloyed
The
quently employed for this purpose.
the
fre-
is
following
formula gives the quantities necessary for the preparation of 20-carat gold plate suitable for clasps, and
whenever
quired
and additional strength are
elasticity
re-
:
Gold Plate.
.
.
.
.
2
Silver
.
.
i
i
.
.
22 dwts.
„
Standard gold
Copper
.
.
o
„
Silver
.
.
i
„
,,
Platinuui
.
.
i
.,
20 dwts.
Pure gold
Copper
Platinum
20 carats fine.
.
„
In France the following alloys are used for " dental
gold plate *
"
:
Xo.
18
Gold
Silver
.
.
Copper
Platinum
Xo.
I.
20
cts.
Xo.
2.
21
cts.
No.
3.
For
cts.
4.
clasps.
20
.
18
...
20
...
21
...
.
2
...
2
...
i
...
i
4
...
2
...
2
...
2
—
...
—
...
—
...
i
.
.
Alloys Prepaeed from French Gold Coin (900 fine).
Xo.
18
Gold coin
Silver
Copper
Platinum
.
.
.
.
.
.
.
.
.
.
.
.
.20
.2
.2
.
No.
I.
For
cts.
—
Preparation of Gold Plate.
2.
clasijs.
20
...
...
0.4
...
C.3
...
0.75
— Alloys
•
for gold
by melting the constituents together
in a plumbago crucible, which should be carefully
A
annealed in an inverted position before use.
small quantity of charcoal powder should be placed
plate are prepared
on the surface of the metal to form a protective
coating and prevent the oxidation of the copper
*
Communicated
to
tli(;
author by Andre
I'.
(irillitliH.
I
DENTAL METALLURGY.
lO
the crucible should also be covered with a
crucible
is
then
heated
a
in
lid.
The
furnace at a
suitable
good bright heat, and when the mixture is melted the
whole should be stirred with an iron rod (previously
made red
hot) in order to promote
between the constituents of the
more intimate union
The alloys of
alloy.
gold should not be over heated but poured immediately
The metal
after complete fusion has taken place.
cast into an ingot-mould (see
rolled
into
sheets
of
the
p.
is
76) and subsequently
required
thickness.
The
mould must be blackened or greased to prevent the
metal sticking, and must be dry and warmed before
Care should be taken to prevent the charcoal
powder from running into the mould with the metal,
use.
otherwise
it
will
up clean scrap
cause a faulty casting.
When
for the production
plate the pre-
of
melting
cautions given on p. 66 should be considered.
Gold Solders. These are alloys of gold employed
—
for effecting the union of the various parts of
composed of pure gold or of gold plate.
To do
this successfully the solder used
articles
must have a
lower melting-point than the materials to be joined
with it the fusing-point of the solder should, however,
;
approach as near as it conveniently can to that of the
material to be soldered, in order that a more perfect
and more tenacious joint may be obtained.
varieties of gold solder of different degrees of
" softness " and " hardness," i.e. of fusibility, are pro-
Many
duced by adding to the gold variable proportions of
the more fusible metals silver, copper, and sometimes
—
zinc.
Gold solders are very frequently made from the same
is
carat gold as that of which the article to be soldered
GOLD.
1 I
composed, the melting-point being lowered by
and
tion of copper
tlie
I
addi-
or of standard silver and
In some cases gold plate of lovs^
standard may be employed as a solder for gold plate of
sometimes of
silver,
brass.
As
a higlier standard.
several standards of gold are
used in dental work, solders of different degrees of
fineness are employed, the solder most suitable for the
work
in
hand
being
selected.
range for gold solders
50 per cent, of
15 to
is
The most
from 20 to 12
carats, or
many
although
alloy,
desirable
from
consider
i2-carat solder too coarse for dental work.
of zinc renders
employed
The presence
more fusible, but when
the solders
make
should only be in quantities sufficient to
the gold flow readily and evenly at a diminished
heat;
when used
it
becomes objectionable.
Gold solders containing zinc are alwaj^s more or less
brittle, and consequently difiicult to roll into plate
in excess it
without breaking into
The following
many
alloys are
pieces.
largely
employed
in this
country as gold solders for dental work. They are
very fluid and flow readily in a state of fusion, and
effect a perfect
combination between the parts united
by them.
No.
I.
Gold
.
Silver
.
Cop[)er
.
No.
"Best Quality."
.15
.
.
.
.
Silver
.
.
.
Standard gold
.
,,
Silver
.
.
4.0
„
5
»
Cop]ier
.
.
3.5
„
24
„
4
.
16.5 dwts.
24.0
"Medium."
2.
(iold
Copper
dwts.
15-cARAT Solder.
ij-carat Solder.
13 dwts.
Standard gold
.
6
,,
Silver
.
.
5
r
Copper
.
.
24
.•
I
.
14 dwts.
6
4
24
,.
I
DENTAL METALLURGY.
12
No.
"Most Fusible."
T..
Gold
i2-carat Sor.nEn.
6
„
Silver
Copper
6
„
Copper
24
,1
The following formula
dwts.
iSUindard gold
12 dwtss.
Silver
6
.
5
24
*
may be used
with 18- to 20-carat gold plate, and
in connection
16 carat fine
is
:
16-CAKAT SOLDEB.
Pure gold
6 purts or 16 dwts. o grs.
Silver
2
))
5
"
^
I
„
2
„
16
24
11
O
Copper
.
„
II
6.5 parts or 17 dwts. 8 grs.
Standard gold
Silver
II
2.0
.
Copper
0.5
,,
5
„
8
„
„
I
„
8
„
24
The following formulae
carat solders
will furnish
15-caratand
18-
:
15-CAEAT Solder.
Pure
gl^
Silver
Copiier
.
15.0 parts
Brass
16.8 parts
36
.,
Copper
2.4
„
„
Brass
1.2
.,
„
4.2
1.2
Standard gold
Silver
3-6
24.0
24.0
18-CARAT Solder.
Pure gold
Silver
.
Copper
Brass
.
18.00 parts
Standard gold
is
2.66
2.66
2.66
1.
,,
Copper
068
„
Brass
0.68
always used as a flux with gold solders.
* Harris, "
Dental Surgery," No.
3, p.
666.
,,
00
24.00
24.00
Borax
19.66 parts
Silver
.,
GOLD.
I I
o
Preparation of Gold Solders.— lu preparing
gold solders the metals are carefully weighed and then
melted together in a plumbago crucible in a furnace at
a bright red heat.
A
little
charcoal powder
is
sprinkled
on the surface to prevent oxidation. When complete
fusion has taken place. the metal is stirred and
then
poured into an ingot-mould to obtain a thin ingot
suitable for rolling.
When
zinc or brass enters into the composition of
the solders it should be added after the other
stituents are completely melted, care
conbeing taken to
avoid excessive heating.
The alloy should then be well
and poured immediately.
The metals employed for the preparation of gold
solders should be free from impurities,
and great
stirred
care
should
be taken to insure uniformity of com-
position.
Calculation of the Carat Fineness of Alloys.
—The
several calculations in connection with the
carat
fineness of various mixtures may be readily
made by
the aiDplication of a simple method devised
some years
ago by Mr. A. Mc William, of the University
College,
Sheffield, for the calculation of all kinds
of steel
tures, and now extensively used by
mix-
students and in the
works.
A
beiug one -^^th part (see
p.
105), the
of ounces (or other unit of weight)
multiplied
carat
number
by the carat fineness gives the number
of 24ths of an
ounce of fine gold present in an alloy,
and this new
unit (^Vth ounce) is termed the
"carat ounce."
This
new
unit will be
found very convenient in
calculating the carat fineness of
gold alloys, for
obvious that in any alloy
.
JI
it
is
DENTAL METALLURGY.
114
ciira t
oimces
^
^.^^..^^^
_
quqcq^.
=
carat ounces.
ounces
carat ounces
cai'ats
ounces x carats
application of this
The
method
will
stood from the following examples
be readily under-
:
Carat Fineness of an
I. To ascertain the
Alloy from a given Mixture
is given for the
Examiilc i.— The following mixture
:
preparation of a gold solder
Pure
:
gold, 6 ozs.
;
silver,
Total, 9 ozs.
produced.
6 ozs.
Ascertain the fineness of the alloy
of gold,
contain 6x 24, or 144 carat ounces
2 ozs.
copper,
;
i
oz.
pare gold
and
as this
is
the
amount
carat fineness of the alloy
liAj^axa^^w^
of gold in 9 ozs. of alloy, the
is 16.
_
J
5 carats
tine.
9 ozs.
solder in the preExample //.-Again, take a gold
standard gold has been used
paration of which English
instead of pure
gold, the quantities
bemg 48
dwts.
dwts. silver 12 dwts.
standard gold (22 carat), 16
48 dwts. standard gold conTotal, 76 dwts.
copper.
tain 48
X
22, or
1056 carat dwts.
i^^gi^^
i-
A^^r^<
(^^Q
carats as the tineness of the
= {'^-^iS
from the given mixture.
Standard
To Reduce Gold to a Required
the
:
II
The standard
of a gold alloy
may be lowered by
these,
of silver, or an alloy of
addition of copper, or
such as silver coin.
/;.;a«^2;ie
4
ozs.
/-Reduce
.
^
, ,
pure gold to i6-carat gold.
,
4
ozs.
pure gold contain 4 X
24, or
96 carat
ozs.
:
GOLD.
g6'
uiu'iit oxti.
1
6
ozs. is
=
t-
6 ozs.
5 carats
the weight of the alloy of i6-carat fine, and
as 4 ozs. of gold are used, 2 ozs. of other metal
must be
added to reduce the pure gold to l6-carat gold.
Mmni'plc II.
— Reduce
2 dwts.
of l8-carat gold to
l6-carat gold.
2 dwts. of
2X
i8-carat gold contain
i8, or
36 carat
dwts.
—
carat dwts.
36
^
7
1
ID carats
Hence
-]
=
,
,
,
2j dwts.
dwt. of other material must be added.
To Raise Gold to a Higher Carat
may
This
be done by adding either pure gold or gold
alloy of a higher standard than that to be prepared.
Example
I.
—Raise
10 dwts. of
gold to
i8-carat
20-carat gold.
The 10 dwts. must be raised 2 carats, and this will
require lO x 2, or 20 carat dwts.
The pure gold (i.e. 24 carats) added must be considered to retain 20 of its own carats, and hence there
are only 4 carats available for enriching.
20 carat dwts.
\
4
5
dwts. of pure gold
=
,
S
,
dwts,
cai-ats
must therefore be added
to raise
10 dwts. of i8-carat gold to 20-carat gold,
EjXLtnple
20-carat
II.
gold
— Raise
10 dwts. of
gold to
l8-carat
by the addition of standard gold (22
carats).
Standard gold has 2 carats available for enriching.
20 carat dwta.
- -
=
.
2 carats
s
,
,
10 dwts.
,.
ol
,
,
,
,
,
,
,
,
,
,
standard sdid
to be added.
"
I 1
DENTAL METALLURGY.
6
Example i//.— Raise 9 dwts. o£ 13-carat gold
gold.
i6-carat gold by the additiou of 20-carat
9 dwts. raised
= 27 carat dwts.
- 16 = 4 available
to
3 carats
20-carat gold has 20
_^7_5f^If^Ldw^^ ^
gn
^^,vts.
carats.
to be added.
4 (available) carats
Colouring of Gold.—This term
process
by which a
obtained on articles
their appearance,
and
superficial
made
is
of
film
is
applied to the
of fine
gold
is
gold alloys to improve
effected by externally dissolv-
with which the gold
ing out the copper or other metal
article to
In conducting the process the
is alloyed.
dull redness in a Bunsen
be coloured is first heated to
and then plunged into
flame or flame of a spirit lamp,
weak solution
which means the
a
acid bath, by
of nitric acid or other
dissolved,
copper, &c., on the surface is
gold of a deep, rich, yellow
leaving behind a film of pure
colour.
T
J
by a
produced
The same effect is also frequently
" dry colouring," which
method known as
consists
m
coloured for a few minutes
placing the article to be
in a paste,
composed of a mixture
of saltpetre,
common
gold
Twelve-and-a-half to thirteen carat
subjected
that can be satisfactorily
is the lowest quality
and unirich
and retain a
to the colouring process,
showing irregularities on" the
salt
and alum.
form appearance without
^''(^Iding
—By
low standard
this process articles of
made to resemble high carat gold
or of base metal are
gold deposited on their surface.
by having a thin film of
The method now
known as "
that when
pmijose is
usually adopted for this
and is dependent on the fact
electro-gilding,"
a current of electricity
is
passed through a
GOLD.
117
suitable solution of a metal decomposition of the liquid
takes place, the constituents of the liquid being liberated
and the metallic constituent deposited.
Large articles are gilded in cold solutions and smaller
A
articles in hot solutions.
small articles
solution for electro-gilding
maybe prepared by
dissolving 15.4 grains
aqua regia and evaporating nearly to
The gold chloride thus formed is dissolved in
of pure gold in
diyness.
water, and a solution of
potassium cyanide carefully
added as long as a precipitate of gold cyanide
The
precipitate
poured
off,
is
allowed to
settle,
is
given.
the clear liquid
and the precipitate dissolved by the addition
The solution is
then diluted with water to one quart. The temperature
of the bath shoald be about 165° F., and the cui'rent
of
more potassium cyanide
solution.
strength 2.0 to 2.5 volts.
The process is conducted by first thoroughly cleansing
the article by immersing it in a hot solution of caustic
potash, and sometimes in an acid bath, and also by
means of a scratch-brush.* The article is then rinsed
in water and transferred to the plating solution.
A
plate of pure gold
suspended in the bath from
a suitable support connected with the positive pole of a
is
battery, while the article to be
plated
is
suspended
by thin copper wire connected with the negative pole.
By this means an electric current is passed through
the plating liquid, which causes the deposition of a
film of metallic gold on the article.
The gold solution is kept hot during the operation
(as above stated), and remains constant in strength.
*
8
This conniHtH
in. loiif;,
left
I'l'i'i'
til
ol;
ii
biindlo of
liiK^, liiird
Ixmiid roimd Vci'v tightly with
ronii
:i
brush.
hniss wiiv; iibont 6 in. or
otli(!r
wire, (lio (mhIs heing
DENTAL METALLURGY.
Il8
owing
to the gradual dissolving
When
sufficient gold has
away
of tlie gold plate.
been deposited, the
article is
removed and well rinsed in water the dull brown surburnishing.
face is then made bright and lustrous by
The electric current employed is usually derived from a
;
and the proportion of gold cyanide,
potassium cyanide, and water in an electro-gilding
Bunsen
battery,
solution
may vary very
greatly without detriment to the
process.
A
process for
making dental bases by
electro deposi-
preparation, was
tion on the plaster cast, after suitable
patented by
Ward
in 1889.
are sometimes gilded
Articles
Fire Gilding.—
old
process,
known
as Jire gilding.
receive the deposit of gold
is
first
The
by the
article
to
cleansed and then
by which
dipped into a solution of mercuric nitrate,
It
means it becomes coated with a film of mercury.
a pasty amalgam of gold
is afterwards pressed upon
(see p.
134), a portion of
which adheres
to
The
it.
behind a
mercury is then expelled by heat, leaving
burnished.
deposit of gold which is subsequently
of Gold from Scrap.— Dental scrap
Recovery
consists chiefly of plate clippings
proper care
platinum,
is
and old
plates.
If
of
taken to prevent the introduction
and to
or particles of base metal,
filings,
scrap
together, the
keep clippings of definite standard
and again converted into
only requires to be remelted
plate or other
form
When, however,
for use.
the
scrap
platinum, and
mixed
filings,
solder,
&c., the gold
contaminated with
fragments containing
is
must be recovered before
it
can
fresh plate.
be worked up again into
first partially refined by
For this purpose the scrap is
119
GOLD.
melting with a
little
with from 2 to
3
borax and
times
its
nitre.
It is then alloyed
own weight
and
of silver
the resulting alloy granulated and parted as described
on p. 87. If platinum is present and does not form
more than 10 per
cent, of the original alloy,
it
will
be
dissolved with the silver after prolonged boiling in acid.
The
silver is precipitated as chloride (see p.
1
69),
platinum subsequently separated with zinc or
and the
ammonium
and converted into spongy platinum.
If more than 10 per cent, of platinum is present the
operations of inquartation with silver and parting must
be repeated, or the gold may be dissolved in aqua regia.
chloride
The
solution thus obtained
evaporated, and potas-
is
sium chloride and alcohol added to precipitate the
platinum.
/ After allowing the platinum precipitate to settle the
clear liquid is poured off and ferrous sulphate or other
added to precipitate
precipitating agent (see p. 96)
the gold.
The
finely divided metallic gold is collected,
washed, dried, and then fused in a crucible, with the
addition of a little potassium bisulphate as a flux, after
which
it is
cast into an ingot
The platinum
is
and
recovered
is
in
ready for use.
a
spongy form in
the metallic state by strongly heating the precipitate
obtained.
—
Sweep
or Lemel. These terms
are applied to the material which accumulates in the
dental laboratory and other places where gold is
Purification of
worked.
It
consists
of
fine
metallic
particles
con-
taminated with dust and organic matter, such as
wax, &c., and varies considerably in composition.
A
magnet is first passed through the filings to remove
any iron which may be present. The lemel is then
I
DENTAL METALLtTUGY.
20
by burning
purified
off
the organic matter, and melted
These neces-
in a fireclay crucible with suitable fluxes.
vary according to the quantity and nature of the
impurity mixed with the lemel, but the following prosarily
portion
may be
conveniently taken
:
5°
Lemel
Sodium carbonate
Borax
5
Potassium bisulphate or nitre
Common
salt
.
.
.
.
.
.
•
.
i
5
to 2
5
•
mixed with the fluxes, with the
exception of the salt, which is kept as a cover for the
mixture, as it prevents the mass rising too much and
The lemel
is
well
which oxidises the
base metals, and potassium bisulphate should be sparThe crucible should not be more than
ingly employed.
half full to commence with, and should be gently
overflowing
the crucible.
Nitre,
heated at first, the temperature being raised gradually.
Towards the end of the operation, when the violence of
the action has nearly ceased, a more intense heat is
employed, and when the whole mass is thoroughly
which
liquid it is well stirred with an iron rod, after
into
the crucible is removed and the contents poured
an ingot-mould, care being taken to prevent the "slag"
running into the mould. The ingot thus obtained will
in
many cases be
brittle,
the alloy
with a
little
in a suitable condition for rolling.
may be
"
toughened
charcoal powder.
When
"
it
If
by remelting
is
desired to
ingot must be
obtain the gold, &c., in a pure state the
and alloyed
cleaned from any adhering slag, weighed,
silver, the
of
weight
with from two to three times its
granulated by
molten alloy being well stirred and then
carefully pouring into water.
aotD.
of alloy are collected, placed iu a
The small granules
aud parted in acid as described on p. 87.
If much platinum is present the alloy is best dissolved in nitro-hydrochloric acid, and the metals resuitable vessel,
covered as described for the treatment of scrap.
Purple- of-Cassius.
—This compound
employed
is
by manufacturers of porcelain teeth for obtaining the
necessary pink tint;
it
is
also
used in the arts for
imparting a rose or pink colour to porcelain, enamel,
and
red or brown, according to
by adding a solution of stannous chloride
It is obtained
(SnCl.,),
from violet to a purplishthe method of preparation.
It varies in colour
glass.
containing also stannic chloride (SnCl^), to a
By this means
dilute neutral solution of gold chloride.
a fine flocculent purple precipitate
allowed to
settle,
is
obtained, v^hich
then collected, washed, and
is
dried.
The exact nature
of this precipitate
understood
supposed to be a combination of
it
;
is
is
not thoroughly
stannic oxide, coloured with finely divided gold or one
of its oxides.
A
very fine product
is
obtained by adding a solution
of stannous chloride to ferric chloride, until the solution
and becomes a pale green. This
mixed solution is then added to the gold solution to
produce the purple precipitate. Many other methods
are also employed.
The purple-of-Oassius used by the
loses its yellow colour
manufacturers of porcelain teeth, in the preparation of
gum-enamel, is sometimes prepared by the following
method.* An alloy consisting of
Silvin-
Gold
Till
....
.
,
*
Kssifi,
.
.
.
.
.
.
40 parts or
85.
1
per
coil
4
„
8.5
„
3
..
6.4
,,
Di'iitMl Mc(:illiir^-y,"
1893, p. 150.
t.
122
DENTAL METALLURGY.
prepared by melting the constituents in a crucible,
under a cover of borax. The alloy is granulated by
is
pouring into water, and the granules treated with nitric
acid and gently heated, until all the alloy has been
acted upon.
The
having thus been entirely dispoured ofE and the purple residue
silver
solved, the solution is
carefully washed, until the last trace of silver solution
is
removed.
After several washings, the purple-of^Cassius is dried
by gentle heating, and is then ready to be incor-
porated with the silicious materials for the preparation
of gum-enamel.
dHAtTER
Vli.
MERCURY,
SYMBOL, Hg
Occurrence.
in the
(Hydrnrgyi-um).
—Mercury
metallic
inated through
state,
is
ATOMIC WEIGHT,
frequently found in nature
almost pure,
usually
globules.
ores in small
its
2Q0.
dissem-
It is also
found in combination with iodine and chlorine, and in
union with gold and
silver, as
native amalgams.
Its
combination with sulphur, constituting cinnabar (HgS),
forms, however, the most important ore of the metal,
and that from which almost the whole of the mercury
of commerce is derived.
Preparation. The method almost exclusively
employed for extracting mercury from the natural
—
sulphide consists in heating the ore in a suitable kiln or
furnace, to which a series of large condensing chambers
By
the action of heat and air the ore
is
connected.
is
decomposed, the sulphur being oxidised to sulphvir
and the mercury liberated and volatilised.
The gases and mercury vapour in passing from the
kiln are introduced into the condensing chambers,
where the mercury condenses. The metal thus obtained
is always more or less contaminated with other metals
derived from the ores treated
it therefore needs
])urirication.
Small (quantities of mercury may be predioxide,
;
DENTAL METALLURGY.
124
pared free from admixture of other metals by operating
upon a pure compound of mercurj^ which is decomposThus, the red oxide readily yields mercury
by simple distillation, while the sulphide (pure vermilion)
is best treated after the admixture of an equal weight
able by heat.
of lime.
—This metal, known
Properties.
difEers
also as quicksilver,
from other metals in being liquid at ordinary
temperatures, but, unlike ordinary liquids,
it
runs
off
non-metallic surfaces without wetting them, while with
many metallic surfaces the mercury unites with the
metal and deposits a film of an amalgam upon it.
a
It has an almost silver-white colour and possesses
not
strong metallic lustre. When pure, mercury is
tarnished by exposure to dry or moist air. If, howtakes
ever, other metals are present, oxidation rapidly
and the surface of the metal becomes covered by
of
a grey powder: this fact forms a ready method
If
detecting any considerable amount of impurities.
place,
mercury be maintained in contact with the atmosphere
the metal
at a temperature just below its boiling-point
Mercury is very
is slowly oxidised to mercuric oxide.
slowly
hydrogen, but
acid.
metal.
is
it
Water and
the
presence
nnaflfected
alcohol
of
sulphuretted
by exposure
are without
to carbonic
action on the
not attacked by hydrochloric acid
the
the concentrated acid is heated with
Mercury
even when
metal.
in
tarnished
is
It is scarcely affected
by
dilute sulphuric acid,
heat acts on
but the concentrated acid with the aid of
Nitric acid is its best solvent, and disit readily.
Alkaline solutions have
solves it with great energy.
Mercury solidifies
or no action on mercury.
little
when cooled
to
-39'
<^'->
and
in the act of freezing it
125
MERCURY.
considerably,
confci-cacts
malleable mass that
hammer
or welded,
out with a knife.
and
forming a tin-white, ductile,
may be beaten out with the
also capable of
it is
boils at 350°
Mercury
being easily
C, producing
a colourless vapour which is very poisonous, giving rise
The density of the metal varies much
to salivation.
with
the
When
high coefficient
mercury is shaken with
triturated
with sugar, lead, and
temperature, owing to
of expansion for heat.
oil,
when
or
it
is
its
obtained in a very finely
divided state in the form of a dull grey powder. This
operation is known as deadening, and is employed in
other bodies, the
metal
is
the preparation of grey mercurial ointment.
Use
for Dental Purposes.
—Mercury
is
chiefly
used ia the dental laboratory for the production of
amalgams for filling purposes. It is also used to a
extent
small
Compounds
as
a
of
constituent
"fusible"
alloys.
mercury are used in the manufacture of
of
dental rubbers.
Testing the Purity of Mercury.— It
is
very
important that the mercury employed for dental purposes should be quite pure, otherwise it will not readily
amalgamate with other metals. All doubtful specimens
Mercury which
should therefore be purified before use.
has been squeezed out in the preparation of amalgams
should not be returned
to
invariably contains small
derived from
merce,
the mercury-holder, as
quantities of
the alloy used.
unless
specially
The mercury
purified,
is
it
other metals
of
com-
frequently con-
taminated with small quantities of the volatile metals.
Zinc and bismuth, which are sometimes present in
mercury
lead,
ores, are distilled over
antimony,
tin,
with the mercury, while
and bismuth are added as adultera-
DENTAL METALLURGY.
The comparative purity of mercury
is readily observed by allowing a drop of it to run
lightly down a slightly inclined surface, when it ought
to roll as a perfect sphere and not elongate or drag a
tions to the metal.
be tested by briskly
shaking a small quantity of the metal in a bottle with
"tail" behind
air,
when
it
may
It
it.
should retain
also
bright metallic lustre.
its
If base metals are present, they are oxidised and form a
grey or black powder upon the surface of the mercury.
—
Purification of Mercury. The method most
frequently employed for freeing mercury from these
impurities
to
is
distil
it,
of
surface
the
the metal
being covered during distillation with clean iron filings
to the extent of about one-sixth the weight of the
The
mercury used.
and
iron filings retain the impurities
also help to prevent the spitting of the mercury,
which, however, cannot be completely avoided.
distilling small quantities of
mercury
used, while earthenware or wrought-iron
The
for large quantities.
retort,
For
a glass retort is
is
employed
about one-third
full
by imbedding it in a
sand-bath, while the neck is inclined and made to dip
beneath the surface of the water, with which the
of mercury,
receiver
is
is
carefully heated
half
filled.
The
receiver
is
still
further
with
cooled by placing it in a large vessel also filled
On the application of heat the mercury boils
water.
while
and distils over, and is condensed in the water,
the other metals are
filings.
retained by the layer of iron
The mercury thus
obtained
is
generally
which is readily
covered with a thin film of oxide,
removed by treating the metal with a little hydrochloric
is well washed and dried
acid, after which the mercury
at a gentle heat.
A
better
method
is
to substitute
;
MERCURY.
coarsely powdered
cinnahar for the
iioii
filings,
the
former being added to the extent of about one-fifth
The cinnabar suffers
the weight of the mercury used.
decomposition during distillation with the liberation of
its mercury, while the impure metals are largely converted at the same time into sulphides, which remain in
In distillation processes a small pox'tion of
the retort.
the more volatile impurities
generally carried over
is
and condenses with the mercury
therefore, when very pure mercury is required, the
separation of the impurities is effected by other means.
The best method of effecting this is to treat the mercury
into
the
receiver
with nitric acid diluted with from six to eight parts of
water and expose
it
to a gentle heat of about 55° C.
(131° F.) for some hours.
impurities and more
very
little
of the
The
acid dissolves out the
readily oxidisable metals, while
mercury
is
dissolved.
In order to
bring the mercury into intimate contact with the acid
it
or
should be exposed in thin layers in a shallow vessel
frequently shaken
method
consists
up with
the
in dropping the
acid.
Another
mercury in a
fine
stream through a high column of dilute nitric acid.
Mercury which has become contaminated with dust,
or from which the impurities have been oxidised by
shaking in air, may be cleansed by filtering through a
cone of paper, the apex of which has been pierced with
a pin.
It may also be filtered by squeezing through
a piece of chamois-leather.
Electrolytic Purification of Mercury.
— Elec-
methods have been recently introduced for the
purification of mercury for dental and other special
purposes, but the details of the processes employed have
not been published.
trical
DENTAL METALLURGY.
128
Mercury may be obtained
from
-by electro-deposition
a solution of the metal in nitric acid or in sulphuric
acid,
with about
per cent, of free acid.
5
In a method devised by Johnson* commercial mercury
is employed as the anode and carbon rods as the
cathodes.
The mercury is placed in a flat basin and
the carbon cathodes suspended above
consisting of
nitric acid
solution
a
and 4 per
the electrolyte
it,
17 per
containing
of
cent,
An
cent, of potassium nitrate.
employed, the current being interrupted at suitable intervals to prevent mercury from
going into solution. As long as the voltage is kept
E.M.F. of
I
volt
below 0.75 very
is
little
mercury leaves the anode, but
the impurities, zinc, cadmium, copper, lead, &c.,
The
currents
weak
very
into solution.
of long
pass
duration, the electrolyte
Six hours were
being renewed from time to time.
found
all
work best with
process is said to
about 2
sufiicient for the purification of
the ordinary commercial mercury.
The theory upon which the process
is
based
lb.
is
of
that
than that of
the ionising pressure of hydrogen
the impurities and greater than that of the mercury
is
the solution of the impurities
the current.
Vermilion.
pound
of
—Mercuric
mercury
is
is,
less
therefore, assisted
sulphide,
This com-
HgS.
extensively used as a colouring
pigment in vulcanisable rubbers and
vermilion of commerce varies
much
celluloid.
quality
*
is
—Vermilion
made by
of fine colour
the Chinese.
The
in tint and purity
its
of colour, slight differences in the details of
facture impairing or improving its colour.
Preparation.
by
manu-
and superior
The process
W. M. Johnson, horn Electric World and Engineer,
of
manu-
37, 634, 1901.
MERCUEY.
129
facture consists in heating a mixture of
one part of
sulphur with four parts of mercury in a shallow iron
pan, the mixture being stirred to effect combination.
The
product, which
a reddish or black powder,
is
is
placed -in iron pans provided with earthenware domes
and strongly heated for eighteen hours to sublime the
The
sulphide.
vessels are then allowed to cool slowly,
found adhering to the
when most
of the vermilion
surface
the dome, that attached to the iron pan
of
finely
is
powdered, then put into a large
vessel containing water
and allowed to
the fine sediment or residue
The powder, which
through muslin and
of the
The purest portion
being of inferior quality.
sublimate
is
is
settle,
when
and
dried.
collected
is
of a very fine colour,
is
then ready for
is
sifted
sale.
by wet
processes, one of the best being that of Brunner, which
It consists in rubbing together
is frequently employed.
for some hours a mixture of 100 parts of mercury
and 38 parts of flowers of sulphur, and then mixing
Vermilion of good quality
is
also obtained
the resultant mass with one part of potash dissolved in
six parts
of water.
After heating this mixture for
about eight hours the mass begins to exhibit a red
colour, and when the right tint has been attained the
mass
is
action,
quickly washed with water to prevent further
and
is
Detection
then dried.
of
Ivipurities.
—Vermilion
is
sometimes
adulterated with red lead, red oxide of iron, and fre-
quently with
gypsum
and
other
impurities.
The
presence of these impurities can be readily ascertained
however, as pure vermilion
is
volatilised
is left it
when heated
in a glass tube
without leaving any residue.
If a residue
denotes the presence of some impurity.
i
DENTAL METALLFRGY.
T30
Fivpcrlics.
—When vermilion
is
bvouglit into contact
and other metals having an aftinity.
for sulphur, it is decomposed with the formation of
metallic sulphides, and it is this fact which renders the
witii silver, copper,
combination of
silver and.vulcanisable
rubbers imprac-
ticable.
unaffected by water, alcohol, or alkalis,
insoluble in nitric, hydrochloric, and sulphuric
Vermilion
and
is
It is readily soluble,
acids.
chloric
is
:
this
however, in nitro-hydro-
mixed acid should therefore not be used
in removing tinfoil applied as a coating for plaster casts
in rubber work, which may adhere so tenaciouslj^ that
cannot be removed without the aid of a solvent.
Hydrochloric acid is the only solvent that will accom-
it
plish the removal of the tinfoil satisfactorily without
injury to the rubber.
"
Pure vermilion
in combination
not likely to produce deleterious effects
when worn in the mouth, nor is it probable that this
compound can be decomposed chemically and converted
with rubber
is
into a poisonous salt of mercury or cause salivation
the saliva." *
by
The discomfort some-
mere contact with
times caused by wearing artificial dentures of vulcanised
rubber is probably due to a certain extent to the
presence of deleterious substances present in the vermilion used for colouring the rubber.
Amalgams. "When mercury is one of the con-
—
an alloy the mixture is called an amalgam.
Mercury unites with most of the metals when brought
metals are in
into contact with them, especially if the
Many of
of foil.
a fine state of division or in the form
metals unite with mercury at the ordinary tem-
stituents of
the
assistance of heat.
peratnre, while others require the
* Essig,
'•
LViital Metallurgy," 1S93
I'dit. p.
223.
MERCITRY.
The
at
with which combination often takes
facility
ordinary temperature
the
li([uid
is
i)lace
jn-obably cine to the
condition of mercury, which facilitates
its
being
brousrht into intimate or molecular contact with other
metals.
is
With most
easily effected
of the metals, union with mercury
but with platinum, iron and nickel
;
combination takes
formation of amalgams
an evolution of
certain
amount
only with difficulty.
.place
The
sometimes accompanied by
is
indicating the existence of
heat,
of chemical affinity
:
in other cases
absorption of heat takes place, but as a rule
little
a
an
or no
thermal disturbance results from the combination of
The formation
metals with mercury.
a
few of the metals
is
of
amalgams of
attended with
considerable
diminution in bulk, while in some cases expansion
takes place, but generally the union of mercuiy with
other metals
volume.
is
accompanied by
The amalgams
little
or no change in
some metals are
of
fluid like
mercury, while others are solid or semi-solid.
solid
amalgams appear
consist
to
of
The
metals united
with mercury in atomic ])roportions, forming what are
regarded by
many
the liquid
amalgams generally
as definite chemical
dissolved in an excess of mercury.
frequently be
compounds, while
consist of a
compound
This excess can
separated by simple pressure through
chamois-leather, the solid
amalgam
many
probably consisting in
behind most
cases of metals united in
The chemical
atomic ])roportions.
left
affinities
between
the constituent metals, however, are only very feeble,
as
many amalgams
atomic proportion
jeoting thpTu
to
in
which the metals are united in
may
))e
partly decomposed by sub-
very great pressure, a part of the
mercuiy being thus forced
out, while
an amalgam con-
DENTAL METALLURGY.
132
taining a larger proportion of the other metals remains
behind.
In many cases liquid amalgams acquire a
form on standing, the excess of mercury
being separated the crystallised body thus formed is
the true amalgam, and, as before stated, probably a
crystalline
;
compound.
Although amalgams are usually obtained by the
direct union of the metals with mercury, other methods
are frequently employed for their production, espereadily.
cially for metals which do not amalgamate
Amalgams may also be produced— (i) by adding mermetal
cury to a solution of a metal (2) by placing the
salt; and
to be amalgamated in a solution of a mercury
definite chemical
;
(3) by the action of a
weak
electric current
produced
by placing the metal in contact with mercury and an
The properties of the amalgams of the common
acid.
metals are as follows
:
Aluminium Amalgam.
minium and mercury cannot be
— The
union of
alu-
effected readily at the
of comordinary temperature, but mercury is capable
the
heating,
bining with finely divided aluminium on
of
beiug attended by a considerable evolution
union
heat.
Although mercury and aluminium are not
oxi-
ordinary temperature,
dised by exposure to air at the
oxidation rapidly
yet after combination has taken place
readily covered
ensues, the resulting amalgam being
very
oxide.
with a thick film of white aluminium
accompanies the
considerable increase of volume also
instruments or
combination. When using aluminium
remember the affinity
apparatus, it is very important to
A
of
and
the
mercury under suitable conditions,
in any form in
to avoid the use of aluminium
The same
contact with amalgam fillings.
aluminium
also
mouth
in
for
MERCURY.
results are
T33
experienced on bringing aluminium into
contact with mercury
salts.
Antimony Amalgam. — Antimony combines with
mercury in the cold with great difficulty, but more
perfectly when heated, producing a soft plastic amalThe amalgamation is also facilitated by the
gam.
addition
of
amalgam
a
dilute
little
is soft,
hydrochloric
or shaken in air the
amalgam
acid.
The
When triturated
white and granular.
gives up the antimony in
the form of powder.
Bismuth. Amalgam.
solving a considerable
—Mercury
is
capable of dis-
quantity of bismuth without
losing its fluidity, the union being readily effected, even
by simply mixing the metals. When heat
is applied combination takes place more rapidly.
With
two parts of mercury and one part bismuth the amalgam
is pasty
it hardens after standing and becomes more
or less crystalline.
Bismuth amalgam, when pressed
iu chamois-leather, passes through the pores like
in the cold,
;
mercury.
Cadmium Amalgam. — Mercury
readily
is,
is
combine
at the ordinary
cadmium
and
temperature
;
the union
however, much more perfectly effected when mercury
added to molten cadmium, When mercury is com-
pletely saturated with
cadmium
a
compound
is
formed
parts of mercury and 21.7 parts of
cadmium, agreeing with the chemical formula Hg.,Cd.
consisting of 87.3
Cadmium-amalgam
brittle mass, heavier
is
a silver-white, crystalline, very
than mercury.
When
moderately
heated it softens and can be kneaded like wax. From its
property of gradually hardening it was formerly used
as a stopping for teeth, but, owing to the action of
the sulphuretted hydrogen in the mouth, the
lilling is
DENTAL METALTATRUY.
134
readily covered with a yellow film oE
Cadmium
easily dissolves in
cadmium
warm mercury,
sulphide.
giving rise
a solid compound, corresponding to the formula
An amalgam of one part by weight of cadHgjCd.,.
to
mium
with six
point of 16' C.
mercury has the low melting-
]iarts of
(60.8^^ F.).
Copper Amalgam.
—This
amalgam may be ob-
tained by the direct union of copper and mercury. It
possesses the property of becoming hard and crystalline
when
left for a
few hours, while
its soft
and
plastic
character can be restored by continued kneading or
pounding of the amalgam.
It also
becomes
and
soft
water,
])lastic when gently heated or placed in boiling
but recovers its hard crystalline character after standCopper amalgam cry stallises readily when hard
ing.
:
it
is
malleable, and can be rolled or
hammered.
It
admits of a good polish and retains its lustre well in
sulphuretted hydrogen.
air, but is readily blackened by
The density of this amalgam is the same in the soft and
does not expand in hardening,
and thus fills cavities, when hard, into which it has been
Copper amalgam is used for
pressed in the soft state.
hard states
;
therefore
it
its
stopping teeth, but is objectionable on account of
Amalgam,
great tendency to blacken (see Dental Copper-
P- 146).
Gold Amalgam.— Gold
iu a fine state of division
is
quickly dissolved by mercury, even iu the cold
if
the mixture
place
is
much more
considerable
slightly heated,
rapidly, the
proportion
of
;
but
amalgamation takes
mercury absorbing^ a
gold without losing
its
liquidity.
The amalgam
is
of
two parts of gold and one
of
mercury
and readily
white in colour, of a pasty consistency
MERCURY.
soluble in mercury, forming
solution
of
.of
It
is
.1
licjnid
Wlieu
mass.
this
strained through chamois-leather, the excess
mercury passes through together with a small quantity
gold, while a white pasty amalgam remains behind.
is probable that definite compounds of gold and
mercury exist. When heated to redness, gold amalgam
is decomposed, the mercury being distilled off', leaving a
residue of gold.
Iron Amalgam.
— An
amalgam
of iron cannot be
obtained by direct union of the metal with mercury,
but by introducing sodium amalgam into a clear, strong
solution of iron sulphate a viscid
which, in small globules,
is
amalgam
is
obtained,
attracted by the magnet.
Liead Amalgam.— These amalgams may be readily
formed by simply rubbing lead filings with mercury or
by pouring mercury into molten lead. The amalgams
they grow more and more pasty
are not entirely liquid
;
as the percentage of lead increases.
By
centrifugalis-
ing them in a chamois bag, crystals are obtained of the
composition Pb.,Hg. When the percentage of lead has
reached 65, the amalgam
tion
takes
place
Contrac-
entirely solid.*
is
during combination, the amalgam
being denser than either of the constituent metals.
Nickel Amalgam. Nickel does not amalgamate
—
when rubbed with mercury, nor can a nickel amalgam
be obtained directly. An amalgam may be obtained
by adding sodium amalgam to a strong solution of a
nickel
salt.
Palladium Amalgam.
—This amalgam
is
obtained
by rubbing finely divided palladium with mercury.
Union takes place at the ordinary temperature, but
not with great facility.
*
l''iiy
Mini Niirdi. Aiiirr
'I'he
('hriii.
combination
is
attended
Jmini.. 1901. vol. xnv- pp- 216 231.
DENTAL METALLURGY.
136
by an evolution of
explosion.
It
is
heat, leading in
some instances
to
therefore probable that chemical union
takes place between the two metals.
amalgam expands
Palladium
This amalgam
is
used as a
filling
probably the most durable of
on cooling.
for teeth, and is
slightly
the amalgams for
all
this purpose, although it is a little difficult to
late.
forms a good watertight
It
filling,
disadvantage of turning quite black.
manipu-
but has the
It does not,
how-
any staining of the tooth substance.
Platinum Amalgam. Platinum in the compact
with
form, such as plate or wire, does not amalgamate
ever, lead to
—
By
mercury.
triturating
spongy platinum (such
as
chloride
that precipitated from a solution of platinic
by means of zinc) with mercury in a warm mortar
amalgam is obtained of a silvery appearance. The
mercury
tion
of
expelled from this amalgam on the applicaleft
heat, and a grey residue of platinum
is
behind.
With
12 per cent, of platinum the
amalgam
greasy
metallic in appearance and possesses a soft,
the proportion of
feel, but it becomes more solid as
is
platinum
is
increased.
An amalgam
of these metals
does not harden well.
Silver
Amalgam.— Mercury slowly dissolves silver
much more rapidly
at the ordinary temperature, but
The more
and perfectly on the application of heat.
finely divided the silver the
mation take place.
more rapidly does amalga-
Silver precipitated from
its
solutions
washed and
of metallic zinc or copper, then
condition for amalgamadried, is in a very favourable
silver thus
tion (see Precipitated Silver, p. 171)-
by means
When
prepared
is
added to hot mercury combination takes
place rapidly.
MERCURY.
mercury for silver is almost etjiial to
that of mercury for gold, but there is a greater tendency
towards crystallisation in the case of silver. The combination of silver with mercury is usually attended by
The
affiuity of
an increase in volume, although in certain proportions
the union appears to be accompanied by a contraction
The amalgam
in volume.
varies in character, accord-
ing to the composition and.
mode
It is readily dissolved in
granular, or crystalline.
soft,
of formation, being
excess of mercury, but the excess can be separated from
the pasty amalgam thus formed by squeezing through
chamois-leather. The soft white amalgam left gradually
becomes hard and brittle, and is generally regarded as
a chemical compound. By adding mercury to a slightly
acid
is
and
amalgam
form, known as a
dilute solution of silver nitrate, the
obtained in a beautiful crystalline
"silver-tree " or
Arbor Diancc.
Silver amalgam,
if
heated
to redness, gives off the mercury, the silver, however,
sometimes retaining traces of mercury.
The union
of these metals in certain proportions is
accompanied by a considerable elevation of temperature.
Littleton has pointed out * that when an amalgam of
silver
and mercury
is
moderately heated, considerable
swelling takes place, and the mass becomes hard, brittle,
and
crystalline in
behaviour was
remarkable
was noted that
It
structure.
most
this
marked when the
and mercury were present in the proportions
corresponding with the formula AgHg^, and that,
silver
when
these metals were brought together, the silver
the state of
in
mercury
*
Ti-itiix,
i8g6,
v()l.
sim])ly
a
line
poured over
Chriii. Sir.. 1895. vol. Ixviii.
(i.
220.
powder, and the
crystalline
it,
|i,
there was v(M'y con239
;
mikI
I'rai'. Chriii. Siir..
DENTAL METALLURGY.
138
amounting to 38 or 40*" C,
so that the amalgam could not be borne on the palm of
the hand without pain. The amalgam, just after its
siderable lise of temperature,
production,
native
is
are
combined
Silver
ai-e
and mercury have been
compounds in which the constituents
of
silver
in atomic proportions.
amalgam has been used
for teeth, bnt
Several
a soft, pasty, semi-fluid mass.
amalgams
found, v?hich
'
it
as a filling material
becomes discoloured
ovi^ing to
the action
of sulphuretted hydrogen.
Tin Amalgam.
even at the
—Tin
and mercury unite
ordinary temperature,
vigorously at the raeltiug-point
of
readily,
but much more
With small
tin.
proportions of mercury the amalgams are brittle and
granular
;
an amalgam of
equal
parts
of
tin
and
mercury is solid, while those with excess of mercury are
more or less soft and plastic. With one part of tin and
ten parts of mercury the amalgam is liquid, like mercury,
but does not flow so readily. Tin amalgam has a tinwhite colour and is more or less brittle and granular,
according to the proportion of mercury present.
the excess of mercury
is
removed from
a fluid
When
amalgam
by squeezing through chamois-leather a flexible mass
remains, which hardens in a few days. The union of
diminutin with mercury is attended by a considerable
Tin amalgam was formerly used as a
in bulk.
tion
hardens slowly and imperceptibly
and also contracts, thus possessing a tendency to draw
away from the edges of the cavity.
Amalgam.—-Zinc amalgamates slowly with
filling for teeth,
but
it
Zinc
mercury
at the ordinary
and
still
poured into molten
zinc.
readily "if heated,
is
temperature
more
:
but
readily
it
combines
when mercury
MEROTTRY.
The amaliiain
of
one part of zinc with fouv or
is
white, granular, and brittle.
parts of mercury
When
1
39
five
the mercury largely predominates the amal-
gam becomes
pasty.
Zinc
is
occasionally
employed
as
a constituent in dental amalgams.
d(r<tt.^
—
V'
/
•
Ilt^^f -C/VW^
CHAPTER
A^III.
VD^^^A-L ^MAI^AMS.
preioared from
Amalgams
many
different formula' have
The
been used in dentistry as fillings for teeth.
majority of the well-known alloys from which the
dental amalgams are prepared are composed of tin and
It has
with small additions of other metals.
been previously stated that the union of tin and mer-
silver
attended by contraction, and that tin dissolves
very readily in mercury, giving an amalgam which
hardens slowly and imperfectly. On the other hand,
cury
is
expansion generally takes place when silver enters into
combination with mercury, the union being effected
and producing an amalgam
The manufacturers of
which becomes very hard.
tin and
for dental amalgams, therefore, use
with
much
less facility,
alloys
silver
in
different
proportions,
utilising
the
good
one to counteract the inferior qualities
obtaining an amalgam
in the other, with the object of
a filling
which will meet the requirements necessary for
The following qualities are necessary in an
qualities in the
material.
amalgam
1.
to be used for dental purposes
Strength to withstand the force of mastica:
tion.
2.
Sharpness of edge.
DENTAL AMALGAMS.
expand or contract in
3.
It should not
4.
It should retain its shape.
5.
It should
6.
It
setting.
not become discoloured.
should be free from metals liable to form
soluble, injurious salts.
not stain the substance of the tooth.
In the formation of amalgam for dental purposes the
best results will most probably be obtained by uniting
7.
It should
the constituents in atomic proportions to form what are
believed to be definite chemical compounds.
in
amalgams appear for
consist of metals united with mercury
atomic proportions, and capable of being dissolved
in
an excess of mercury.
As previously
the most part to
stated, the solid
an alloy are intimately mixed with
a measured quantity of mercury by thoroughly knead-
When
filings of
ing the mass entirely
mercury combining
has greatest
new compounds
first
with the metal for which
affinity.
slowly
formed.
readily,
If
while with
sufiicient
After
a
short
interval
others
mercury has
been employed, the mass soon becomes of a
consistency.
it
With some metals these com-
pounds are produced very
they are
are formed, the
soft,
pasty
a process
of
commences, which may be accompanied
by a change in volume, the mass thickens slightly, and
when pressed carefully between the fingers emits a
})eculiar grating sound, caused by the rubbing or grating
This mass may
of the crystals against each other.
crystallisation
probably represent a definite chemical
compound
(or
the metals of the alloy in
compounds) of mercury and
atomic proportions and cr\'Stallised, the whole being
dissolved in an excess of
this plastic
compound
mercury.
as a filling
In order to use
inalerial
the excess
DENTAL METALLURGY.
142
must be removed. This can be done to a
certain extent by straining through chamois-leather
by compression with pliers. All the excess of mercury
of mercury
cannot, however, be satisfactorily removed in this way,
and the mass left in suitable working condition.
the most recent experiments* it appears that
Dr. Bonwill's and similar methods t for removing the
excess of mercury are those most likely to give the best
Prom
results with this class of filling.
Tomes has recently shown J the advantage of employing old amalgams for filling purposes these should
;
heated to soften them, and then used alone or
rubbed up with a small quantity of freshly prepared
amalgam. Amalgams which have set and become
hard are softened to a workable consistency by gently
be
first
heating
which
;
is
they harden again on cooling, a phenomenon
ascribed to a state of amorphism, into which
the amalgam passes from the
the process of softening.
crystalline condition in
Old amalgams have the ad-
vantage of having undergone the shrinkage, alteration
which takes place, more or less, when
Although there may be diffifresh amalgam is used.
old amalgams
cnlties with regard to the manipulation of
of shape, &c.,
* "
Notes on Amalgams," C.
S.
Tomes, Brit. Juurn. of Bcntal
Si-ipiwr, 1895, vol. xxsviii. p. 242.
amalgam lan'ly
Bouwill's method consists in inserting tlie
instruments
suitable
with
cavity
the
in
plastic, and squeeiiing it dry
l)ilnilous paper are
of
Pads
pressure.
much
of
l,v the application
the mercury thus pressed
repeatedly placed over the cavity to absorb
of the filling, into whu^h
surface
The softer portions upon the
„ut
t.lso removed from tune
are
s,,uee/.ed,
been
has
the excess of nun-cury
instead of bibulous
Tn some cases gold-foil has been use.l
totin.e.
t
Di-
vol. xxxviii.
''''^"7^nY.-./<wn^ »f Drntal Srirmr, 1895.
1896, vol. xxxix. p. 529.
p.
242; also
DENTAL AMALGAMS.
T43
on accouut of rapidity in setting, there can be no don lit
amalgams tends
to give
watertight pkigs and very satisfactory results.
When
that the use of ready-formed
old
it
amalgam
is
used for the whole operation of
filling-
should be heated in a spirit or Bunsen gas-flame, and
then laid on a hot plate over the flame, in order to keep
With the exception
it soft.
of copper and of palladium
form the basis of all the
These alloys
dental amalgams used at the present da}^
are composed of varying proportions of silver and tin,
ranging from sixty parts of silver and forty of tin to
amalgams,
silver-tin alloys
forty parts of silver
made with
are
alloys
"These
and
alloys in the
sixty of
a larger
form of
Occasionally
tin.
proportion of
filings or
silver.
shavings are
mixed with varjang proportions of mercury, which
generally range in ordinary practice from 30 per cent,
mercury and 70 per cent, of alloy to equal parts of
each by weight, a larger proportion of mercury being
used in exceptional cases." * Silver-tin amalgams vary
of
with regard to working properties, those
most tin being usually
and
soft
and slow in
plastic
setting, while those with excess of
containing
silver are quick-
much harder, " the quickest setting amalgam
being that made from an alloy containing 72.5 per cent,
The amalgam
of silver and 27.5 per cent, of tin." t
setting and
obtained after removing the excess of mercury becomes
more or
less
generally
hard within a few hours, but does not
acquire
the
degree of
full
twenty-four to forty-eight hours.
brittle
It
mass which may be dressed with a
like other metallic bodies.
*
•j-
(i.
V. I'.lnck. Dciitiil
Jh'iil..
1.S9G, vol.
is
file
then a hard,
and polished
The disadvantage
Ciixiiifix.
xxxviii.
hardness for
|i.
.Inly 1S95, vol. .\xx\
9S6,
of this
ii,
DENTAL METALLURGY.
144
material as a filling
in shape
and
is
is
that
liable to
a tendency to alter
As the
discoloured.
lias
it
become
the qualities necesit has
sary for the production of a dental amalgam,
for
been the practice of many manufacturers of alloys
modiof
view
this purpose to add other metals with a
silver-tin alloys
do not possess
all
properties
fying or improving the chemical and phj^sical
The metals usually added
of the resulting amalgam.
occasionally zinc, cadare gold, copper, platinum, and
the
and antimony. The composition of some of
mium
most frequently used
given in the annexed table.
alloys
for
dental
amalgams
The effect of the presence of different metals
the following list.
tin amalgams is given in
is
in silverIt
must
are
individual
be pointed out, however, that the
quantity of metal added
greatly dependent on the
but
addition of gold is usually very beneficial,
efi"ects
thus, the
by experiment* that it is
Dr. Bonwill has ascertained
than 7 per cent, of gold to
not desirable to add more
The ratio between the main consilver-tin
amalgam.
stituents of the
amalgam
is
also of
importance in con-
other metals. The presence
nection with the addition of
of zinc may be beneficial in one
of a small quantity
while a larger quantity of zinc may be
silver-tin alloy,
in this particular alloy, but very
a decided disadvantage
of different composiadvantageous in a silver-tin alloy
of a small
The effect produced by the addition
tion
is frequently very much
quantity of a certain metal
besides silver and tin, are
modified when other metals,
Thus,
constituents of the amalgams.
also present as
silver-tin amalgam appear to be
the properties of a
any
addition of platinum
greatly impaired by the
m
*
IJrnfal Cosmos, vol. xxiv. p. 422.
DENTAL AMALC4AMS.
1^
o
O M
O u-1
>o
o
O
o
O
O
o
o
in
o o
o
IN
<5
7J
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•iffitll
000
o
o
o o
^o
o^nJ^oooooo
lOMVOOOOOOO
000
O ro
o
O
O
o o o O
O O vo
.-n O
o
o
a
0000
0000
CO
^
o o
U-)
NC^ro:l-^^a>or^OO^^•^^o^';^
o
O
^t-o co
U-]
U-1 Tt-
O
00
00
0
"o
roo 000001
0000
o>nooooooooo
OOO'Ol
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10
'*-<0
uS 10
r-I
irj
o'
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^
rood
!>. o'
M
t-I
in »o N
Tt-T^-irjio
IT)
invOirju^'^t^fOfniovo^iniriioininioio
0
d
5
-2
TT
'
'
'
4
'
'
'
-1-
^
3
TT"^
'
S'
1;
a 3
— 3p
Mm
~B
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'»
.
>
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—
-
"l'*j;ir;^g;::ODS
-
= —
b ^
IS
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= 5 s
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.ii
ii
'
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= = S
-tJ ^-^
> " -
a,
'
:
^
'a-
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—^—
-F
^1
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g
'-tj
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i
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1^
'^^.i^
-ri
„
-f^
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bu
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K
-5
DENTAL METALLURGY.
146
considerable (juantity, except
when gold
is also
present,
properties
in which case the platinum confers useful
on the amalgam. The following list must, therefore,
the
be regarded as giving only the general effect of
amalgam.
various metals when added to the silver-tin
The effect of the presence of silver and of tin in the
amalgam
is
also inserted for convenience in reference.
Effect of Different Metals in Amalgams.—
mercury is usually
/S'iVrc/-.— As the union of silver with
with
accompanied by exjMnsivn, and the union of tin
silver
mercury by contraction, the direct influence of
the
lessen
to
upon an amalgam of tin and mercury is
Silver has the
contraction and increase the hardness.
discoloration
disadvantage, however, of increasing the
sulphide
silver
formation of
of the filling, owing to the
hydrogen in the
by the actfon of the sulphuretted
the
also tends to stain the tooth owing to
mouth.
It
formation of soluble silver
Tin
facilitates
discoloration
setting,
and
;
salts.
amalgamation and helps
but
it
causes
to prevent
shrinkage, 'slowness in
loss of edge-strength.
cleaner and easier
Gold in amalgams renders them
produces good edgeto work, reduces the shrinkage,
to maintain a good
strength, and assists the filling
colour.
Its presence affects the
power
of setting.
shrinkage, gives
Copper facilitates setting, diminishes
preservative influence
great edge-strength, and exerts a
largely increases, however,
on the tooth structure. It
the tendency to discoloration.
appears to
Platinum in any considerable quantity
of a silver-tin amalgam,
oreatly impair the properties
slowness in setting, and
causing dirtiness in working,
tendencv to shrinkage.
When, however, platinum
is
DENTAL AMALGAMS.
addeti
to
amalgam containing
silver-tin
a
ai)pears to confer the properties of
gold,
setting
it
quickly,
great hardness, and retention of shape after hardening.
Zinc is occasionally employed as a constituent of
amalgams. It appears to control
shrinkage, add whiteness to the filling, and also helps
the
dental
for
alloys
amalgam
to retain its colour.
But
it
causes rapid
Amalgams
setting and a tendency to change of form.
containing it possess good edge-strength.
Cddmium was
in
at
amalgams, but
that
purpose.
It
it
one time used as a constituent
is
causes
very white and
condemned
generally
quickness
make good
fillings,
for
and
setting
in
Amalgams containing
expansion.
facilitates
now
it
are
but they readdy
owing to the formation of yellow cadmium
sulphide. The tooth substance is also stained an orangeyellow on account of the formation of soluble salts of
cadmium.
Antimony has been occasionally used as a constiIts presence appears to facilitate amalgamation
tuent.
discolour
and control shrinkage, but
and very
it
makes the amalgam
soft
dirty to work.
Fallacliiuii as a constituent
of silver-tin
amalgams
has been condemned, experiments* having proved that
it makes the amalgam very dirty to work, gives leaky
plugs,
that
and
is
blacken
amalgams containing palladium
greater extent than those
stated
It is
altogether unsatisfactory.
from which
it
is
to
a
absent.
(See also Palladium Amalgam, p. 135.)
Bisiimtli
greatly facilitates
amalgamation and the
working properties of the amalgam
But
ex|)ansion.
*
it
;
it
also
reduces
makes the amalgam very dark,
b'letclicr, ///•'/. ./oiini. JJnital
Srinin:
DENTAL METALLURGY.
148
the edge-strength, and
lessens
hardness
:
hence
it is
the
greatly reduces
seldom used as a constituent.
never employed in dental amalgams unless
accidentally present as an impurity in the metals
Lead
is
appears to be similar to that
It facilitates amalgamation, but causes
of bismuth,*
slowness in setting and makes the amalgam very
employed.
Its action
dark.
Aliivdnmm has not been used
as a constituent in
experiments
dental amalgams, but from recent
its
f
presence appears to give a soft pliant mass which is
slow in setting. It also greatly increases expansion
and the tendency
to alter in shape,
the action of the fluids of the
and would
facilitate
mouth on the
filling.
developed in mixing alloys containing it with
(See Action of Mercury on Aluminium,
mercuiy.
Heat
is
p. 132.)
Change
of
Volume. —Much
diversity of opinion
and expansion
exists with regard to the contraction
silver-tin
of
amalgams, some claiming that contraction
takes place,t while others state that the amalgam first
The composition
contracts and then finally expands. §
of the alloys
and the quantity
necessarily influence the
these questions.
of
results
mercury used
of
experiments on
The recent researches
of Dr.
the latter conclusion.
appear to support
that alloys containing
first
*
p.
will
He
Black
than 50 per cent, of silver
shrink and then expand. Alloys with 50 to 62
less
Experiment by G. V. Black, Dental Cosmos,
989.
1896, vol. xxxviii.
t
Hitchcock and Tomes, Trans. New York Odoiit. ,Soo., 1874.
J
Science, July 1888, vol.
Kirby, Brit. Mini, of Dental
§
part
ii.
xxxvui. p. 975.
De7ital Cosmos, 1896, vol.
II
||
found
ix.
DENTAL AMALGAMS.
149
Those with 65 to 75
expand when fresh cut, but shrink
per cent, of silver shrink only.
per cent, of silver
when
fully "
(See
agcdr
p.
1
Alloys containing
56.)
over 75 per cent, of silver expand only.
of Testing Change of Volume.—
The change of volume which takes place more or less
with most dental amalgams constitutes one of the dis-
Methods
The
advantages of this class of material as a filling.
shrinkage or expansion is usually determined by careglass
fully packing the amalgam into a small shallow
tube until
and then making the surface perfectly
contraction has taken place the filling
full
When
level.
will frequently
slide readily
expansion
is
seen
with
projection
of
the
filling
the
out of the tube,
of
a lens
by the
the
mouth
of
aid
above
while
the
tube.
The contraction and expansion of silver-tin amalgams
has been studied by Black,* who examined them under
For this purpose the amalgams were
the microscope.
inserted in Wedelstaedt test-tubes,
made
of hardened
deep and one inch in diameter,
with a cavity three-eighths of an inch in diameter and
The top of the tube is
one-fourth of an inch deep.
ground flat, and the margin of the cavity brought to a
steel
one-half inch
The tubes
perfect edge.
are placed on the stage of the
microscope, and so arranged that every part of the
margin of the cavity is brought under the lens as
the
stage
is
rotated.
A
groove
was
cut
in
the
tube at the bottom to hold the
filling at that point, so that in case of shrinkage
the surface of the filling sinks down into the tube.
inner wall
When
of
the
comparative results are re(|uired the amonnt
*
Dental
(JiiKiiiox,
vol. xxxvii. 1895, p.
648
DENTAL METALLURGY.
of contraction
and expansion
is
measured with a micro-
meter.
Several forms of apparatus have also been constructed
by different investigators for studying the change of
volume in amalgams. One of these, devised by Kirby,
consisted of a V-shaped metal trough (Fig. 32) having
a movable end, to which a delicate screw micrometer
was attached, and so constructed that any change of
and accurately measui'ed. The
be tested was made up in the way generally
volume could be
amalgam
to
easily
Fif!.
adopted for
filling teeth,
"52.
then placed in the trough and
means of this
allowed to remain for some time. By
of expansion
apparatus the most minute change, either
was readily indicated.
adjustOther forms of apparatus, with micrometer
principle, have also been
ments, embodying the same
or contraction,
devised.
the
"The advantage of the tube test over that
of doing a
amalgam micrometer is the possibility
time, as tube
number of experiments in a limited
ot
aside for results,
tube can be packed and set
each packing has to remain
while with the micrometer
the result is obtained. This
in the instrument until
many months for each
requires from several days to
after
^5^
DENTAL AMALGAMS.
experimeut
;
but while the tube test
is
imtdical, reliable
*
more accurate."
ascertained by taking
The change of volume is also
amalgam.
the specific gravity of the
alloy or
stated, when the density of an
micrometer work
is
As previously
amalgam is less than
that of the
mean
of the constitu-
place during
shows that expansion has taken
density denotes
combination, while an increase in the
the union of the
that contraction has accompanied
ents, it
in amalgams
For ascertaining the change of volume
exceedingly delithe specific gravity method f an
by
must be used and a large number
cate balance
precautions taken, in
of
obtain accurate and
order to
important being
concordant results, one of the most
heat is given out
the consideration of the fact that
during the setting of some amalgams.
with
Alteration of Shape.— Much has been said
" spheroiding " of
reo-ard to the so-called
* Fliio-g, " riastic Filling Materials," p. 72.
fallacious rule is freciueatly given for
+
A
amalgams
or
computing the specihc
alloying of given quantities ot
-ravity tliat should result from the
no condensation or expantwo metals of known densities, supposing
Thus, it is said that iC gold_ and
sion of volume to take place.
the computed specific gravity is
eoiiper be united in equal weights
numbers denoting the
HHireiy the arithmetical mean between the
the computed
incorrect
is
however,
This,
gravities.
two
specific
;
obtained by the following rule
siiecific gravity of the
by the product of the two
weights
the
sum
of
Multiply the
and multiply each speciftcsi)ecitic-gravity numbers for a, numerator
weight of the otluM- constituent, and add the
alloy
:
is
;
gravity
number by the
denominator. The (luotieut obtained
tlie truly
by dividing the said numerator by the denominator is
On comiiariug with
specific gravity of the alloy.
two products
togetiier for a
computed mean
that density
the
whether expansion or condensatiou
bination."' —lire's Diet., vol.
i.
11.
l)c
seen
lias ;i(ti'iidc'd (lir
com-
by experimeut,
density found
of voluiuf
92.
it
will
DENTAL METALLUEGY.
tendency to assume the spherical form. "The phenomenon from which this term splieroiding has been
mostly derived appears to be the tendency of some
amalgam fillings to rise in the middle and assume a
convex form on the surface." *
This alteration of
shape, or tendency of some fillings to assume a convex
form on the surface, after having been dressed flat, is
probably due to a change of volume. The amalgam being
down on all sides but one during expansion
tend to flow towards the point of least resistance,
firmly held
will
thus causing the surface
Kir by
that
is
become
slightly convex.
of opinion, as the result of his experiments,
" is
it
to
due
to
unequal distribution of mercury
throughout the mass, and that the alteration
is
pro-
duced by the passage of the mercury from one part of
the filling to the other, causing contraction in the
portion containing excess and expansion in the drier
When
mercury is distiubuted equally
throughout the filling, no change in shape takes place,
since there will not be any passage of mercury from
portion.
tlie
one place to another.f
The alteration of sbape will be appai'ent in making
tests for
of a
change of volume, and may be seen by the aid
good
lens.
Change of Colour. — Dental amalgams
differ con-
by
exposure in the mouth copper and palladium amalgams
being those which darken most rapidly. The addition
of gold is an advantage in helping amalgams to retain
siderably with respect to their liability to darken
:
'
their colour, while copper greatly facilitates discoloration.
*
Fillings containing an
Brit. Jm/ni. of
t Smale and
fJc/itiil
Srip.iirr,
excess
of mercury are
1895, vol. xxxviii.
Colyer, " Diseases of Teeth," p. 186.
i).
901.
DENTAL AMALGAMS.
more
liable
when
inserted.
to
T53
blacken than those which are drier
Discoloration
is
largely dne
to
the
formation of sulphides, resulting from the action of
sulphiaretted hydrogen in the mouth, produced by the
Silver
decomposition of the oral secretions.
and mer-
cury, under the conditions in which they exist in the
Dismouth, both have a great affinity for sulphur.
coloration is also due to the presence of vegetable acids
to the action of drugs
in articles of food, such as fruit
;
taken as medicines
fluids of
fillings
:
or to
The
the mouth.
may
abnormal conditions of the
surface of
be kept bright by friction, whether pro-
duced by mastication or by a brush
will
probably blacken
if
they are protected from
On
fillings
friction.
fully preserve the
the other hand, an
but such
;
they occupy positions in which
An amalgam may become
and yet
many amalgam
discoloured at the surface
teeth from further decay.
amalgam ma}^
retain its original
colour and surface brightness and yet not protect the
tooth, the
tooth-substance being darkened, thus in-
dicating chemical action at the edges.
of the substance of the tooth is
The darkening
due to the formation of
soluble salts, resulting from the action of the oral fluids
upon the metals composing the amalgam.
Imperfect adaptation
is
frequently the cause of the
discoloration of the tooth, as this favours the ingress of
the oral fluids which form the eroding agent.
Change
by packing a small quantity
of the amalgam into a small glass tube and covering it
with a dilute solution of sulphuretted hydrogen water
of colour is usually tested
(about one part of strong solution with about four parts
of^water).
In this way the
filling is
of sulphur in the foi'm in which
it
exposed to the action
exists in the
mouth.
DENTAL METALLURGY.
154
Gradual discoloration
is
seen better in dilute solutions
than in strong.
Leakage.
— One
of
the disadvantages experienced
the
using amalgams as fillings is
getting absoliTtely watertight plugs.
in
The leakage
packing used.
is
difficulty
largely dependent on the
Amalgams
method
are tested for leakage
of
of
by
packing them into small circular holes, about one-eighth
in
of an inch in diameter and a quarter of an inch
depth, bored right through slips of bone or of ivory,
which are clamped to a flat surface of ivory whilst being
then plunged into ink, Draper's
for
dichroic being frequently employed, and are left
On being removed the plugs are split and
time.
filled.
The
slips are
some
of the
the surfaces carefully examined for the ingress
fluid used.
Human
same
teeth have also been employed for the
pui-pose.
Edge-Strength.—This
term
is
used to denote the
mass
degree of resistance the edge of an amalgam
amalAn
fracture it.
offers to a force which tends to
suffigam used for filling purposes should always be
edge under the
ciently strong to retain its integrity of
" The stress in the ordinary use
force of mastication.
to be from sixty to
of the teeth has been shown
molars of medium
eighty pounds upon the area of two
would give from seven
size. This, if evenly distributed,
occupying oneand a half to ten pounds on a filling
This would be a
fourth the area of one of these teeth.
frequently happens
of ordinary size; but it
filling
that the miing must bear
edge-strength of amalgams
* Black, Dcivtal
all
is
of this stress."*
The
sometimes approximately
Comox, July
1895, p. 554-
DENTAL AMALGAMS.
determined by mixing the amalgam in the ordinary
" button " and testing
way, then forming it into a small
it with the
the strength of the edge by breaking
This,
thumb-nail when the specimen has hardened.
method
however, cannot be regarded as a satisfactory
For accurate and reliable
for comparative testing.
work some form of dynamometer or instrument
measuring force
is
for
This usually consists of a
used.
and graduated metal beam upon
which a sliding weight is placed. A chisel-shaped steel
rod is also fixed to the balanced beam and so arranged
carefully balanced
of
that the pressure necessary for testing the strength
the amalgam filling can be applied to the chisel by
moving the sliding weight along the graduated scale.
The instrument is also provided with suitable screws
The amalgam to be tested is
ordinary fillings and made into small
for accurate adjustment.
mixed
as
for
blocks in order to obtain the greatest edge-strength of
After allowing the
which the specimen is capable.
amalgam to harden it is carefully secured in position
upon the instrument, so that the point of the chisel rests
The sliding weight
upon the edge of the specimen.
then slowly pushed out along the graduated scale on
the beam until the pressure produced is sufficient to
is
In this way the
break the edge of the specimen.
position of the weight indicates the point at which
"crush" or fracture occurs, and the relative edgestrength of
various samples, with the accompanying
toughness and brittleness,
is
determined.
Permanence in the Mouth. —The permanence
of
amalgam
largely
in
fillings
dependent
on
the
the
mouth
care
is
necessarily
bestowed
on
the
manipulation of the material, on the proper prepara-
DENTAL METALLURGY.
156
tion
of
the
cavity,
tooth in which
it is
the condition
on
and
placed.
the
of
dependent on
It is also
the metals present in the amalgam used, as each of
these materially affect the character of the amalgam
Careful observation
of which it forms a constituent.
and experiment with each amalgam can only satisfactorily solve the question of permanency in the
mouth.
Amalgams
containing large
metals possessing an
silver,
affinity
for
proportions
of
such
as
sulphur,
copper, and cadmium, are more liable to waste
or wear away, and
containing
those
are usually less permanent than
only
small
proportions
of
such
metals.
Metals which are more or less readily acted upon
by alkaline and acid fluids under ordinary conditions
are sometimes protected from action when alloyed with
other metals.
Copper and
zinc, if
used alone, would
mouth, but when added
in small quantity to other metals employed for amalgams
they are largely protected from corrosive action.
The tendency of some amalgam fillings to shrink and
be attacked by the
fluids of the
draw away irom the edges would be favourable
to the
thus
ingress of the erosive fluids of the mouth, and
possibly reduce the permanency of the filling.
Possible Action on other Metals in the
Mouth.— When amalgam fillings come into contact
usually
with other metals in the mouth, galvanic action
Galvanic action
takes place, as described on p. 30-
tends to facilitate the
filling.
of
the amalgam
given to a peculiar change
in the working
takes place with the lapse of time
after being
silver-tin alloys for amalgams
Ageing.
tl.at
—This term
"wasting"
properties of
is
DENTAL AMALGAMS.
cut.
In some cases amalgamation
" ageing"
;
in other cases it
of alloys for dental
is
facilitated after
is
The
retarded.
"
ageing"
amalgams has been attributed
to the
being
formation of a film of oxide, the silver-tin alloys
particularly susceptible
Although
to oxidation.
this
would greatly tend to retard amalgamation, the recent
subject
experiments of Black* in connection with this
in
have demonstrated that the changes that occur
the temperaa cut alloy are largely dependent upon
He showed that the change
ture at which it is kept.
known
as
the
in
"ageing" was universal
silver-tin
different formute
alloys, but varying in degree with
the temperaalso that it could be produced artificially,
;
was effected varying with the composiThe explanation offered by Professor
tion of the alloy.
Black for the changes which occur in a silver-tin alloy
ture at which
it
by subjecting it to heat is that in cutting the alloy it is
hardened and undergoes a molecular change. Heating
normal
the alloy anneals it and causes it to return to its
condition.
That certain alloys undergo molecular change when
subjected to mechanical treatment or to change of
temperature has long been known and has been the
subject
much experimental
of
Some
investigation.
kinds of brass wire become extrejnely brittle in the
course of time, at ordinary atmospheric temperatures,
especially when kept in a state of tension or subjected
An
to vibration.
alloy of tin
and
lead,
which
is
com-
used in pattern-casting for
brass foundry work, becomes after a time so soft as
paratively
to
hard,
be no longer
*
fit
and
is
for use.f
Dental
O1.111WK, vol.
xxxviii.
t Percy, " Mutallurgy," vol.
i.
\).
p.
976.
21.
DENTAL METALLURGY.
158
Quantity of Mercury needed.
—The
quantity
merciuy used with aa alloy to form an amalgam is
very variable and necessarily differs with every alloy.
The proportions usually vary from 30 to 50 per cent,
Sufficient mercury must be used to satisfy
of mercury.
the chemical affinity of the metals present and thus
of
form a true amalgam.
If insufficient is added the mass
will consist of a
mixture of amalgam with particles of un amalgamated
The two inethods most frequently employed for
alloy.
obtaining the right quantity of mercury are
—
i.
To
Fiti. 33-
shavings of alloy to a globule of mercury
produced.
until a mass of proper working consistency is
excess of mercury and then remove the
add
2.
filings or
To add
with the
excess by straining through chamois-leather
By the first method there is no indicaaid of pliers.
when the proper amount of filings has been
tion as to
added
to
the
exactly satisfy the chemical affinity of
second method is
quantity of mercury employed. The
of alloy is
objected to by some, as a small quantity
squeezed through
removed in solution by the mercury
This method is also open to
the pores of the leather.
remove all the mercury in
the objection that it does not
most satisThe methods which appear to give
excess.
DENT A L AM A LG AMS.
mercury is
factory results are those in which sufficieut
mixed with the filings to give a fairly plastic amalgam
and
and the excess forcibly squeezed out in the cavity
removed by means of bibulous paper or gold-foil.
in
In order to obtain the right quantity of mercury
correct
preparing amalgams, after ascertaining the
emproportion to be used, balances are sometimes
represents a balance designed by
Pig.
ployed.
33
which turns to the fraction of
The small metal pin acts as the weight and
a grain.
balanced beam
is inserted in the different holes on the
according to the quantity of mercury required.
Kirby
for this purpose,
Fig.
34.
Another balance designed by Fletcher
is
represented
The filings are placed in the large cup and
in Fig. 34.
the mercury in the two small cups, according to the
quantity required.
Mixing Amalgams, — Different
methods are em-
ployed for effecting the union of the filings or shavings
That most frequently
of alloy with the mercury.
adopted
consists in simply rubbing
the
filings
and
mercury together in the palm of the hand. This is
perhaps the most expeditious way of eff"ecting union,
but it is open to the objection that the moisture or any
film of dirt on the hand may retard amalgamation and
possibly
bring
about
failure in the
result
desired.
Amalgamation is also effected by means of small porcelain Wedgv/ood mortars, but owing to the attrition of
l6o
DENTAL METALLURGY.
the pestle the particles of alloy become more or less
burnished, and union is thus liable to be retarded.
Amalgamation
heating
greatly facilitated,
is
however, by
and effective
appliances have been introduced for promoting amalgamation by percussive force. Fletcher has introduced
the
mortar.
Several
simple
the glass mixing-tube shown in Fig. 35. The required
weight of filings is put into the tube, the
mercury added and the tube well shaken for
a few seconds, the open end being closed
with the thumb.
By the jiercussive force
thus produced union readily takes place. If
necessary, the tube
facilitate
shown
be gently heated to
Another form of
mixing, introduced by Kirby,
Fig. 36.
It consists of two
amalgamation.
apparatus for
is
may
in
tubes provided with a handle for convenience
in shaking, each tube being closed
by means
of a rubber stopper.
Preparation of Alloys for Dental
Amalgams. Alloys for dental amalgams may be
—
readily prepared
by melting
the
constituents
in a
graphite crucible heated in a suitable furnace, any of
the forms previously described being well adapted for
As previously stated, the metals entering
the purpose.
into the composition of alloys for
silver
and
amalgams
are mainly
tin with small additions of gold, platinum,
and copper.
All these metals possess an affinity for
one another, but they vary considerably with regard to
the temperature required to melt them the alloys
produced are very easily oxidised, care is therefore
needed in preparing them.
The constituent metals are placed in a crucible and
;
•«3
DENTAL AMALtJAMS.
l6l
a little charcoal added to prevent oxidation.
The cru-
and the temperature raised
sufficiently high to thoroughly melt the metals and
obtain a uniform alloy, but excessive heating should be
cible is placed in the furnace
avoided as
The molten
tion.
into
leads to loss,
it
a
suitable
employed
alloy is
owing to unnecessary oxidathen well stirred and poured
mould.
ingot
Borax
to prevent oxidation, but
is
frequently
when using
it
care
must be taken to prevent the molten "slag" from
running into the mould with the alloy on pouring. If
zinc is a constituent of the alloy it should be added in
Fig. 36.
needed in the alloy, in
by oxidation, which invariably
slight excess of that actually
order to allow for loss
The ingot should be
takes place.
required for use, a coarse
purpose.
It
may be
file
freshly filed off as
being employed for the
pointed out that, owing to
segregation which invariably takes
alloys during
solidification, it is
very
the
place with these
difficult to
obtain
ingots which agree exactly in composition or correspond
to a given formula,
Qualitative
Amalgams. — it
know how
even when every precaution is taken.
Examination of Alloys for
is
important that the dentist should
to ascertain the composition of the alloys
used in the preparation of amalgams
scheme
is
;
the following
therefore given for detecting the presence of
the various metals usually present.
A
small c[uantity,
L
DENTAL METALLURGY.
l62
about one gram (or lo to 20 grains),
nitric acid, gently
heated until
all
is
treated with
action ceases and
all
red fumes are expelled, then diluted with water, the
insoluble residue allowed to settle and filtered
Residue.
—May contain
tin, srold, or phitinuni.
A
lohite rexidve denotes
the presence of t'ui, which
is oxidised to niutastanuic
acid.
—
Solution. May contain silver,
platinum, copper, nine, cadmium
add liydrochloric acid a white precipitate denotes the presence of
:
xilvnr.
evaporate the clear soluFilter
add some
tion nearly to dryness
potassium chloride solution, tlien
A yellow
alcohol, and stir well.
precipitate denotes tlie presence of
:
A
purple rcsidnc denotes
the presence of ijuld, which
is insoluble and forms purple-of-C'assius
with
off.
when present
plafiimm.
tin.
Black
:
pmtirlc'f in
the
residue denote the presence of plat iiuniij which is
only partially dissolved in
some cases. When present
in small iiuantities, howit is completely dissolved and should be tested
for ueparately in the solution as given.
Allow the precipitate to settle,
pour oil' the clear liquid, boil to
espial alcohol, and then dilute.
Divide the solution into two portions.
ever,
First Fortiuii.
excess of
ammonia: a deep
blue coloration
denotes the presence of copper.
— Add
Add to theblue
PorSecond
Pass a current of sulphuretted hydrogen,
filter oil' the precipitate of cadnuum sulphide,
solution a solu-
then
tion of potassium
cyanide until
monia
colourless, pass a
current of sul-
phuretted hydroA bright
gen.
precipiyellow
tate denotes the
presence of cad-
mium.
Note.— It am-
monia gives
nu
blue colour, copper is absent and
sulphuretted hydrogen may be
passed at once.
add
am-
the
to
clear solution.
white precipitate
denotes the presence of zinc.
A
DENTAL AMALGAMS.
Wheu
old
amalgam
fillings are tested
they should
be heated to redness to remove the mercury, the
residue crushed to ]iowder in a mortar and then treated
first
with acid as previously directed.
Dental Copper Amalgams.
Sullivan's
Amalgam.
—This
is
prepared by mixing
pure precipitated copper with mercury, but there are
slight differences in the methods of manufacture.
The copper
is
generally pi-epared by placing rods of
zinc or of iron into a hot dilute solution of copper
sulphate and allowing the action to go on until
copper
is
The
precipitated.
the
all
dull red flocculent precipi-
tate of copper thus obtained is thoroughly
washed with
and sometimes finally with alcohol or ether.
It is next ground in a mortar with mercury, the combiuation being facilitated by the addition of water
cold water
slightly acidulated with sulphuric acid.
is
then washed with
dilute
ammonia
The amalgam
to neutralise traces
rubbed in the mortar, and
subsequently washed with hot distilled water and dried.
of acid, again thoroughly
It is finally rolled into small pellets or lozenge-shaped
pieces
to set for about twenty-four hours
and allowed
before
using.
remove
all
Care should be taken to thoroughly
moisture from the pellets before allowing
them to set.
The precipitate
is
sometimes
first
moistened with a
whereby it receives a thin
coating of mei'cuiy, and then mixed with the required
The amalgam usually consists
quantity of mercury.
solution of mercuric nitrate,
of
3
It
is
parts
of
stated
copper
that
to
copper
6 or 7 parts of mercury.
precipitated
by
iron
is
DENTAL METALLURGY.
164
more
serviceable
and durable
with zinc, and iron
is
than
obtained
that
usually employed for the
now
purpose.
.
_
The
copper should be freshly prepared
when
required,
on exposure to air and becomes
This amalgam,
practically useless for amalgamation.
the
in common with all copper aumlgams, possesses
hardening
property of softening with heat and again
as it readily oxidises
This phenomenon, as previously stated, is
which the
ascribed to a state of amorphistn, into
passes from the crystalline condition in the
on cooling.
amalgam
When
one of the small pellets of
heated, small globides of mercury ooze
process of softening.
amalgam
is
then, more suddenly, a greater
by a hissing
(juautity is set free, sometimes accompanied
mercury
If the heating is carried too far the
sound.
"
burnt."
be driven off and the copper oxidised or
slowly to the surface
;
will
When
employed as a
hlling,
one of the pellets
is
gently
flame of a
heated in a small iron spoon or ladle over the
into a plastic,
spirit-lamp, and then crushed and rubbed
workable mass in a mortar.
With some
varieties of this
amalgam
it is
recom-
rubbing in a mortar, to clean with water
then wash with
acidulated with sulphuric acid and
mended,
after
Much
diver-
salt.
water or dilute solution of commbu
the point at which to stop
sity of opinion exists as to
some discontinue the heating
the application of heat
on the
when globules of mercury begin to appear
;
surface
;
others continue
till
the excess
is
driven out.
shown* that the strength of the filling
removed from
affected when the amalgam is
Dr. Black has
is
seriously
appearance of globules. Great
the source of heat on the
'
Dental Cusiim. 1S95,
p. 738-
DENTAL AMALGAMS.
165
diversity of opinion also exists in regard to the merits
and demerits of copper amalgams as a filling material.
All copper amalgams, however, have the disadvantage
that they discolour readily and stain the tooth sub-
undergo a process of "wasting,"
resulting from the combined action of the acid and
alkaline fluids of the mouth and of the sulphuretted
They
stance.
also
hydrogen always present in the mouth to a greater or
Copper amalgam is also said to possess
less extent.
therapeutic properties and thus arrest decay.*
Other copper amalgams
are
also
used for
filling
purposes, but these only differ in slight alterations in
the method of manufacture and in the addition of
small quantities of other metals, mainly tin and silver,
with a view to helping the amalgam to better retain its
colour.
Filings of silver coin (alloys of silver and copper)
employed for preparing amalgams for
are also
filling
purposes.
*
For
fiirthpi- details
regnTtling the advantages
and disadvantages
the studenl is referred to
of coiiper
an interesting paper on the subject by Badcock, read before the
Odontological Society of Great l?ritain (see Pn>(\ Odonf. Sue. (1S97),
amalgam
vol. xl. p. 295).
as a
tilling material,
CHAPTER
IX.
SILVER.
SYMBOL, Ag
Occurrence.
—
(Avgentuin).
Silver
ATOMIC WEIGHT,
in
occurs
nature
io8.
in
the
metallic state, occasionally in masses weighing several
hundredweight, and usually alloyed with small quantities of
other metals.
It
is
also
frequently found
in combination with sulphur and chlorine.
present in most
Silver is
ores of lead, notably with rjalcna (lead
sulphide), argentiferous lead ores constituting one of
the main supplies of
silver.
Preparation.— The methods employed
for
the
very
separation of metallic silver from its ores are
three
varied; they may, however, be classed under
heads, namely
1.
Amalgamation processes involving the use
2.
mercury.
Smelting processes involving the use of
3.
Wet
of
lead.
processes.
Amalgamation Processes.— "^he
finely
ground ore
is
then well
formed into a thin mud with water, and
amalgam
mixed with mercury, by which means a silver
mercury
This is collected and the excess of
is formed.
squeezed out; the residual amalgam
is
then heated in
167
SILVER.
a retort to
distil
off'
the mercury, leaving J^ebiud the
melted and cast into bars.
smelted with lead
Smelting Processes.— Sihev ores are
lead and silver is obtained,
ores, whereby an alloy of
silver,
which
is
from which the
silver is extracted
by a process known
which the alloy is melted in a furcalled a cupel. ^ A
nace on a porous bed of bone-ash
which oxidises
of air is blown over the surface,
as cupel kdion, in
blast
partly absorbed
the lead and the oxide fuses and is
whilst the silver
by the cupel and partly flows away,
remains behind.
by
considerable portion of silver is also obtained
produced
smelting argentiferous galena, the lead thus
A
concentration of
being subjected to a process for the
from the
the silver which is subsequently extracted
enriched lead by cupellation.
convert
Wet Processes. The ore is roasted with salt to
out of the
the silver into chloride, which is dissolved
such as hot
roasted ore by means of a suitable solvent,
The silver is then precipitated either by placing
brine.
—
copper in the solution or by some other means,
dried and
the "spongy" silver thus obtained being
strips of
melted.
Properties.
— Silver possesses
a pure white colour,
of taking
has a very high metallic lustre, and is capable
It is not acted upon under ordinary
a good polish.
temperature,
conditions by exposure to the air at any
the
hydrogen
sulphuretted
l)ut in the presence of
the formasurface becomes rapidly tarnished owing to
Water is withtion of a black film of silver sulphide.
dilute
out action upon silver, and hydrochloric acid aud
metal.
the
sulphuric acid have little or no action upon
Hot concentrated sulphuric
acid converts
it
into silver
DENTAL METALLUEGY.
sulphate, while nitric acid
readily
silver
at
the
is its
best solvent, dissolving
ordinary temperature.
It
is
In malleability
only exceeded by gold, and is
slowly attacked by alkaline solutions.
and
in ductility silver is
capable of
than
not more
being hammered into leaves of
thickness, which
^^'^^
TTTcTooo-*^^
are
capable of transmitting light giving a bluish or bluishBy hammering and wire-drawing the
green colour.
and requires more
frecjuent annealing than gold under the same conditions.
metal becomes more or
The presence
less brittle,
of small quantities of other metals, such
as antimony, bismuth, tin, zinc,
silver brittle
and
liable to crack
harder than gold and softer
considerable tenacity.
Of
and
when
arsenic, renders
Silver
rolled.
is
than copper, and possesses
all
the metals
it is
the best
It fuses at a
conductor of heat and of electricity.
temperature of 960" 0. (1760" ¥.), a little below that
required to melt gold and copper, and
when
liquid
possesses the power of absorbing oxygen from the
which
it
gives
up on
solidification.
When
it
air,
silver is
quickly cooled after fusion it solidifies on the surface
before the oxygen has escaped from the interior this
;
gas then bursts through the crust, the evolution being
attended with the projection of small portions of the
metal into a number of protuberances on the surface
" spitting "
constituting the phenomenon known as the
or vegetation of silver.
If,
however, silver be melted
beneath a layer of borax or of charcoal powder, the
absorption of oxygen is prevented and the spitting
Silver contracts on solidification, the decrease
avoided.
in volume being about equal to that of zinc
to volatilise at a white heat.
poured into water
it
When
;
molten
it
begins
silver is
becomes "granulated," and
is
169
SILVER.
usually employed in this condition for the preparation
of alloys.
The
specific gravity of
than that of lead
;
Uses
and
it
= -H
.00193
;
while
its
— Owing to the
nature of pure silver and
seldom used
is
expansion per
.
Dental Purposes,
for
flexible
sulphur,
is
lower
specific heat is nearly equal to
its
that of palladium, being .0570
unit of length
10.5, a little
silver is
the
in
soft
affinity for
its
dental
laboratory
other
metals.
hardened by the addition of
When alloyed with platinum it is employed as a base
for artificial dentures; it also forms an important
unless
constituent in the alloys used for dental amalgams.
Preparation of Pure
Silver.
— Scrap
and when
dis-
hot water.
If
silver is dissolved in dilute nitric acid,
solved
the
solution
is
any gold or platinum
diluted with
present *
is
it
dissolved as a fine black powder;
remain un-
will
the solution after
diluting should, therefore, be allowed to stand
the residue has completely subsided.
is
then carefully poured
or old
The
until
clear solution
heated nearly to boiling-
off,
and an excess of a solution of common salt or
hydrochloric acid added to precipitate all the silver as
point,
On
chloride.
stirring the hot
solution
very briskly
for a few minutes, the precipitate will readily settle,
leaving the supernatant liquor perfectly clear.
*
If
sci-ajis
of
(liiiital
(which
alloy
consists
of
After
silver
and
platininn) arc also present with the material treated, the nitric ar\d
will
dissolve
platiiinni
will
6iit
the silver in the alloy, hnt a part only of the
he dissolved, the
residue which iinist he filtered
(with hydrochloric acid) and
may
remainder
oil'.
filterinfi,
he recovered hy introdticiuj;
n
T)yiiij;
h^ft
as
a lilaek
AfU'.v pnicipitatinfi' the silver
tli(!
platinum
in
the solution
clean strip of x.iuc which pr(!cipi-
tates the i)hitinnni in the metallic state as a hiack si)onge.
DENTAL METALLURGY.
170
and
the
with repeated quantities of
hot
subsidence the acid liquor
chloride well washed
water to free
is
from copper
it
poured
solution.
off,
It is
then dried
and mixed with four times its own weight of anhydrous
sodium carbonate, and the mixture placed in a crucible
and heated in a furnace, first at dull redness, and then
gradually raised to bright redness. The reduction is
complete in about thirty minutes, and when tranquil
the contents of the crucible are poured into a suitable
mould and allowed to cool, after which the coating of
sodium chloride, produced by the reaction, is removed
from the button of silver by means of a hammer, and
As carbonic
the silver finally cleaned in hot water.
acid is given off freely during the reduction, care should
be taken not to have the crucible more than three parts
full,
and to avoid a high temperature
otherwise the charge
may
boil
at the beginning,
over and occasion
The silver thus obtained is practically pure.
The silver may also be obtained from the
loss.
chloride by
covering it with water acidulated with a few drops of
hydrochloric acid, and then adding two or three pieces
of clean sheet-iron,
hours until
all
and allowing
the chloride
is
it
reduced.
to stand for
some
The undissolved
then removed, and the spongy mass of silver
parwashed with hot hydrochloric acid to dissolve any
acid
the
After standing a few minutes
ticles of iron.
iron
is
and the silver washed several times
then dried and
with hot water by decantation. It is
Plates of
melted in a crucible, and cast as required.
is
poured
off,
used instead of iron to
case the spongy
reduce the silver chloride, but in this
more washing, in order to free it from
copper or of
zinc
may be
silver requires
the copper or zinc solution.
:
171
SILVER.
Precipitated Silver.— This
is
prepared
by
dis-
with hot
solving pure silver in dilute nitric acid, diluting
or of zinc in
water, and then placing a strip of copper
Silver is thus precipitated in the metallic
the solution.
form of a spongy mass, which is washed
when it is
several times with hot water and then dried,
" Precipitated silver has long been
use.
state in the
ready for
^
known as forming an excellent
colours the teeth greatly."*
Alloys of Silver.— Silver
with most of the
common
is
filling,
though
dis-
it
capable of combining
metals by direct fusion of
The
alloys.
the constituents, forming a series of useful
laboratory are
alloys of silver chiefly used in the dental
as follows
Silver
and Copper.— These
proportions
metals combine in
all
together, the resulting alloys
when melted
comparatively homogeneous, though ingots of
composition
are not absolutely identical in
being
^
the alloys
many
throughout;
of
them undergo
a
of
process
molten
liquation " on cooling, however perfectly the
In some cases the interior of the
alloy may be mixed.
"
exterior
richest in silver, while in other cases the
These alloys are white in colour until
contains most.
ingot
is
the copper amounts
alloy
;
beyond
to
nearly 50 per cent,
this limit the tint
the
of
becomes yellowish,
with the increase in the amount of
The density of these alloys is less than the
copper.
mean of the constituent metals, owing to the expansion
which takes place during combination. The effect of
finally red
and
cop])er is to increase the hardness
of the alloys being harder and
more
the hardest alloy consisting of about
*
Tomes,
"
and
elasticity,
elastic
than
most
silver,
parts of silver
5
Notes on Anmlgmiis," Odont. Soc, of G.
B.,
and
1896.
DENTAL METALLURGY.
172
1 1
The
of copper.
ductility is also very considerable,
but slightly inferior to that of pure
silver.
Although
not oxidise on
copper alloys are subject to change when heated in
the application of heat, silver-
silver does
owing
to the oxidation of the copper.
The coating
oxide formed on the surface of standard silver
annealing
may
air,
of
during
the silver whitened
be removed and
by heating the metal and plunging it while still hot
The most important appliinto dilute sulphuric acid.
cations of silver-copper alloys are for the purposes of
which uses pure or
fine silver is too soft to withstand the necessary wear
consequently copper is added to obtain the required
coinage, plate, jewellery,
&c., for
;
hardness.
—
British silver coin and plate conof silver and copper regulated
proportions
tain definite
Standard
by law.
Silver.
The
alloy for
silver
coin contains
1 1
ozs.
2 dwts. of fine silver per lb. Troy, or 925 parts of
silver per 1000, the remaining 18 dwts. or 75 parts
being copper. This alloy is designated sterling or
standard
silver,
and has a fineness
merce the purity of
silver is
of
925.
In com-
referred to this standard,
other specimens of different composition being reported
in terms of pennyweights letter or ivorse than the stan-
Thus, the French and American coinage, which
contain 24 dwts. of copper per lb. Troy (900 parts
dard.
of silver per
1000), are stated to be
worse
6
dwts.
(24-18 = 6); while the Indian rupee, containing only
12 dwts. of copper in the Troy lb., is described as better
In England all sterling silver goods are
stamped, at offices appointed for that purpose, with a
" Before the
special mark known as the " Hall Mark."
6 dwts.
introduction of vulcanised rubbers as a base for
artificial
SILVER.
dentures, standard silver was employed in the United
an
States for temporary dentures, where cheapness was
important consideration." * Standard silver, however,
cannot be regarded as a suitable alloy as a base for
dental substitutes, on account of the affinity which its
constituents possess for sulphur and the readiness with
which it is tarnished under the conditions which exist
in
the
mouth.
Filings
of
sometimes employed for dental amalgams.
Silver and Gold.— (See Gold Alloys,
and Platinum.— Alloys
Silver
are
alloys
silver-copper
p. 103.)
of these metals
obtained by fusion of the constituents, small
proportions of platinum rendering silver harder but
may be
greyish-white in colour.
As the proportion
become
melt.
num,
of
platinum increases the alloys
malleable and ductile, and more difficult to
Owing to the very high melting-point of platiless
it
alloys is
be thought that the preparation of these
When, however,
a matter of great difficulty.
may
a small quantity of platinum-foil or
to an excess of the
condition,
it
more
added
fusible metal silver in a molten
melts without
furnace temperatures.
are
is
readily combines with the silver, producing
an alloy which
num
"sponge"
much more
The
difficulty
at
alloys of silver
ordinary
and
fusible than platinum itself
plati;
they
are also less readily tarnished than silver or ordinary
silver alloys.
In preparing these alloys there is always a tendency
for the two metals to separate ou cooling according to
it
their densities, the platinum settling to the bottom
stir the molten alloy
is very essential, therefore, to well
;
before pouring.
*
Essig, "
In preparing "dental alloy"
Don till Mutalkirgy,"
p. 182,
jrd
cil.
it
is
DENTAL METALLURGY.
174
necessary to remelt the alloy in order to obtain as
uniform a product as possible.
An
alloy of silver
and
platinum, containing only 2 per cent, of the latter
but if the
metal, completely dissolves in nitric acid
;
platinum much
exceeds that proportion, part of it
remains undissolved. With sulphuric acid the silver
only dissolves.
Dental Alloy.
—This name
is
given to an alloy of
and platinum used by dentists which contains
silver
from 20 to 30 per cent, of platinum according
to the
Two "qualities" of this alloy are in general
([uality.
use in England, the " first quality " consisting usually
of 2 parts of silver
"
second quality
platiniun,
but
" of
the
stronger
rigid
part of platinum, and the
3 parts of silver
artificial
and
i
part of
composition varies slightly with
than standard
largely employed.
ing,
I
Dental alloy
different makers.
and more
and
denture,
The
for
alloy is
is
much mo re du rable
silver,
and makes a
which purpose
it
is
hardened by hammer-
and requires annealing during swaging.
much less tendency to blacken than
when exposed in the mouth, although
It
has
silver-copper alloys
the presence of
platinum does not wholly protect silver from the action
Dental
of sulphuretted hydrogen and the oral fluids.
alloy comes into the market in the form of wire, sheet,
and perforated sheet, the last named being used as a
base for strengthening vulcanite pieces.
Nitric acid attacks this alloy, and dissolves a considerable quantity of the platinum along with the
Concentrated sulphuric dissolves out the silver,
leaving the whole of the platinum in the metallic state
silver.
and dipping it
On
heating a plate of dental alloy
into dilute sulphuric acid, the silver on the
as a black residue.
SILVEE.
surface
of silver
"An
dissolved, leaving the platinum.
is
alloy
for pivots
and platinum was used by dentists
*
of artificial teeth before 1835."
The union of two or more pieces of dental alloy is
effected
by means
Von
of gold solders (see p.
Eckart's Alloy.—This
an
is
1
10).
alloy consist-
ing of silver 3.5; platinum 2.4; and copper 11.7;
dentures.
which is used in France as a base for artificial
which latter
It is hard, malleable, and very elastic,
property it retains after annealing. It is less tarnished
by the atmosphere than silver-copper
Owing
capable of receiving a high polish.
proportion of copper
it
ened in the mouth
contains,
by the
it is
and
alloys,
is
to the large
gradually black-
sulphuretted hydrogen
present..
metals combine readily
when fused together to form alloys which have about
They are more or less
the same colour as pure silver.
and Tin.— These
Silver
brittle or semi-ductile
tion
a very
of
small
The
and in general hard.
quantity of tin renders
addisilver
brittle.
Experience has shown that different portions of a
mass of any of the solidified alloys of the silver-tin
except the eutectic alloy, exhibit a want of uniformity in composition. This is no doubt due to the
series,
Heycock
presence of the eutectic alloy (see p. 39)and Neville t have ascertained that the eutectic alloy,
which is mechanically homogeneous, consists of 3.53 per
cent, of silver
and 96.47 per
cent, of tin,
and
solidifies
at 220'" 0.
They have
*
also
shown that the
Percy, " MetiilLurtjy of Silver,"
p.
initial
solidifying-
668.
vol. cLt-Kxix. (1897), pp. 25-70.
t Prac. Roy. Soc,
DENTAL METALLURGY.
176
point of an alloy containing 60 per cent, silver aud
40 per
cent, tin
is
about 500"
0.,
consisting of 40 per cent, silver
about 450" C.
It is evident,
and that of an alloyand 60 per cent, tin
therefore, that, in
.
the
range of temperature between the
points of these alloys and that of the eutectic alloy
initial solidifying-
abundant op poi't unity
afforded
is
mass to
hence
the
for
arrange itself as previously indicated (p. 40),
the divergency in composition.
On
These alloys are very oxidisable.
heating theui
with bichloride of mercury (corrosive sublimate) the tin
is
volatilised in the state of chloride, while the silver
left
behind in a comparatively pure
state.
is
Alloys of
these two metals are, as previously stated, largely em-
ployed in admixture with mercury for stopping teeth.
The density of the silver-tin alloys is l^s than the
mean
result of the densities of the
two constituents,
thus showing that chemical combination has probably
taken place and that expansion has occurred during
the union of the raetals.
and
Silver
Mercury.
— Silver
amalgams
are
white, soft, granular or crystalline bodies, accordiug to
the composition aud
mode
They harden
of preparation.
slowly, and expansion takes place during combination.
The properties of silver amalgams are given under
Mercury,
p.
136.
Silver Solders.
—The
articles of silver are usually
alloys
used for soldering
composed of
silver,
and zinc in variable proportions, with
sometimes of
tin,
the latter metal being added to the
silver to increase the fluidity
when
fused.
copper,
the addition
and cause
Several qualities
of
it
silver
to
run well
solders
are
employed according to the nature of the work upon
1/7
SILVER.
to
which they are
various degrees
The
be used.
of
using
the silver solders are obtained by
which enter into
different proportions of the metals
Alloys of silver and copper form
their composition.
difficult to melt.
the hardest solders— ir. those most
while the
The addition of zinc gives a medium solder,
a
are prepared with the addition of
fusibility of
easiest or softest
certain proportion of tin.
dental depots is
silver solder frequently sold at
The
composed
fine silver
3 parts
of
and
part of brass.
I
This represents a percentage composition of
Fine silver
Copper
Zinc
.
.
•
•
.
.
•
.
.
.
•
•
:
7S-00 per cent.
16.66
„
8-33
99-99
Kichardson* gives- the following formulte for solderino- articles
No.
Fine silver
Copper
Zinc
.
of standard silver
made
:
No.
I.
.
.
.
.
.
.
-
.
66 parts
30
10
2.
.
•
60 parts
.
.
.
20
„
-
.
lo
.
„
Fine silver
Copper
Brass
employed in the form of
however, are sometimes used.
Silver solders are usually
plate;
thin
filings,
generally soldered with gold solder, as
too readily in the
silver solder would blacken much
Dental alloy
is
mouth.
borax, as
flux used with silver solders is always
during soldering, but also
it not only prevents oxidation
required
greatly facilitates the flow of the solder into the
The
places.
Preparation of Silver
*
Uichanlson,
may be
>S'o/(/«'S.— Silver solders
" Mei-li!iniciii
Dnitistry," 1894,
p.
1 1 1,
6th ed.
M
DENTAL METALLURGY.
178
and copper together
under a layer of charcoal powder in a plumbago
The zinc, which
crucible heated in a suitable furnace.
slight
excess of that
in
heated
and
should be previously
required, is cautiously added after the silver and copper
prepared by melting the
silver
and the whole well stirred with an iron rod
and then poured into a flat ingot mould to obtain a
are melted,
plate of alloy suitable for rolling.
When
rolled into a sheet of
Brass
thickness.
is
and zinc separately
is
removed from the mould and
about one-sixtieth of an inch in
cool the ingot
;
is
invariably used instead of copper
it
should be added after the silver
Silver coins are sometimes used instead of
melted.
and copper separately, in which case the solders
are prepared by adding to the coin from one-tenth to
silver
one-sixth
its
weight of
Assay by
zinc.
Cupellation,
The operation
or
Dry Method
of cupellation has for
removal of base metals in a gold or
oxidation and by
its
of Assay.
object the
silver
alloy
by
the aid of fused litharge (lead oxide).
based upon a property which characviz. that they
terises the precious metals
It is
—
are not oxidised
a
condition to
metals,
oxidised.
Lead
or silver, as
it is
when
is
when exposed
current
of
air,
in a Tuolten
while
similarly treated, are
base
readily
always added to the impure gold
readily converted into litharge (lead
which fuses and dissolves the oxides (formed
during the operation) of base metals in the alloy. The
"
operation is conducted in a small vessel termed a " cupel
porous,
(Vig. 37), made of bone-ash, which, being very
oxide),
absorbs the molten oxides, leaving the unoxidisable
metals gold and silver on the cupel.
—
—
T79
SILVER.
The assay
is
of silver alloys
by the cupellation method
conducted as follows
fair sample of
1. A
:
2.
the
alloy
accurately
is
weighed in a delicate balance.
This weighed portion is then wrapped in
thin sheet-lead and cupelled, to remove the
base metals present.
3.
The button
is
of silver
remaining on the cupel
weighed.
In conducting the assay I gramme (or 10-15 grains)
of the alloy is usually taken and carefully wrapped in a
weighed quantity of lead-foil. The amount of lead to
be added to an alloy of silver and copper varies in
accordance with the composition of the alloy, and is
greater in proportion as the quantity
creases.
copper in-
of
English standard silver (925
fine)
requires
weight of lead for cupellation.
After wrapping the alloy in the required weight of
heated
lead-foil it is charged into the cupel, previously
If the
in a muffle furnace kept at a uniform red heat.
about six times
its
right temperature
is
attained the charge quickly melts
and cupellation begins, the metallic globule steadily
diminishing in size until, after the expiration of a,bout
twenty to thirty minutes, the lead and base metals
have become completely oxidised and absorbed by "the
cupel, leaving a bright globule of pure silver.
as the cupellation
is
finished the muffle
is
As soon
allowed to
down, in order to avoid the spitting of the silver,
and the cnpel withdrawn when the silver bead is solid.
The bead is then detached, brushed, and weighed.
Tlie weight of the silver bead does not, however, give
cool
the true proportion of silver in the alloy, as there are
always small losses of silver due to volatilisation and
i8o
DENTAL METALLURCtY.
by the
absorjDtion
These are determined by
cupel.
placing in the muffle with each batch of assays one or
more proof
same weight and of
similar alloy but of knoion composition.
The checks
are prepared from pure silver and copper, and when the
or check assays of the
approximate composition of an alloy
is
not known a
preliminary cupellation must be made to ascertain this
before suitable " checks " can be prepared. When these
checks are cupelled side by side with the assay piece
is
concluded that the
same.
loss of
silver
on each
will
it
be the
In order, therefore, to obtain the true per-
centage of silver in the alloy submitted to assay, the
calculated loss sustained
by the check
added as a
is
correction to the weight of the silver bead from the alloy.
When
gold or platinum
is
present in the alloy
remains on the cupel in combination with the
and must be subsequently separated
(see
it
silver,
Gold Assays,
P- 99)-
Silver alloys, such as those used for dental amalgams,
containing
tin,
or zinc, must be subjected
fication " before
first to
" scori-
metals produce
cupellation, as these
oxides which are not absorbed by the cupel.
Scorifica-
tion consists in mixing a weighed quantity,
usually
5
grammes
(or 50 grains), of
the alloy with about 10 times
its
weight of
granulated lead in a small saucer-shaped
vessel of
fire-clay,
termed a
" scorifier
''
this in a muffle furnace at a bright
(Fig. 38),
and placing
red heat.
By this means the base metals are oxidised and
form a fusible " slag " by combining with molten lead
oxide, produced by the oxidation of a part of the lead,
while the unoxidisable metals remain in combination
with the metallic lead present in excess.
As
the scorifier
l8l
SILVER.
" slag " floats
not made of absorbiug material, the
is comabove the excess of lead. When the operation
is
the scorifier are poured into a"
" slag " detached, and the
suitable mould, the glassy
lead " button " cupelled in the ordinary way.
plete the contents
of
Wet Assay of Silver. — Silver is usually estimated
A
in the wet assay by precipitating it as chloride.
weighed quantity of the alloy
is
dissolved in
nitric acid with the aid of a gentle heat.
solved (see note) the solution
is
dilute
When
diluted with
dis-
boiling
hydrochloric acid added to
The solution is well
precipitate the silver as chloride.
completely
stirred, and when the silver chloride has
water and an
excess
separated, leaving the
of
supernatant liquor clear,
it
is
and washed well with hot water. It is then
of
carefully dried and weighed and the percentage
chloride
One hundred parts of silver
silver calculated.
filtered off
contain 75.27 parts of silver.
treated
_yy^e_Aiiy gold, tin, or platiiumi present in the alloy
oil'
liltered
be
must
wlduli
residue,
insoluble
would V)e left as an
before precipitating the silver.
Electro -plating.—This term is applied to the
is
process by means of which a film of metallic silver
deposited on the surface of articles made of German
give them
silver, copper, brass, and other base metals, to
the appearance of silver, and
is
similar to electro-gilding.
be plated is first thoroughly cleaned,
It is next dipped
as described for gilding on p. 1 16.
into a solution of mercuric nitrate, whereby it receives
The
article
to
a thin deposit of mercury, then
rinsed in water, and
immediately suspended by means of thin copper wire
ot
in the plating li(|uid, which consists of a solution
silver
cyanide in potassium cyanide.
'Phe
article
is
m
DENTAL METALLURGY.
l82
of
then couuected to the negative pole
battery,
while a strip of pure silver
the positive pole and
An
is
a suitable
connected to
suspended in the plating liquid.
electric current is thus
passed through the solution,
a coherent form, to be precipitated
upon the article, while the silver plate is gradually
dissolved, forming silver cyanide, thus maintaining the
causing
silver, in
The deposit of silver is
the solution.
usually dull or " frosted," but the addition of a few
drops of carbon disulphide to the solution causes the
strength of
silver deposit to
form with a bright surface.
Recovery of Silver from Scraps.— The
of dental alloy are treated with
nitric
acid,
scraps
and the
platinum removed as described on p. i8g. Strips of
copper or of zinc are then placed in the solution to
precipitate the silver.
is
The spongy
washed, dried, and then melted.
silver thus obtained
CHAPTER
X.
PLATINUM.
SYMBOL,
Pt.
ATOMIC WEIGHT,
Occurrence.— Platinum
is
always
i95-
found
in
tlie
or flattened grains
metallic state, generally as rounded
metallic lustre, occurof a lio-ht steel-grey colour and
and gold-bearing
ring in alluvial deposits, detritus,
contains iron
It is never pure, but invariably
sands.
found in platinum
osmium, and
ores— viz. palladium, iridium, rhodium,
The
group:'
ruthenium, known as the "platinuvi
from the Ural
largest supply of platinum comes
districts.
Mountains, but it is also found in other
The mettJ is first separated, by
and a group of rare metals
chiefly
Preparation.—
sandy,
washing operations, from much of the
ore, the residue
earthy, and lighter portions of the
careful
with gold, &c.
consisting of grains of platinum, along
residue with
The platinum is extracted by treating the
associated copper, lead, or
nitric acid, to
remove any
hydrowith water, and treating with
heating with
chloric acid to dissolve the iron, and then
The solution thus obtained
aoid.
silver,
washing
it
nitro-hydrochloric
chloride),
then mixed with sal-ammoniac (amnionic
of
whereby a yellow precipitate of the double chloride
is
platinum and
ammonium
is
obtained.
The
precipitate
DENTAL METALLURGY.
washed, dried, and ignited iu a plumbago crucible,
when the metal is obtained as a grey spongy mass
is
known
ammonia
as spongy platinum, the
The
chlorine being expelled.
whiteness, and
hammered
fine
until
chloride and
powder
it
is
is
heated to
welded into a
homogeneous mass, or it is melted in a crucible of
lime or gas-coke by means of the oxy-hydrogen ilame.
Properties. Platinum is a white metal with a
greyish tinge, and when polished it has a very high
It does not become tarnished by exmetallic lustre.
posure to the atmosphere at any temperature, even in
—
presence
the
the
resists
agents
nitric,
hydrogen.
sulphuretted
of
action
water and
of
of
most
Platinum
chemical
not attacked by hydrochloric, sulphuric,
or any single acid, except wheu alloyed with a
;
it is
large proportion of silver, in which case it is soluble in
It dissolves slowly in nitro-hydrochloric
nitric acid.
acid,
which
is its
This property of with-
best solvent.
standing the action of chemical agents, coupled with
its non-oxidisability at all temperatures, makes it a
valuable material for dental purposes.
The pure metal is slightly harder than silver and
is
very malleable and ductile, being only inferior to gold
and silver in ductility, while in tenacity it is only
Platinum is
surpassed by iron, steel, and nickel.
hardened by rolling and mechanical treatment, but
may be
five to
softened by heating to a bright red heat for
ten minutes and allowing
inferior to both gold
and
for electriciiy.
stances in nature,
is
and
its
it
to cool.
It is
much
silver in conductivity for heat
It is
one. of
specific
the heaviest sub-
gravity being 21.5.
attainable
infusible at the highest temperature
ordinary furnaces, but
may be
fused by the
It
in
electric
185
PLATINUM.
by the oxy-liydrogeu blowpipe flame. It
much
becomes soft and workable at a temperature
the
below its meltiug-poiut, and at high temperatures
Like
metal can be welded by pressure or hammering.
oxygen when
silver, large masses of platinum absorb
to
molten but expel it on cooling, causing the mass
curreut, or
"spit."
When
heated
platinum
the
possesses
re-
markable property of absorbing considerable quantities
a
and other gases, especially when it is
of
m
hydrogen
fine state of division.
Use in Dental Laboratory.— Platinum
is
used
continuous gum-work; for pins for
attaching teeth for backing and other minor operaAlloyed with silver, it
tions of the dental laboratory.
as
a
base
for
;
is
largely used as a base for artificial dentures.
Brittle Platinum.— Experience having proved
that the platinum pins attached to mineral teeth are
frequently brittle and very liable to break, an investigation into the composition of brittle platinum
* with
pins was undertaken by Prof. Hartley of Dublin
a view to ascertain the cause.
For this purpose fragments of
brittle pins
were sub-
mitted to a very careful spectroscopic examination.
The results of the experiments showed that the brittle
and crystalline character of the platinum was in all
probability due to the presence of minute quantities of
phosphorus or of carbon, and by remelting in a limecrucible under the oxy-hydrogen tiame its malleability
was greatly improved, thus confirming the accuracy of
the conclusion arrived
Platinum
beaten
out
*
at.
Foil.— IMatinum
into thin foil,
l>i;w. Cliriii.
Sue,
may be
and can
be
vol. xviii. (1902),
11.
rolled
used
30.
in
or
this
DENTAL METALLURGY.
form
for filling purposes.
of platinum adhere
In order to make the leaves
when pressed
together the surface
covered with a film of pure gold by electro-deposition.
The foil must be thoroughly annealed when used in
is
order to
make
it
work
work compared with
easily.
gold.
The metal
—
harsh to
Fillings of platinum have
the advantage of being almost white
Platinum Black.
is
when
finished.
Platinum in an extremely fine
forms a black powder known as " platinum black," which resembles lampblack in appearance
and soils the fingers in the same way. This finely
state of division
may be
divided platinum
obtained in various ways.
A common
method of preparing it is by precipitation
with zinc from a solution of platinic chloride containing
an excess of hydrochloric acid, or by adding an excess
of a mixture of sodium carbonate and sugar to a solution
of
platinic chloride
and then boiling
until the
formed becomes perfectly black and the
supernatant liquor colourless. The soft black powder
precipitate
washed, and dried at a gentle
It is also prepared by fusing platinum with
heat.
twice its weight of zinc, powdering the alloy thus
produced, and dissolving out the zinc with sulphuric
is
collected
acid,
when
on a
filter,
the platinum remains in the form of a black
powder.
Platinum black possesses remarkable and powerful
chemical properties; it absorbs and condenses gases,
that the
especially oxygen, within its pores so rapidly
becomes red hot. When exposed to a red heat
mass
assumes the
the black substance shrinks in volume and
and no longer
metallic appearance of spongy platinum,
soils
the
fingers.
When
platinum with zinc and
prepared
from
otbei' n.etals, the
alloys
of
black powder
PLATINUM.
1
87
an opeu vessel to a temperature couwith a hissiug noise,
sLderably below redness deflagrates
sometimes detonating like gunpowder.
when
LeaLecl iu
Spongy Platinum.—This name
is
applied to the
metallic platinnm
spongy, slightly coherent form of
the double
obtained by heating to bright redness
latter
platinum and ammonium. This
chloride
of
formed as a yellow precipitate when
to a solusal-ammoniac (ammonic chloride) is added
by dissolving
tion of platinic chloride, obtained
compound
is
platinum in aqua
regia.
The yellow
precipitate
is
gives
decomposed on the application of heat and
spongy
of
chlorine and sal-ammoniac, leaving a residue
off
By the application
spongy mass when at a bright
may be welded together, when
platinum.
of
pressure
the
to
^
red heat
its particles
assumes the form
Like the
and appearance of commercial platinum.
of inducing
other forms of platinum, it is capable
combinations in the mixture of certain comit
chemical
bustible gases.
Detection of Platinum in Alloys.— Platinum
described
usually detected in alloys for amalgams, as
on p. 162. The
in the qualitative examination of alloys
exceeds
(quantity of platinum in these alloys seldom
is
I
per cent., and
the alloy
is
is
usually completely dissolved
when
treated with nitric acid.
platinum in gold plate may be
regia,
detected by dissolving a few chippings in aqua
The presence
of
removing excess of acid by evapoi'ation, diluting and
filtering off any residue of silver chloride, then concentrating by evaporation and adding ammonium chloride
and alcohol as before.
Ill
silver alloys (such as dental alloy) the
presence of
DENTAL METALLURGY.
i88
platinum may be detected by treating the alloy with
nitric acid, when the platinum is partly dissolved, the
remainder being left as a black insoluble residue. The
platinum in solution may be detected by adding ammo-
nium
chloride
and alcohol
as before, after precij)itating
the silver with hydrochloric acid and
filtering.
Estimation of Platinum in Alloys. — i. In
Dental Amalgams.
proportion
of
— Owing
tin
to the comparatively large
present in alloys used
for
amal-
somewhat difficult to accurately estimate
the small amount of platinum usually present. The
most satisfactory method consists in scorifying (see
gams
it
is
80) 5 grams, or 50 grains, of the alloy with from lO
to 1 5 times its weight of granulated lead, whereby the
p.
tin
1
is
removed and the
retained
in
gold,
the resulting button of
The
cupelled.
silver,
silver
button
and
lead,
platinum
which
(containing also gold
is
and
platinum) obtained by cupellation is treated with dilute
nitric acid to dissolve out the sUver and platinum.
The residue
of
gold
(if
any)
is
filtered
off
and
After
the silver precipitated with hydrochloric acid.
filtering off the silver the solution is evaporated to very
small bulk, then
ammonium
and alcohol are
chloride
added to precipitate the platinum, the precipitate thus
obtained being dried, heated to redness to obtain
metallic platinum, and weighed.
The small quantity of platinum usually present in
amalgam alloys will probably all go into solution with
but when large quantities are present a
the silver
;
part of
it
will
remain with the gold
;
the residue left
any), after being treated with nitric acid, should
therefore be dissolved in acpia regia and the platinum
(if
precipitated and weighed as previously directed.
PLATINUM.
alloys
Platinum may also be estimated in amalgam
alloy in a small crucible
by melting the
and gradually
the tin is
adding mercuric chloride, by which means
This must be done in
as a volatile chloride.
removed
a draught cupboard
it is
left
to carry off the
fumes produced,
as
silver
dangerous to inhale them. The button of
present).
behind contains the platinum (and gold if
above described.
may be conveniently
2. Platinum in dental alloy
alloy
estimated by treating a weighed quantity of the
It is treated with nitric acid, as
with nitric
which dissolves
acid,
On
of the platinum.
all
the silver and part
introducing a sheet of zinc into
precipitated,
the solution the silver and platinum are
and on treating this precipitate with nitric acid the
silver only is dissolved.
The two
quantities of platinum
and
are then put together, washed, heated to redness,
weighed. The platinum precipitate may also be dissolved in aqua regia, the metal precipitated with
nium
chloride
and weighed
as
ammo-
spongy platinum
as
previously directed.
The
silver
may be
recovered from the solution in
way by precipitation as chloride (see
Alloys. Platinum will alloy with most
.the usual
—
other metals
under the influence of
bodies which
are
than platinum
itself.
usually
heat,
considerably
Platinum and Gold.
—These
p: 169).
of
the
producing
more
metals
fusible
combine
with the formation of alloys which are more fusible
than platinum, the melting-point being lowered as the
quantity of gold increases.
The
alloys are elastic
and
ductile,
approaches more or
less to that of
tion of the latter
increased.
is
and their colour
gold as
tlie
])rupor-
I
DENTAL METALLURGY.
go
Platinum and
tinum by
fusion,
malleable, ductile,
Silver.
—
Silver unites with pla-
forming alloys which become more
and
fusible
as the
proportion of
silver increases.
Dental Alloy.
—This
alloy of silver
and platinum has
been described under Silver Alloys (p. 174).
Platinum and Iridium. These metals unite in
different proportions, but the union is only effected by
—
the use of the intense heat of the oxy-hydrogen flame.
The presence of iridium gives increased stiffness, hardness and elasticity to platinum. An alloy consisting
of nine parts of platinum and one part of iridium is
extremely hard, as elastic as
It
to fuse than platinum.
exceedingly beautiful
polish
steel,
and more
is capable of
and
difiicult
taking an
unalterable
is
on
Alloys with 20 per cent, of iridium
worked.
are malleable, ductile, and capable of being
Platinum containing a small quantity of iridium is stated
exposure to
by Essig*
gnm-work
air.
to be of value for strengthening continuous
by forming the backing of it, especially in
partial lower sets.
It is also of value in
combination with
It
cases.
vulcanisable rubber for either entire or partial
countermay be perfectly swaged by the use of a zinc
used as a solder with these alloys.
Platinum and Copper.— Platinum unites with
a high temperacopper in all proportions by fusion, but
of these alloys.
ture is required for the production
require the oxyThose containing excess of platinum
The alloys
hydrogen flame to effect combination.
die.
Pure gold
is
ductility, and tenacity,
possess considerable malleability,
and are
less tarnished
by the atmosphere than
copper with base metals.
*
"
Dental Metallurgy,"
p. 201.
1S93
i-dit
alloys of
.
THIDIUM.
—
Recovery of Platinum from Scraps. Platinum
may be conveniently recovered from scraps of dental
alloy
by the method described on
p.
189 for estimating
platinum.
Solder for Platinum.— Pure gold
alloys.
joint,
for
solder
suitable
platinum
and
is
the only
platinum-iridium
Ordinary gold solders do not make a strong
and are not suitable for the purpose. For con-
tinnous-gum and porcelain bridge-work "platinum
solder," composed of gold 4 parts and platinum I
part, is supplied * for use with an oxygen blowpipe.
IRIDIUM.
SYMBOL,
Ir.
ATOMIC WEIGHT,
193.
found in the form of grains, which
consist essentially of an alloy of platinum and iridium,
called " platin-iridium," and are usually associated with
Small particles of alloy
the grains of platinum ore.
of osmium and iridium (called " osmiridium ") are also
This metal
is
found.
Properties.
—Iridium
is
a white, lustrous,
steel-
metal slightly heavier than platinum, its density
being 22.4. It is not acted upon by air at the ordinary
like
temperature
oxidised,
heating.
but
it is
heat.
at a red heat, however, it is superficially
:
but regains
its
metallic
lustre
on further
extremely hard and brittle when cold,
rendered somewhat malleable at a bright red
It is
by the oxy-hydrogen blowpipe
not acted upon by ordinary acids or aqua
It is fusible only
llame.
It is
regia.
When
alloyed with
much
platinum, however,
dissolves in a(pia regia.
*
C. Asli
.'i;
Sons, Ltd., IJst
M
it
DENTAL METALLURGY.
192
Alloys.
— Iridium
alloys
creasing their hardness, but
gold.
With platinum
it
with
it
most
metals,
in-
cannot be alloyed with
forms alloys remarkable for
and hardness. (See Platinum Alloys.)
Dentistry. Alloys of platinum and
their strength
Use
in
—
iridium are sometimes used as a base for
also in the
form of wire
for pivoting,
dentf-,1
plates,
and occasionally
for the manufacture of nerve instruments.
CHAPTEE
XI.
PALLADIUM.
SYMBOL,
Occurrence.
ATOMIC WEIGHT,
Pd.
— This
metal
found in the
chiefly
is
io6.
nature in small quantities associated
metcallic state in
with platinum and gold.
Preparation. In order to extract the metal the
ore is heated with aqua regia, which dissolves the
—
Ammonium
metals as chlorides.
added
precipitate
to
chloride
then
is
the platinum present.
This
is
filtered off and the solution neutralised by the addition
solution of mercuric cyanide
of sodium carbonate.
A
is
added to
of palladium
then
form
whitish,
insoluble
washing,
drying,
palladium in the
precipitate the
which
cyanide,
heating
redness,
to
metallic palladium in a spongy state,
welded
into
solid
a
mass
as
a
This compound, after
substance.
and
separates
the
in
yields
which may be
same manner
as
platinum.
Properties.
— Palladium
sembling platinum and
is
is
a
white
capable of
metal,
re-
being highly
upon by atmospheric air
at the ordinary temperatures, but when heated to
dark redness it assumes a violet or blue colour, owing
polished.
It
is
not
acted
to a superficial film of oxide
•,
at a higher temperature
DENTAL METALLURGY.
'94
the oxide
lustre.
is
It
hydrogen,
it
It
is
also
ever,
by hot
acid
acid.
and
acid
and
slowly
is
boiling
in
also
best solvent,
Its
which
regia,
acids than platinum.
nitric
sulphuric
aqua
is
upon by
hydrochloric
in
concentrated
metallic
sulphuretted
of
action
its
not attacked by water, but
is
easily acted
dissolved
soluble
the
resists
l^alladium
more
is
reduced and the metal regains
readily
dissolves
howthe
metal.
Palladium
fairly
malleable,
hammered
it
is,
rather
platinum,
viz.,
it
is
drawn
than
ductile
less
into fine wire
;
platinum.
somewhat lower temperature
a
at
;
and tenacious, and can be
ductile,
into thin plates or
however,
Palladium fuses
than
platinum
slightly harder than
is
1500"
C.
(2732"
cannot be fused in an ordinary furnace.
in the oxy-hydrogen flame
When
volatilises
it
but
F.),
in
it
heated
greenish
vapours.
When
is
the melal
evolved
is
melted
when the metal
"spit" as in the case
of
it
absorbs oxygen, wliich
solidifies,
silver.
sesses the property of absorbing a
hydrogen.
900 times
At
its
a red heat
own
it
cavising
Palladium
large
it
to
pos-
quantity of
absorbs, or occludes, about
volun\e of hydrogen, while even at
ordinary temperatures
it is
capable of absorbing over
absorption of gases
300 times its
forms one of the most characteristic properties of
volume.
This
palladium.
Palladium
is
specific gravity
only one-half as heavy as platinum,
being
its
12.
Although palladium resembles platinum it ma}' be
readily distinguished from this metal by placing upon
it a drop of tincture of iodine, which upou evaporation
PALLADIUM.
by heating produces a black stain with, palladium, while
platinum is not acted upon by this substance.
Use for Dental Purposes. Palladium in a
finely divided state is used for the preparation of
palladium amalgam, but this forms its only use in
The unalterable nature of palladium in the
dentistry.
—
air, its fine
which
silver-white colour,
it
does not lose
on exposure to sulphuretted hydrogen, and
ness
make
dentistry,
its
light-
a very suitable metal for use in prosthetic
it
and
it is
for this purpose
quite probable that
if
its
it
would be used
high price did not exclude
from the dental laboratory.
Palladium Precipitate.
—This
is
it
the form in
which the metal is employed for the preparation of
palladium amalgam. It is usually prepared for dental
by placing strips of zinc in a solution of
palladium chloride, whereby the palladium is precipitated as a fine black powder, which is then carefully
washed and dried. The powder appears to lose its
purposes
mercury after long exposure to the air.
Palladium and Silver. These metals unite by
affinity for
fusion in
—
all
proportions.
An
alloy of three parts silver
and two parts palladium is white, hard, elastic, and
malleable, and it is not blackened by sulphuretted
hydrogen. Even when alloyed with as much as three
times
its
weight
of
silver,
palladium retains
in the presence of that gas.
of a high polish
silver
to
An
dentists.
Palladium and Gold.
is
brilliant surface.
per cent, of palladium and 62 of
was formerly used by
palladium
colour
These alloys are capable
and retain their
alloy containing 38
its
—The
effect
of
gokl on
produce alloys that are usually white
or grey in colour, hard and ductile.
DENTAL METALLURGY.
196
Palladium and Mercury. — Palladium amalgam
may be formed by rubbing the finely divided metal
with,
mercury.
tion of heat.
The union is accompanied by an evoluThe properties of palladium amalgams
have been given on
p. 135.
CHArTER
XII.
ZINC.
SYMBOL,
Occurrence.
ATOMIC WEIGHT,
Zn.
—Zinc
stated
is
65.
have been found
to
in the metallic state in small quantities in Australia,
chief forms of occurrence are in combination
with sulphur as zinc-blende, and with carbonic acid as
but
its
calamine, these being by far the most important and
abundant ores
The metal
of zinc.
is
found in
also
combination with oxygen.
Preparation.
— In
extracting
zinc
from^
its
ores
taken of the volatility of the metal at a
bright red heat. The metal is chiefly prepared from
the carbonate and sulphide, these minerals being tirrt
advantage
is
powdered and roasted to expel the carbonic acid and
The zinc
sulphur, and convert the zinc into oxide.
oxide is then mixed wirh powdered coal and heated
to bright
oxide
oxide,
redness in earthenware
when the
carbon mon-
retorts,
reduced with the formation of
which escapes, while the metallic
is
liberated distils over
and
is
/.inc
thus
collected in clay or iron
receivers.
The metal thus obtained
zinc oxide, from which
before
it is
it
is
is
contaminated with a
little
separated by re-melting
ready for the market.
Zinc ores frequently
DENTAL METALLURGY.
198
contain small quantities of cadmium, but as this metal
is
more
the
readily volatilised than zinc
it
passes over in
portions of the distilled product, and can thus
first
be collected.
(See p. 224.)
Properties.— This metal,
mercially
possessing
as
"spelter,"
when
polished
which
is
known com-
bluish-white
is
bright
a
in
colour,
metallic
lustre,
and when freshly broken a crystalline surface.
It is not acted upon by exposure to dry air
at the
ordinary tempei-ature, but at a red heat it rapidly
oxidises and burns with a bluish-white flame, with
the production of a white floccalent powder of zinc
If exposed to a moist atmosphere at the
oxide, ZnO.
temperature
ordinary
coated
its
surface
with a grey layer or
film
rapidly
of
becomes
oxide,
which
does not, however, increase by exposure, but protects
the metal from further oxidation. When carbonic acid
is
present the coating
sists
is
formed more rapidly and con-
then of zinc carbonate.
not attacked by pure cold water, but it is
slowly oxidised by hot water and by water containing
Zinc dissolves readily in hydrochloric
carbonic acid.
Zinc
is
and sulphuric acid it is also soluble in nitric
and is slowly acted upon by alkaline solutions.
acid
;
At ordinary temperatures zinc is
when heated to between 100' and
acid,
a brittle metal, but
150' C. (212" and
becomes both ductile and malleable, and
may be rolled or hammered, after which treatment it
302" F.)
it
retains its malleability
when
cold.
When
the heat
is
again
increased to about 205" C. (401° F.) the metal is
in an iron mortar.
brittle, and may be readily pulverised
hardened by rolling and hammering, and recjuires
malleaannealing at a lo'io temperature to restore its
Zinc
is
199
ZINC.
It melts at
bility.
C. (779° ^')
415
volatile at
^^'"^
the
It contracts on solidification,
a bright red heat.
with that
shrinkage being considerable when compared
or
It is a harder metal than gold
of other metals.
silver, and has a density of nearly 7.
of the
Zinc has the property of precipitating most
metals from their solutions.
galvanised iron,
It is extensively used for making
dipping
of iron plate coated with zinc by
which consists
Iron thus
the iron into a bath of the molten metal.
of air
treated is better able to withstand the action
or
moisture, the zinc preventing its corrosion
and
rusting.
Use
for
Dental Purposes.— The
zinc in the dental laboratory
is
chief use of
in the formation of dies
is
used in swaging metal plates, for which purpose it
the
almost the only metal employed, as it possesses
extent
properties required for this purpose to a greater
Several of the compounds of
preparation of
zinc are also largely employed for the
than any other metal.
"
cement"
fillings.
Zinc Dies.— The use of /inc for dies has been objected
to
by some on account of the shrinkage which takes
place
when
sally
employed
plates,
as
it solidifies,
it
for the
but this metal
is
almost univer-
formation of dies for swaging
possesses
the
properties
of
hardness,
toughness, and malleability, and melts at a comparaExperiments by the late
tively low temperature.
Professor iVusten * have demonstrated that an averagesized
contracts
*
die
zinc
Tw^th
••Mutiillic
l)i(;s.''
measuring
of
two
inches
transversely
an inch from the extremities of
Aiiirriniii
Jiiiirii. i[f
DriiUil S'-ir^icr, vol. vi.
200
DENTAL METALLURGY.
the alveolai- ridge, being
equivalent in
thickness to
about three or four ordinary leaves of a journal.
In a moderately deep arch (about half aa inch in
depth) the shrinkage between the level of the ridge
and the
floor of the palate
would be nearly yoVoth of an
inch, or rather thicker than one leaf of a journal.
question of shrinkage
arches
most serions in the deepest
is
in the case of shallow arches
;
rtTTTTrth
or
When
^oljTrtli
is
it
only about
of an inch.
melting zinc for the preparation of dies
necessary to remember that zinc castings
high temperature are more or
when
Hue, but
The
less brittle
made
and
it is
at a
crystal-
cast at a temperature only a little above
the melting-point of zinc they are comparatively malleable
care should always be taken therefore to avoid
;
Zinc dies which are cast at a high
excessive heating.
temperature
In some
will re(|uire
annealing by gentle heating.
the die will
cases
be
sufliciently
annealed
during the process of taking the counter-die.
Zinc
may
is
also occasionally
che zinc die, provided
taken.
render
the metal
If
it
fluid
without fear of
the
thin film
Adhesion may
with a
little
cold the die
if
used for counter-dies, which
be obtained by pouring the metal directly upon
the
only heated
is
may
it
be cast
adhesion,
this
to
sufficiently
upon the zinc
die
being prevented by
on the surface of the die.
also be avoided by rubbing the surface
of
oxide
blacklead powder before casting.
and
Purification of Zinc.
— The
zinc of
pure for ordinarv- purposes
dental laboratory
When
conntei--die will separate as readily as
lead had been used.
sufliciently
necessary precautions are
it
;
commerce
but
in
is
the
becomes deteriorated by constant
20I
ZINC.
melting, owing to
tlie
fact tliat a small <]aantity of zinc
by the metal. It also becomes contaminated with iron from the ladle. If a small (juantity
of charcoal is placed on the surface of the metal when
oxide
dissolved
is
oxidation
meltino-,
The
minimised.
i«
may
zinc
be
by placing a few lumps of ammonium chloride
(sal-ammoniac) on the surface of the molten metal, then
When
stirring well with a stick of wood and pouring.
melting zinc in an iron ladle care should be taken to
purified
avoid excessive heating, as zinc forms an alloy with iron
under favourable conditions. A malleable iron ladle
more readily attacked,
some cases penetrating the ladle and escap-
should be used, as cast iron
the zinc in
is
coating the inside of the ladle with whiting
or a wash of clay and heating carefully, accidents of
When zinc has become
this kind may be avoided.
ing.
By
accidentally contaminated with lead
from the
latter
slowly.
On
it
may be
by melting and allowing
account of
the bottom and
its
of zinc are those
to solidify
density the lead will
fall to
may then be removed by means
chisel.
Compounds
it
separated
of Zinc.
—The
following compounds
most frequently employed by
Zinc Oxide (ZnO).
Known
known compound
of a
dentists.
also as Zinc White.
This
oxygen and
and
of
is
the only
is
the chief ingredient in the plastic filling-materials
known
zitic,
and oxy-phosphates.
It is prepared on a large scale by the combustion of
metallic zinc in air, the fumes produced being led into
as oxy-chlorides
a series of
condensing chambers where the oxide
is
deposited.
For pharmaceutical and dental jiurposes
it
is
usually prepared by adding sodium carbonate to a
solution of
ziuc sulphate.
The white
precipitate of
DENTAL METALLURGY.
202
is washed and dried, and
then heated to expel the carbonic acid and water, leaving
zinc carbouate thus obtaiuecl
the zinc oxide as a powder.
Zinc oxide
when
a pure white, soft substance, which,
is
heated, becomes yellow, but
becomes white.
carbonic acid
is
It is insoluble in
by
and strong solutions
again
water except when
present, in which case
It is unaffected
it
dissolved.
is
dilute alkaline solutions, but acids
The
the oxy-hydrogen flame, and
of alkalies dissolve
oxide does not fuse even in
it
on cooling
readily.
it
possesses the advantage of not being blackened by
exposure to sulphuretted hydrogen.
Zinc
Chloride (ZnCl,,).
—This
compound
usually
is
prepared by dissolving metallic zinc in hydrochloric
acid and boiling down the resultant liquid, until on
cooling
it
becomes
by the
It is also prepared
solid.
direct combination of zinc with chlorine gas.
Zinc chloride
is
a soft, greyish -white, easily fusible
substance, which resembles
It is extremely deli(|uescent
is
Dry
as a caustic,
employed
and a
distilled.
on exposure to moist
very soluble in water and in
powerfully caustic.
is
wax and may be
alcohol, its
zinc chloride
is
air,
and
solution being
used in surgery
dilute solution of the salt in water
as an antiseptic.
(ZnSOJ or White Vitriol.— Zmc sulformed when zinc is dissolved in sulphuric
Zinc Sulphate
phate
is
on a large scale by roasting the
natural sulphide (blende), whereby the oxygen of the
air partially converts it into sulphate, which is then
acid.
It is obtained
dissolved out with water and allowed to crystallise.
of
It is extremely soluble in water, with evolution
heat, but only slightly acted
temperature of about
300'^
C.
upon by
alcohol.
(572° F.)
it
At
a
loses water
203
ZINC.
converted iuto the anhydrous comj)oiind, a white
is converted
friable substance, which at a white heat
Zinc sulphate, in common with all
into the oxide.
taste and is
the soluble zinc salts, has an astringent
and
is
poisonous.
These three compounds of
zuic, viz., the oxide, chloride
and sulphate, when mixed together or
with other substances, form the basis
class
known
materials
of
are
Three varieties
fillings.
as
in
combination
of the valuable
osteoplastic
commonly
cement
or
under
used,
the names of oxy-chlorides, oxy-phosphates, and oxysulphates.
The cement used as a filling for teeth should be
capable of being worked easily and should not set too
It should also possess the following qualities.
rapidly.
It should
:
and harden under water (2) be
(i) be dense
;
unaffected by contact with saliva
(3) be devoid of irritating chemical action
(4) be free from shrinkage or
;
;
expansion; and (5) adhere firmly to the walls of the
cavity.
The materials used for the preparation of the cements
consist of a powder and a liquid, which are different for
the several varieties made.
Oxy-Chloride.
—The
paration of this cement
is
powder used for the prefinely powdered zinc oxide,
which has been heated almost to whiteness for about
two hours, whereby it loses neaily half its original
bulk.
to
The
liquid
which borax
is
is
a dilute solution of zinc chloride,
sometimes added.
A
paste
made by
moistening zinc oxide with zinc chloride rapidly sets to
Each special preparation of oxy-chloride
a hard mass.
naturally differs a little in detail of manufacture, but
the powder in
all
consists of zinc oxide with a small
DENTAL METALLURGY.
204
admixture of other ingredients,
glass or silica,
sucli as finely
for tlie purpose of
mechanically con-
ferring greater hardness on the mass
mixture in
common use*
gether in a mortar
(silica),
and 30 parts
mixed these
This
is
i
is
powder by grinding.
A
to-
part of fine silex
When
thoroughly
and heated
called the " frit,"
mass
set.
prepared by grinding
of zinc oxide.
cool the semi-coherent
three times
when
are placed in a small crucible
to bright redness.
fine
is
parts of borax,
2
powdered
and when
again reduced to very
It
is
mixed with
The
then
its weight of calcined zinc oxide.
liquid usually
employed with
deliquesced zinc
chloride
following proportions
—
I
this
powder
diluted with
consists
of
water in the
ounce of zinc chloride dissolved
drachms of water.
Oxy-chloride cements as a class are readily acted
upon by the alkaline and acid fluids of the mouth,
They are, therefore,
especially at the cervical edges.
They usually set
valueless as permanent fillings.
in 5 or 6
and a notable shrinkage generally takes place.
Oxy-Phosphate. In this cement the powder is
zinc oxide and the liquid is one of the varieties of
The oxy-phosphate powders are
phosphoiic acid.
slowly,
—
similar mixtures to the oxy-chlorides, and, like them,
only in minor details of
manufacture. The liquid used is frequently prepared
by dissolving glacial phosphoric acid (ortho-phosphoric
the various preparations
acid) in pure water
until
differ
and then evaporating the
solution
attains the syrupy consistency of glycerine,
which a crystalline mass is deposited on standing.
it
from
Phosphoric acid
is
extremely soluble in water
a pleasant, purely acid taste, and
* Essig,
••
Deiitiil
is
;
it
has
perfectly free froiu
Metallurgy," 1893, p 241.
205
ZINC.
When
smell.
phosphoric
oxide, the latter
is
acid
is
mixed with
zinc
dissolved and zinc phosphate formed.
Crystals of pyrophosphoric acid are sometimes employed
They
instead of the liquid, and are preferred by some.
are carefully melted in a platinum or porcelain spoon
the
over a spirit-lamp, ebullition being avoided, until
liquid attains the consistency of glycerine.
Oxy-phosphates are soluble in the alkaline secretions
cements
of the mouth, the period of duration of these
They are
varj-ing from two to about seven years.
chlorides.
antiseptic, though less strongly so than the
a class the oxy-phosphates are considered preferable
As
to the oxy-chlorides, as they are
more permanent and
less irritating.
Oxy- Sulphate.— The powder
sists of
phate
;
for this
cement con-
a mixture of zinc oxide and calcined zinc sulthe liquid consists of a solution of gum arabic.
The following proportions are frequently employed:*
part of calcined zinc sulphate with
2 or 3 parts of zinc oxide ; for the liquid, 15 grains of
gum arabic in oz. of pure water, to which when completely dissolved i grain of sulphite of lime is added.
for the
powder,
i
-|-
The
solution
In
is
then
purest form
its
substance, which
is
through absorbent cotton.
filtered
gum
is
a yellowish-white
soluble in cold
water, forming a
arabic
viscid, adhesive, tasteless solution.
These cements usually lack hardness, but they are
The oxy-sulphates are
acted upon by the alkaline and
non-irritating and set rapidly.
all
more or
less readily
acid fluids of the mouth.
,
Alloys of
alloys, to
Zinc— Zinc
forms a number of
i^seful
which when present in certain proi)Oitions
*
Fliigg, " I'lastiu FilliiifrH,"' p. 156.
it
2o6
DENTAL METALLTT-RGY.
gives hardness without impairing the malleability of
the alloy
while in larger proportious
;
brittleness.
Zinc
lowers
the
it
often induces
melting-point of
the
metals with which
it is alloj^ed, and for this reason is
added to gold solder
it also renders the metals with
which it unites less liable to be affected by exposure to
;
the atmosphere.
Zinc and Copper.
— These metals nnite
in all pro-
portions to form the numerous varieties of brass, which
are the most important alloys of zinc.
p. 222.)
— Alloys
Zinc and Tin.
readily prepared
by
of these
(See Copper,
two metals can be
forming combinations that
fusion,
are generally softer than zinc, harder and less malleable than tin, and
The
alloys
more or
contract
less crystalline in structure.
than
less
zinc;
the amount of
shrinkage varies, however, according to the proportions
of the constituent metals, those containing excess of
zinc contracting most.
ployed in the arts for
patterns
;
emcasting ornamental objects and
Zinc-tin alloys are chiefly
they have also been used as a substitute
zinc in preparing dies for swaging plates.
in re-melting is greatest
cess of ziac.
all
alloys
(See Alloys for Dies,
Zinc and Lead.
in
in
— Zinc
may
for
The waste
which contain ex-
p. 47.)
be melted with lead
proportions, but on cooling the mass does not
remain homogeneous
;
the lead on account of
its
greater
density sinks to the bottom, leaving a layer of zinc on
top.
zinc,
The
lead will, however, retain a small quantity of
which has the
effect of
impairing its malleability.
hardening the lead without
(See Lead,
p. 212.)
Zinc and Bismuth. — These two metals
alloy
when
molten, but on solidification two layers are foruied, the
207
zrN(
zinc with about 2 per cent, of bisnuifch rising to the
top, while the bismuth on account of its density settles
at the bottom,
and contains about 8 to 14 per
cent, of
/inc.
Zinc and Mercury.— (See Zinc Amalgam,
p. 138.)
Zinc unites readily with gold, silver, platinum and
the alloys produced are described in the
palladium
;
chapters dealing with these metals.
Zinc enters into
the
composition
of
the English
bronze coinage to the extent of about one per cent,
and is also present in varying proportions in the
different qualities of
German
silver.
(See
p. 252.)
CHAPTER
XIII.
LEAD.
SYMBOL, Pb
ATOMIC WEIGHT,
(Plumlnini).
Occurrence.
— Lead
quantities in
tlie
lias
been found in nature in small
The
metallic state.
the metal, however,
is
207.
chief source of
combination with sulphur as
in
sulphide,
Galena PbS, this being the ore from which
the metal
is chiefly
bination with
obtained.
oxygen,
It is also
found in com-
carbonic acid and
phosphoric
acid.
Preparation.
galena
;
the ore
with free access of
is
—Lead
is
is
very readily obtained from
roasted in a reverberatory furnace
air,
whereby a portion
of the sulphide
oxidised to sulphate, whilst in another portion of the
sulphide the whole of the sulphur is burnt off as sulphur
dioxide,
and lead oxide formed.
The
and the
temperature
air excluded,
lead react
giving
off
of
the
furnace
when the
is
then
raised
sulphate and oxide of
upon the undecomposed sulphide of lead,
sulphur dioxide and leaving metallic lead
behind.
Galena almost invariably contains a small quantity of
silver, which will remain alloyed with the lead after
smelting, and is subsequently extracted by the process
of cupellation described
on
p.
167.
LEAD.
Auofcher
sists iu
method
209
of extracting lead froui galeua con-
heating the ore in contact with metallic iron
;
the iron combines with the sulphnr, and the lead thus
liberated isinks to the bottom of the furnace, while the
sulphide of iron or rcrjulm collects above
Properties.
— Lead
is
it.
a bluish-grey metal which,
may
be cut with a knife or scratched by the finger nail,
being the softest metal in common use.
freshly cut
A
surface possesses a bright lustre, which, however, be-
comes rapidly tarnished on exposure to the air.
Lead is both malleable and ductile at the ordinary
temperature, possessing the former property to a considerable degree.
It can easily be rolled out to thin
which form
sheets or
foil,
used as a
filling for teeth, as it also
in
perty of welding
when two
it
has occasionally been
possesses the pro-
clean surfaces are pressed
together.
Its tenacity is inferior to that of all the other ductile
cannot be drawn into fine wire. It
is tlexible and non-elastic, and may be bent backwards
and forwards repeatedly without fracture. On account
metals, so that
it
and the readiness with which
of its flexibility
made
to
it
may be
flow," thin sheet lead is frequently em])loyed
for obtaining patterns, &c. in the dental laboratory.
It is a very
tricity.
bad conductor of both heat and
Lead fuses
at 325" 0. (617" F.),
sensibly volatile at a red heat
on
solidiKcation.
When
;
it
elec-
and becomes
also contracts sliffhtlv
heated to a temperature just
below ita melting-point it becomes brittle, a property
which accounts for the fact that lead counter dies are
liable to be broken if they are accidentally dropped
immediately after casting.
If lead is kept in a state
of fusion in contact with the air, rapid oxidation
takes
o
DENTAL METALLURGY.
2IO
melted repeatedly it beof a
comes hard and brittle owing to the formation
metal.
small quantity of oxide which dissolves in the
soft and
This oxide may be removed and the lead made
place on the surface.
When
powder
malleable again by placing a layer of charcoal
stirring it
on the surface of the molten metal or by
Commercial lead is frewith a stick of green wood.
and malleable
(juently almost pure and extremely soft
quantities of other metals are sometimes
yet small
whiter and less
present, the impure lead being usually
Metallic lead, on account of its
soft than pure lead.
and the
softness and pliability, its low melting-point,
of water and many
fact that it withstands the action
common metals, is
acid liquors better than most of the
great variety of
largely employed in the arts for a
purposes in the form of sheets and pipes.
Use
for
Dental Purposes.— Lead
ployed for the
form
with
is
chietly
production of counter-dies and
em-
in the
When
alloyed
of thin sheets for cutting patterns.
important purother metals it is used for several
poses in the dental laboratory.
of the
Alloys.— Lead may be alloyed with most
The general
common metals by melting them together.
to lead is to harden
of the addition of other metals
effect
it
.
and impair
its malleability.
Lead and Antimony.-The
alloys
of
lead
and
than either metal
antimony are harder and more fusible
than lead, but if antialone and also more oxidisible
proportion the alloys
mony is present beyond a certain
which
and brittle. Alloys
are very crystalline, hard
imthe
exceed 15 percent, have
the antimony does not
on cooling, a property
portant property of expanding
castings.
makes them well adapted for
m
which
LEAD.
Mdid.
Ti/pc
—
I
I
one of the chief alloys
Tliis constitutes
and antimony.
of lead
2
For large types
it
consists of
lead with about one-fourth to one-eighth of its weight
of antimony, while for small types tin is invariably
added, and for
small quantities of
special purposes
other metals such as copper and iron.
harder than lead, and brittle
dies,
and
dies.
also,
though much
;
it is
Type metal
less frequently, for
(See also Alloys for Dies,
—
is
sometimes used for
counter-
p. 45.)
Tin, These metals when fused together
readily unite in any proportions, the resulting alloys
having a somewhat darker colour and less brilliancy
than tin. They are generally harder than tin and contract less on cooling than either of the constituent
uietals_, but they are not so fluid when melted, and
Lead and
castings
alloy of
made with
4 or
5
these alloys lack sharpness.
parts of lead
and
i
The
part of tin burns like
charcoal at a red heat, producing a " cauliflower "-like
niass.
Lead-tin
alloys with the
addition
of a small
proportion of other metals are used for dies instead of
'/sine.
(See Alloys for Dies,
p. 49.)
4 parts of tiu with i part of
lead, but small (juantities of other metals are somePcivter is an alloy of
times added.
Soft Solders.
—These
are alloys of
lead aud tin
in
various proportions, the fusibility of which generally
increases
with the
amount
of
tin.
Goiiiiiloh.
Su/dcr
two metals Fine Solder
is composed of i
part of lead and 2 of tiu; while
I'li'inherH Solder is made by melting together 2 parts
of lead and I of tin.
Alloys of these metals are remarkable for the facility with which they ignite and
burn when raised to a red heat.
consists of e(iual parts of the
;
2
I
DENTAL METALLURGY.
2
Lead and
proportions
Zinc.
—
l^hese
two metals
when molten, but
their densities on solidification.
alloy in all
separate according to
(See
p.
206.)
Lead which has become contaminated with zinc may
be " softened " by melting it and exposing the surface
of
the molten
metal
to
oxidation
with
occasional
In this way the impurities are oxidised and
form a scum on the surface which may be readily
removed.
Lead and Mercury. (8ee Lead Amalgam, p.
stirring.
135-)
CHAPTEE
XIV.
TIN.
SYMBOL,
ATOMIC WEIGHT,
Sn (Stnnnnm).
Occurrence.
—All
commercial tin
tin-fitonc or cassiterite,
oxide of
tin,
is
iiS.
obtained from
SnO,, this mineral
forming practically the only ore of tin. Tin ore is not
very widely distributed, only occurring in large quantities in comparatively few localities.
Preparation.— To
crushed
with
is
which
oxide
is
being
after
ore,
matters,
the
metal
washed
from
obtain
roasted to expel any sulphur
may
it
The
be associated.
then mixed with
the
finely
all
earthy
or
arsenic
purified tin
powdered anthracite and
smelted in a suitable furnace
;
the
carbon
of
the
anthracite combines with the oxygen to form carbon
monoxide and thus
obtained
with
is
billets
separation of
liberates
purified
of
green
a
scum
by
the
stirriug
wood,
tin.
the
The
tin
so
molten metal
which results
or dross carrying with
in
it
the
the
impurities.
The
known
pecnliar
structure
of
the
commercial
metal
produced by heating ingots of
the metal to a temperature at which they become
brittle and breaking tliem
by dropping Croni
a
height.
as urain-tin
is
DENTAL METALLURGY.
214
Properties.
—Tin
is
one of the whitest metals, but
possesses a peculiar faint yellow tinge
in
and
]ustre
polish.
its
surface
undergoes
It
;
it
rivals silver
capable of taking a fine
is
change in dry or moist
little
at ordinary temperatures, but
it
air
tarnishes slowly in the
presence of sulphuretted hydrogen owing to the formaIf heated in air it rapidly
tion of a film of sulphide.
which forms the
well-known polishing putty powder, but the i^ure metal,
if melted at a low temperature and poured out, retains
Tin has
its resplendent lustre for a considerable time.
oxidises
to
stannic
oxide
(SnO.,),
becomes evident when
the metal is warmed by being held in the hand for
It is a little harder than lead but softer
a short time.
a characteristic odour which
than gold.
Water has no
action on the metal, but
soluble in hot hydrochloric acid
acid
sulphuric
acts
violently
the action of the dilute acid
nitric
acid acts violently
is
upon
it
is
readily
boiling concentrated
;
on
the
metal,
less energetic.
it,
while
Dilute
liberating nitrous
fumes, and converting the tin into metastannic acid,
which settles at the bottom of the vessel as a white
powder.
Tin
bar of tin
known
is
when
also soluble in alkaline solutions.
as the cry of tin, caused
crystalline particles.
Tin
of the metals, only lead,
inferior to
it
A
bent emits a peculiar crackling sound,
is
by the
friction of the
one of the least tenacious
antimony and bismuth being
in this respect
;
it is,
however, very malle-
able and can be easily rolled out to thin
foil of less
than yyVsyth of an inch in thickness. Tin may be
welded by the application of pressure, when two clean
It |iossessPS little
surfaces are brought into contact.
At a
be
drawn
into wire.
ductility, but with care may
,
TIN.
215
temperature of 392" F. (200° C.) it becomes so brittle
that it may be readily powdered.
It melts at a temperature of 232" C. (449 F.) and
'
contracts slightly on solidification.
Tin
conductor of heat and of electricity
;
it
an inferior
is
has a density
of 7.3.
Tin
is
by treating the
sulphuric and nitric
easily crystallised superficially
surface with a mixture of dilute
the ornamental appearance seen on tin boxes, &c.
known as " moiree metallique," is obtained in this way.
acids
;
Tin
is
also
obtained in a crystallised
deposited from
by
solutions
its
electrical
when
state
agency, the
prepared by this means being in the form of
metal
brilliant elongated needles.
Uses in Dental Laboratory. — Tin was
used as a base for
artificial teeth,
formerly
and more recently
it
has been introduced as one of the constituents in the
alloys used for the " cheoplastic " process.
It is some-
times used for counter-dies and occasionally for dies.
"
When
.
employed for dies
in connection with a lead
counter the latter should not be obtained directly from
the die,
as
the
comparatively high temperature of
molten lead would produce, when poured upon the tin,
partial fusion of the latter and consequent adhesion of
the
As
two pieces."*
its
affinity
for sulphur
is
so
swaging operations, for
supplied in thick and thin sheets
tin is largely used in
slight,
which purpose
it
is
as " Soft Metal."
Tin as before stated enters into the composition of
.alloys used for dental amalgams, and for dies.
Clean surfaces of pure tin
by
compression,
*
and
on
Eichardson, " Mechiinicnl
may be made
this
account
to cohere
tin
in
Dt'iitistry," 1894. p. 125.
the
DENTAL METALLURGY.
form of thin
foil
frequently used as a
is
filling for
" Tin-foil
teeth.
is very little employed as a filling
by itself, being generally used in combination with gold.
The advantages claimed for it are that (i) it is easy
to work
(2) it has a preservative action ujjon the
—
;
For the latter reason it is generally
used as a lining to cavities and at cervical margins.
It has one distinct disadvantage in the fact that it
tooth substance.
becomes black." *
Tin-foil. Pure
—
tin-foil
is
made by
casting the
metal into slabs about one inch thick and reducing
these to foils of the desired thinness by passing
repeatedly through a rolling mill.
soapsuds are allowed to flow on the
sticking to the
rolls.
Ordinary
During the
foil
them
rolling
to prevent its
about
tin-foil is
-pfyLy^th
of an inch thick, but for dental purposes foils of vary-
ing degrees of thickness are made and are numbered
in a
manner
(See p, 91.)
similar to that
employed
for gold foils.
—
Tin-plate. The material Ivnown in commerce as
Lin-plate is composed of thin plates of iron coated with
tin by dipping them into a bath of molten tin, the
object of the coating being to prevent the formation of
which takes place when iron plates are exposed
unprotected to the action of air and moisture.
Alloys of Tin. Tin enters into the composition
rust,
—
number
of a large
of useful alloys,
many
of which are
of considerable impoi'tance,
—
—
Tin and Silver. (See p. 175 and also chapter viii.)
Tin and Zinc. These metals alloy readily when
fused together.
(See p. 206 and
Alloys for
P- 47-)
*
Smale and Colyev,
" Diseases of Teeth."'
p. 183.
.Dies,
TIN.
Tin and Copper,
— Tin unites readly with
co]>per,
the most important alloys being the various bronzes, &c.,
described under Copper Alloys, p. 222.
Tin and Mercury.
— Tin
(See Tin. Amalgam,
mercury.
readily combines
with
p. 138.)
Tin and Antimony.— These
metals unite when
antimony being to harden
the tin and generally to impair the malleability and
ductility, making it more or less brittle.
The brittlemelted together, the
effect of
An
ness increases with the proportion of antimony.
alloy of
4 parts of
and
tin
ciently malleable to be
I
part of antimony
hammered and
—This
is suffi-
rolled cold.
an alloy of tin and antimony in very variable proportions, to which small
Britannia Metal.
is
quantities of other metals are also frequently added.
and ductile alloy, and can
and
be
stamped into various shapes.
It
takes a high polish and is largely employed for the
manufacture of impression trays and other articles used
An inferior kind of Britannia metal
by dentists.
"
known as Queen's Metal " consists on an average of 75
It is a hard, very malleable
rolled out
per cent, of
tin, 8.5
cent, of lead,
per cent, of antimony, with 8.5 per
cent, of bismuth.
and 8 per
Meter ilfe/a/.^This
is
composed
of
tin,
antimony,
and lead it is used in the dental laboratory for making
matrix and polishing plates. It possesses certain valu;
it to be worked up in a
steam swager, a thin diaphragm of the alloy being-
able properties that enable
made
to give accurate copies
and adapt
itself
to the
Owing to its fusibility
may be melted over a good Bunsen burner.
Detection of Tin in Alloys.— To detect the
surface of the model with ease.
it
presence of tin in an alloy advantage
is
taken of the fact
DENTAL METALLURGY.
2l8
that the metal
is
converted
into
a
white
insohible
powder (metastannic acid) when acted upon by
nitric
acid.
A small
quantity of the alloy to be tested
is
heated
with dilute nitric acid until the whole of the material
is
acted upon.
white residue of
The
solution is then diluted
tin, if present,
allowed to
and the
settle.
If gold is also present in the alloy, the residue will
be purple in colour, owing to the formation of a small
([uantity of
"purple of Oassius."
CHAPTER
XV.
COPPER.
SYMBOL,
Occurrence.
Cii
(Cuprum).
— Copper
ATOMIC WEIGHT,
63,
found in the metallic state
is
in various parts of the world, notably in the neighbour-
hood of Lake Superior, where
occurs in enormous
it
masses which are frequently several
found
It is also largely
oxygen and carbonic
Preparation.
in
tons
in weight.
combination with sulphur,
acid.
—From
ores containing no
such as the oxides and carbonates, the metal
by smelting the ore with
or
coal
whereby the copper
monoxide formed.
furnace,
Ores containing sulphur are
is
is
sulphur,
obtained
coke in a blast
liberated and carbon
first
subjected to a pro-
cess of concentration in either blast or reverberatory
furnaces to obtain a
known
as "regulus."
compound
of sulphur
This "regulus
whereby a portion of the copper
is
" is
and copper
then roasted,
oxidised to copper
oxide, which, as the temperature rises, reacts
upon the
undecomposed copper sulphide, giving metallic copper
and sulphur dioxide, which last escapes. The copper thus
obtained is impure and is subjected to a refining process.
Properties. Copper possesses a peculiar red colour
and a bright metallic lustre. At ordinary temperatures
—
220
DENTAL METALLURGY.
this metal is uot altered by
when heated
oxidises
it
temperatures ia moist
acid, it
air,
rapidly
;
while
at ordinary
becomes coated with a green layer or
known
rapidly tarnished in the
also
retted hydrogen
owing
copper sulphide.
but
air,
in the presence of carbonic
copper carbonate, commonly
is
exposure to dry
scale of
as " verdigris."
pi'esence
It
of sulphu-
to the formation of a film of
Water and
cold hydrochloric acid
have no action upon copper, and
it
only slowly
is
soluble in strong hydrochloric acid.
Strong and dilute
when heated, but its
nitric acid slightly diluted, in which acid
sulphuric acid acts on the metal
best solvent
is
soluble.
Copper is highly malleable,
and tenacious, and can be hammered or rolled
into thin sheets or drawn into moderately fine wire, but
it
readily
is
ductile
b}^
these operations the metal
is
hardened and requires
frequent annealing or softening during the processes.
When
wrought
it
ranks next to iron in tenacity
;
sur-
passing platinum and silver in this respect.
Copper is
one of the best conductors of heat and of electricity,
being inferior only to silver.
The melting-point of
copper
is
lower than that of gold but a
than that of
silver,
being 1050°
contracts slightly on solidification.
temperature just below
its
C.
little
(1922*^
When
higher
F.)
;
it
heated to a
melting-point copper becomes
may be readily fractured.
" granulated " by pouring the molten metal
very brittle and
Copper
is
into water,
metal
is
and
is
frequently sold in this form.
The
largely used for a great vai'iety of technical
and domestic purjooses.
Effect of Impurities on Copper.
— The
physical
properties of copper are materially impaired by
presence of even small proportions of impurities.
the
The
22
COPPER.
1
most common impurities in commercial cop]ier are iron,
arsenic, silver, and copper oxide, and occasionally
bisnnitli, tin, antimony, snlphnr and lead.
Of these arsenic, sulphur, and antimony are the most
injurious, as they harden the metal and impair its
malleability and tenacity.
Molten copper has the property of dissolving copper
The effect of
oxide, which makes it more or less brittle.
iron is to render copper harder and paler in colour.
Bismuth
lessens the toughness of the metal.
Use in Dental Laboratory.
bined state copper has very
dental laboratory, but
in small quantities
forms a valuable constituent in alloys
other
metals,
conferring
upon
the uncom-
application in the
little
when added
— In
it
of gold and
them many
useful
with most
other
properties.
Alloys.
— Copper
unites
easily
metals, and forms the basis of a large
number
of im-
portant alloys.
Copper and Gold.
metals alloy in
all
— When
proportions,
melted together these
and when the copper
does not exceed lO to 12 per cent, the malleability is
thus 21 carat gold and higher qualities
little altered
—
are practically as malleable as pure gold.
Gold Alloys,
p.
103.)
Copper and
all
Silver.
— These
(See also
metals combine
in
proportions, the resulting alloys ranging in colour
copper through yellowish tints to the
white colour of silver. These metals form a series of
most valuable alloys, having a great variety of applica-
from the red
of
tions in the arts.
(See also Silver Alloys,
Copper and Zinc. — Copper
zinc,
unites
forming alloys generally known as
p. 17 i.)
readily
brass.
with
2
DENTAL METALLURGY.
22
Alloys of these metals, however, are
known
in commerce by a variety of names, such as Tombac, Muntz's
metal, Mosaic gold, Pinchbeck, Mannheim gold. Prince's
metal, &c.
Ordinary brass (commonly called composition) consists of 2 parts of copper with i of zinc.
Certain varieties of brass are exceedingly malleable
and
but these properties vary with the composition and the temperature.
Some varieties are only
ductile,
malleable
when
temperature.
rolled hot, others can be rolled at
Brass
is
fore better adapted to
any
harder than copper, and there-
wear and
resist
melted these alloys alter somewhat in
tear.
When
composition
owing to the readiness with which zinc is oxidised.
The easy fusibility of brass, and its fluidity when melted,
render
it
valuable for casting purposes, as
very fine impressions from
of
receiving
On
this account it
was
dental laboratory.
Cast brass
tin,
the mould.
is
generally more or less
being very pronounced in the
containing excess of zinc.
Copper and Tin.
with
capable
at one time used for dies in the
crystalline, this property
brittle varieties
it is
— Copper
in combination
is
extensively alloyed
with which
it
forms many
valuable bodies generally termed " Bronzes."
The
effect of tin
wise modify
on copper
its properties.
is
to
The
harden
it
or other-
alloys are capable of
taking a high polish, and present a beautiful metallic
They melt at a moderate temperature, and
when melted, thus forming excellent alloys
lustre.
fluid
casting.
Bell-metal
variable projiortions.
and
I
Metal.
is
is
for
an alloy of coj^per and tin in
With about 2 parts of copper
of tin an alloy is
This
are
produced known as SpcciUam
a very hard, brittle, steel-like alloy,
capable of receiving a very high and uniform polish.
OOPPEll.
Gun
il/r/^/^.— This
is
22.^
a variety of brouze formerly
used to a large extent for ordnance, hence its name.
It consists of copper, alloyed with from 8 to lo per
cent, of tin
;
the term "
exclusively confined to
gun metal," however, is not now
alloys of copper and tin, as small
proportions of other metals are very frequently added.
Vulcanising flasks for dental purposes are made largely
of
gun
metal,
as
it
is
a hard alloy and gives good
castings.
Ck)pper
and Aluminium.— These
when melted
metals unite
together, forming alloys which are
more
or less golden-yellow in colour.
With lo per cent, of aluminium it forms the alloy
known as aluminium-bronze. With excess of aluminium
the alloys are hard, brittle and crystalline.
Copper and Nickel.
these metals unite in
all
—When
melted
proportions.
together
The resulting
with the addition of zinc and sometimes of other
metals, are largely used in the arts under the name pf
alloys,
German
silver, &c.
Copper and Mercury. — In
a fine state of division
copper readily amalgamates with mercury, the resulting
amalgam becoming hard and cr\-stalUne after the lapse
of a
few hours.
as a material for
p.
1
34-)
Copper amalgams have long been used
(See Copper Amalgam,
filling teeth.
CHAPTEE
XVI.
CADMIUM.
SYMBOL.
Cd.
Occurrence.—This
metallic
state
in
ATOMIC WEIGHT,
metal
nature.
is
It
112.
never found
is
usually
combination with sulphur, associated
the
in
found
with
tlie
in
ores
of zinc, in small quantities not exceeding two or three
per cent.
Preparation.— Being more
than
zinc,
cadmium
distils
fusible
over with the
and
volatile
first
portions
of zinc during the smelting of the ores of that metal.
The product thus obtained consists of a mixture of
cadmium and zinc, contaminated with oxides of these
mixed with charcoal and ag-ain distilled,
when the metal which passes over first contains a larger
proportion of cadmium.
To obtain pure cadmium the
mixture of cadmium and zinc from the last distillation
metals.
is
It
dissolved
is
in
hydrochloric acid
and metallic zinc
placed in the solution, which precipitates the cadmium
in a spongy crystalline form.
When melted, this is
cast into small cylindrical rods about half an inch thick,
which form it is usually sold.
Properties. Cadmium resembles tin in colour and
appearance and takes a high polish. It is slowly oxidised on the surface by exposure to the atmosphere, and
in
—
CADMIUM.
when heated in
cadmium oxide.
hydrogen
it
air it
burns with a brown flame to
presence of sulphuretted
In the
gradually becomes coated with a yellow
cadmium
film of
225
sulphide.
The metal
is
not acted
upon by water, but is soluble in hydrochloric acid
and in sulphuric acid. Its best solvent is nitric acid,
in which it is readily dissolved.
Acetic acid (vinegar)
also acts
on the metal, and
tions of the alkalies.
it is
slowly soluble in solu-
These tendencies to corrosion make
unfit for use as a filling material, as it
would not
withstand the action of the fluids of the mouth.
Cad mium is malleable and ductile and may be rolled
into thin sheet or foil or drawn into wire at the ordinary
it
temperature, but at 80° C. (176° F.) it is very brittle
and may be readily powdered in a mortar. It melts
at the low temperature of 320° C. (608° F.) and may
be
distilled
Cadmium
knife.
is
harder than
tin,
but
may
C.
heavier,
its
specific
(1418" F.).
be cut with a
It also possesses greater tenacity
somewhat
is
at a temperature of 770°
than
tin
gravity being
and
8.7.
Cadmium
has no direct use in the arts, but is of value
as a constituent of certain alloys, especially those with
bismuth and lead,
Use for Dental
tin,
cadmium
Purposes.—The
only use for
in the dental laboratory is in combination with
other metals as "fusible metals" and other alloys.
It
has also been employed as a constituent in alloys for
dental amalgams, but its employment for this purpose
now been abandoned. The advantages and diradvantages of cadmium in amalgams and alloys may be
has
classified as follows
:
AiJVANTA(fKH
J.\
Amal(;am,s.— Cadmium was at one
time employed as a constituent of alloys for dental
I'
DENTAL METALLURaV.
226
amalgams, as its presence gives whiteness to the fillings
and tends to produce a good ping. On account of its
affinity for mercury it also facilitates amalgamation and
dauses quickness in setting.
In Alloys.
— Cadmium,
like bismuth, has the valuable
property of lowering the melting-point of
some of which are
many
alloys,
readily fusible in boiliog water.
It
therefore a useful constituent in the so-called "fusible
metals " described on p. 50 and is occasionally used for
is
dental purposes.
—
Although cadmium
amalgams pi'oduced from
alloys containing it, it has been generally condemned
It is readily acted upon
as a constituent of these alloys.
by the joint action of sulphuretted hydrogen and the
alkaline and acid fluids of the mouth with the formation of an orange-yellow film of cadmium sulphide and
the production of soluble salts which stain the tooth
Disadvanta(;es
in
Amal(jams.
confers useful properties on
substance.
—
In Alloys. When present in alloys in
cadmium tends to make them more or
many of
its
large quantities
less brittle,
but
combinations are capable of being hammered
and rolled. Owing to the affinity of cadmium for
oxygen when molten, a considerable loss is liable to
take place
when
excessive heating
taken
to prevent
alloys
is
containing
it
are melted,
if
not avoided and every precaution
oxidation.
On
this
account
it
is
extremelj^ difficult to obtain an alloy of definite composition.
XML
CHAPTER
BISMUTH.
SYMBOL,
Occurrence,
metallic
state
Bi.
ATOMIC WEIGHT,
—Bismuth
and
occm-s
iu
207.5.
nature
in
the
combination with oxygen,
sulphur and other elements, but the bismuth of commerce is chiefly obtained from the native metal.
also in
Preparation.— To
extract
the
metal
from the
taken of its
matters accompanying
it,
advantage is
low melting-point, namely, 268° C. (514" R).
The
crushed ore is placed in a series of iron tubes or retorts
set in an inclined position in a brickwork chamber
provided with a fire-grate, by means of which the retorts are heated externally.
The upper end of each
retort,
through which the ore
charged,
is closed by
an iron door; the lower end is also closed witii an iron
plate provided with a small aperture.
On the appliis
cation
of heat the bismuth melts
and the liquid
metal soon begins to flow through the small apertures
in the lower ends of the tubes and falls into iron
bowls, in which
ladles
a
collects
and cast into ingots.
metal has
and
it
entirely
fresh
the retorts.
and
is
dipped out
As soon
ceased the
with
as the flow of
raked out
once introduced into
The metal thus obtained is refined by
charge of
ore at
residue
is
DENTAL METALLURGY.
228
various methods to obtain bismuth of good commercial
quality.
Properties.
^
— Bismuth
greyish-white
a
is
metal,
having a decided reddish tinge and a bright metallic
It is not sensibly altered by exposure to the
lustre.
atmosphere at the ordinary temperature, even in the
presence of sulphuretted hydrogen, but when heated in
air
bismuth
is
readily oxidised
and
at a high temperature
burns with a bluish flame and gives
known
yellow colour,
without
little
it
its
effect
off
fumes of a
Water
as Jl.oircrs of hisimtth.
Sulphuric acid
when hot and concentrated
;
onl}^ attacks
while nitric acid forms
Alka-
best solvent, attacking the metal vigorously.
is brittle
is
on bismuth and hydrochloric acid has but
action on the metal.
line solutions
light
have no action on bismuth.
and can be
easily pulverised
;
This metal
when broken
it
Bismuth fuses
presents a highly crystalline surface.
at a comparatively low temperature, 268° C. (514° F.),
and at a high temperature may be volatilised or distilled.
It expands very considerably on solidification, the solid
more space than the liquid
metal occupying about
metal, so that bismuth is denser in the liquid than in
the solid state; the density of solid bismuth being 9.8.
When a large quantity of bismuth is melted, allowed to
cool slowly until the surface begins to solidify, the crust
broken and the
still
liquid metal
poured
out, fine crystals
are obtained.
Bismuth
is
the poorest conductor of heat and
amongst the common metals.
The brittleness of bismuth renders it unfit
of
electricity
for use
itself,
but in combination with other metals
alloys
which are frequently employed in the
it
arts.
by
forms
The
BISMtlTH.
salts of
229
bismuth are somewhat extensively used
iii
mecliciue.
Use
Dental Purposes.
for
bismuth in the dental laboratory
certain alloys,
more
— The
is
only use for
as a constituent of
especially those
known
as fusible
metitls.
Alloys of Bismuth.
—The
alloyed with other metals
which are readily
fusible,
bismuth when
usually to form bodies
is
effect of
hard and expand on
solidifica-
tion after fusion.
Bismuth and Antimony. — These
metals
when
united yield alloys which are hard and brittle and
expand considerably on
Bismuth and Tin.
cooling.
— These metals readily combine
in all proportions
when
fused together.
A
very small
proportion of bismuth imparts to tin more hardness,
and fusibility. The alloys of bismuth and tin
are more fusible than either of the metals taken
lustre
separately.
Bismuth and Lead. — These metals unite in various
proportions by melting
them
together.
If the propor-
tion of bismuth does not exceed that of lead the alloys
and more tenacious than lead.
These properties, however, are diminished with an inare ductile, malleable
crease of bismuth.
Fusible Metal.— Bismuth
and lead by
fusion,
forming a
unites readily with tin
series of alloys
as fudhla imtah, a full description of
which
known
will
be
found on page 50.
An
alloy of etpial parts of
bismuth and
with 2 parts of
tin, is
account of
low melting-point.
its
lead, alloyed
used as a solder by pewterers on,
Bismutli
is
also
an
DENTAL METALLURGY.
occasional coustitueut of Britannia metal and Queen's
metal.
—
Bismuth and Mercury. Bismuth readily amalgamates with mercury at the ordinary temperature, the
amalgam
without losing
Mercury
amount of bismuth
(See Amalgams, p. 133.)
retaining a considerable
is
its fluidity.
frequently adulterated with bismuth, but
the presence of this metal
be detected by shaking
air, when, if bismuth be present, a
powder separates out.
(See Purifica-
the mercury with
crystalline black
may
tion of Mercury, p. 126.)
CHAPTER
XVIII.
ANTIMONY.
SYMBOL,
Occurrence.
ATOMIC WEIGHT,
Sb (Stibium).
— Antimony
120.
found in the metallic
is
state in nature in various parts of the world, notably in
Borneo.
siibnitc
It also occurs in
combination with sulphur as
and with oxygen, the former being the chief
source of the metal.
Preparation.
—To obtain the metal from the native
sulphide the purified ore
is
broken up and heated in
a large crucible along with scrap iron.
As
the charge melts the antimony
is
liberated and
bottom of the crucible, while the sulphur
combines with the iron, forming iron sulphide, which
remains on the surface of the molten antimony. The
settles at the
antimony
is
cast into suitable
moulds and subsequently
refined.
Properties.
bluish-white
surface
when
— Antimony
metal,
fractured,
readily powdered.
is
possessing
It
and so
is
a
a
comparatively hard
highly
crystalline
brittle that it
can be
not sensibly altered by ex-
posure to the atmosphere at ordinary temperatures,
and
is
only slightly tarnished by sulphuretted hydrogen,
but when heated
in air it burns with a bluish-white
flame, producing thick
white
fumes
of
antimonious
DENTAL METALLURGY.
Water and
oxide.
dilute sulphuric acid
action on the metal,
trated
sulphuric
sulpbate.
acid
as
but when heated with concen-
acid
it
converted into antimony
is
It is easily dissolved
well
by cold aqua
as
are without
by hot
regia.
hydrochloric
It
is
rapidly
oxidised without solution upon treatment with nitric
white oxide formed collecting at the bottom
acid, the
of the vessel.
Alkaline solutions have no action on the
metal.
It melts at a
temperature a
little
above that required
to melt zinc, its melting-point being 632'' C. (l 170° F.),
and
is
volatilises
the air at a bright red heat.
in
the next lightest metal to aluminium,
being
its
It
density
6.8.
Uses
for
Dental Purposes.
—The
antimony in the dental laboratory
of aboys for dies and counter-dies.
Alloys.
—The
effect of
metals with which
it is
is
antimony
chief use of
as a constituent
is
harden the
to
alloyed and generally to impair
the malleability and ductility of the malleable metals,
in
some cases rendering them
brittle.
Antimony and Lead. — The
metals
is
readily
antimony the
of
effected
-
crystalline.
With
on cooling.
(See
alloys
union
by melting.
are
hard,
of
these
With excess
brittle,
and very
than 15 per cent, of antimony
lead alloys have the important property of expanding
less
]).
210.J
Antimony and
Tin.
—These
form alloys which are hard and
tin,
metals
less
unite
to
malleable than
and become brittle as the proportion of antimony
These metals when united form the basis
increases.
termed Britannia metal, many vaiieties of
This
which coiisist of tin hardened with antimony.
(,f
what
is
ANTIMONY.
alloy
and
is
is
233
used for the mauufacture of impression trays,
described on p. 217.
Antimony and
Gold.
— Antimony alloys
readily
with gold, but has a very injurious
effect upon it, the
presence of 0.5 per cent, of antimony rendering the
gold quite brittle.
Antimony and Copper. — Copper
and antimony
combine well together, producing a crystalline, brittle,
alloy, known as " Eegulus of Venus," which,
however, has no practical use in the arts.
violet
CHAPTER
XIX.
IRON.
SYMBOL, Fu
Occurrence.
(tV'iTuiii).
—Irou
is
ATOMIC WEIGHT,
56.
one of the most abundant and
widely distributed elements, being found in nature in
the metallic state in small quantities as vietcoric-iron of
ultra-teiTestrial origin
;
also in combination with
forming the minerals magnetite and red
oxygen
hajinatitc,
with oxygen and water the brown hasmatites, and with
carbonic acid, the spathic
ore,
these minerals forming
the chief sources of the metal.
Iron
and
found largely in combination with sulphur
but these compounds are not employed for
is also
arsenic,
the extraction of the metal, owing to the difficulty of
completely separating these substances from the iron,
and
theii-
]n'esent.
deleterious effect on the final product
The
when
commerce exists in three distinct
iron, wrought iron and steel, each
iron of
forms, namely, cast
of which exhibits different projjerties.
Cast Iron,
or pig iron,
is
the j)roduct obtained by
and besides iron
usually contains from -2 to 4 per cent, carbon from
0.2 to 3 per cent, silicon and varying proportions of
smelting iron ores in the blast furnace,
manganese (generally under
2 per cent, in
ordinary-
cast irons); with small proportions of sul])hiir
and of
IRON.
phosphorus.
Cast iron varies in composition according
to tlie materials operated
this
upon
and
for its product ion
varying composition with differences in the method
of treatment (mainly the rate of cooling) causes
it
to
vary considerably also in appearance and mechanical
properties, giving rise to three
main
varieties
known
as
and grey, from the appearance of the
white, mottled
White
fractnred surfaces.
iron has practically
carbon in the combined form, and
while grey iron
is
comparatively
is
soft,
hard and
the
all
brittle,
having the carbon
mainly present as graphite, scales of which may often
be picked off the fractured surface with a penknife,
and mottled iron as its name implies is a mixture of
grey and white.
In
ii'on
all its varieties,
and
steel
however,
it
does not admit of being welded,
iron.
Owing
melts
at a lower
but
it
from wrought
by being almost void of ductility
not so tough, and
steel,
differs
to
is
it is
also
more
harder than
usually
the presence
of carbon,
;
it
brittle,
malleable
cast
iron
temperature than wrought iron or
requires a bright yellow heat to melt
Grey iron contracts very
little
it.
on solidihcation, and gn
that account has been proposed as a suitable metal for
dies,
as
it
is
also hard
and
runs perfectly in open
sand in the usual manner of casting dies for dental
purposes.
however,
is
The high temperature required to melt it,
a considerable drawback to its use for this
purpose.
Wrought
Iron, or malleable iron, represents the
nearest approach to pure iron which can be produced
by manufacturing processes upon a large scale, and
generally contains from 0.05 to 0.3 per ceut. of
carbon.
Its
mechanical properties are totally distinct
DENTAL METALLURGY.
236
from those
malleable
of cast iron
for while the latter
;
not
is
and has a low tenacity varying from 7
to
15 tons per square inch, wrought iron
is comparatively
very malleable and ductile with a tenacity in its
soft,
purest form of 20 tons per square inch.
is
very
difficult of
Wrought
fusion (1600° C.) and before becoming
liquid passee through a soft or pasty condition.
in
this state
iron
clean surfaces
pressed or
if
When
hammered
together cohere and weld into a single mass.
Wrought
iron
may be magnetised by
bringing
it
contact with a magnet, but
it
the removal of the magnet.
plunged into cold water, it
If heated to redness
original
its
Steel
about
o.
is
I
flint
into
this property
on
and
not hardened, but retains
thus differing from tool
softness,
which become
is
loses
steels,
hard when similarly treated.
a malleable alloy of iron (containing from
to over 2 per cent, of carbon with small pro-
portions of other elements), which has either been cast
direct into a malleable mass, or
becomes
flint
hard when
heated to a bright red heat and cooled rapidly as by
quenching in cold water or brine. This definition excludes wrought iron, which will not become flint hard
and has been formed in a pasty condition, and also
cast iron
mass.
like
which has been
It includes all
wrought
become
cast
but not into a malleable
commercial
iron, has
steels, for
Shear Steel,
never been molten as such, but
hard on quenching, while structural or
mild steels do not become flint hard on quenching, but
have been cast direct into malleable ingots. Carbon is
the element which has the greatest effect in modifying
will
flint
the properties of iron.
amount
Steels containing only a small
of carbon, say about O.
sometimes termed mild
steels,
i
to 0.5
per cent, are
and have a tenacity
moN.
237
and the better
qualities when fractured by a tensile stress, show a fine
silky appearance on the edges of the broken surface.
varying from 2^ to 50 tons per
These
sq. in.,
from 0.4 to
steels generally contain
manganese and small proportions of
phosphorus, usually less than
o.
silicon,
per cent,
i
sulphur, and
per cent, of each.
i
Tool
from about 0.8 per cent, of carbon, upwards
with from 0.05 to 0.4 per cent, of manganese, and generally less than 0.2 per cent, of silicon, and 0.03 percent,
steels contain
each of sulphur and phosphorus.
Preparation.
compounds.' The
—Iron
readily reduced from
is
its
ore, as oxide, together with carbon in
the form of charcoal, coal, or coke, and with suitable
fluxes to
combine with the earthy matters of the ore and
render them fusible at the temperatures employed,
charged into a blastfurnace, whereby the ore
is
is
reduced
by the gaseous carbon compounds produced by the action
The iron thus set free takes up carbon and
of the blast.
other elements during
its
becoming
nace, and thus
passage
down
the blast fur-
temperature
fusible at the
of the furnace, gradually sinks to the hearth,
At
accumulates.
intervals
it
moulds, and constitutes what
is
is
where
it
tapped into suitable
known
as
cast
or
pig iron.
Wroufjht or MallcaUe Iron.
—This
is
obtained by
melting the cast iron in a reverberatory furnace and
gradually removing the impurities by oxidation the
;
iron "
coming
to
nature
" in
small pasty particles, which
are gathered into a spongy ball of iron particles and
cinder, which
by hammering and rolling
a solid mass, the great
expressed.
is
welded into
bulk of the cinder being thus
The purest forms, however, always contain
some entangled
cinder,
which may be clearly seen under
DENTAL METALLITRGY.
^3^
the microscope, thus forming a convenient
distinction
between wrought irons and mild steels.
may
be produced either from wrought iron by
the addition of carbon or from cast iron by removing
the carbon. In the former process, known as " cementaSteel
tion," small bars of
and heated
thus
made
wrought iron are buried
for several days to a red heat.
is
blister-steel is piled, welded,
required form of bar,
is
Carbon
is
to pass into the iron, which presents a blistered
appearance, and on that account
When
in charcoal
it
is
known
termed
Uister-steel.
and worked
to the
as shear steel,
which
a favourite hardening steel for some tools.
When
broken up and melted with suitable
additions (of manganese, &c.) in a crucible, cast into
an ingot, and hammered or rolled into bars of various
blister-steel
is
sections, the product is
known
as crucible cast steel,
and
mostly used for tools required to harden and keep a
cutting edge. The mild steels are generally produced
is
either
by the Bessemer
or
Siemens processes.
The Bes-
semer process consists in oxidising the carbon and some
of the other impurities by blowing air through molten
pig iron, adding manganese to remove excess of oxygen
and carl)on according to requirements, by means of
suitable alloys of iron rich in
carbon and manganese.
In the Siemens process the impurities are oxidised by
the addition of iron oxide as iron ore to the molten bath
of pig iron, and the process finished in a similar manner
to the
Bessemer process.
The metal in each case is
generally tapped into a ladle and thence into ingot
moulds.
Properties
(see also Wrought Iron, p. 235).— Iron
a white metal with a bluish-grey tint.
It undergoes
no cliange in perfectly dry air, or in water free from
is
IRON.
aiv,
but
it is
rapidly coated with a scale of oxide or mist
exposed to the action of moist air. When heated
to redness it oxidises rapidly with the formation of a
if it is
It is soluble in dilute nitric acid (i-i),
scale of oxide.
hydrochloric, and dilute sulphuric acids, but
much
affected
by strong sulphuric
acid.
it
is
not
Alkalies have
no action on the metal.
Effect of Impurities on Iron. The properties
of tenacity, malleability, and ductility in iron are power-
—
fully influenced
by the presence of only small quantities
of certain impurities.
As
the carbon content of iron
city increases in a general
of 1.2 per cent,
is
way
is
increased, the tena-
until a carbon content
reached, but the malleability and the
ductility steadily decrease.
From
will
0.9 per cent, of carbon and upwards the steel
harden and temper (see next paragraph), but
manganese
is
if
also present, the steel will take a cutting
than 0.9 per cent, of carbon.
Very small quantities of sulphur render steel red-
edge with
less
short or unworkable at a red heat, while phosphorus in
makes the steel cold-short. Manganese
is found to counteract to some extent the evil influence
of sulphur, and a certain proportion of phosphorus has
more effect in high-carbon than in low-carbon steels.
Until recently arsenic has been considered somewhat
small (juantities
similar to phosphorus as to its mechanical
but recent research has shown that
moderate quantity,
is
its
efl^ect
on
iron,
influence, even in
almost negligible.
Silicon,
when
present up to 4 per cent, imparts hardness and brittleness with a gain of tenacity.
Copper in small quantities has little effect.
From these remarks it will be seen that the influence
DENTAL METALLURGY.
240
of iuipnrities on iron is a very complicated matter, owing
to the considerable influence they exert on one another,
and for several other reasons, but the statements above
will give a fair
general idea of the facts.
Hardening and Tempering.— When
steel
is
heated to redness, and then plunged while red hot into
cold water, or is otherwise suddenly cooled, it acquires
great hardness and brittleness.
hardened
steel, which is very hard and brittle,
re-heated to redness and allowed to cool slowly it
again becomes soft and malleable, or if it is re-heated
below redness and allowed to cool it is also partly
If this
is
made
softened and
and
less brittle, the decrease in
hardness
depending on the temperature employed, the higher the temperature the softer and less
brittle the steel is made.
in brittleness
This re-heating to different temperatures to obtain
the compromise between hardness and brittleness necessary for the tool being made is called tempering.
The
steel is first
tempered or
hardened
let
in the
down by
manner described and then
re-heating
it
to a definite
tem-
perature, varying according to the degree of hardness
and then cooling it quickly. The temperature
necessary is usually judged by the colour of the thin
film of oxide which appears on the polished surface of
required,
the steel
when
heated, the tint of the film varying with
the temperature, being yellow
when
heated, then passing gradually to
and
the steel
is first
brown and purple,
deep blue as the temperature increases.
The temper necessary for various steel articles depends
finally to
upon their application thus, most surgical instruments
and razors are tempered at 232" 0. (450" F.), indicated
by a pale straw tint, while the temper given to fine saws,
;
IRON.
241
indicated by full blue, correspouds to a temperature of
293
0. (560^^
The following
corresponding
table indicates the temperatures
colours
necessary
various articles used in dentistry
and
"tempering"
for
:
Tc'iuiiLTiitiirt'.
'l'(Mii)iL'r ol'
Colour.
vai'ioiis
artick's.
Kalir.
Cunt
430"
221'
Very pule yellow
450°
232'
Piile
470"
243"
254°
Full yellow
490="
510
265^
55°^
2SS'
Lancets
/'Enamel chisels and niosi,
surgical instruments
Excavators
Pluggers
strnw
Brown
Brown dappled
/'
twitli
purple spots/
blue
Bri,i;-ht
In "tempering" or letting
.Saws,
L*cc.
Watch-springs
down
dental instruments
be employed, the instrument after hardening being held in the flame and
carefully rotated to ensure uniform heating. The
flame
should strike the instrument at some distance frota
the
cuttiug end, and when the end attains the desired
colour
it should be
instantly quenched in cold water and
the flame of a spirit lamp
may
allowed to remain in the water until cold, to
jirevent
" letting
down
The same
" further.
result
may
also be conveniently effected
by
heating a small
block of iron to dull redness and
placing the instrument to be tempered
upon it, then
removing it as soon as the desired tint appears
and
plunging into cold water.
It is advisable to continually rotate the instrument in order
that it may be
uniformly heated.
DENTA.L METALLURGY.
242
Annealing.
—
Iron and sfceel which have become unduly hard or brittle by hammering, rolling, or otherwise
working the material, may be softened and made malleable by annealing, i.e., heating the metal to about a
cherry-red heat and allowing
This
it
to cool very slowly.
frequently done by withdrawing
is
it
from the
source of heat and then immediately covering
it
with
ashes or other bad conducting material such as sand,
lime, &c.,
under which
it is
allowed to cool
ordinary temperature before
it is
removed.
p. 12.)
Burning of Iron and
iron or steel
air,
is
down
Steel.
to the
(See also
—When malleable
heated to redness and exposed to the
oxidation proceeds veiy rapidly with the production
of a "scale" or layer of oxide of considerable thick-
By
ness.
excessively long or intense heating the iron
" burnt," is friable, incapable of being welded,
becomes
and cannot be restored completely to its original state.
Steel requires much more precaution in heating than
iron,
and does not bear the same degree of heat as iron
Steel which has been slightly over-
without injury.
heated
may
be restored to a certain extent by judicious
hammering at a lower temperature, but the improvement effected in bui'nt steel by this treatment is very
slight.
CHAPTEK XX.
ALUMINIUM.
SYMBOL,
Occurrence.
dant of
ail
of clay, but
Al.
ATOMIC WEIGHT,
— Aluminium
is
27.
one of the most abun-
the elements, being found in every variety
it
has never been found in the metallic
state.
In combination with oxygen it constitutes the minerals
coruncluvh or emery
is
and
batoxite,
mainly extracted on a large
from which the metal
scale.
Some
of its
com-
binations with oxygen are of great beauty and hardness,
such as ruby, sapphire, and garnet.
Another mineral from which aluminium sometimes
is obtained is cryolite, which is foiind in abundance in
Greenland, and consists of aluminium in combination
with sodium and fluorine.
—
Preparation. Aluminium is almost exclusively
obtained by means of the electric furnace, which consists of a large iron
forming the
electrode
is
box or crucible lined with carbon,
negative electrode,
while
a bundle of carbon plates.
the
positive
The
crucible
contains a bath of readily fusible compounds, to which
the aluminium oxide (alumina)
time, and dissolved.
is
When
is
added from time
to
a powerful electric current
passed through the bath the alamina
is
decomposed
DEXTAL METALLURGY^
244
and the metallic aluminium thus liberated falls to the
bottom, whence it is drawn off at intervals.
The
oxj^gen set free combines with the carbon to form carbonic oxide, which escapes and burns in the air formingcarbonic acid.
It is only within recent years that
alnminium has
been prepared in sufficiently large quantities and at a
sufficiently low price to enable it to be classed with the
other metals in
common
use.
—
Properties. Aluminium is a white metal possessing a colour between that of silver and zinc.
It is
remarkably light, being only about two and a half times
as
heavy as water
it is unaffected by air, even in the
presence of sulphuretted hydrogen, and consequently
;
preserves
its colour in an atmosphere in which silver
would rapidly become black. It is extremely malleable
and ductile, the pure metal being regularly rolled into
sheets one-thousandth of an inch in thickness, and also
drawn into very fine wire. Aluminium is most malleable between lOo" 0. (212'" I\)and 150" C. (302" F.)and
can be worked some time at that temperature before
becoming hard. When rolled and worked cold it needs
more frequent annealing. It is highly sonorous, and is
a good conductor of heat and of electricity.
The melting-point of aluminium
being a
that of silver;
it
(i 157'' F.),
melts somewhat slowly and
is
viscous
for casting purposes.
The vegetable
acids exert no perceptible action on
aluniinium, consequently
vessels.
625° C.
higher than that of zinc but lower than
little
when poured
is
it is
well adapted for culinary
It is readily dissolved in either'dilute or strong
hydrochloric acid and also in solutions of caustic potash
or soda.
'
ALUMINrrTM.
Use
Dental Purposes.
for
245
—
()u account of the
aluminium and the
facility with which it retains its colour, attempts have
been made for several years to employ it as a base for
artificial dentures, both by swaging a plate of the metal
lightness, strength,
in the ordinary
and whiteness
way and by the
these attempts
of
cheoplastic process, but
have only been partially successful.
Although some of the physical difficulties encountered
in the effort to render aluminium available in prosthetic
dentistry have been overcome,
its
great susceptibility
by the action of alkaline solutions is the
The diffichief obstacle to its use for this purpose.
culty of obtaining a suitable solder by which pieces of
to corrosion
the metal
may be
vented
use in the dental laboratory.
its
securely united has also largely pre-
Experiments in casting the metal for dental purposes
have not been entirely successful on account of the
amount of contraction which takes j^lace on cooling and the somewhat high temperature required to
" At the present time the use of
melt the metal.
large
aluminium
is
rarely attempted except as a base in con-
nection with rubber or celluloid, the latter substances
being employed as a means of attaching the teeth."*
When combined
with copper
it
forms an alloy which has
been used to a limited extent in Germany as a base for
artificial dentures. (8ee p. 248.)
Impression traj'^s and
now made of aluminium.
Plate for Dentures. When alu-
other dental appliances are
Aluminium
minium
is
—
used for the construction of
an
denture the method most frequently a,dopted
artificial
is
to
swage
a plate of the metal in the ordinary way.
During the swaging the metal becomes
*
Ricluirdsdirs " Meclianiciil
Ueiitisti\\',''
1S94
I'd.
rigid
|i.
120.
and
DENTAL METALLUEGY.
246
hard, but
it
may be
softened by heating. to dull redness
and cooling quickly by dipping into cold water. Thin
slieets may be softened by putting into boiling water
and letting them cool with the water. After swaging
.
the plate the teeth are attached with rubber or celluloid
in a
manner
a gold plate
similar to that sometimes emplo3fed
is
used.
forated with a
Por
number
this
purpose the plate
is
per-
of countersunk holes along the
part covering the top of the alveolar ridge.
to Essig * " sets of teeth
known
when
made
in this
According
way have been
to do good service for eight or nine years, but
they showed unmistakable evidence of the action of the
oral fluids."
Casting
Aluminium
application of
aluminium
several difficulties are
very
met
for
to
Dentures.
the
the cheoplastic process
aluminium contracts
witb, as
much on solidification and
— In
requires a high tempera-
it.
For casting in closed moulds the best
have been obtained by the application of a slight
ture to melt
results
pressure to the
artificial
still
liquid metal in the
mould
immediately after pouring.
The addition
of a little copper to
aluminium causes a
decrease in the contraction and renders
it less liable
to
corrode in the mouth, but the presence of copper increases the hardness of the aluminium.
Essig
that " aluminium
t states
may
be cast upon
plain teeth with comparative safety, provided the metal
is
prevented from overlapping the necks of the teeth.
But when gum teeth
are employed, either singly or in
sections, their fracture is almost certain to follow the
contraction incident to the cooling of the metal."
*
.
Essif;-,
"
Dental MetiiUurgy,"
f Ihid. p. 252.
3r(l ed. p.
253.
ALUMINIUM.
Solders for Aluminium.
247
—The
difficulty of sol-
dering aluminium has prevented a more extensive appliIt
cation of the metal for dental and other purposes.
obtain a clean, bright surface owing to the
is difficult to
rapid formation of a very thin film of oxide which
cainnot be
removed by the ordinary fluxes used
in solder-
ing operations, such as borax, &c., as these are liable to
attack the surface of the metal and prevent union taking
place.
It has also a very high conductivity for heat and
A
thus chills quickly at the joint.
large
number
of
aluminium have been patented within recent
yea.rs, but comparatively few have given satisfaction.
Two solders containing aluminium are recommended
solders for
by Schlosser* as being specially suitable
dental
laboratory on
use in the
for
account of their resistance to
chemical action.
Platimm-Aluminium
Gold
.
Platinum
Silver
.
.
.
.
.
Aluminium
.
Gold
Copper
'
i
.20
.
Aluminium
Solder.
|
30 parts
.
dolil
Solder.
100
Silver
..
.
.
...
AluminiTin:
,
.
Another solder consists of zinc 22.5
50 parts
.10
.
.
.
.
parts,
10
20
„
aluminium
With regard to these solders
Richardson remarks f that "none of them are suitable
copper
1.5 parts,
i
part.
for attaching artificial teeth."
Two
pieces of
aluminium may
also
be united with
ordinary solder, with silver chloride as a flux, by means
of which a film of metallic silver is deposited on the
silver chloride is
The
powdered fused
spread along the lines of contact and
surface of the aluminium.
finely
the soldering completed in the usual
Das Lothen,"
|-
•'
way with the blow-
p. 103.
Mechanical Dentistry," 7M1 cd. 1898,
p. 109.
DENTAL METALLURGY.
2^8
pipe or otlier device.
The uuiou thus obtained
is said
to be perfectly strong and reliable.*
Aluminium Bronze.—This is an alloy of copper
with aluminium, and usually contains lo per cent, of
the latter metal.
—
Preparation. Aluminium bronze is prepared by
simply melting the constituents in a crucible or by first
melting the copper and then adding the aluminium.
The union
heat,
white heat
attended by a considerable evolution of
is
which
raises the
it is
;
temperature of the whole
to a
therefore necessary to use crucibles of
good quality when preparing the alloy. The alloy is
brittle when first prepared, but when re-melted two or
three times the brittleness
point of aluminium bronze
silver,
is
is
The meltintrnearly the same as that of
removed.
being about 950' 0, (1742° F.). It shrinks on
about twice as much as brass.
solidification
Pkopkrties.
that of gold
:
—It has a
fine yellow colour
scarcely tarnished
it is
sulphuretted hydrogen.
or
It
by exposure
The
alloy
is
to air
the action
resists
chemical agents to a large extent and
a high polish.
resembling
is
of
susceptible of
malleable at the ordinary
temperatures, but far more so at a red heat. It becomes
very hard and
when worked and
stiff
requires frequent
done by heating the alloy at a
hright-ml heat for sometime, then cooling to redness
and plunging it into cold water to temper it. Alumi-
annealing.
This
is
nium bronze may be swaged
but
it
requires fi'equeut annealing during the process.
When the
is
as readily as 20-carat gold
alloy is placed in dilute nitric acid the copper
dissolved from the surface, leaving the aluminium,
thus changing the colour of the alloy on the surface.
*
Chemiciil yeicx,
iv. Si.
:
:
ALUMTNTUM.
Aiumiuium bronze
Crermany as a base
used
is
to
i8-carat gold.
on the
alloy, it
extent
limited
a
in
for artificial dentures, as it is strong,
and capable of resisting
hard,
249
as
as well
attrition
As chemical agents do not readily act
is only slowly discoloured by exposure
month.
in the
Aluminium Bronze.— Eighteen-
Solders for
carat or fourteen-carat gold solder with the addition of
a little copper is sometimes used as a solder for alumi-
nium bronze, the union of the pieces being effected
without difficulty. The following alloys are recommended * as effective and convenient solders for o per
i
cent,
aluminium bronze
Nh.
Xo. U.
IJavd SoUlev.
r.
Mf<}inm linn]
2T.s-ciivat.
(jold
Silver
....
....
Copppr
.
.
Ciold
SS.88
.
....
.
.
4-68
Silver
6.44
Copper
.
Xo.
Copper
Till
.
.
.
.
II f.
5440
.
.
27.00
18.60
.
.
100.00
100.00
.
Sniilcr.
i3-c.ai-iit.
Snfl Solilcr.
yolwrcent.
y
30
....
_
J
Gold
.
.
Silver
.
.
Copper
.
.
14-30
.
.57-10
14-30
.
100.00
Alloys of Aluminium.
— Dr. Carroll has used
casting
following
n alnmiiiinm alloys for
tures
9°
Aluniiiiiniu
Silver
5
Copper
o
* liichards,
'^Aluminium," 3rd
artificial
93
I'i"'''^
••
9
"
,.
1
,.
ed. p. 569.
th(
den
DENTAL METALLUEGY.
These alloys when cast under slight pressure
give
good castings, are very white, and easy to work.
The
addition of the copper
mum
is said to decrease to a minithe shriukage of the alloys and also to give
a
closer grain.
CHAPTEE
XXI.
NICKEL.
SYMBOL.
Occurrence.
ATOMIC WEIGHT,
Ni.
—Nickel
59.
occurs chiefly in combination
with arsenic and sulphur, and
its
ores almost invariably
contain small quantities of cobalt.
Preparation. Nickel is extracted from
—
first
concentrating
arsenic or
the metal
in
its
ores
by
combination with
The product
sulphur in blast furnaces.
then roasted to expel the arsenic or sulphur,
and the nickel oxide thus formed reduced to the
metallic state with carbon at a high temperature.
obtained
is
Properties.
—Nickel
a lustrous metal, approach-
is
almost to a silver whiteness in colour, but possessing
It is very hard and takes a fine
a slight yellow tinge.
It does not readily tarnish by exposure to the
polish.
atmosphere at ordinary temperatures, but when heated
in o-
in air
to
it is
The metal
slowly oxidised.
any appreciable extent
retted hydrogen.
Water
is
not tarnished
in the presence of
sulphu-
without action on the metal,
is
only slowly soluble in hydrochloric acid or
dilute sulphuric acid or even in concentrated sulphuric
and
acid.
it
is
On
the other hand,
nitric acid or in
aqua
it
regia.
dissolves readily in dilute
The metal
by alkaline solutions or vegetable
acids.
is
not attacked
-52
DENTAL METALLURGY.
It is very malleable
and
and may be
ductile,
rolled out into thin plate or
drawn
very tenacious, in which quality
into wire;
easily
it is
also
only exceeded by
steel. It is magnetic like
iron, but possesses this quality
to a much smaller degree, and
loses its magnetism by
heating to 250^ C. (481^ F.), recovering
the quality
again, however,
temperature
it
is
upon cooling.
to
fuse
it,
being 1600' C. (29 1 ^
2
It requires a very high
the melting-point of nickel
F.),
and
it
may be welded
at a red
heat.
Use
the Dental Laboratory.— Oast and
sheet nickel muffles are now extensively
employed for
dental furnace work the metal appears
in
to
;
first
have been
introduced for this ])urpose in 1886.
Alloys of Nickel.—The
chief alloys of nickel are
those in combination with copper and zinc in
varying
proportions, producing a series of alloys of much
value,
and
to denote
which different manufacturers employ
fanciful names.
German Silver, or nickel silver, consists of nickel,
copper, and zinc in proportions varying with the
uses
to
which
applied, the best qualities containing a
larger proportion of nickel than the inferior qualities.
German
it
is
silver, as
made by good makers,
of one part of nickel,
one part of
consists usually
zinc,
with two or
three parts of copper.
Prepakation.— Various
methods are
pursued for
the manufacture of
German silver, but that generally
adopted at the present time consists in first alloying the
zinc with one-half of the copper, the brass so formed
lieing cast
into thin plates, so that
it can be easily
broken up, while the nickel is melted with the remaining portion of the copper in another crucible, to
NICKEL.
which, after thorough mixing, the brass is added in
small pieces nntil the necessary composition has been
high temperature required for
the fusion of the nickel and the low melting-point and
oxidisabie nature of zinc, the preparation of this alloy
Owing
obtained.
to the
attended with a considerable loss of zinc
care is accordingly required in its production.
is
re-melting the alloy
zinc to
add
it is
When
loss,
and
it is
advisable to
zinc after the' fusion of the alloy has been
On
effected.
amounts
special
necessary to add a portion of
compensate for the
this
;
account of this oxidation the relative
of the constituents are altered
:
it is
therefore
In
difficult to obtain an alloy of definite composition.
all cases a layer of charcoal should be placed on the
surface to prevent oxidation as far as possible.
Properties. ^German silver is greyer in colour and
—
harder than
ductile,
the
and
is
capable of receiving a high
and
and works well under the hammer or between
It
polish.
silver,
is
also
tough,
tenacious,
malleable,
rolls.
and requires careful
annealing before rolling or hammering, but after the
crystalline character has been thus overcome the alloy
It is
crystalline
after casting
be rolled and hammered into a variety of shapes.
Sound castings are secured by the use of borax, glass,
may
or other good flux.
German
When
exposed to the atmosphere
silver acquires a yellow tint
due
to the presence
of sulphuretted hydrogen, and in acid solutions, such as
vinegar, with access of air, it becomes gradually coated
with
a
layer of green verdigiis.
oxidised
when heated
in air,
and
It is
superficially
at a bright red heat
the alloy fuses, a pro])ortion of the zinc burning away.
The
alloy
is
readily soluble in nitric acid.
Impression
DENTAL METALLURGY.
254
trays, matrices,
and a number of other dental aiDpliances
made of German silver.
Nickel and Iron.— These metals unite when
are
melted together to form a series of alloys which are
very
hard and tenacious and little affected by the atmosphere.
The
alloys
more
are
than ordinary steel when
melted, set more rapidly, and can be readily hammered
and rolled. Nickel steels are extensively used for
fluid
armour-plates.
Nickel Plating.—This
articles of iron, copper,
the process by which
and other metals are coated
is
with metallic nickel by means of an electric current in
a manner similar to gold and silver plating.
The
solution usually employed
of nickel
is
the double sulphate
and ammonia.
It is of great
importance that the
articles to be coated
should be absolutely clean and that any existing film of
nickel should be entirely removed, the cleaning of the
article being even more important in nickeling than in
silvering or
Small
gilding.
articles
are
frequently
cleaned by rubbing with fine emery cloth, but a chemical
method is more often employed, which consists in
dipping the articles for a brief period into an acid bath.
On account of its extreme hardness the nickel deposit
cannot be burnished like deposits of gold and
is
before immersing in the plating solution.
ing every
in
a
trace
solution
rinsing
in
a
of
water,
plating bath
of
silver
:
it
essential, therefore, that the articles be well polished
suitable
of
grease
potash
the
;
is
removed by
then,
article
After polish-
ia
after
a
dipping
thorough
transferred to
the
and connected with the negative pole
battery, a plate of pure nickel
connected with the positive pole.
being
Generally speaking.
NICKEL.
to four hours
from half an hour
will
suffice
for the
deposition.
When
the thickness of coating
is
sufficient the article
removed from the solution and thoroughly washed in
water, dried in hot sawdust or a small stove and then
is
finally
Articles of
polished.
cast
iron
are
usually
covered with a film of copper before being suspended in
the plating solution.
Nickel-plating
articles of all
the metal
is
is
now
largely
employed
for coating
kinds on account of the brilliant polish
capable of taking and
its non-liability to
tarnish under ordinary atmospheric conditions.
A
thin coating will also resist the wear and tear of
hard use owing to the hardness of deposited nickel.
PART
II.
EXPERIMENTS RELATING TO THE PHYSICAL
AND CHEMICAL PROPERTIES OP METALS
AND ALLOYS.
Ix order that the student
may
acquire a more practical
knowledge of the properties of the various metals given
in Part L, the following simple experiments hcwe been
which may be readily conducted in a
moderately well equipped dental laboratory. In addiarranged,
all
of
tion to the following experiments,
it
would be well
for
students to perform also the various experiments mentioned in the text of Part
I.
The
quantities of metal
necessary for the various experiments are given in
grammes,
as the metric
ployed for
iisually sold
all
system
now
is
experimental work
;
universall}^
em-
but as the weights
with scales for dental purposes are Troy, the
((uantities are also given in grains for convenience.
In
most cases larger quantities of material may be taken
with advantage, but with due care satisfactory^ results
can be obtained with the <[ uantities given.
The experiments
may be j)er~
anvil when a
relating to malleability
formed with a hammer and bright
rolling-mill is not available.
steel
—
;
GOLD.
,
Material Required.
GOLD.
— About
5
grams, (or 75 grains)
of 22-carat or other carat gold.
Experiment
i.
— Dissolve the gold alloy in aqua regia
;
evaporate nearly to dryness to expel excess of acid
add a solution of
dilute with about a pint of water;
iron sulphate
and gently
precipitated as a fine
filter
paper,
heat,
when the gold
brown powder.*
will
be
Filter through a
wash the precipitated gold repeatedly
witli
and warm till perfectly dry. Carefully rub a
brown powder with some hard smooth
surface, such as a steel or agate burnisher, and note
that the characteristic yellow colour and metallic lustre
water,
of the
little
of gold appear.
of the
powder
Reserve about
.5
gram, (or
5
grains)
Experiment 14. Transfer the rea suitable support and melt into a globule
for
mainder to
by means of the blowpipe, heating gently at first to
avoid loss.
Note that it requires a bright red heat to
fuse
it.
suspending
fine silk,
—
Determine the density of the gold by
from the arm of a balance by means of
and accurately weighing it in air. Then place
E.C2)erimcnt 2.
it
a small vessel of water in such a ]30sition that the gold
completely immersed while still suspended, carefully
remove air bubbles by means of a camel's-hair brush,
and then note the weight in water.
The gold will appear lighter than before, the loss in
is
weight being exactly equal to the weight of an equal
volume of the water.
Calculate the specific gravity of the gold as follows:
*
\\\y of
till)
n;iif;oiits
procipitiiting tho gold.
muiilioiiud uii luigu 96
iiiiiy
bo used fur
DENTAL METALLUEGY.
Weight
ill
air
between weight in
and weight in water
-Difterence
3.— Strongly
J^xperiment
aii-
_
"
^'^^^
heat the globule of
" fine "
gold before the blowpipe for a few minutes and observe
that no oxidation takes place, the surface remaining
perfectly bright
there
;
allow to cool in
air,
and notice that
no alteration of the surface due to the liberation
of oxygen, as in the case of silver when similarly
is
treated.
(See
Uxperivicnt
its softness.
p. 168.)
4.— Cut the gold
Eoll or hammer
with a knife to ascertain
it out into a strip, and
great malleability, the edges remaining perfectly smooth.
Note that mechanical treatment tends
prove
to
its
make
it
ness, allow
hard and " springy."
it
Heat the strip to redto cool, and observe that it is soft and
pliant after thus
JExpcj-iiiteut 5.
annealing."
— Cut
off
two small pieces of
one on top of the other on an
anvil,
gold, place
strike with
a
hammer and notice that the two pieces weld. They
may also be welded by passing between the rolls.
Kiperivient 6.
— Place
the strip of gold in dilute
sulphuretted hydrogen water and observe that no discoloration takes place, proving that gold has no affiuity
under these conditions.
Uxperiment 7. Melt i gram, (or 10 grains) of gold in
for sulphur
—
a small crucil^le with the addition of .005 gram. (-Vth
of a grain) of lead, and roll or hammer out as before.
now
Notice that the edges
small
crack,
showing that
amount of lead has rendered the gold
lias also altered
Experiment
brittle
this
;
it
the colour.
—Melt
gram, (or 10 grains) of gold as
beforo. with the addition of antimony instead of lead,
8.
i
.
GOLD.
259
and in the same proportion. Observe that the same
effect is produced as with lead.
Uxpcrimcnt 9. Re-melt the gold from Experiments
7 and 8 in a small crucible, and when fusion has taken
place cautiously add a few crystals of nitre (potassium
—
nitrate).
solidifj-,
Pour the gold into a suitable mould, or let it
and then break the crucible. Roll or hammer
out and note that
Experiment
it is
10.
now
malleable after being refined.
— Dissolve
.5
gram, (or
5
grains) of
pure gold in aqua regia as before and dilute to about a
Reserve a small portion of the solution
pint.
Experiment 1 1
Heat the solution
oxalic
acid
" spongy "
bottom.
to
slightly,
precipitate
for
then add a solution of
the gold and observe the
mass which settles at the
wash with water, then diy
nature of the
Filter off the gold,
and examine with a lens. Notice that the spongy mass
is made up of minute crystals.
Beautiful spangles of metallic gold are obtained by
The
using a more 'dilute solution of gold.
may
precipitate
not appear until the solution has been standing for
a short time.
Experiment
11.
tion prepared for
—Take
a small quantity of the solu-
Experiment 10 and further
dilute with
water to obtain a very dilute solution of gold.
solution of stannous chloride,
mixed with a
little
Add
a
stannic
chloride, shake well
and notice the purple precipitate
(purple of Cassius).
This forms a very delicate test for
gold.
Experiment
12.
—Melt
.5
gram, (or
'5
grains) of gold
in a crucible or before the blowpipe, with the addition of
two and a half times
its
weight of
silver.
resulting alloy into a thin strip, place
it
Roll out the
in dilute nitric
26o
acid,
DENTAL METALLITEGY.
and heat.
Observe that the silver is dissolved,
leaving the. gold behind as a brown residue.
Pour off
the silver solution, wash and dry the gold thus "parted,"
and then heat to redness. The gold assumes its characteristic yellow colour
—
and
also contracts in volume.
Note.
The silver may be recovered as directed
Experiment i6.
Experiment
—Melt
in
gram, (or 10 grains) of gold
in a crucible with the addition of .2 gram, (or 2 grains)
13.
i
of copper, using a thin layer of charcoal
powder and
also a cover to prevent oxidation.
Allow the resulting
and turn out when cold.
with sand and water and notice that the
alloy to solidify in the crucible
Clean the alloy
colour of the gold
and prove
is
deepened.
malleability
its
Roll out into a strip,
and hardness
as
compared
Anneal it at a red heat and notice the
discoloration which takes place owing to the oxidation
with pure gold.
of the copper jiresent.
Plunge the
strip while still Lot
into dilute nitric or sulphuric acid, and observe the
" colouring " which takes place owing to the dissolving
of the copper on the surface.
Experiment
— Place
14.
about
.5
gram, (or
5
grains)
of finely divided gold (Experiment i) in a clean glass
add a few drops of mercury, warm gently
and shake for a few seconds, closing the top of the tube
with the finger. Notice that amalgamation takes place
readily.
Squeeze the resulting amalgam in chamois
test-tube,
leather with a pair of pliers and observe the nature of
the amalgam
left.
Allow
it
to rest for
some days and
note the "hardness."
Experiment
15.
— Heat the amalgam in a small porce-
mercury is expelled. Notetbe
character of the residue and weigh.
lain crucible until all the
261
SILVER.
This experiment sliould be perfox-med iu connection
with a suitable tliie for carrying off the mercury fumes,
as these are poisonous if inhaled.
SILVER.
Material Required.
— About 10 grams, (or 200 grains)
of standard silver or silver scrap.
— Dissolve
the silver in dilute nitric
acid in a glass beaker of about one pint capacity, then
add distilled water until three parts full heat nearly to
Experiment
16.
;
boiling
and carefully add a strong solution
salt to precipitate
common
of
Stir briskly
the silver as chloride.
with a glass rod for a few minutes, allow the precipitate
to settle, then carefully pour off the clear supernatant
add hot water to the precipitate, stir, allow to
again decant the clear liquid, and repeat this
settle
operation three or four times in order to remove all the
liquid
;
;
copper solution.
Wash
the precipitate into a basin,
sodium carbonate, well mix,
transfer to an earthenware crucible, and fuse at a good
red heat for about twenty minutes then pour into an
ingot mould, cool, and detach the slag, the last portions
of which may be removed by dissolving in hot water.
dry, add twice the bulk of
;
The heat should not be
the charge
raised too suddenly, otherwise
may boil over owing
to the rapid escape of
carbonic acid.
Experiment
17.
—Melt the
silver
on a cupel or suitable
support by means of the blowpipe flame, and keep in
the molten condition for a few minutes.
it
requires less heat to fuse
metal does not tarnish
in
it
Observe that
than gold, and that the
contact with the
the silver to cool quickly iu contact with
air.
air,
Allow
when the
262
DENTAL METALLURGY.
oxygeu, which has been mechanically absorbed
by the
molten metal, is disengaged on the metal
solidifying,
causing a number of small excrescences on
the surface.
This action is called " spitting."
Experiment 1 8.— Re-melt 2 grams, (or 20 grains) of
the silver with the addition of one-fifth of its weight
of
copper, cool in air as before, and notice that the
presence
of copper prevents " spitting."
Erpcriment ip.^Melt the remainder of the
with sufiicient
silver
common
salt to cover the metal, so that
the metal cools under a layer of salt, to prevent absorption of oxygen, and notice the smooth surface.
Eaypcriment 20.
— Determine the density of the
as directed for gold in
Experiment
2,
silver,
after carefully
removing the salt adhering to the metal.
Experiment 21.— Roll the silver into a thin strip,
noting its malleability and elasticity heat to redness,
allow to cool, and note that it is now pliant and " soft";
;
cut with a knife to ascertain
its
"hardness."
22.— Place
Experiment
the strip of silver in dilute
sulphuretted hydrogen water, and observe that it readily
blackens owing to the formation of a film of silver
sulphide.
Experiment 23.
—Melt
the silver in a crucible under
a layer of charcoal powder,
fifth
of
When
and when molten add oneweight of platinum in the form of foil.
thoroughly melted, pour out and roll the alloy
its
into a strip
observe its hardness and toughness compared with pure silver anneal at a red heat and note
the effect by bending.
;
;
Ex23erimcnt
24.— Place
and cover with dilute
num
is
left
the strip in a glass beaker
nitric acid.
Observe that
plati-
undissolved as a black residue, while the
263
SILVER.
silver (with a small
quantity of platinum)
is
dissolved.
water,
Pour o£E the solution, wash the residue with hot
burnisher
dry and heat to redness when cold rub with a
and notice the bright metallic surface of platinum.
ExperiExperiment 25.— KoU the button from
and
ment 18, observing that it is malleable, tough,
and
than pure silver. Heat the strip to redness
;
harder
notice that discoloration takes place
owing to the pre-
Ee-heat the strip and plunge while hot
Notice the "frosted"
sulphuric acid.
sence of copper.
into
dilute
" in acid, and
appearance produced by thus " pickling
lustre is restored
also observe that the bright metallic
by burnishing.
Experiment 26.— Dissolve
i
gram, (or
1
5
to 20 grains)
about oneof pure silver in dilute nitric acid, dilute to
a strip of
third of a pint with hot distilled water, place
crystalline
copper in the solution and observe the grey
precipitation
precipitate of silver produced. Allow the
on for about half an hour, remove the copper,
allow the
carefully wash off all silver adhering to it,
and
precipitate to settle, pour off the copper solution,
with hot
then wash the precipitate two or three times
to go
water.
dry,
Eemove
small portion
a
and examine with a
lens.
the precipitate,
of
Notice
its crystallised
character.
Experiment 27.— Place the precipitated silver in a
takes
mortar, add mercury, and rub until amalgamation
place.
Remove
excess
product in a piece of
character of the
soft
mercury by pressing the
chamois leather; observe the
of
amalgam
left
behind.
Reserve
the remainder
a portion for Experiment 28, and allow
harden, then break and examine with a lens, noting
to
its crystalline stfite
and
brittleness,
264
DENTAL METALLURGY.
Experiment
28.-Carefully pack a small quantity of
the amalgam into a small
glass tube until full, level the
surface, and allow to rest
until hard. Ascertain whether
expansion or contraction has taken
place by examining
carefully with a lens.
(See p. 149.)
Experiment 29.—Heat a small portion of the amalgam
in a porcelain crucible (in a suitable
draught) and expel
the mercury.
Examine the product left behind and
note
^
its
character.
Experiment 30.— Dissolve
Sliver in dilute nitric acid,
Heating,
with
dilute
.5
gram, (or
5
remove excess
grains) of
of acid
by
hot
water; then pour a small
quantity of mercury into the vessel containiug
the
and allow it to stand undisturbed for
Observe the crystallised amalgam or
which is formed.
silver solution,
several hours.
'•'silver tree "
MERCURY.
Material lieqidred.
— 20 grams, (or 300 grains)
of pure
mercuiy.
Experiment
—Take a small
31.
quantity of mercury
:
observe that
it
has a silvery-white colour and bright
lustre;
it
is
that
.
and that it is liquid at
Pour a few globules of mercury
tasteless
ordinary temperatures.
;
on to a clean sheet of glass, notice that the globules
and leave no "tail," and that the sur-
are spherical
face of the glass
liquids.
not " wetted," as with ordinary
Heat a very small quantity of mercur}^, preis
ferably in a muffle, and observe that
volatilised.
No
oxidation
takes
it is
place
at
completely
the
ordi-
nary temperature, or on gently heating, but at the
boiling-point of mercury (350° C.) the metal begins
to oxidise.
MERCURY,
mercury into dilute
hydrogen water, and observe that no
Expe^'iment 32.
sulphuretted
— Pour
265
a little
discoloration takes place.
Experiment
— Place about 4
33.
mercury in a mortar, add a
of
grains, (or
little
50 grains)
lead and either tin
or zinc, but not sufficient to destro}^ the liquidity of the
mercury, and rub until amalgamation takes place. Then
cause the globule of impure mercury thus obtained to
roll
down
a slightly inclined surface.
Observe that the
mercuiy does not maintain the spherical shape, as
in
the case of pure mercury, but that the globule elongates,
carrying a
with
tail
Place the globule in a small
it.
glass tube, shake well,
and
obsei've the thin film of
oxide which forms on the surface, impairing the lustre
of the mercury.
Experivient 34.
— Introduce a small
quantity of mer-
cury into a long glass tube closed at one end.
until the metal
Heat
has volatilised, and observe that the
mercury is condensed at the cold end of the tube in
the form of very minute globules, which adhere to the
surface of the glass, thus proving that mercury
may
be.
readily distilled.
—
Experiment 35. Pour a little mercury into a mortar,
add flower of sulphur and well mix, when black mercury
suljihide will be formed.
Transfer this to a small porce-
lain crucible, cover with a close-fitting lid, heat gently
for
some time; allow
to cool,
and observe the small
red crystals of vermilion.
Place a
when
little
of the sulphide in a glass tube
and heat,
the vermilion will be completely volatilised with-
out leaving any residue.
vermilion add a
little
To another portion
red lead or oxide of iron, heat in
a tube as before, and notice that the impurity
a residue.
of the
is
left as
266
DENTAL METALLUEGY.
PLATINUM.
—
Material Required. About
5 grams, (or 100 grains)
of platinum plate or wire.
Experiment
— Determine the density
36.
of the metal,
as directed in
Experiment 2. Observe that it is heavier
than any of the other metals in common use.
Experiment 37. Roll a piece of platinum to ascertain
—
its
malleability
and
" stiffness."
Heat
it
strongly in the
blowpipe flame for five to ten minutes allow to cool
and observe that annealing has made it soft and
;
flexible.
Experiment 38.— Heat a strip of platinum at a bright
red heat for some minutes, then cool in the air. Notice
that the surface remains b?ight, no oxidation taking
place.
Experiment 39.
sulphuretted
untarnished,
—Place
hj^dz'Ogen
as
a clean strip of platinum in
water.
has
it
The
metal
no
practically
remains
affinity
for
sulphur.
Experiment 40.
suitable support
possible
—Place a small piece
and heat
temperature
for
of platinum on a
some time
attainable with
to the highest
the
blowpipe.
Observe that the metal does not melt or even show
signs of fusion at the sharp edges.
—
Experiment 41. Take two small pieces of platinum
with clean surfaces place one on the toj) of the other,
:
and heat to a white heat for five minutes, then squeeze
quickly and hard with a pair of pliers. Notice that
the pieces have welded and cannot be readily separated.
Experiment 42.
— Heat a piece
of clean platinum to a
white heat, and while at this temperature place a small
PLATINUM.
upon
piece of pure gold
it.
267
Observe that the union of
the metals takes place at once.
Experiment 43.
—Repeat
A
instead of gold.
Experiment
similar result
cold place the strip of platinum
and
is
42, using lead
When
obtained.
thus treated in the vice
hammer. Notice that the presence
lead makes platinum brittle.
strike with a
of very little
—
Experiment 44. Dissolve i gram, (or 1 5 grains) of
platinum in aqua regia cautiously evaporate nearly to
dryness re-dissolve the residue in a small quantity of
;
;
water
;
divide the solution into
one portion
for
of a solution of
Experiment 45
ammonium
;
two portions reserve
to the other add excess
;
chloride (sal-ammoniac), then
about an equal bulk of alcohol allow to stand in a
warm place for a few hours until all the platinum is
wash the yellow precipitate with
Filter
precipitated.
;
;
alcohol;
dry and ignite,
metallic platinum
is
left
A
grey spongy mass
behind (see
the sponge to a white heat for
place on a bright anvil and
five
p. 187).
of
Heat
minutes, quickly
hammer
mass, which will have the appearance
into a
compact
and metallic
lustre of platinum.
Experiment 45.
— Further dilute the solution
of i)]ati-
from Experiment 44 with a
small quantity of hot water, add a few drops of hydro-
num
chloride reserved
chloric acid, place a clean strip of zinc in the solution,
go on until the liquid is colourRemove the zinc, wash off any adhering pre-
and allow the action
less.
to
spongy
and then
cipitate of metallic platinum, allow the black
precipitate to settle, pour ofE the clear liquid,
wash the residual platinum first with a little hydroPlace the
chloric acid, and then with hot water.
platinum in a heated mortar, and add a little mercury
2
05
DENTAL METALLURGY.
and rub well for some time. Amalgamation is readily
effected by continual mixing, producing a
more or less
unctuous mass. The amalgam may also be obtained
by using finely divided platinum, such as that produced
by heating the precipitate of double chloride of am-
monia and platinum, as described in Experiment
44.
After removing excess of mercury by squeezing in
ch amois leather, allow the amalgam to stand for some
days, and note that it hardens very imperfectly.
TIN.
Material Required.
pure
— 150
grams,
2500 grains)
(or
of
tin.
Ex2Jeriinent 46.
— Melt 50
grams, (or 1000 grains) of
tin in a small crucible or ladle,
and notice that
it
melts
at a very low temperature, the melting-point of
tin
being lower than that of any of the other metals in
common use. Allow the tin to cool and cast into a flat
open mould at as low a temperature as possible (i.e.,
just before solidification takes place).
dross from getting into the
placed across the
lip
mould a
To prevent any
stick should be
of the crucible
when pouring.
Allow the
tin to cool without disturbance, and observe
the clear, white, and bright surface of the metal when
cold.
If the tin is too hot when cast the surface will
be discoloured owing to oxidation.
Commercial tin often contains small portions of other
metals, and when impurities are j)resent they impart to
the tin a more or less dull and frosted appearance.
Hold the ingot
close to the ear
peculiar crackling sound,
will
be heard.
known
and bend
as the
it,
"cry"
when
a
of tin,
269
TIN.
Kvjm'iriicnt 47.
by weighing in
ment
air
density of the metal
and in water as directed in Experi-
Notice that the specific gravity of tin
2.
hio;her
—Ascertain the
than that of
Experiment 48.
is
slightly
zinc.
— Cut the
metal with a knife, noting
Test the malleability of pure tin by
Cut a strip of sheet tin about one-eighth of
rolling.
an inch wide, fix one end firmly in a vice, hold the
other end securely in the pliers, and observe that little
softness.
its
force
is
required to produce rupture, the tenacity of tin
being very low.
—
Experiment 49. Melt 50 grams, (or lOOO grains) of
cool and then fracture
tin, cast into an ingot mould
by placing in a vice and bending backwards and
forwards with a hammer. Notice the toughness of
;
the metal.
Ee-melt,
cast
into a
warm mould, then
Notice
remove quickly when solidified and break.
readily.
that the metal is more or less brittle and fractures
Experiment 50. Melt 50 grams, (or lOOO grains) of
—
tin,
and
raise to a red heat
;
the surface of the metal
be speedily covered with a layer of oxide. Allow
the metal to cool somewhat, then cast into a warm iron
mortar and pound with the pestle as soon as solidificawill
Observe that the metal is readily
powdered, tin being brittle at a temperature near its
tion takes place.
melting-point.
Experiment
sheet
tin,
through
51.
—Take
place one
the
rolls
two perfectly clean
on top of the other,
or strike several blows
strips of
and pass
with
a
hammer. Observe that the two pieces become welded.
The strips should be scraped with a knife to clean
them, as any dirt or film of oxide on the surface tends
to prevent union taking place.
270
DENTAL METALLURGY.
Experiment 52.— Place a clean strip of tin
in
sulphuretted hydrogen water, and notice that no
black
film is formed, as in the case
of silver when thus
treated.
ExpcHvunt 53.— Put about
of tin in a glass beaker,
and warm.
The
gram, (or 10 grains)
.5
add a little dilute nitric acid,
upon with the formation of
tin is acted
a white residue (metastannic acid).
Experiment 54._Melt 2 grams, (or 20 grains) of
with a little charcoal powder to prevent oxidation,
\t
tin
add
20 grains) of lead, then
4 grams, (or
40 grains) of bismuth stir and then cast the resultingf
alloy into a mould, and note its brittleness.
Place the
2
grams, (or
;
alloy in boiling water, observing that
it melts readily.
Determine the melting-point
p. 52,
^
Part
of the alloy as directed
on
I.
Experiment 55._Melt 6 grams, (or 60 grains) of
add 4 grams, (or 40 grains) of tin, using a layer
silver,
of charcoal to prevent oxidation.
Clean the surface of
the resulting alloy with emery, then heat it and
observe
that it is easily oxidised.
Out with a knife or file
it to determine the hardness;
place in a vice and
fracture, noting its brittleness. Eepeat the
experiment,
using 6 grams, (or 60 grains) of tin and
4 grams, (or
40 grains) of
silver.
Note the
characteristics of the
alloy as before.
Exjjerimeut
by placing
56.— Test
the affinity of tin for mercury
tin foil in a
mortar and adding mercury.
Observe that amalgamation is speedily effected. Mix
well with the pestle, place in chamois leather, and
remove excess of mercury by squeezing.
portion of the plastic
amalgam
for
Eeserve a
Experiment
57,
and
allow the remainder to stand for a few days until
it
271
ZINC.
colour, fracture with a
Note its white
hardens.
aad observe
hammer,
its brittleness.
Experiment 57.— Pack the plastic amalgam into a
glass tube, as directed in Experiment 28, and note
whether expansion or contraction takes place.
Expcrimeni
58.
—Take
pared in Experiment
55
;
filings of
each of the alloys pre-
add a little mei'cury to each, and
observe that amalgamation takes place with less facility
in the case of the alloy containing excess of silver.
zmc.
Material Beci'mred.
— 100
grams, (or
1
500 grains) of
zinc.
Eo:pcrimcnt 59.
—Melt 50
grams, (or
1000 grains) of
zinc, cast into
an ingot mould (similar to that described
on
I.) to
Part
obtain a
Observe that
zinc requires a slightly higher temperature to melt it
p. 76,
than lead.
flat
ingot.
Place the ingot in a vice and strike with a
hammer, when the metal will break off short, thus
showing its brittleness at the ordinary temperature,
and its crystalline structure. Cut the metal with a
knife, and ascertain its hardness.
Take one-half of
the ingot, heat to about 150 C, place it on the anvil
and hammer, observing that it is now malleable. Heat
again if necessary, and roll into a thin sheet. The
ingot
may
require annealing once or twice during the
operation by heating to about
50 C.
Heat the other
200°
half of the ingot to a temperature of
to 300° C,
i
'
and prove the brittleness of zinc at this temperature by
hammering or powdering in an iron mortar.
Experiment 60.
—Melt
10 gx'ams. (or 200 grains) of
zinc in an open crucible with free access of air
;
observe
^72
DENTAL METALLURGY.
that the surface of the metal
is readily covered with
a
film of oxide.
Raise the temperature to a bright
red
heat notice that the zinc is
volatile aud burns with a
brilliant bluish-white flame,
forming a very light white
powder, which is zinc oxide.
;
E.pcrimcjit 6x.—V\i,ce the strip of sheet
zinc from
Experiment 59 into dilute sulphuretted
hydrogen
water observe that no discoloration takes
place.
;
Er2m-imcnt
62.— Take
or 500 grains) of zinc
equal parts (abont 30 grams,
aud
lead, melt well together, and
pour into ail upright ingot mould. When
cold remove
from the mould and carefully inspect the
surface of the
a line will be observed where the
two metals
have separated on cooling. Place the
ingot in the
vice, as near as possible at the line
of junction of the
ingot
;
two metals, and
strike with a
break
off short.
Hammer
anvil;
notice
which
hammer, when
it
will
each half separately on the
that the
upper half consists of zinc,
hard, crystalline, and brittle
while the lower
lead, being very malleable and
soft.
is
;
half
is
63.— Place a little mercury in a mortar,
add zinc filings, and rub with tbe pestle until
amalgamation takes place.
Obsei've the character of
Mjj^erimerit
the
amalgam produced
effected.
;
also
Amalgamation
that
union
is facilitated
of water slightly acidulated with a
is
not readily
by the addition
few drops of
acid.
LEAD.
Material Reqaircd.~ioo grams, (or
1
500 grains) of
lead.
Erperimcnt 64.—Melt 50 grams, (or 1000 grains) of
Observe tbat it melts at a
lead in a crucible or ladle.
LEAD.
comparatively low temperatiive and that oxidation takes
Pour into an upright
place when the metal is molten.
ingot mould, remove
when
one end in the
cold, place
backwards and forwards with a hammer
brealcs, thus proving the toughness of the metal.
vice,
bend
until
it
it
Cut with a knife and notice that it is very soft roll
Take two
into a thin sheet and prove its malleability.
pieces of the sheet lead, clean the surfaces by scraping,
place one piece on top of the other and pass through
;
the rolls or
hammer on an
have welded.
Experiment
6'^.
anvil.
Notice that the pieces
— Prepare an ingot
of lead as in
Ex-
periment 64, remove at once from the mould when set,
place the ingot across two iron supports about i finches
apart
;
heat the centre by means of
held in the hand.
melting,
When
a'
shows
the lead
remove the burner
at
Bunsen
flame,
signs
of
once and strike the
centre of the ingot one sharp blow with a hammer,
when the metal will break, showing the brittleness
of
lead
at
this
Examine the
temperature.
verse columnar structure of the
compare
it
broken
with that obtained by fracturing lead
cold.
Experiment 66.
—Melt 50 grams,
trans-
surface
and
when
(or lOOO grains) of
gram, (or 20 grains) of antimony, stir well
and cast into an ingot mould. When cold remove,
Notice that the presence
place in a vice and fracture.
lead,
of
add
i
antimony has made the lead
brittle
;
cut with a knife
and observe that the alloy is much harder than pure lead.
Experiment 67. Determine the density of lead as
described in Experiment 2, observing that it should be
classed with the heavy metals.
—
Ecperimcnl 68.
— Place a clean
strip
of sheet lend in
s
DENTAL METALLURGY.
dilute sulphuretted
metal
is
hydrogen water
cand notice that the
tarnished.
I!xperime7it 69.— Clean a piece of sheet lead, place it
in a vessel with a little vinegar, and allow it to stand.
Observe that the metal
acted upon somewhat readily.
is
COPPER.
Material Required.
— 50
grams, (or 750 grains) of
sheet copper or thick copper wire.
—
Experiment 70. Cut a piece of copper with a knife
and notice its hardness test the malleability of the
metal by rolling or hammering observe that mechanical
;
;
treatment renders
it
hard.
Heat the
redness, observe'that the metal
contact with the
into
cold
;
notice
pliant
after
dilute
sulphuric acid
oxide
is
readily tarnished in
is
Plunge the metal while
air.
water
slip of cojjper to
that
Ee-heat
annealing.
;
the metal
observe
and
that
is
and
soft
plunge
the
hot
still
into
coating
of
removed from the surface by the action of the
acid.
—
Exim-iment 71. Take a small coil of copper wire
and determine the density of the metal as directed in
Experiment 2.
Eayperiment
72.
—Place
dilute sulphuretted
a clean strip of copper in
hydrogen water.
Notice that
coloration of the copper rajoidly takes place
dis-
owing
io
the formation of a film of sulphide.
Clean a piece of copper, place
it
in a vessel with a
few drops of vinegar, and allow it to remain for a day or
two.
Observe that the copper is acted upon, with the
formation of a green coating of " verdigris."
Erpeiiment 73.
— Hold
a piece of copper in contact
COPPER.
with the tongue and notice that
it
possesses a peculiar
faint, nauseous, metallic taste.
grams, (or 50 grains) of copper
on a cupel or charcoal support by means of the blowNotice that the temperature required to fuse it
pipe.
melt gold. Keep in
is a little below that required to
B.q)cnmcnt 74.— Melt
5
the molten condition for some minutes, allow to solidify,
then roll or hammer. Observe that the metal is more
owing to the presence of dissolved copper
The copper is more readily melted in a small
or less brittle
oxide.
crucible in a suitable furnace.
Exfcriment 75.
—Melt 30
grams, (or 500 grains) of
copper in a crucible with the addition of a little charcoal
powder and add i gram, (or 20 grains) of metallic arsenic.
When mixed pour into a suitable mould. EoU or
hammer the resulting alloy and observe that the
presence of the impurity causes brittleness.
—About half
the quantity of arsenic will probably be lost
by volatilisation when conducting the experiment.]
l^Xote.
—
Experiment 76. Melt 30 grams, (or 500 grains) of
copper and add .5 grams, (or 10 grains) of antimony.
Roll or
hammer
antimony
is
as before,
and notice that the
effect of
very similar to that of arsenic.
[JYute— Home of the antilnony will be lost owing to oxidation.]
Experiment 77.
— Place
a
strip
of
bright metallic
copper in a solution of mercuric chloride (corrosive subA silvery white deposit of metallic mercury is
limate).
obtained, which,
metallic lustre.
Experiment 78.
when gently rubbed, shows
— Dissolve
i
a bright
gram, (or 20 grains) of
copper in a small quantity of dilute nitric acid when
all fumes are expelled dilute with water and place a strip
;
of iron plate into tbe solution.
Allow
it
to stand for
DENTAL' METALLURGY.
276
some time
until the copper
the iron, pour
Eemove
precipitated.
is
the solution, wash the spongy copper
off
precipitate well with repeated quantities of cold water,
then transfer to a mortar,
a,dd a little mercury and rub
well with the pestle until amalgamation is complete.
The union may be
by the addition of a little
hot water and a few drops of sulphuric acid, or by adding
facilitated
a solution of mercuric nitrate to the precipitate before
the introduction of the mercury.
Eemove the excess
of mercury, if necessary, by squeezing through chamois
leather,
and allow the resulting plastic amalgam
for about twenty-four hours.
quite hard.
Hammer and
Notice that
observe
jDOund or knead in a mortar until
it
to stand
becomes
it
its malleability,
acquires
its
then
original
Allow to stand for a few hours, and notice that
recovers its hard crystalline character.
Experiment yg. Prepare a small quantity of copper
softness.
it
—
precijjitate
as directed in
.
Experiment
78, allow
stand exposed' to the air for a short time
it
;
it
to
observe that
becomes rapidly coated with a film of oxide and
is
unfit for amalgamation.
CADMIUM.
Material Required,
—40
grams,
(or
500 grains) of
cadmium.
Experiment 80.
crucible
readily
;
observe
oxidised
;
—Melt
its
cadmium
the
mould.
heat to bright redness,
Test
its
— Place
small
it
is
when the
Cast the metal into a
toughness, softness, malle-
and welding properties
Experiment 64.
ability
Ex'im'imcnt 8i.
a
low melting-point and that
metal burns with a brown flame.
suitable
in
as described for lead in
a clean strip of
cadmium
in
bismuth;
sul]ihuretted
hydrogen water.
277
'
Notice that the metal
is
sulphide.
soon covered with a yellow film of cadmium
Mix together in a mortar mercury
Exferiment
and cadmium observe that combination readily takes
82—
;
producing a soft tin-white mass. Allow it to stand
brittle mass
for some time, when it hardens and forms a
which softens when moderately heated and can be
place,
kneaded
like
wax.
BISMUTH.
Experiment 83.— Prove the brittleness of bismuth by.
Heat the metal in a crucible
crushing in a mortar.
a
observe its low melting-point and that it burns with
;
blue flame
when heated
to a high temperature.
the metal into a mould, and notice that
Cast
expands in
it
the act of solidifying.
Experiment 84.— Prepare an amalgam of bismuth by
shaking powdered bismuth with mercury in a tube.
Notice the liquid character of the amalgam obtained.
ANTIMONY.
Experiment 85.— Crush a little antimony in a mortar
Melt the metal,
to prove its extreme brittleness.
notice
noting its melting-point, raise it to a red heat;
burns with a white flame, forming the white oxide.
Experiment 86.— Place a little powdered antimony
and mercury in a glass tube, shake well and observe
that
it
that union does not take place readily even
when heated.
IRON AND STEEL.
Experiment
notice that
it
87.— Take
a
piece
of
soft
bends readily without breaking
iron wire;
;
heat
it
to
2
DENTAL METALLUEGY.
7^
redness and plunge while hot into cold
water
that it still retains its softness and
;
observe
bends readily.
Exim-imcnt 88.— Take a piece of
wn-e)
;
observe that
it is
eteel wire (pianoforte
" stilT" and hard, but
can be
bent;
heat to redness and plunge into cold water;
notice that the wire is now very hard
and brittle and
breaks readily,
Heat another piece
water to harden
of the wire to redness, plunge into
clean the
surface carefully with
emery, heat gently over a Bunsen flame until it acquires
a blue tint, then plunge at once into cold water.
Observe
that the wire has lost its brittleness and can
now be bent
it,
after thus tempering.
Experiment 89.— Heat a piece of soft iron wire at the
temperature attainable with the blowpipe;
observe that it does not melt.
Continue heating for
notice that the metal is oxidised and
5 or 10 minutes
" burnt " and becomes more or less
brittle.
^
highest
;
Ejjjcriment 90.
pieces,
place
— Cut
some hoop
iron
into
small
about
50 grams, (or 500 grains) in a
crucible, raise to a red heat and add small pieces of
sulphur at intervals. When the whole is melted pour
when
into a mould, and
and notice that
it is
bronze-like colour.
cool fracture the iron sulphide
more or less brittle, and has a
(See Spence's "Metal," p. 47.)
hard,
ALUMINIUM.
—
Experiment 91. Take a sheet of aluminium and
determine its density as described in Experiment 2.
Observe that it is the lightest of the common metals.
Melt a small piece of the metal before the blowjMpe
observe that it requires a bright red heat to melt it and
that
it
is
somewhat ''pasty "when molten.
Eoll the
NICKEL.
metal to prove
and toughness, heat
malleability
its
279
redness and drop into cold water, thus proving that
(See p. 246, Part I.)
softened by annealing.
— Place
Experiment 92.
sulphuretted hydrogen water
tion takes place.
Experiment 93.
strip
a
— Prepare
;
of
notice that no
is
it is
metal
in
discolora-
a solution of sodium car-
bonate, put a strip of aluminium into
that the metal
the
to
it,
and observe
acted upon.
—
Experiment 94. Remove the aluminium from the
solution in the preceding experiment and rub a little
mercury on the surface the plate will soon become
;
covered with a white film of oxide,
the surface and
may be
detached in
which swells up on
flakes.
NICKEL.
—
Experiment 95. Take a piece of nickel wire or plate,
clean with emery, observe that it is white, malleable
when hammered
and
difficult to
or rolled, very tenacious, hard, tough,
break.
Heat
it
at the highest
tempera-
ture obtainable with the blowpipe, and notice that
does not melt, and that it is oxidised on the surface.
it
Experiment 96.— Place a clean strip of metal in
sulphuretted hydrogen water observe that no discolora;
tion takes place.
THE BLOWPIPE FLAME.
Experiment 97.
charcoal, place in
— Make a
it
small cavity in a piece of
a piece of lead foil
and heat before
the oxididmj flame of the blowpipe (see p. 57, Part I.).
Notice that the lead is gradually converted into oxide.
28o
DENTAL METALLURGY.
Enperivicnt 98.
— Clean a piece
of copper
before the oxidising flame, observing that
"
and Leat
it is
it
quickly
blackened " or oxidised.
Kqwrwicnt
99.
—Place a
little
lead oxide (red lead)
in a cavity in charcoal
of the blowpipe (see
is "
reduced
" to
and heat with the reducing flame
The lead oxide
p. 57, Part T.),
the metallic state in the form of
little
globules.
Mqjerirnent 100.
— Heat
a clean sheet of copper before
the reducing flame, and notice that the metal
readily tarnished than in the oxidising flame.
is
le?s
7S
2
)
APPENDIX
Common
List of the
Elevients, toiih their
Symbols
and Atomic Weights.
[
V„^,,._The words in brackets are the Latin names of the elements
from which
t\ie
symbols have been derived.]
Atomic
c>
Xavuc.
Wciylits.
111 yjyjKt
Aiiiiroximate
Values.
Al
Aluminium
Antimony {Stibium)
Sb
As
Arsenic
Bismuth
Bromine
.
•
.
27
120
Bi
75
207.5
Br
80
More Exact
Values.
27.04
iig.6
74-9
—
79.76
Carbon
Cd
C
Chlorine
01
35-5
35-37
Cu
F
Au
63
63.
Cadmium
Copper
.
.
(CKjJrviii)
Fluorine
.
Gold [Auruiii)
.
H
Hydrogen
Iron (Fcrruni)
.
Lead (I'ii(iiihiiw)
Mercury {Ihjdruriiy.
V in
12
III.
n7
i.y/
1
T
1 T
19
197
1
19.06
196.8
I
Ir
127
192.5
Fe
Pb
56
207
Hg
200
Ni
59
14
I
Iodine
Iridium
1
.126.54
5788
206.39
199.8
5S.6
14.01
15.96
106.2
Nickel
Nitrogen
O.xygen
Palladium
Phosphorus
Platinum
Potassium {K(tliuni)
Pd
P
106
Pt
Silver {Art/rn(niii)
Ag
Na
19s
39
108
30.96
194-3
39-03
107.66
23
32
118
22.99
31.98
117-35
.
.
Sodium
{N(itrium)
Sulphur
Tin (Stannviii)
Zinc
0
K
S
.
.
N
.
Sn
Zn
16
31
90.4
DENTAL METALLURaY.
282
CONVERSION OF CENTIGRADE AND
FAHRENHEIT DEGREES.
The thermometric
scales in use in this country are the
Centigrade and Fahrenheit
;
the former of these
is
rapidly
becoming universal for scientific purposes. The two
ai-e mutually convertible by the following rules
scales
:
1°
C.
=
1.8° F. or 4° ¥.
—
To Convert Centiynide into Fahrenheit. Multiply by 9,
5, and add 32.
To Convert Fahrenheit into Centigrade. Subtract 32,
multiply by 5, and divide by 9.
divide by
—
ENGLISH WEIGHTS.
APOTHECARIES' WEIGHT.
Ounces.
I'oiiiitl.
fb
=
I-
Drncliiiis.
=
12
51=
=
=
96
8
Grniiin.
Hcriijilis.
=
=
=
=
288
24
51=
3
3
I
5760
480
60
Gr. 20
AVOIRDUPOIS WEIGHT.
tt)
1
Drachms.
Ounces.
I'ouiul.
=
16
oz.
I
'J'l'oi/
=
=
=
256
-
=
16
dr.
I
Grains.
7000
437.5
27.344
RELATIVE VALUE OF TROY AND AVOIRDUPOIS
WEIGHTS.
PouihL
I
Troy
I
Avoirdupois
I'ound.
I'onnds.
=
=
0.822857 Avoir.
1. 215277
Troy
=
=
Ounces.
o
...
I
..
13
2
Grains.
72.5
..
.
.
280
APPENDIX.
283
IMPEKIAL MEA,SUltE.
Flu id
Pints.
(liiltoii.
=
I
Fluid UiiKccs.
.
8
:=
160
=
1280
I
=
20
=
=
160
I
I
gallon
I
fluid
.
.
.
ounce
(j'o
I
gallon
I
fluid
JJrachms
.
pint)
=
=
—
437-5
„
-i
277.280 cubic inches
—
ounce
S
70,000 grains of water
1-733
n
!:
METMC SYSTEM
OF WEIGHTS AND
MEASURES.
In the French or decimal system the smaller denominations are obtained by taking a tenth, hundredth, thousandth,
&c., of the unit chosen, and are designated by the Latin
the higher denominations are 10 times, 100 times, 1000, &c. times the unit,
and are named by the Greek prefixes deca-, hecto-, kilo-, &c.
examples of this will be found in the tables given below.
prefixes deci-, centi-, milli-, &c., whilst
;
The
of
I
of
iinit
cubic
the gkamme, which
loeight is
centimetre of water, and
is
is
the weight
equal to 15.432
grains.
The unit of
length
is
the
metke, and
is
one ten-
millionth of the distance on the earth's surface fi'om the
equator to the pole.
The unit
It is 39.37 inches.
mPMSure of capacity
oj
cubic decimetre, and
is
the litre, which
is
equal to 1.7 61 pints.
The chief
convenience arising from the use of the metric system is
that the difl'erent denominations can be written as one,
I
is
since they are either multiples by 10 or are decimal frac-
tions of the
decigramme.«,
gmmmes.
Tlius 6 decagrammes, 2 grammes, 5
milligrammes would be written 62.503
unit.
3
DENTAL METALLURGY.
METRICAL MEASURES OF WEIGHT.
I
gram.
=
the weight of
i
cubic centimetre
GiMius.
(c.c.)
of water at 4° C.
Cir;iius.
Avoirdupois.
1
1
1
Milligram.
Centigram.
Decigram.
.001
54323
0.0
100.0
000.0
10000.0
1
oz.
I
lb.
I
lb.
Avoir. =28.3675 grams.
=437.5 grains
Avoir. = 16 ozs. Avoir.
.
.....
....
Troy =12 ozs. Troy
Troy
A voirdupois
I
oz.
I
lb.
I
cwt.
I
ton
Jrms.
0
0
3
5.65
8.5
22
I
2
235
154323 48800
grain
_
gram. = 15.43235 grains = 0.032151 oz. Troy =
oz. Troy = 3 1. 1
04 grams. =480 grains
I
oz.
0
lljs.
15-43235
154-32349
1543-23488
15432.34880
1
Mjriogram.
1
1-
1.0
Kilogram.
I
0-
.1
Gram.
Decagram.
Hectogram.
I
0.01543
15432
.01
0.0649 gram.
0.0352736
1.
=
-
097 1
oz.
oz. Avoir.
Avoir.
0.91 14 oz. Troy.
7000 grains.
5760 grains.
31.1035 grams.
453-593 gi-ams.
50.8024 iiilograms.
(Icilos).
The
.
1016 kilos.
followiijg
approximate relations
G raiiiiiies.
I
5
10
20
may be found useful
Grains.
.
-
77i
.
155
.
310
28A
100
.
142
.
.
I
oz.
32 oz.
5 oz.
10 oz.
285
APPENDIX.
METRIC MEASURES OF LENGTH.
Millimetre
\_
(mm.)
J
Centimetre
Decimetre
Metre
Decametre
Hectometre
Kilometre
Myriometre
0.001
=
=
=
=
=
=
o.oi
0.1
1.0
lo.o
100.0
1000.0
10000.0
=
=
yard =
mile =
=
=
=
=
=
=
=
03937=
•
3937079=
393.70790=
3937.07900=
39370.79000=
393707.90000=
inch
.0254 metre
I
foot
.3048
I
39371=
3.93708=
I
I
Mile.
Ins.
Motrc.
„
.9144
=
=
=
Fl't;-.
Ins.
Yds. Ft.
- — - — — — —
— — — J
— —
— —
— 4
6
I
10
109
2
213
4
156
0
•°3937
.39371
3.937X
3-371
9.7
I
I
10.2
6
2.5425 centimetres.
3.048 decimetres.
9-144
"
1.609 kilometre.
METRIC MEASURES OF CAPACITY.
I
litre
=
Liti-c.
Millilitre
=
=
=
=
=
=
=
Centilitre
Decilitre
Litre
Decalitre
Hectolitre
Kilolitre
Myriolitre
-ooi
-oi
-i
'-o
lo.o
100.0
1000.0
Tints.
Cubic Indies.
1
or'i
Cubic centi- V=
metre (c.c.) J
1
cubic decimetre.
I
=
.06103
=
=
=
=
=
=
.61027
6.1027
61.027
610.27
6102.7
10000.0
-
=
0.00176
=
=
0.01761
0.17608
1.76077
17.60773
176.07734
1760.77341
17607.73414
=
61027.0
610270.0
=
:
1
I
cubic inch
=
=
=
.01639 litre
=
16.39 c.c.
2S.31531 lifes-
I
cubic foot
I
gallon
I
litre
=1000 cubic cm. = 61.02705 cubic inches =1./ 6
I
pint
=
4-54336
34-66 cubic inches.
.
,
^
pin
DENTAL METALLURGY.
of Substances which are knoion by
Names, with
their
Coiuuiou Name.
Alum
Chemical
Common
Names ami
or Popular
Formula}.
Chemical Nauio.
Foriiiul.v.
/Double sulphate of]
aluminium and po-
A1.,(S0,)3,K,S0,
1
[
Aqua
fortis
Aqua
regia
|
calcium hypochlo-
I
rite
Calomel
or
Corrosive sublimate
salts
or
)
spirits of salt
Plaster of
gypsum
\
Ca.lPOj).,
HgXl.,
NallO
Calcium carbonate
CaCO.,
KHO"
Sodium chloride
NaCl
Mercuric chloride
Magnesium sulphate
HgCl,
MgSO„7H20
Sodium sulphate
Lead oxide
NaoSOj
Silver nitrate
AgNO;,
VhO
Hydrochloric acid
HCl
Calcium sulphate
CaSOj
/
Paris or
Ca(OCl)Cl
Potassium hydrate
Sodium hydrate
J
salt
Glauber's salt
Litharge
Lunar caustic
Muriatic acid
HN63
3HCI + HNO3
J
/"Nearly pure calcium')
phosphate
\
j
Mercurous chloride
Bono ash
Caustic potash
Caustic soda
Chalk, marble
limestone
24H.,0
I
1
Epsom
J
Nitric acid
f Mixture of nitric and")
hydrochloric acids J
(
^Compound of cal-'j
cium chloride and
Bleaching powder or
chloride of lime
Common
tassium
j
Prussic acid
Hydrocyanic acid
Putty powder
HCy
Tin oxide
Quicksilver
Mercury
Oxide of iron
SnOo
Hg'
Rouge or colcothar
Sal ammoniac
Salts of
lemon
Saltpetre or nitre
Spirits of
Ammonium
/Citric acid and po-)
\ tassium oxalate
j
Potassium nitrate
wine
Tartar emetic
Alcohol
Vermilion or cinnabar
Vitriol (oil of)
„
blue
green
white
„
Washing soda
White lead
f
1
tartrate
Mtrcury sulphide
Sulphuric acid
Copper ^ulphate
Iron sulphate
Zinc sulphate
Sodium carbonate
(crystallised)
Lead carbonate
KNO^
C.HoO
/"Potassium antimony^
\
„
FCoOt
Am"ci
chloride
/
4(SbO)K(C4H,0„)
HgS
H.,S0,
CuSOj
FeSOj
ZnSOj
"1
/
Na^COnioHoO
PbCO.T
INDEX.
Acids, action on
„
mct:il8,
alloys,
n
Aluminium bronze, 248
34
preparation, 248
„
43
properties, 248
„
„
Ageing- of araalg:im alloys, 156
solders,
„
on metals, 33
Alkalies, action on metals, 35
Air, action
249
Amalgams, 130
Alloys, 37
colonr, 41
„
„
contraction, 131
„
dclinition,
expulsion, 131
130
„
condnctivity, 42
„
„
constitution of. 38
„
preparation, 132
„
ilefinition,
„
properties, 131
„
density, 41
„
dental, 174
.,
entcctic, 39
37
Amilgams, Dental, 140
action in muutli,
„
„
156
ageing, 156
for amalgams, T43
„
„
dies,
shape, 151
solders, 55
fusibility of,
„
fusible,
42
50
baUnccs for, 158
change of colour,
„
„
„
„
„
„
„
,,
152
176
„
li(|uation, 41,
„
preparation, 43
„
properties, 41
„
Von Eck irt's,
175
composition, 145
copper, 163
248
„
alloys,
„
amilyam, 132
„
annealing, 246
„
casting,
„
„
detection of gold
„
„
detection of pla-
„
„
discoloration, 152
,,
„
edge
in, 102,
„
246
effect of mercury, 132
exijcriments with, 278
„
for d(!ntnres, 245
„
in dental
prepiration, 243
„
])roperties,
„
solders,
„
swaging plates
161
tinum, 161, 188
strength,
154
amalgams, 148
„
„
vol-
change of
ume, 148
Aiuininium, 243
„
of
alteration
„
„
44
„
(HVectof dilVerent
„
lo;ikag(!,
melals,i44,T46
244
154
mixing, T59
247
of,
245
uses of In dentistry, 245
licriniincnci'
tlie
in
mouth, 155
288
INDEX.
Amalgiinis, Dental, pveparation, 160
"
"
proiioi-ties,
><
1,
finalitativc
1.
<,
(luilities
1,
„
(inaiitity of uicr-
ing
of,
sary,
„
161
iiopus-
oxyhydroyen, 64
iSnr ix, 79, 8t
222
Hr.iss, 48,
158
Sullivan's
Uritiiiinii metal,
217
Brittle! H'old,
ciiji-
por, 163
tnbos
mouth, 58
Owen's, 61
„
test-
140
ciiry,
IJlowpipcs, theory of,
57
143
f ir uiixiM'4-,
90
iiriti le platinum, 185
Brittleness of met Us, 12,13
Bronze, 222
Buruiut;- steel, 242
Anno iluiL;',
242
12,
Antimony, 231
.'liloys,
„
Cadmium, 224
232
advant
anialiiani,
133
oxperinuMits willi, 277
ill dental am ilyams,
147
UMtion, 231
lire))
„
proiiertios,
„
solvents for, 36, 232
use in dentistry, 232
„
!.
refii
Ass i,v of
„
,.
1.,
231
„
IJase metals, i
liellows for blowiiipe, 63
,1
„
alloys,
amalgam, 133
229
50
amilgam,
,,
cxperiment.s, 277
in dental anial-jam,
„
])rep iration,
„
projierties,
227
228
„
solvents for, 228
„
UBC
dentistry, 229
Hlast-fnruace, 3
147
prei)aration, 224
„
projierties,
„
solvents for, 36, 225
uses in dentistry, 225
224
alkalies on, 203
,,
for lining, 20T
of
volume
in metals.
Constitution of alloys, 38
Contraction of dies, 45, 199
„
„
met:ils,
30
Copper, 219
action of
.acids,
air,
«
220
220
58
alkalies,
automatir-. 62
snlphuri!! ted
35
hydrogen, 220
57
liot-ljlast, 59.
29
„
„ metals, 7
Colcmring gold, 116
„
238
llanie,
147,
Colour of alloys, 41
„
ill
alli).v.s,
„
Change
„
„
„
in dental
C'liiTt and fineness, 105
Cast iron, 234
Cements, action of acids on, 203
Bismntli, 227
lllowiiiju'S,
fusible
„
.^6
Balance, Fletcher's amalgam, 159
Kirby's amalfiiim, 158
„
r.lister steel.
„
225
178
liAliniTT METAI,,
:'.m il-
226
experiments with, 276
99
silver,
133
H'.un,
36
ijold,
ilgMii,
dis idviMitase of, in
Appendix, 281
A<iii
amalgam,
in
alloys, 51
am
„
„
'.ge of,
225
62
„
„
watei',
220
289
INDEX.
Flame, blowpipe,
221
CoppL'i- alloys,
„
„
cffoct o£ Impuvitic's,
FlotcUer'a balance, 159
220
oxpoi'iiuouts witli, 274
ill
„
doutal amalgams, 146
iivcpai-ation,
„
propcrtios, 220
solvents, 36,
liot-blast
„
mixing-tube, 160
Fi-actnre of metals, 20
of metiils, 14
Fluxes, 79
Foil gold, 91
220
uses in ilcntistvy, 221
,,
blowpipe, 59, 62
„
Flow
219
„
tliuory of, 57
Flatting mill, 77
amalgam, 134
dental amalgam, 163
platinum, 185
„
tin, 216
Furnace, blast, 3
„
Crucibles, 68
Crystalline ch'.iraeter of metals, 20
crucible, 5
„
Cupellition, 167, 178
fusion,
Cupels, 167, 178
5,
69,
73
muffle, 5
Density or alloys, 41
metals, 9
„
„
oil,
Dental alloy, 174
Fusible met.Us, 50, 229
„
amalgams, 140
copper amalgiims, 163
„
gold plate, 106
„
72
reverbcratory, 4
„
determining melting-
„
point
,,
Detection of gold, 102, 162
„
.,
„ tin, 162,
„
„
52
preparation
pliitinnm, 162, 188
Dies, alloys for,
of,
Melotte's, 52
of,
51
use in dental labora-
„
218
tory, 52
Fusibility of metals, 18
44
properties ol, 44. 199
Draw-plate, 15, 78
Galvanic action,
Ductility of alloys, 43
„ metals, 15
„
German
Edge sthenctii of amalgams,
154
alloys, 42
Electrical conductivity of
„ metals, 25
„
of
purification
silver,
252
Gilding, 116
mercury,
air.
„
alkalies, 89
„
„
sulphuretted
gen, 89
Electroplating, 116, 181
water, 34, 89
Eutectic alloys, 39, 17S
„
Expansion of amalgams, 148
28
witli metals,
Extraction of mctuls, a
FrNF.NF.SS OF flOLO, IO5
Fire gilding,
n8
89
„
127
Experiments
156
Gold, 85
action of acids, 89
„
Elasticity of metals, 17
„ metals,
30,
Galvanised iron, 199
Gauge-plate, 77
256
alloys,
103
„
amalgam, 134
„
assay,
„
beating, 91
„
Ijrittle,
„
carat,
„
colouring, irO
,.
CI
99
90
105
ysl 11,98
T
bydro-
290
INDEX.
Gold, detection of, 102, 162
eft'ect of iminirities,
„
90
„
estimation, 102
„
„
experiments with, 257
fineness, 105
„
foil,
„
„
„
93
„
liarduess, 11, 88
„
impiu'ities in,
„
in dental
„
Lamm's shredded, 97
„
„
meltiug-point, 19, 89
occnrronco, 85
„
parting-,
„
plate,
„
precipitauts, 96
precipitated, 96
„
solvents for, 36, 239
„
wrought, 235, 237
„
Lamm's snnEDDEn gold,
97
pniTDle-of-Cassius, 121
raising standard, 115
recovery from scrap, 66. It8
reducing standard, 114
Ladles, 74
Lead, 208
„
air,
,>
!.
no
solders,
„
solvents for, 36, 89
II
„
spongy, 96
„
„
standard, 105
sweep, 119
„
„
„
tests for,
„
Gun
action of acids, 34, 210
11
„
„
experiments, 150
mixing tiiho, 161
„
106
„
„
„
Kihby's balance, 158
„
„
234
239
experiments with, 277
preparation, 237
properties, 238
86
„
„
cast,
effect of impurities,
„
preparation, 85, 87
properties, 88
pnro, 87
„
„
„
„
90
amalgams, 144, 146
234
amalgam, 135
annealing, 242
burning, 242
„
cohesive, 93
non-coliesive,
I,
„
Iron,
„
„ prepanition, 91
gilding, 116
»
Iridium, use in dentistry, 192
33
alkalies,
35
sulphuretted hy.
drogeu, 33
to ascertain fineness of,
113
„
water, 34, 210
210
amalgam, 135
experiments with, 272
in dental amalgams, 148
preparation, 208
uses in dentistry, 89
„
properties, 209
„
sheet,
„
102
Watt's crystal, 98
metal, 223
Habdening steei,, 240
Hardness of metals, 10
Heat conductivity of metals,
INOOT-MOULD, 76
simple, 65
,,
Iridium, 191
„
alloys,
209
solvents for, 36
uses in dentistry, 210
„
Lemel, pm-iflcation of, 119
„
Limit of
elasticity, 18
Lustre of metals, 7
25
Liqu.ition of alloys, 41, 176
Malleability of metals,
„
43
„
alloys,
„
properties, igr
192
12
effect of alloying
Melotte's fusible metal, 52
Melting appliances,
INDEX.
MeltiDg-points
„
Metals, fracture, 20
42
iilloys,
oJl
„ metals, 18
„
scrap, 66, 118
„
Mercury, 123
„
action of acids, 124
124
air,
„
124
„
„
alkalies,
„
„
sulphiu-cttcd
„
„
water, 124
liy-
drogeu, 124
„
adulteration ot, 125
„
(listillat'on of,
„
electrical
„
127
experiments with, 264
126
purification
of,
127
„
filtration of,
„
for dental amalgams, 125
„
impm-ities
,,
in,
preparation
fusil)ility,
„
„
galvanic action, 30, 156
hardness, 10
„
lustre,
„
malleability, 12
„
„
methods of extracting, 2
micro-structure, 24
123
7
„
native, 2
„
noble, I
„
occurrence
„
physical properties,
„
solvents for, 36
„
„
specific gravity, 9
heat, 27
„
„
taste, 8
„
tenacity, 16
„
useful, 5
used in dentistry, 6
125
of,
i8
„
2
of,
Sleter metal, 217
„
properties
„
purification of, 126
Micro-structure of metals,
„
solvents for, 36, 124
„
stilpliide of,
Moldine, 52
Moulds, ingot, 65, 76
Muffle furnace, 5, 75
of,
124
128
Motallui'gy, definition of, 2
Metals, 7
action of acids on, 34
„
33
„
„
„
„
alkalies,
35
sulplmrctted hy-
Native metals,
„
drogen, 33
water, 34
„
alloying, 37
appliance* for melting, 65
„
base, I
„
brittlencss in, 13
„
capacity for heat, 27
„
change of volume, 29
colour, 7
„
conductivity
aiiS
„
alkalies,
„
„
of,
alloys,
251
sulphuretted hydro-
densily, 9
ductility, 15
„
ehisticity,
17
„
„
expansion by heat, 28
„
cxperluieuts
colli,
cxposMn'
„
How
ill
14
„
experiments with, 279
„
preparation, 231
„
properties, 251
„
solvents Cor
Noble metals,
cllect of
.,
amalgam, 135
plating, 254
f_
„
252
„
25
crystalline character, 20
of.
251
»
„
gen, 251
„
„
action of acids, 251
„
water, 251
„
„
2
Newton's metal, 51
Nickel, 251
i
19
witli,
256
the moulli, 35
Occurrence or metals,
2
Ores, 2
(
(
203
)xy-hydroyou blowpipe, 64
(xy-cliloride, niuc,
292
INDEX.
Oxy-phoBphato,
zinc,
Oxj-.suliiliatc, zinc,
204
Platiunm, properties, 184
205
solvents for, 36, 184
sponge, 187
uses in dentistry, 185
welding-, 187
„
„
I'ALLADrUM, 193
„
action of acids, 194
„
"
air,
»
alkalies,
..
"
194
Polishing- putty, 214
Precipitated gold, 96
35
sulplim-etted
»
„
Piu'iflcation of lemel, iig
liydi-ogeii,
194
"
«atei-,
..
alloys,
M
„ mercury, 126
„ sweep, 1T9
Purple-of-Cassius, 121
194
Pyrometers,
c-4
195
amalgam, 135
i>
„
„
(iUICICSILVER, 124
in duutal amalgams, 147
precipitate, 195
(inoen's metal, 217
)i
preparation, 193
Keitnino gold, 86
»
properties, 28, 193
Kevcrboratory furnace,
4
Rolling mill, 77
»
solveuts for, 36, 194
use for dental piiriioses,
11
»
Hose's fusible metal, 51
195
I'artiug: gold,
I'ott ter,
I'liysical
II
Scrap, melting,
86
211
properties of alloys,
37
II
„ dental amal-
gams, 141
„ metals,
i:
I'iiis,
brittle platiunm,
7
11
II
Silver,
185
„
action of acids, 184
184
„
air,
»
,1
alkalis,
)i
11
sulpliiu'etted
„
-miter,
II
,,
alloys, 189
amalg:am, 136
black, 186
„
brittle, 785
„
dental alloy, 174
detection, 187
estimation, 188
„
„
.,
„
„
„
„
184
experiments with, 266
foil, 185
from scrajis, 118
gronp, 183
iu dental amalgam.-i, 188
preparation, 183
182
166
action of acids, 167
167
II
„
air,
11
I,
alkalies,
II
II
sulphuretted hy-
11
„
water, 167
168
drogen, 167
35
liydrogeu, 184
11
silver, 119,
i>
Scorilication assay, 180
Platinum, 183
„
66, 118
recovery of gold from, 118
platinum, 118
„
„
„
alloys, 171
„,
amalgam, 136
„
assay, 178, i8i
„
chloride, 169
„
cupellation, 167, 178
„
experiments with, 261
amalgams, 143, 146
in s(j-ap, 182
„
„
in dental
181
„
plating-,
„
precipitate, 171
„
preparation, 166
„
i)roperties,
„
pure, 169
167
solders, 176
II
„
preparation
nf,
177
iNDEX.
Tin, action of air, 214
Silver solvents, 36, 167
168
„
spittins^ of,
„
stiiiulai-il,
„
uses in duntistry, 169
172
alumminm, 247
249
for dies, 47, 206
„
amalgam, 138
„
detection
„
no
216
„
„
„ platinum, 191
„
„ silver, 176
„
,,
of,
experiments
foil, 216
grain, 213
„
prepiiriition of, 55, 113,
„
soft, 55,
witli,
„ fusible alloys,
„
177
218
268
amalgams, 140, 146
in dental
hard, 55
„
50
216
„
plate,
„
preparation, 213
Solvents for metals, 36
Specific gravity of alloys, 41
„
properties, 214
„
solvents for, 36, 214
„
uses in dentistry, 215
211
metals, 9
heat of metals, 27
„
Speculum metal, 222
welding, 214, 216
T6uchstone, 100
Type metal, 45, 211
„
Spelter, 198
Spence's metal, 47
Spongy
„
gold,
96
Vermilion, 128
platinum, 187
impm-ities
Standard gold, 103, 105
silver, 172
„
in,
„
aunealiug, 242
properties
„
A'arieties of blowpipes, 57
„
burning, 242
Von
„
definition of, 236
„
hardening, 240
Water,
,,
tempering, 240
Watt's crystal gold, 98
Welding gold, 91
Sullivan's
of,
238
amalgam, 163
Sulpluiretted
hydrogen, acliou
on
metals, 33
Swaging- metal plates, 12, 108, 174
Sweep, purlHeatiou of, 119
129
preparation, 128
„
Steel, 236,
liyilro-
water, 214
„
„ g-old,
sulphuretted
alloys,
„
Soldering-, tlioory of, 80
-bronze,
„ aliiiniui urn
alkalies,
„
gen, 214
Soft-soldcviug, 83
Solders, 55
for
„
2x4
„
130
Eckart's alloy, 175
action ou metals, 34
209
„
lead,
„
ijlatiuum, 187
„
tin, 214,
2i6
Wn-e-ilriiwing, 15, 78
Wood's metal, 51
Tastk of metals,
8
Wrought
iron,
235
Tempering, 240
Zinc, 197
Tenacity, 16
Testing amalgam, 149, 161
Tests for gold, 100, 162
„
„
jdatinum, 162, 187
„
tin,
218
„
„
.
action of acids, 198
„
alkalies, 198
„
sulphuretted
gen, 198
Tin, 213
action of acids. 214
„
w-ator, 198
liy.lro
294
iiSTDEX.
.
Zinc alloys, 205
I,
ti
„
Zinc, melting-
amalgim, 138
brittle, 13, 200
chloride
of,
202
„
compoiiuds
of,
„
contraction
of,
„
counter
„
dies,
),
dies,
199
experiments with, 271
fusibility of, 19, 198
hardness of, n, 199
in dental
„
oxy-cbloride, 203
„ -phosphate, 204
„
199
108, 200
-sulphate, 205
preparation
„
properties, 198
puriiioation, 200
of,
197
„
solvents for, 36, 198
„
sulphate, 202
uses in dentistry,
„
amalgams, 147
London
„
„
„
white, 201
Printed by Ballantynu:,
200
oxide, 201
„
2or
of,
„
Hanson
Edinburgh
6)^ Ci
199
No.
J.
JUNE,
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1905-
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Glasgow University Library
A MAI^UAL
ON
DENTAL METALLURGY
BY
ERNEST
A.
SMITH
ASSOCIATE OP THE ROYAL SCHOOL OP MINES,
LONDON FELLOW OF THE
CHEMICAL SOCIETr AND OP THE SOCIETr OF
CHEMICAL INDUSTRY
LATE ASSISTANT INSTRUCTOR IN METALLURGY,
;
•
'
ROYAL COLLEGE
OF SCIENCE, LONDON
SECOND EDITION
LONDON
&
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7
CHURCHILL
A.
GEEAT MARL130K0UGH STREET
1903
J
PREFACE.
The
present manual
syllabus
of
dental
is
based largely upon the new
metallurgy,
1897,
issued
by the
Eoyal College of Surgeons of England, and is
primarily
designed for the nse of students preparing
for. their
examination.
In
the
preparation
of
the
manual
I
have also
endeavoured to place in the hands of dental
students
an outline of the scientific principles involved
in the
extraction of the metals from their ores,
their physical
properties,
and their application
the dentist.
Attention
to the requirements of
has been drawn to the fact
"that metallurgy has not received hitherto
its
due
share of attention at the hands of the
dental student,
and of
its
importance to him there can be no doubt. "
While the properties
of all the metals
*
which have any
application, directly or indirectly, in the
dental labora-
tory have
been dealt with, special consideration has
been given to those most frequently used
by dentists.
*
Howard Mummery,
delivered
at
London, 1897.
Esq., M.K.C.S., L.D.S.
In an Address
the Trize Distribution, National Denial
Hospitnl.
PREFACE.
IV
Full descriptions of metallurgical processes are out
of place in a text-book of dental metallurgy,
be sought in metallurgical text-books.
and must
Only such con-
densed outlines, therefore, have been given as are
methods by which the
sufficient to explain briefly the
metals are obtained in a state suitable for industrial
purposes.
An
elementary knowledge of chemistry and
physics on the part of
my
readers has been taken for
granted.
Although
student a
have endeavoured to present to the
I
condensed
and
succinct
account of the
physical properties of the metals and their chief alloys,
it
a
must be borne
in
mind that the mere reading
of
text-book will never give the student a practical
knowledge
It is only
of these properties.
by handling
the metals and their alloys, and subjecting them to
various mechanical tests, that he can become acquainted
with the
toughness, hardness,
qualities of the metals
observation, for
and know,
I
and other
as a result of his
what purposes each
Acting upon this principle
two
fusibility,
is
own
best suited.
have divided the book into
parts.
Part
I.
properties
dental
contains a brief sketch of the metals, their
and
alloys, their special application in
laboratory,
and other
details
the
required in the
syllabus of the Royal College of Surgeons.
In this
portion of the book special attention has been given to
the preparation and properties of alloys for amalgams,
as this subject
now
occupies a conspicuous place in
V
PREFACE.
denttil practice.
is
extensive,
be done
;
Although the literature on
much
it is
this subject
experimental work yet remains to
hoped, however, that the matter given in
the present work will prepare the student for a fuller
comprehension of the subject.
Part
II.
consists of a series of simple experiments
which can be readily performed, thus enabling the
student to acquire a practical knowledge
perties of the raetals
and their
()f
the pro-
alloys.
I have omitted all chemical equations
and detailed
descriptions of the chemistry of the metallurgical processes
for
extracting
the metals,
confining
myself
merely to a short mention of them in a few general
remarks at the commencement of the various chapters.
The author
cordially
kindly rendered by Mr.
acknowledges the assistance
Oswald E. Smith and Mr.
A. Jarman in executing some of the drawings, and by
Mr. F,
J.
Padgett in reading the proof'-sheets.
His
thanks are also due to Messrs. Claurlius Ash and Co. for
the loan of several blocks.
E. A. S.
RoYAi, College of Sciesce, London.
PREFACE TO SECOND EDITION.
A SECOND edition o£ this volume having become necessary,
the opportunity has been
taken to correct the few-
typographical and other errors of the
to completely revise
The additions
will
first
and
and amplify the work.
be found principally in the chapter
on the physical properties of the metals.
illustrations
edition,
have also been introduced.
Several
new
Great advances
have been made in the study of the structure of metals
and
of alloys during the past five years,
has been
made
to these in the
new
and reference
edition.
In revising the work several valuable suggestions have
been offered by Mr. A. McWilliam, A.R.S.M., especially
with regard to iron and
steel,
and these the author
gratefully acknowledges.
The chapter on iron and
steel has
been rewritten and
brought up to date.
The Author hopes that
this edition
may meet
with
the same cordial reception as that which was accorded
to the first edition.
E. A. S.
Assay
Oi-'Kice,
Sheffield.
1
i
-
CONTENTS.
PAET
I.
INTRODUCTION
CHAPTER
I.
PHYSICAL PROPERTIES OP THE Uy^TALS.
......
.............
LUSTHE AND COLOUR
TASTE
DENSITY
HARDNESS
MALLEABILITY
BRITTLENESS
.
.
.
.
J
9
...........
...........
...........
'
.
.
.
'
.
.
lO
12
13
FLOW UNDER PRESSURE
I4
DUCTILITY
TENACITY
ELASTICITY
75
FUSIBILITY
.
.
.
.
•
,
•
.
.
.
.
EFFECT OF COLD
FRACTURE
CRYSTALLINE CHARACTER
MICRO-STRUCTURE
CONDUCTIVITY OF HEAT AND OF ELECTRICITY
CAPACITY FOR HEAT
EXPANSION BY HEAT
.
CIlANflE OK VOLU.ME
.
.
.
.
.
.
.
,
16
I7
18
19
20
20
....
ON SOLIDIFICATION
24
25
27
28
29
<iALVANIt VCTION
3O
CHAPTER
II.
ACTION OF CERTAIN AGEXTS ON METALS.
33
Hl'LPHURETTED IIVDROOF.N
,-3
X
CONTENTS.
PA.6E
WATER
ACID.S
34
— NITRIC
34
HVDBOCIILORlf
34
suLpnuRic
ACETIC
ALKALIES
EFFECT OF EXPOSURE IN THE .MOUTH
SOLVENTS FOR METALS
34
35
.
•
•
35
35
3^
CHAPTER
III.
ALLOYS.
37
DEFINITION
PIIVSICAL PROPERTirS
41
PREPARATION
ALLOYS FOR DIES AND COUNTER-DIES
FUSIBLE METALS
PREPARATION OP FUSIBLE METALS
DETERMINATION OF MELTING-POINT OF FUSIBLE ALLOY
SOLDERS
PRKPAUATION OF SOLDERS
.
.
.
.
.
.
.
•
•
CHAPTER
•
•
43
44
SO
51
.
52
55-
,
55.
IV.
THEORY AND VARIETIES OF BLOWPIPES.
57
58
THEORY OF BLOWPIPE FLA.ME
MOUTH BLOWPIPES
BELLOWS BLOWPIPES
BLOWING APPARATUS
OXY-HYDROGEN BLOWPIPE
61
63
64
.
CHAPTER
V.
FLUXES.
MELTING APPLIANCES, FURNACES, AND
MELTING APPLIANCES
65
68
CRUCIBLES
FORMS OF FURNACES
69
.
MUFFLE FURNACE
INGOT-MOULDS
ROLLING lNOOT.«
WIRE-DRAWING
75
76
.
•
78
.
CONTENTS.
XI
P.VGR
FLDXES
79'
TIIEORV Of SOLDEKINCi
80
HOFT SOLDEUlNli
83.
CHAPTER VI
GOLD.
occunnENCE
PBEPARATIOX
PARTING HOLD FROM SILVER
PREPARATION OF PURE GOLD
PROPERTIES OF GOLD
'
.
.
85
85
86
87
.
88;
.
USE FOR DENTAL PURPOSES.
EFFECT OF IMPURITIES ON PROPF.RTIKS OP GOLD
BRITTLE GOLD
GOLD FOILS
PRECIPITATED AND SPONGY GOLD
.
...
CRYSTAL GOLD
ASSAY OF GOLD
ASSAY BY' TIJE TQUCHSTONE.
.
.
100
....
CARAT AND FINENESS
GOLD PI,ATE
PREPARATION OF GOLP PLATE
GOLD SOLDERS
PREPARATION OF GOLD SOLDERS
TO ASCERTAIN THE CARAT FINENESS OF A GIVEN LLLOY
TO REDUCE GOLD TO A REQUIRED CARAT
TO RAISE GOLD TO A HIGHER CARAT
COLOURING OF GOLD
.
....
.
...
.
'CILDINO
.
.
I02-
103
loS
106
109
no
113
113
114
"5
116
116
RECOVERY OF GOLD FROM SCRAP
PURIFICATION OF SWEEP OR LEMEL
PURPLK-OF-CASSIUS
91
96-
99'
DETECTION AJfD ESTIMATION OF GOLD, IN ALLOYs'
ALLOYS. OF GOLD
.
90.
90
98
,
.
89:
118
119.
.
121
CHAPTER
VII.
MERCUUY.
OrCURRE.NCE
PKRPARATION
123
.
PROPERTIES
'SB FCP. DENTAL PURPOSES
123
124
12
c;
CONTENTS.
Xll
PAGE
TESTING THE PURITY OF MERCURY
PURIFICATION OP MERCURY
VERMILION AND DETECTION OF IMPURITIES THEREIN
•
.
.
.
•
•
.
.
^^5
126
.128
130
AMALUAMS
.
.
.
•
CHAPTER
VIII.
DENTAL AMALGAMS.
140
•GENERAL CONSIDERATIONS AN O PROPERTIES
•COMPOSITION
146
EFFECT OF DIFFERENT METALS
CHANGE OF VOLUME
METHODS OF TESTING CHANCE OF VOLUME
ALTERATION OF SHAPE
•CHANGE OF COLOUR
.
.
•
.
.
.
•
.
.
•
•
148
149
•
•
154
LEAKAGE
EDGE-STRENGTH
THE MOUTH
POSSIBLE ACTION ON OTHER METALS
PERMANENCE
IN
^54
•
155
.
IN THF.
IIOUTH
156
AGEING
158
liUANTITV OF MERCURY NEEDED
MIXIN<i
156
AMALGAMS
.
.
,
•
PREPARATION OF ALLOYS FOR DENTAL
•QUALITATIVE E.XAMINATION
•
AMA
AM S
161
163
DENTAL COPPER AMALGAMS
CHAPTER
159
160
IX.
SILVEK.
166
OCCURRENCE
PREPARATION
.
.
166
•
•
.
.
•
•
167
PROPERTIES
USES FOR DENTAL PURPOSES
PREPARATION OF PURE SILVER
PRECIPITATED SILVER
ALLOYS OF SILVER
.
•
.
•
169
.
169
171
171
.
DENTAL ALLOY'
.
174
176
SILVER SOLDERS
PREPARATION OF SILVER SOLDERS
ASSAY BY CUPBLLATION
WET ASSAY OF SILVER
ELECTRO-PLATING
RECOVERY OF SILVER FROM SCRAPS
.
177
178
181
181
182
CONTENTS.
CHAPTER
xiii
X.
PLATINUM AND IRIDIUM.
PAGE
......
..........
PLATINUM
OCCURRENCE AND PREPARATION
183.
183
PROPERTIES
USE IN DENTAL LABORATORY
BRITTLE PLATINUM
184
PLATINUM FOIL
PLATINUM BLACK
SPONGY PLATINUM
DETECTION OP PLATINUM IN ALLOYS
ESTIMATION OF PLATINUM IN ALLOYS
ALLOYS OF PLATINUM
185
.........
..........
.........
........
............
.........
.........
IRIDIUM
PROPERTIES
ALLOYS OF IRIDIUM
USE IN DENTISTRY
CHAPTER
185.
185.
186
187
187
188
189
191
191
I92
I92:
XI.
PALLADIUM.
.......
...........
........
.........
.........
OCCURRENCE AND PREPARATION
PROPERTIES
USE FOR DENTAL PURPOSES
PALLADIU.M PRECIPITATE
ALLOYS OF PALLADIUM
CHAPTER
193
193
I95
195
I95.
XII.
ZINC.
OCCURRENCE
PREPAn.VTION
...........
...........
.........
..........
...........
..........
..........
PROPERTIES
USE FOR DENTAL PURPOSES
ZINC DIES
I97
197
198
I99
199
200
PURIFICATION OP ZINC
COMPOUNDS OF ZINC
20I
O.XV-CIILORIDE
203
O.W-PIIOSPIIATE
0.\Y-SULPII.VTE
ALLOYS OF ZINC
204
205
205
CONTENTS.
XIV
CHAPTER XIIL
LEAD.
PAGE
OCCinRENCK
208
PBEl'ARATION
PROPERTIES
2°^
209
•
2IO
USE rOR DENTAL PURPOSES
ALLOYS OF LEAB
2IO
CHAPTER
XIV.
TIN.
OCCURRENCE
PREPARATION
213
PROPERTIES
214
USES IN
213
DENTAL LAHOHATOliV
215
TIN-FOIL
216
TIN-PLATE
ALLOYS OP TIN
DETECTION OF TIN IN ALLOYS
216
2l6
21?
.
CHAPTER XV.
COPPEK.
OCCURRENCE
PREPARATION
PROPERTIES
^^9
EFFECT OF IMPURITIES ON COPPER
USE IN DENTAL LABORATORY
220
^^9
221
ALLOYS
CHAPTER
XVI.
CADMIUM.
224
OCCURRF.NCE
.
PREPARATION
.
.
USE
ITS
FOIl DENTAL PURl'OSUS
ADVANTAGES AND UI8ADVANTA0ES
224
224
PROPERTIES
225
IN
ALLOYS AND AMAI.CA.MS
225
CONTENTS.
CHAPTER
XV
XVII.
BISMUTH.
OCCL'UUENCE
yilEPARATION
PROPERTIES
227
227
USE FOR DENTAL PURPOSES
ALI.OVS OF
........
BISMUTH
228
229
229
CHAPTER
XVIII.
ANTIMONY.
•OCCURRENCE
....
...........
...........
.........
PREPARATION
PROPERTIES
USE FOR DENTAL PURPOSES
ALLOVS OF ANTIMONY
231
23I
231
232
232
CHAPTER XIX.
IKON.
...........
...........
............
...........
...........
•OCCURRENCE
CAST IRON
234
234
"WROUGHT IRON
STEEL
PREPARATION
235
236
PROPERTIES
•EFFECT OF IMPURITIES ON IKON
IIARDENINO AND TEMPERING
.......
ANNEALING
BURNING OF IRON AND STEEI
237
238
239
24Q
342
242
CHAPTER XX.
ALUMINIUM.
•OCCURRENCE AND PREPARATION
PROPERTIES
USES FOR DENTAL PURPOSES
244
ALUMINIUM PLATE FOR DENTUUEH
CASTING ALUMINIUM FOR DENTURES
245
246
243
245
CONTENTS.
XVI
SOLDERS FOR ALUMINIDM
ALUMINIUM BRONZE
SOLDERS FOR ALUMINIUM BUONZK
ALLOYS OP ALUMINIUM
247
.......
248
249249.
CHAPTER XXI.
NICKEL.
OCCURRENCE
PREPARATION
PROPERTIES
USE IN THE DENTAL LABORATORY
ALLOYS OF NICKEL
^S'^
252
^5-
GBRMAN SILVER
-5^
NICKEL PLATING
^54
PART
II.
EXPERIMENTS RELATING TO
COLD
.
SILVER
MERCURY
PLATINUM
TIN
ZINC
LEAD
.
.
COPPER
CADMIUM
BISMUTH
ANTIMONY
IRON AND STEE
ALUMINIUM
NICKEL
EXPERIMENTS WITH THE BLOWPIPE FLAME
APPENDIX
INDEX
A MANUAL ON
DEKTAL METALLUEGY.
PART
I.
INTRODUCTION.
When
only a few of the metals were
divided into two classes,
viz.
known they were
—noble or precious metals
and base metals.
Noble Metals.— Those having a very
feeble affinity
for oxygen,
which renders them incapable of rusting or
tarnishing by oxidation in the air at common tempera-
tures or on heating.
Base Metals.— Those which
lustre or are oxidised at
lose
their
metallic
an ordinary temperature or by
heating.
The term " noble
" or
" precious
" is
applied to gold,
and platinum (and some of the rarer metals found
in combination with platinum), as none of these metals
silver,
rust
or oxidise at the ordinary temperature or on
heating; on the contrary, the oxides of these metals cease
to exist
on heating, the metal being set free and the
oxygen given off". Mercury is also included sometimes
as one of the noble metals.
Thus it will be seen that
A
DENTAL METALLURGY.
2
the
number
of
noble metals
so-called
is
very small
so-called base metals.
in comparison with that of the
Metals.—
Occurrence and Distribution of
distributed
sparingly
The majority of the metals are
rare occurrence and
nature, and some are only of
little
m
are ot
practical importance.
occur
a few of the metals
majority
uncombined state, the
Native Metals.-Only
in nature in the free or
combination with oxygen,
being generally found in
Those
element.
sulphur or some other non-metallic
are gold, silver, copper,
that occur in the metallic state
mercury, bismutb
platinum (and its allied rarer metals),
stated
Lead and zinc are also
iron.
antimony and
to have been found
in the
uncombined
state,
but their
occurrence requires confirmation.
occur
Ores.-As above stated, metals usually
non-metals formmg a series
nature in combination with
Native
as mdcdlifa'cym .nm.r«/s.
of bodies known
included under this heading.
metals are also generally
which contain a metal
Those mineral substances
as to admit
in such association
sufficient quantity and
extraction
advantageously treated for the
of their being
of
known as ores. The proportion
of that metal are
vary
a mineral an oi;e will
xnetal necessary to constitute
the
mineral and the value of
with the nature of the
mineral
to subject the
It is usually necessary
metal.
mechanical preparation to
which contains the metal to
mineral matter or " gangue_
free it from the valueless
Metallurgy is
associated.
with which it is invariably
preparmetals from their ores and
the art of extracting
manufacturei
uses of the artisan and
ing them for the
em-
m
m
Methods
of
Extraction—The
processes
metals from
their ores
ployed for extracting
i.he
may
INTRODUCTION.
be divided iuto two classes,
Wet
viz.
2
—Dry
processes and
processes.
Dry Processes.—Those
which are conducted in
furnaces, or their equivalent, at a relatively
high temperature.
The operation of extj-acting
metals from
their
by fusion
ores
in
a
furnace with suitable fluxes
is
known
as smelting.
The metallurgical operaconducted at a high
temperature require the use
tions
of furnaces
built or lined
with some material capable
of
withstanding
excessive
heat and the wearing action
of the materials with which
it
comes in contact.
Wet
Processes.
Those in which the metal
is extracted by a suitable
solvent after being, in
cases, first
some
converted into a
more readily soluble compound.
Metallurgical
naces.— The
of
furnaces
Fur-
various forms
Fig.
I.
employed are
conveniently divided into (i.) Blast
furnaces (ii ) Reverberatory furnaces
(iii.) Muffle furnaces
and (iv )
Crucible furnaces.
;
;
;
Blast Furnace (Fig. i)._The
construction
the modern blast furnace varies
much
(i.)
and the proportion of
of
as to shape, size
its
parts,
accoi'ding
to
the
DENTAL METALLURGY.
4
fuel
em-
and of the
nature of the ore to be smelted
essentially ot a
For iron smelting it consists
ployed.
feet high),
chamber or " stack " (about 80
vertical
m
ing.
and formed as illustrated
by
top
the
admitted at
The charge of ore and fuel is
arrangement, which closes
means of the cup and cone
hot blast is forced through
the furnace, and a powerful
" placed round the base of the
"
small pipes or tuyeres
off at intervals
The molten metal is drawn
circular in section,
i.
furnace.
Fig.
2.
the "slag,
as
it
base, while
from a tap-hole at the
an open^
at intervals through
accumulates, is tapped off
W known
" slag hole."
as the
are
The waste gase
furnace through a side
Ub
drawn off at the top of the
for heating P-P-^;^
and subsequently utilised
used
in section,
furnaces, rectangular
smelting.
lead and copper
(ii )
are largely
Reverberatory Furnace
furnace,
a horLontal
(Fig.
fJfor
2)—This
is
"consisting
--^^^l^^^^^^
the
^^^^^
chimney at
one end, a stack or
narts-a
material
the two, on which the
^e
and ^a bed between
_^
other nnd
^
^^^^
^^^^^
C
fireplace at
l^^^X
" fire-bridge,"
called the
and both are
INTRODUCTION.
covered by an arched roof.
On
5
the sides of the bed are
openings through which the ore
may be
stirred
when
necessary.
The flame
to the
downwards or rGverheratcd
spread over the bed, whence the name
stack
on the ore
is
in its course
from the
fireplace
reflected
reverheratonj furnace." *
(iii.)
istic of
Muffle Furnaces.—The
these furnaces
does not
come
is
essential character-
that the material being heated
into contact either with the fuel or the
products of combustion.
The furnaces
are
made
in
many
forms according to the purpose for which they are to
be used.
As a type, the assay furnace on p.
75 may
be taken.
Crucible Furnaces.— Furnaces of this class
are chiefly used for melting metals and alloys.
They
consist essentially of a closed fire-brick chamber with
(iv.)
fire
bars at the bottom, and a small flue at the top.
is usually fitted with a door by means
of
The ashpit
which the draught
on
p.
73
is
is
regulated.
The laboratory furnace
a type of this class.
Useful Metals.— Although
a large number of
metals are known, about twenty-one only of these are
of any considerable industrial importance, viz.
Alimiiiiiuni.
Copper.
Antiiiioiiy.
Gold.
Platiniiiii.
A rufi/iir.
Iron.
Putassiuiii.
Bi.smiith.
Lead.
Silver.
f'lidwiuiii.
Miiijiirfiiiuii.
Nickel.
Snd'iHiii.
(lirnniinni.
Aid IIIJII ItfKC.
Tin.
Ciiliall.
Mercury.
Zinc.
Of
these, only about thirteen (those printed in Eoman
type) are employed in the metallic state for industi-ial
*
l'er(;y,
" Mebilliiruy," vol.
i.
p.
45.
DENTAL METALLURGY.
6
purposes or in the dental laboratory. Of those printed
in the metallic
in italics a few are used to a small extent
while their various compounds are extensively
for other
used in the arts as colouring pigments, or
purdental
The application of metals to
purposes.
origin, as " gold
poses cannot be regarded as of recent
fixing artifiwas employed in Eome for the purposes of
centuries before the Christian
cial teeth more than three
Tables makes exception
era, and a law of the Twelve
it to be buried
with regard to such gold, permitting
state,
*
with the dead."
*
C'ic.
do Leg.,
ii.
24
.
" Metallurgy," Phillips, p.
2.
CHAPTER
I.
PHYSICAL PROPERTIES OF THE
METALS.
Although
the division of the elements into metals and
non-metals does not admit of exact definition, yet the
metals as a class possess certain generic properties
which the non-metals either do not possess at
all
or
exhibit only in a very slight degree.
All
with the single exception of mercnry
metals,
(a liquid), are solid at the ordinary
temperature they
high power of reflecting light
they are
opaque except in the thinnest possible films, in which
possess
;
a
;
state they allow light to pass
they are better conductors of heat and of electricity than the non-metals, and,
;
have higher densities than these, and
with few exceptions, malleable and ductile. The
metals diffisr widely from each other both in their
as a rule, they
are,
physical
and in their chemical properties, and are
accordingly adapted for different uses.
The most important physical properties possessed by
the various metals, rendering them fit for purposes
which could not be
are as follows
fulfilled
by non-metallic substances,
:
Lustre and Colour.— One
teristic properties
of the
possessed by metals
is
most characthat of a high
DENTAL METALLURGY.
8
power whereby a peculiar
reflective
appearance
is
presented,
known
briglit glittering
as the metallic lustre.
in a state of fine division the metals frequently
When
appear in the form of black or grey powders, and the
be
metallic lustre is not noticeable, but it can readily
subobserved when the powder is rubbed with a hard
stance, such as polished steel or agate.
The peculiar lustre characteristic of metals
is,
how-
as certain
ever, not wholly confined to these substances,
some of the non-metals exhibit a closely
compounds and
an example.
Although the light reflected from polished surfaces
similar lustre
gi-aphite
is
;
nearly white, yet frequently there is
best seen when the
a slight tinge of colour, which is
the metallic surface.
is repeatedly reflected from
most metals
of
is
light
other metals
Thus, whilst tin, silver, platinum and
appear alike
have a nearly pure white colour, and
distinct
equally polished, lead and zinc have a
'
when
and bismuth a slightly
bluish shade, iron a greyish hue,
brownish
tint.
from a gold surface,
tint is deepened to a
the characteristic pale yellow
by looking
orange-red, which may be readily seen
When
light is repeatedly reflected
full
obliquely into an
internally.
by
empty metal
The red colour
vessel
which
is
gilded
of copper is also deepened,
reflection, to a bright scarlet.
thin leaves are
Certain metals in the form of very
transmitted light
transparent, and when viewed by
metals
different to those possessed by the
possess colours
light and
Thus, gold-leaf transmits green
transmitted light.
silver-leaf appears blue by
to the
of the metals when applied
in mass.
Taste.—A few
tongue
"
le"ave a peculiar
metallic" taste, which
is
pro-
PHYSICAL PROPERTIES OF THE METALS.
9
bably due to the action of the saliva.
Copper possesses
a characteristic faint nauseous taste.
Zinc also has a
slight metallic taste.
The majority of the metals, however, are tasteless when pure.
Specific Gravity or Density of a metal
may
be defined as the weight of a certain
bulk of such
metal as compared with the same bulk of
water.
All metals are lighter when molten
than when in the
solid state, with the exception of
bismuth, which attains
its maximum density just before
solidifying (see
p. 30).
The density
of a metal
dependent on the intimacy
of the contact between the molecules,
and is influenced
by the purity of the metal, by the mechanical
treatment, by the temperature of casting, and
by the rate
is
of cooling.*
The density of a metal is increased by mechanical
treatment, such as hammering,
wire-drawing or rolling.
Thus the density of platinum in the
cast state
which
increased to 21.45 by hammering.
Alteration of temperature also affects this
as
is
21.21,
is
expansion
is
Advantage
is
property,
caused by increase of temperature
a given bulk of metal will
therefore weigh less at a
higher temperature than at a lower one.
•
sometimes taken of this property of
density in extracting metals from their ores.
The extraction of platinum and gold are
examples.
The
following table contains the principal
metals, arranged
according to their densities, referred to
water at its
maximum density at 4° C. (39° P.). To facilitate comparison the densities compared with
aluminium, the
lightest of the common metals,
is also given in the
second column.
*
Roberts-Austen, " riitroductiuii to MetalUirgy,"
|).
14
DENTAL METALLURGY.
lO
Specific Gravity op Metals.*
i.
=
H
"c3
Water
1
B
0
11
<.
Heaviest.
Iridium
Platinum
Gold
Mercury,
.
.
22.4
21.5
19.4
8.0
14.4
54
13.6
12.0
5-1
-39°"C.,
/
Mercury, liquid
Lead
8.9
8.7
.
Nickel
Iron
Tin
Zinc »
.
solid, )
Palliidiuiii
7-3
Copper
Cadmiuiu
.
1.4
10.5
1
.
Silver
Bismuth
9.8
4-5
4.2
.
Antimony
Aluminium
.
3-3
8.5
3-3
3-2
7.8
2.9
7-3
6.9
6.8
2.7
2.7
2.6
2.2
I.O
Liglilcst.
3-9
3-7
substance
the resistance offered by a
of another substance.
to the penetrating action
between the degrees
Great differences are observable
metals in common use
of hardness of the various
admit of being scratched with
Hardness
Lead
is
so soft as to
is
can only be scratched by
the finger-nail, while others
The hardness of metals is imvery hard substances.
applications to mdustnal
portant in considering their
manufacture of jewellery
purposes gold used in the
with
is invariably alloyed
and for coining into money
pure
copper, to harden it, as
some other metal, such as
which
resist the attrition to
aold would be too soft to
Gold used
jewellery are exposed.
;
coins
*
is
and
The
articles of
specific gravity of a
metal
the metal.
the specific gravity of
is
determined by
first
weighing
PHYSICAL PROPERTIES OF
for artificial dentures
also
is
TFIE METALS.
I
I
hardened by the addition
of other metals for similar reasons.
The property of hardness is one of importance in selecting a metal for dies to be nsed in swaging metal plates, as
a die must be sufficiently hard to stand the necessary force
applied to it in stamping up the plate to the required
shape without becoming deformed to anymaterial extent.
It is partly on this account that zinc has been selected as
a suitable metal for dies, as it possesses hardness as well
as
most of the other properties necessary for a
On
die.
the other hand, preference
is usually given to
lead in the formation of a counter-die, mainly on account
of its greater softness, this property in a counter being
of practical importance.
The hardness
of metals diminishes with
an increase
The following table gives the relative
hardness of the more important metals compared with
the hardness of the diamond as loo.
To facilitate comparison, the hardness of the metals
when compared with lead, the softest metal in common
of temperature.
use, is also inserted.
Hardness ov Metals.
H
1
•M
o
12
too.
II
Diamond
5"
—
(-1
Diniiiond
Nickel
Tron
.
Copper
Palladium
I'latiniim
Zinc
Antiniony
.
.
.
lOO.O
46.8
45-6
45-2
41.6
36.8
35-8
33-8
6.3
Silver
2-5
Gold
Bismuth
2.4
2.4
2.2
2.0
1.9
1.8
.
Aluuiiniuni
.
(Jadniiiini
Tin
Lead
.
.
.
32-9
32-5
30.2
27-5
25.2
21.6
18.9
1.8
1-7
t.6
'•.S
1.4
1
.2
I.O
DENTAL METALLURGY.
12
The hardness
of metals
may be approximately
ascer-
tained by cutting them with a good steel knife.
Malleability is the property of permanently ex-
tending in
or rolling,
by pressure, as by hammering
without rupture. Most metals possess this
all
directions
property in a greater or
less
degree.
Gold
is
the
into
most malleable metal, and may be hammered
each grain of
leaves ^ swirott of an inch in thickness,
which
inches.
will cover a surface of fifty-six square
be extended to a greater
square inches,
extent and made to cover ninety-eight
silver the leaves
but on account of the lower density of
are thicker than those of gold.
of an
Iron has been beaten into leaves ^W^h
One
grain of silver
inch in thickness.
may
Malleability
is
often affected
by
when present in very
the presence of impurities, even
of ^lyW^h part of
small quantities. Thus the addition
gold quite brittle and
lead or of bismuth would render
are
the malleability of many metals
:
similar efEects on
metals.
produced by small admixtures of other
impaired when
malleability of nearly all metals is
The
long-continued hammering or
they are subjected to
may be restored by «n7^6a/^«^/,
rolling, but this property
metal to a uniform red
which consists in heating the
rapidly or
slowly-
either
heat and allowing it to cool
for
In some cases, as with copper
nsually the latter.
cooled
the metal be
example, it is immaterial whether
It is on
process.
or slowly in the annealing
rapidly
the malleability, by hamaccount of this impairing of
have to
plates for artificial dentures
mering
&c., that
during the process of swaging
be frequently annealed
them more pliable. The molecules
in order to render
positions by
forced into unnatural
of the metals are
PHYSICAL PBOPERTIES OF THE METALS.
M
hammering,
&c., and require occasional annealing or
softening by heat to bring them back again to their
normal condition. The relative malleability of metals
is determined by the degrees of
thinness of the sheets
that can be
irithout
produced by hammering or
by rolling
The more impo]-tant metals are
arranged according to their malleability in the
following table
annealing.
Oedeb op Malleability.
Most.
Mdllmblc.
1.
Gold.
JO.
2.
Silver.
ii_ ii-OQ
3.
Aluminium.
12.
Nickel.
4.
Copper.
13
Mercury
Zinc.
5-
(frozen).
Least Malleable.
6.
Platinum.
7.
Palladium.
^-
Lead.
9.
Cadmium.
Bismuth
Antimony
^
15.
16.
Iridium
J
14.
Brittleness.— When the metals
and have a tendency
leability,
hirittle.
are void of mal-
to fly to pieces
hammered or rolled, they are said to be brittle.
Antimony and bismuth are characteristic
metals at
all
when
brittle
temperatures.
Some metals which are very malleable at one temperature are brittle at another.
Zinc, for example, is
brittle
at ordinary temperatures,
between
but when heated to
100° and 150° C. (2 r 2^-302° F.)
it
becomes
malleable and can readily be rolled into thin
sheets,
whilst at 200° C. (392° F.) and upwards
it
again
becomes
and can easily be powdered in a morOther metals which are malleable at ordinary
temperatures become brittle when heated to a temperabrittle
tar.
ture just below their melting-points
and aluminium are examples.
;
lead, tin, copper,
DENTAL METALLURGY.
14
lead
Bearing in mind these properties of zinc and
be taken in the
at elevated temperatures, care should
metal
of dies and counter-dies for swaging
preparation
remove them
plates to
not allow them to
fall
carefiilly
when
from the moulds, and
hot, otherwise the dies
may
be broken owing to their brittleness.
Flow of Metals.— " When a malleable metal
mechanical processes such as rolling,
is extended by
hammering,
stamping,
ticles of
&c.,
a
true
flow of the par-
the metal occurs, analogous
m
all
respects
exerted
The pressure
fluids.
to the flow of viscous
transmitted in the
upon the surface of the metal is
interior of the
particle to particle,
mass from
direction
to produce ^ flow in the
is least."
and tends
where the resistance
*
like
,.n
^
fl
solid metals flow
application of this fact, that
importance in industrial
viscous fluids, is of great
art
and the production
1
The
by
rolling,
punching, &c.,
by the artificer.
from a single sheet
The manufacture of jelly-moulds,
the striking of a com
copper or other metal, and
when
of the metal
of
forms
of various complicated
entirely depends on the flow
are
suitably guided
the metal,
instances of this property,
into the sunken
pressure, being made to flow
familiar
under
fracturing, thus producmg
portions of the die without
The flow of metals is of much
a true impression.
laboratory, as it is this
importance in the dental
swaging metal plates for
made to flow by
dentures, the metal being
conform to all parts of
it may accurately
property which
artificial
is utilised in
force, so that
» h^,p1 "
vol
!rr395
Metals
").
C'
11
22
•
0" C-'Sn
Kobe.'ts-Aiisteu, Pruc. Hoy. Lid.
Fluids and .olid
I'-oi-'tieB Common to
and
PHYSICAL PROPERTIES- OF THE METALS.
the die.
less
1
which enables seamcrowns to be struck in one piece from the sheet
It is also this jiroperty
metal.
Ductility is the property of permanently extending by traction, as in wire-drawing, and is closely
allied
to malleability.
sarily malleable,
in the
exact
All ductile
but they are
ratio of
their
metals are neces-
not
necessarily ductile
Thus iron
malleability.
very ductile, and may be drawn out into very fine
wire
but it cannot be hammered or rolled out into
such thin sheets as some other less ductile metals.
is
;
Tin and
lead are
fairly malleable
are not sufficiently ductile to be
wires.
Wire
drawn
they
into very fine
manufactured by passing a cylindrical rod
through a steel plate known as a draw-fjlatc,
is
of metal
which
metals, but
pierced with a series of conical holes gradually
diminishing in diameter (see p. 78). It is generally
necessary to anneal the wire from time to time (see
is
otherwise it becomes hard and more or less liable
break after having passed through a certain number
of holes.
In certain cases, however, the annealing is
p. 12),
to
reduced to a minimum, in which case the
to be hard-clrmun.
"wire is said
The following metals are arranged according
ductility
to their
:
OnDER OF
DUCTXIilTY.
Maul DKclilr.
1-
*'^olf'-
2-
^'l^'cr.
8.
Cndniiiiin.
3.
Platinum.
g.
Aluminium.
4-
Ii'»n.
5.
Nicitol.
6.
Copper.
7.
.
,0.
I'illliulium.
Zinc.
II.
12.
Lead.
Least
J)iiclilc.
DENTAL METALLURGY.
i6
Tenacity
the property a metal possesses of re-
is
sisting fracture
when subjected
to a tensile or stretch-
one of the most important properties
their apof the malleable metals in connection with
With an increase
plication to industrial purposes.
This
ing force.
is
a
tenacity of
the
temperature
of
metal
is
usually
metals is
diminished. The relative tenacity of different
exactly
determined by taking bars of pure metals and of
one end and
the same diameter, fixing them firmly at
gradually
applying weights at the other, the load being
each bar is
increased until the utmost tveight which
been exactly
capable of suspending without breaking has
determined.
tenacity in tons per sq. in. of the
following
metals in the cast state is given in the
The approximate
common
table
Order of Tenacity.
Tous per
Tons per
Most Tenacious.
f Steel,
„
2.
3.
4.
5.
special
.
ordinary
Nickel
Iron, wrouglit
Platinum
Iron, cast
6. Silver
7.
8.
10.
Aluminium
38
20-26
11.
Zinc
3-0
12.
Cadmium
2-5
18.0
13.
Tin
2.0
S-15
14.
lO.O
15.
8.5
16.
Bismuth
Antimony
Lead
.
.
Copper
aold
As
25-65
6.7
.
•
.
.
.
.
6.9
.
.
.
Palladium
go-loo
.
.
sq. in.
sq. in.
9.
7-0
the tensile strength of metals
.
.
.
1.2
I.O
I.O
.
Least Tenacious.
is
very gi-eatly
afi^ected
temperatiire,
their purity, structure, and
must not be
given in tables of tenacity
bv variations in
the values
regarded as constants.
increased when metals
The tenacity is usually greatly
rolling,
mechanical treatment, such as
are hardened by
Thus, when copper is
&c.
hammering, wire-drawing,
PHYSICAL PROPERTIES OF THE METALS.
worked, the tenacity
1
may
be raised to over 18 tons per
Annealing will usnally reduce the tenacity to
that of the cast metal.
sq. in.
The
ratio in
which each metal possesses the properties
of malleability,
ductility
from the following
table,
and tenacity may be seen
in which the numbers repre-
sent the order given in the preceding tables
Metiils.
Gold
.
Silver
.
jMiiUeiibilitv.
6
2
.
Copper
Tin
3
9
4
6
5
Platinum
Palladium
Lead
Cadmium
1
1
7
7
8
3
7
12
8
10
10
4
2
5
I
12
14
9
13
14
15
Antimcinv
Elasticity
8
5
->
II
(l'ro>!en)
4
6
9
10
.
Mercury
Bismuth
Tenacity.
I
Aluminium
Zinc
Iron
Nickel
Buctilit}-.
:
12
13
the power a substance possesses
of
resuming its original form after the removal
of the
force which has produced a change in
that form.
The
good
is
elasticity varies considerably in difPerent
steel possesses it to a very high
metals
;
degree, but lead
scarcely exhibits a trace of this quality.
Within recent years advantage has been taken
of the
elasticity or " springiness " of
various metals, more especially of "pianoforte wire," for
regulating the teeth.
The elasticity of metals is also utilised
in matrices,
and is a matter of importance in
clasps employed as
a means of retaining partial
dentures in the
mouth.
DENTAL METALLURGY.
jg
hammering,
The operations of wire-drawing, rolling,
of metals,
&c generally increase the elasticity
annealing generally diminishes it.
gentle
very little elasticity, but by
whilst
Gold wire possesses
hammermg
this
may
made " springy." In this
be increased and the wire
employed for regulating purposes
state it is sometimes
keeps its colour better and
place of steel wire, as it
in
a
as pianoforte wire has
does not blacken the teeth,
its applicaso universal
tendency to do but it is not
elasticity
be used where great
bility, as it can only
often
The elasticity of a metal is
is not necessary.
with another metal (see
developed by combination
m
;
^
property of metals
this
itere Is^a^mit, however, to
their
incapable of regaining
beyond which they are
This point is known as
break.
original form, or even
the
liviit
of elasticity.
Fusibility
-AH
metals
t
when heated
•
iii
^.w
sufficiently
reqmred
state, but the temperatures
pass into the liquid
considerably.
to melt them differ
tenrpera39° C, but above this
Mercury is solid at
therefore always
liquid form, and is
ture it assumes the
Some metals are readily
-
ordinary temperatures.
and a few
heat, while platinum
ed below or at a red
by the highest attammetals can only be melted
,a
flame or the electric arc^
reat of the oxyhydrogen
^
considered as easily
Metals are usually
bright red heat
temperatures below a very
they melt at
melting above that point
lOOO^ C and those
or refractory.
«^ difficult of fusion
the high temperadifficult to judge
fluid at
t
Te
oZZ
Itt somewhat
.
terms commonly
melt metals from the
tures required to
red
degrees of heat, such as
ndicate different
used t
PHYSICAL rnOPERTIES OF THE METALS.
heat, white heat, &c.
but some idea of these temperabe gaiued by regarding a bright domestic
as bright red heat about 900° 0.
(1652° F.).
;
may
tures
fire
1
The following
a convenient practical classification
is
of the metals, founded on their degrees
of fusibility
Melting-points
oi'
Metals.*
Cent.
Mercury
-
Tin
+
.
Bismuth
Fusible at or below a red
heat
at
naces
Cadmium
320°
608°
325°
617°
.
.
Aluminium
temperatures Antimony
Silver
bright red heat Copper
white heat
Gold
Fusible only at the high
"1 Palladi um
est
temperature
at "
iNickel
tained
in
furnaces
Iron
bright white heat
j
Fusible only by the oxy-i
hydrogen flame or the 1^1**'""'"
:
.
415°
779°
625°
1157°
632°
1170°
960°
1760°
1050°
1922°
1061°
1942°
.
to
1500°
2732°
1600°
2912°
1600°
2912°
1775°
2500°
4532°
|'
:
,
electric arc
449
514
Lead
'-Zinc
and
38.2°
268°
Fusible above a red heat
easily attained in fur
l'"ahr.
39°
212°
,
J
3227°
Some metals, such as zinc, cadmium, and
antimony,
are readily converted into
vapour when heated, and all'
metals can be volatilised by the
use of either the oxyhydrogen flame or the electric arc.
Effect of Cold.— It has been pointed
out by Dewar f
when metals are exposed to the very
low tempera-
that
ture of
- 180^^
C, the tenacity
instance, the strength of steel
is
greatly increased.
and of German
For
silver is
nearly doubled at this low
temperature.
In some cases brittleness is
produced by exposure to
*
"Introduction
to
Metallurgy": Roberts- Austen
t Lecture before the Uoyal Institution, Loudon,
lcS9^.
DENTAL METALLURGY.
20
cold
thus, ingots of tin,
:
a Kussian winter,
fell
Fracture.—The
when exposed
to the rigour of
into powder.
appearance of the fractured sur-
as giving in many
face of a metal is of importance
or impurity of the
instances an indication of the purity
pure zinc
Thus the fracture of an ingot of
metal.
set at various
presents bright crystalline surfaces
the frequent impurity
angles, while the presence of
of black specks on the
iron is indicated by a number
and the duller and greyer
faces of the cleavage planes
fracture depends
appearance of the fracture. The
metal and partly on the
partly on the nature of the
manner in which solidification occurred.
relation to the fracThe following terms are used in
appearances can only be
ture of metals, but these
thoroughly learned by practice
satisfactorily
:
and
bismuth are chaGrystalline.-Zinc, antimony and
racteristic examples.
the
a,^amdar.-(Dmr^ from the last only m
As in grey forge pig-iron
size of the crystals.)
Fihrous.-^^oodi
wrought-iron
smaller
broken
partly
by
bending double.
nicking with a chisel and
backwards and forwards
^^^jty.— Tough copper bent
breaks presents a silky lustre.
of commerce,
CWz.m«a7-.-0bserved in^the grain tin
until
at
it
resembles
GonMcd
common
starch.)
'
or Vitreous.-(Glass-like.)
zinc
certain alloys such as
Crystalline
2,
copper
i
Character. -Much
Presented by
(Percy.)
attention
has
constituyears to the molecular
been given in recent
When the molecules of a substance
tion of metals.
regular manner
certain definite and
are arranged in a
cry^aU^^e. When growth
substance is said to be
Te
PHYSICAL PROPERTIES OF THE METALS.
in this
manner has been
free
2
1
and nninterrnpted, geo-
metrical forms are developed externally, characterised
by the constancy of the angles between similar faces in
all individuals of the same species {e.g.,
the same metal).
These definite forms are called crystals and the
substance exhibiting them is said to be crystallised.
If, as
mass of a cooling metal, the boundaries of the
individuals are the result of their mutual
interference
in the
Fig. 3.— Pure Gold.
Magnified 42 diameters.
the definite external forms cannot be
developed
;
but,
on examining the polished and etched surface of
the
metal the same regular internal arrangement is
seen
as
to
exist,
each individual
the mass
is
is still
spoken of as a crystal and
said to be crystalline.
Thus, Fig. 2, is taken from a micrograph *
of the
polished surface of a section of pure gold
etched with
* Taken by Mr. McWilliain
from tlie original sections kindly lent
by Prof. Arnold, Slieffield see
/'J,if/ini-rrim/, P'ebniiiry
:
7,
1896.
DENTAL METALLURGY.
22
aqua regia aud sliows the
by
crystals of the metal
their lines of interference.
Fig.
bounded
4 represents the
with
appearance of a similar section of gold alloyed
It will be noticed that the
0.2 per cent, of copper.
mass of the
copper had apparently remained in the
seen between the two
crystals as no difference can be
crystals, and the
structures excepting the size of the
cent, of copper.
Fig. 4.— Gold alloyed with 0.2 per
Magnified 42 diameters.
metal in the mass
ductile as before.
is
practically as malleable
still
Fig.
5,
and
however, shows the appeargo d
of a similar section of
ance under the microscope
and here the bright
containing 0.2 per cent, of lead,
they are
gold are seen as before, but
yellow crystals of
BOW
separated by thin
substance.
This latter
alloy of gold
and
and
crystallised
lead,
from
avails
is
of a brownish-coloured
a very fusible
and
brittle
and the gold having solidihed
was
centres while this alloy
PHYSICAL PROPERTIES OF THE METALS.
2T,
liquid, the still
thoroughly malleable crystals of gold
are surrounded by au envelope of brittle alloy, and
thus the whole mass
is
individual crystals are
tion of this sample
of the grains
quite brittle.
still
thoroughly malleable, a por-
was pounded in a mortar, and one
was beaten as thin as ordinary
Gold with 0.2 per cent, of
*"IG. 5.
To show that the
—Gold
silver (an
gold-leaf.
element of
hio-h
alloyed with 0.2 per cent, of lena
Magiiitied 42 dianietei-s.
melting-point) has a structure similar to that shown in
Fig. 4, while gold with 0.2 per cent, of tellurium (an
element of low melting-point) is similar to Fig.
5.
In the case of metals showing a fibrous or a silky
fracture the crystals have clung together and drawn out
into the thread-like forms seen on the
ruptured portion,
while in those showing a "crystalline" fracture the
crystals have not
drawn out and the rupture has taken
place along planes of weakness, sometimes
apparently
DENTAL METALLURGY.
24
along crystal junctions, and sometimes as true cleavage, and hence the crystalline appearance of the
fracture.
All metals under favourable conditions
tained in the form of definite crystals.
particularly gold, silver, and copper
may be obMany metals
— occur
—
lised in nature,
and are found most frequently
crystal-
as cubes
Metals usually crystallise on solidification
In order to crystallise a metal artificially
after melting.
a
quantity of it
it is sometimes sufiicient to melt a
or octahedra.
m
solidified, to
crucible, and, as soon as it has partially
possible
the crust on the surface, and as rapidly as
break
very
pour out what remains liquid. By this means
may be
beautiful crystals of bismuth (rhombohedral)
obtained.
To produce
this effect with the less fusible
necessary.
metals larger masses and slower cooling are
condensed
Crystals are also obtained when metals are
electrofrom the state of vapour or are deposited by the
former
the
In
decomposition of metallic solutions.
lytic
case the
more
yield crystals
volatile metals, such as zinc
somewhat
and cadmium,
readily.
crystals
yield
In the latter case nearly all the metals
currents
when deposited from their solution by electric
of feeble intensity.
happens that one metal may be
placing a strip
precipitated in the form of crystals by
In this way
its salts.
of another metal in a solution of
Tree )
lead (known as the "Lead
It also frequently
feathery crystals of
are deposited
when
a piece of zinc
is
placed
of lead acetate.
Micro- Structure.*—Much
*
For
m a sol iition
.
attention
is
now
de-
Stu.ly of
Iloberts-Austen, " Intrc.d,u.ti,.,> to
fuller details, see
Metallurgy."
PHYSICAL PROPERTIES OF THE METALS.
25
voted to the study of the structure of metals and
alloys
by the aid of the microscope, a method of investigation instituted by Dr. H. C. Sorby in 1
864.
As the sections of metals, however thin, are opaque,
they must be viewed by reflected light.
For this purpose it is essential that the surface should
be perfectly smooth, and this is effected by careful
grinding on emery and polishing with rouge. In
most
cases the structure of the metal or alloy is not
shown by
polisliing only, and must be made evident
by physical
or chemical processes which produce different
effects
upon the different constituents.
These processes vary with the nature of the metals
concerned. The carefully polished specimen is usually
submitted to the action of a suitable reagent
(such
as very dilute nitric acid) in order
to develop the
structure.
A
microscope fitted with powers varying from
30 to
350 diameters, and provided with special accessories
for
good
perpendicular
illumination,
generally
is
employed.
By
this
information
method
of
investigation
much
metals, alloys,
gained as to the structure of
and amalgams. For example, the micro-
scopical examination of the gold alloys
has
to
valuable
has been
show why the
done much
qualities of gold are greatly modified
by the addition of very small quantities
of certain
metals fas described on
p. 22).
In the author's opinion much of our future
knowledge
respecting the structure of dental amalgams
will have
to be gained by the aid of the microscope.
Conductivity of Heat and of Electricity.—
The superior power
of conducting heat
and
electricity
DENTAL METALLURGY.
26
is
one of the most prominent characters possessed by
The metals
the metals.
are the best conductors of heat
the solid bodies, but the power
being highest
of transmission varies very considerably,
brittle metalsin silver and copper, and lowest in the
and
among
electricity
bismuth and antimony.
power that
It is on account of their conducting
They are good
feel cold to the touch.
metals always
conductors, and therefore carry
away rapidly the heat
m
they are
from the part of the body with which
contact.
The order
heat
will
of conducting
power of the metals
for
the same, as
for dedricity is comparatively
which the
appear from the following table,* in
and
conductivity of silver
is
assumed
to
be lOO at
o'
C.
Conducting I'ower of Metals.
luir KIn-li-ii-ll !!
/(.( Iloiit.
100.0
oo.o
Silver
73-6
97.8
53-2
Copper
Gold
31-3
65-5
Aliiininiiiiii
Aliiniiniuni
Zinc
28.1
Zinc
20.
Cadmium
15.2
Iron
II.
Platinum
Silver
I
Copper
Gold
.
.
Ciubnium
Tin
Iron
Nickel
.
.
Mercury
Tin
(1
inid)
I3-S
76.7
.
29.6
.
14.6
.
14.4
.
12.9
Nicki'l
Lead
8.4
Antimony
Antimony
4.0
Bisuiutli
1.8
Mercury
Bismuth
.
Platinum
12.
.
8.4
8-5
Lead
14.S
.
Palladium
Palliidiinn
24.4
.
.
.
.
3-6
1.8
1.4
the electrical conrelative values obtained for
(juite
one temperature are not
dactivity of metals at
The
* Beckert, "
Eisenhuttenkunde,"
p. 6.
PHYSIOAL PROPERTIES OF THE METALS.
the same
ductivity
27
those obtaiued at another, as the concHviinuIu'd by a rise of temperature, but
as
is
not always at the same rate in each case.
Capacity for Heat, or Specific Heat.— Equal
weights of different metals require different amounts
of heat to raise them from the same to a higher
given
temperature.
The amount of heat necessary to raise
one part by weight of water from 0° C. to
1°
C. being
amount of heat required respectively to
the same weight of the following metals from
I,
the
to 1° G. will
be as follows
Specific
raise
o' C.
:
Heat of Metals.*
Aluminium
0.2143
Tin
Iron
0.1138
Antimony
0.0508
Nickel
0.1086
Zinc
0-0955
Mercury
Platinum
Gold
Lead
Bismuth
0.0333
0.0324
.
.
Copper
0.0952
Palladiinn
0-0593
Silver
0.0570
Cadniiiim
0.0562
.
.
0.0324
.
0.0314
0.0308
0.0567
.
From the above
table it will be seen that the
capacity for heat of the metals is very
variable.
If
small balls of equal weights of the different
metals are
exposed for the same length of time to exactly
the
same temperature and then withdrawn simultaneously
and placed upon a thin cake of wax, it will
be observed
that the metals having the greatest
capacity for heat,
such as iron, will
much
more
"melt"
rapidly than
their
way through the wax
those
having
a
smaller
capacity for heat, such as bismuth.
The
specific
temperature and
heat
is
their fusing-point.
increases with an elevation
greater
Any
* Kegnniilt, "
as the
action,
of
metals approach
such as hammering,
Courn filCnientairc,"
ii.
28.
DENTAL METALLURGY.
28
which increases the density of a metal, diminishes its
capacity for heat, but it regains its original value
after the metal has been again heated.
heat of
It is important to consider the capacity for
metals used for artificial dentures, as in the mouth they
frequently to
are exposed to varying temperatirres and
hot liquids.
The comparatively high specific heat of palladium,
this
combined with its low conducting power, makes
properties
metal suitable for artificial dentures, as these
plate
gold
would prevent the sudden chill felt with a
similar manner
on drinking a cold liquid, and also in a
liquids. It is
would assist in preventing scalding with hot
advantageously
be
quite probable that palladium would
high price did
in prosthetic dentistry if its
exclude it from the dental laboratory.
employed
not
for heat of aluminium,
combined
would render that metal
also very
The great capacity
with
its
lightness,
its other properties
suitable for dental plates, provided
did not
make
it
unsuitable.
when
Expansion by Heat.— Metals expand
generally in a degree
heated, and, within certain limits,
in temperature.
nearly proportionate to the increase
also in dentistry, it is
In many industrial arts, and
amount of eximportant to ascertain the exact
very
pansion
which
temperature
diff-erent
metals undergo
when
their
is raised.
represent the
the following table
own length, of a bar of the
extension, in parts of its
the
in temperature from
given metal during a rise
boiling-point of
(32° F.) to the
The
figures
Lezing-point
water,
100^^ C.
in
C.
(212° F.):
PHYSICAL PROPERTIES OP THE METALS.
29
Expansion op Metals by Heat.
(r rentes/
Cadmium
Jixpaiisioii.
.
Lead
Zinc
0.00306
=
0.00292
=
= ^l-j
=
= ^hs
=
= -FF?
= ^»
0.00291
.
Aluminium
0.00231
Tin
0.00223
.
Silver
0-00193
Copper
Bismuth
0.00167
.
0.00162
The above
coefficient of
^ij^
Gold
Nickel
0.00145
0.00127
Iron (malleable)
0.00122
Palladium
0.001 17
Iron (cast)
0.00107
Antimony
0.00105
Platinum
0.00089
table indicates
jsr
—
1
1
Least Expansion.
the
linear
increase or
expansion— that is, the increase
Most substances, however, expand
linear
in one direction.
equally in each direction, and the cubical
may be taken
_
—
expansion
as approximately three times the above
fractions.
Change of Volume on Solidification.— All
metals undergo a change of volume when they
pass
from^ the fluid to the solid state.
With the exception
of bismuth, which expands, all metals
contract on
solidification.
This change of volume is a matter of
great practical importance not only in the arts
but in
many branches
of dentistry.
It is one of the most important properties to be considered in the
selection of
a metal for the production of dies for
swaging
metal
plates, as the successful adaptation of
the plate
to a large extent upon the die being
depends
an accurate representation of the precise form of the mouth.
Owing to
this general property of contraction
it is impossible to
obtain a metal which will give an exact
reproduction of
the mouth.
The unavoidable shrinkage, however,
is
partially or wholly
compensated for by the ex])ans'ion
of the plaster model employed, and the
yielding condition of the soft tissues of the
mouth.
Although the
DENTAL METALLURGY.
30
somewhat greater than that of
other metals, it is almost universally employed for the
production of dies, as it possesses most of the other
properties necessary for this purpose (see p. 44). The
contraction of zinc
is
contraction of metals
is
often considerably diminished
by being alloyed with other metals.
The following table gives the percentage of change
the
in volume of metals on passing from the liquid to
cold solid state
*
:
Change op Volume on
Bismuth
•
.
.
Solidification.
increase of volume
2.30
1.02
decrease
Iron (cast)
Mercuryt
4-85
Tin
Copper
6.76
7.10
9-93
II. 10
Lead
Zinc
1
Silver
1.20
Other metals in common use, such as gold and
solidification,
aluminium, undergo change of volume on
the latter case
the contraction being considerable in
;
but the exact amount
of contraction of metals has only
been determined in a few
Galvanic Action.
—When
two dissimilar metals
which
in a fluid, the chemical action of
and
energetic on one than on the other,
immersed
are
more
is
cases.
current is
then brought into contact, a feeble electric
analogous
produced known as galvanic action, which is
heating the junction of a
to the result obtained on
antimony.
thermo-couple, such as bismuth and
and a steel
tongue,
silver coin be placed on the
If a
pen
*
t
or iron
nail
under the tongue, and the
Roberts and Wriglitson, Proe.
Grumnach,
Pln/.^: Sor., 5, 1884, PP-
Chem.-Zelt., 1901, 25 [84], p. 9i9-
edges
97-104-
PHYSICAL PROPERTIES OP THE METALS.
brought into contact, a feeble electric current is produced, giving rise to a peculiar bitter taste known
as
a galvanic taste.
This galvanic action is sometimes
experienced
when
mouth, where
different metals are in contact in the
they are continually bathed in the oral
The amount of action
fluids.
states of saliva
dition,
action.
;
infinitesimal in healthy
but in acid, or other unhealthy con-
a very efficient
Many
is
exciting fluid
is
in
constant
known in which galvanic
action has been experienced with combination fillings
instances are
and amalgam, the gold being found subsequently
corroded at the line of junction of the two metals.
In
one case the action resulted from a pin on an
u^jper
of gold
gold
plate striking an
amalgam
filling in
the lower
jaw.*
Seeing that electrical
when
efiects are
always exhibited
different metals are in contact
and moistened by
exciting fluids, and that the wider apart metals
are in
their positive and negative character the
greater will
be the action developed, the selection of amalgam
and
metals for use in the mouth ought to be
carefully
considered and the contact of metals of wide
electrical
differences avoided.
The following
list gives the principal metals,
arranged
according to their usual relative electrical
position to
each other in most lifjiiids.
Commencing with the most elcdro-ner/ntivc and passdown to the most clectro-x)osif,ivc, they
ing regularly
.
have the following order
Negatuk.
— Gold,
:
platinum,
palladium, antimony,
bismuth, lead, nickel, iron, tin,
cadmium, zinc, aluminium,
l'(j,srnvK.
mercury,
silver, coj)per,
—
*
Mr.
iriuiihy, .Invni.
of
J!ril.
Drnl.
.l.v.vor..
vol. xviii. p. 300, 1S97.
32
DENTAL METALLURGY.
In this series each metal is usually nccjative to
those below it, and positive to all those above
all
it;
consequently none are absolutely positive or negative.
The above series can only be regarded, however, as a
with
general arrangement, as the order varies slightly
may be
every different liquid in which the metals
immersed.
CHAPTER
II.
ACTION OF CERTAIN AGENTS ON
METALS.
Air,
—With one or two
go no change in dry
aii-,
exceptions, the metals under-
and are not sensibly altered
in
moist air at ordinary temperatures, those most readily
acted upon being copper, lead, zinc and iron.
In moist
air, in
the presence of carbonic acid, copper becomes
coated with a green layer of carbonate called verdigris.
Lead and zinc are also acted upon, the surfaces of
these metals becoming coated with a greyish-white film.
Iron is readily oxidised, forming a brown coating known
as
riost.
When
heated, the metals are
more readily oxidised
than at the ordinary temperature.
ordinary conditions retains
siderable time, but
its
Thus, tin under
bright surface for a con-
when heated
it is
quickly tarnished.
Sulphuretted Hydrogen.— In
the presence of
sulphuretted hydrogen certain metals are tarnished or
blackened owing to the formation of sulphides.
Silver
and copper are readily blackened, while
also tarnished.
coated with a
tin and lead are
The surface of cadmium becomes slowly
yellow film of cadmium sulphide.
Sul-
phuretted hydrogen has very
other metals.
little
or no action on the
C
DENTAL METALLURGY.
34
Water.
action
— Perfectly
pure water
on the metals.
When
lias
practically
dissolved
no
oxygen and
carbonic acid are present as in ordinary water, copper,
with the
lead, iron and zinc are gradually corroded
formation of a coating of an oxide or of a carbonate of
surface
the metal, which in some cases protects the
from further corrosion.
Acids.
With the exception
of gold, platinum and
all
iridium (and other metals of the platinum group),
upon by
the metals are dissolved or more or less acted
Gold and platinum are not soluble in any single
gold), but are
acid (except selenic, which dissolves
nitro-hydrosoluble in some mixtures of acids, such as
acids.
chloric (aqua regia).
Nitric
Acid.—Tin and antimony
are converted into
other metals,
oxides by the action of nitric acid all
the acid and
with the exceptions quoted, are soluble in
some being readily soluble in the stroug
;
form
nitrates,
attacked by the dilute
acid, while others are more easily
majority of
This acid is the best solvent for the
acid!
the metals.
acid has no action on gold,
little action
platinum, iridium and mercury, and very
It dissolves the
lead, copper and bismuth.
HydrocMoric
on
^cwL—This
silver,
according to the
other metals with more or less facility,
strength of acid used, forming chlorides.
sulphuric acid
Sulplmnc ^cirf.— Boiling concentrated
lead sulphate and
converts lead and antimony into
antimony sulphate respectively.
are
silver, aluminium and mercury
Bismuth,
zinc,
are not
by concentrated sulphuric acid, but
slightly affected by the
acted upon or are only very
dissolved
dilute acid.
All other
common
metals, with the excep-
ACTION OF CERTAIN AGENTS ON METALS.
35
of
tiou
platinum,
gold,
iridium
and palladium, are
soluble in this acid, whether strong or dilute.
Acetic Acid.
— Lead
is
rapidly attacked, and copper
slowly acted upon, by acetic acid (vinegar)
acid has little or
Alkalies.
;
is
but this
no action on the other metals.
— Comparatively
few of the metals are
acted upon by alkaline solutions
;
aluminium, however,
readily dissolved in solutions of caustic potash or o£
soda.
Zinc, lead, cadmium and tin are also slowly
is
attacked by solutions of the alkalies. Alkaline chlorides
convert metallic silver into its chloride, which is dissolved in an excess of the alkaline solution.
slowly dissolves copper.
Exposure in the Mouth.— All
Effect of
metals,
with the exception of
palladium, are
the month.
the
affinity
Ammonia
more or
less
gold,
platinum
the
and
acted upon by exposure in
Copper, silver and cadmium, on account of
which they possess for sulphur, are the
metals most readily acted upon
when exposed in the
mouth, owing to the presence of sulphuretted hydrogen.
Carbonic acid, which is always present, acts with
greater
facility
metals,
while aluminium
on zinc and lead than
alkaline fluids of the mouth.
action
upon other
by the
some cases
readily attacked
is
Although
in
slow in
healthy states of saliva, yet the
presence of vegetable acids in articles of food, such
as fruit,
is
and
of drugs
as
of sulphuretted hydrogen,
niedicine,
greatly
and
facilitate
tlie
the
taking
action,
causing the metals to become black in a comparatively
short period.
The
action
is
also facilitated
when two
metals are in contact in presence of the acid fluids,
thus giving rise to galvanic action (see
Soluble
p. 30).
salts
which
are
injurious
to
health
are
sometimes
DENTAL METALIJJRGY.
36
produced by the action of the
saliva.
The
effect
metals possessing a strong affinity for sulphur
on
may be
modified in a few instances by the admixture of other
Thus, the addition of platinum to silver tends
metals.
to
minimise the
On
sulphur.
affinity
which the
latter possesses for
the other hand, the necessary admixture
of other metals
may
accelerate the action.
Gold in a
pure state retains its colour in the mouth, but when
alloyed with copper it becomes more or less tarnished,
according to the quantity of base metal present.
Solvents for Metals.
—The principal solvents used
to eifect the solution of metals are nitric, hydrochloric,
sulphuric, and nitro-hydrochloric acid (aqua regia). This
when required
last is prepared,
only,
by mixing one part
parts of
of concentrated nitric acid with three to four
concentrated hydrochloric acid. This mixture evolves
chlorine,
The
which attacks the metal and
following
table
contains
solvents for the different metals
Autiniony
Bismuth"
Cadmium
Copper
QqIiJ
Iron
.
list
of
the
:
.
.
.
•
Hydrochloric acid.
Nitro-hydrochloric acid.
Nitric acid.
.
Do.
•
.
.
•
.
.
Do.
Nitro-hydrochloric acid.
.
.
Nitric acid (dilute *) or hydrochloric
acid.
Lead
.
Mercury
jsficliel
Nitric acid.
.
Nitric or nitro-hydrochloric acid.
Do.
Nitric acid
.
.
.
f^ilver
.
rpi,,
.
(liot).
Nitro-hydrocliloric acid.
.
Nitric acid (dilute).
Hydrochloric acid (when heated).
•
.
.
*
•
.
.
Palladium
Platinum
best
Soh-cmt.
Metiil.
AlumiiiiMiii
effects its solution.
a
Hydrochloric or siilphuric acid.
.
Dilute acid
=
equal parts of acid and water.
CHAPTER
III.
ALLOYS.
Most
to
metals are capable of uniting with one another
form a
class
of bodies
termed alloys, in which
the physical properties are sometimes quite different
from those of the constituent metals. Alloys, however,
being composed of metals, will possess all the physical
and chemical characteristics common to metals they
;
have the metallic Instre, are more or less ductile, malleable, elastic,
and sonorous, and are good conductors of
While retaining, however, these
heat and of electricity.
characteristics, the bodies
produced are frequently so
modified in some of their properties that they often do
not resemble either of the constituents and may consequently be regarded as
istics
new
metals, having character-
peculiar to themselves.
The
most generally useful are frequently those
whose constituents are most dissimilar in character.
alloys
By means
of alloys, therefore, the
number
of useful
metals
is multiplied, as it were, and usefulness sometimes given to such as are separately of little value.
Comparatively few of the metals possess properties
such as render them suitable to be employed alone, but
most of them have important applications in the form
of alloys.
Pure gold possesses many good qualities,
DENTAL METALLURGY.
^8
seldom used alone, as it is too soft to resist wear
and tear copper is therefore added to harden it as
Bismuth and antimony have
well as lower its cost.
comlittle application in an uucombined state, but in
bination with other metals they form a series of alloys
dental
of much value, several of which are used in the
from
predict
It is not always possible to
laboratory.
but
is
;
the properties of the various metals employed what
from given
will be the character of an alloy formed
proportions of each.
Thus,
it
might be supposed that
gold and lead, which are both very malleable metals,
would produce a malleable alloy but, although these
obmetals unite readily in all proportions, the alloys
;
utility
tained are in some cases very brittle and without
in the arts.
one
Metals differ in respect to their affinity for
equal facility
another, and do not therefore alloy with
and iron, but the
is difficult to unite silver
;
thus,
it
former combines readily with gold, copper, or
The
much
^
received
subject of the constitution of alloys has
progress
attention within recent years, and great
has been
made
alloys with that
it
lead.
metallic
in connecting the behaviour of
As the result of research
of solutions.
that alloys
has become more and more evident
may
(i) Those which
be divided into two main classes:*
constituent metal?, and
are merely solutipns of the
contain compounds in solution, for
(2) those which
as true chemical comw'hile few alloys are regarded
compounds
solution
pounds, most series of alloys hold in
are disposed to attribute
to which some experimenters
definite chemical formula.
*
ll,,be.-ts-A.>sten,
1897.
'Alloys"; (^uiU.r Lectures, Ho.Mcty
.,r
Arts,
ALLOYS.
As
compounds
these
molten mass of metals,
separate
them
39
dissolve in all proportions in the
it is
very
difficult to satisfactorily-
for examination.
Although metals may be mixed in the fused state,
it by no means follows that they will remain in admixture if they are allowed to cool slowly, or sometimes
even rapidly.
and zinc be thoroughly mixed
and slowly cooled in a deep mould,
If lead
in the molten state,
the two metals separate almost completely
being lighter,
rises to
at the bottom.
the zinc,
;
the top, leaving the heavier metal
With other metals there
is
sometimes
a tendency, on solidification, for one of the constituents
to
become concentrated
in the middle or at the surface
of the mass, thus giving a casting
homogeneous.
It is
now
which
not perfectly
is
well established that most of
the possible associations of any two metals have more
than one point of
solidification,
and do not
pure water does, at a single point.
many
There
" freeze," as
is,
however,
one particular association of
the two metals which is more fusible than the rest
in
series of alloys
of the alloys of the series.
eutedic alloy, and
tion, that
is,
it
This alloy
is
called the
possesses a single point of solidifica-
when the
sharply as a whole at
eutectic alloy
a given
is
cooled
temperature.
it
sets
Many
two metals contain an eutectic alloy
and consequently have two points of solidification.
As a molten mass of alloy cools down it begins to
solidify at a certain point, but the eutectic alloy on
account of its low solidifying-point remains fluid, and
entangled in the portion which has set, until the tem-
associations
perature
alloy, at
of
falls
to the solidifying-] )oint of the eutectic
which temperature
completed.
There
is,
solidification of the
therefore, in
many
cases
mass
is
abundant
DENTAL METALLURGY.
40
opportunity in the interval between the
initial
point of
and that of the eutectic for
the mass to arrange itself in a peculiar way which
frequently results in a want of uniformity of the mass.
solidification of the alloy
A
the
striking instance of this
alloys of the
is
afforded in the case of
silver-copper series,
all
of
which,
except the eutectic alloy, exhibit divergencies in comThe eutectic alloy of the series contains 71.8
position.
preper cent, of silver and solidifies at 778° 0. The
standard
sence of the eutectic has been detected in
per cent, of silver) and in several other
members of the series, and consequently these alloys
silver (92.5
have two points of
solidification.
case of standard silver, the initial solidify883° C.
ing-point of which has been ascertained to be
to
begins
it
As a molten mass of this alloy cools down
To take the
but the eutectic alloy remains fluid,
until the
and entangled in the portion which has set,
the
temperature falls to 778° C, at which temperature
solidify at 883" 0.,
the interval
mass sets sharply as a whole. During
is ample
between these two solidifying-points there
a peculiar
opportunity for the mass to arrange itself in
the mass.
way, hence the want of iiniformity of
The
eutectic alloy in this
and in several other
series
composition corresponding
of alloys occurs exactly at a
has led to the conclusion,
to a definite formula, and this
alloys are chemical
as previously stated, that eutectic
compounds.
is, however,
The exact composition of the eutectic
The most recent experiments
difficult to determine.
eutectic alloys does
have shown that the composition of
with simple atomic propornot in general correspond
metals, and this fact, and the
tions of the component
A.LLOYS.
theory of the subject, point to the conclusion that the
eutectic alloy
is
not generally a compound, and hence
Further research, however,
should not have a formula.
is
necessary before any definite conclusion on this point
can be generally accepted.
The tendency
of the con-
known
as liqucdmi,
stituents to separate on cooling is
and
is
a matter of importance
industrial purposes, as for
difes,
in"
casting alloys
for
In some instances
&c.
where liquation has taken place a more homogeneous
alloy may be obtained by breaking up the ingot and
remelting (see also
p.
175).
Physical Properties of Alloys.
Colour.
—The
strongly coloured
copper and gold, are very
much
metals, such
as
modified in tint by
alloying with metals of light colour, such. as aluminium,
Thus, when 5 per cent, of aluminium
added to copper the resulting alloy has a beautiful
silver
is
and
tin.
golden-yellow colour, and zinc
when added
in certain proportions acts in a similar
colour of gold
is
is
The
manner.
modified by the addition of only one-
twentieth part of
when gold
The colours
to copper
silver,
and
it
alloyed with half
is
entirely destroyed
its
weight of
silver.
of alloys, however, are not always dependent on those of the separate metals.
For example,
when
of
thirty -nine parts of gold are
aluminium
an
ijitensely
obtained.
Antimony,
weight of
copper
also,
added
to eleven parts
ruby-coloured
when
alloy
is
fused with an equal
produces a violet
alloy
known
as
" regnlns of Venus."
Density.
the mean of
—
'I'he specific
gravity of an alloy
is
rarely
the densities of the constituent metals,
DENTAL METALLURGY.
42
When
being sometimes greater and sometimes less..
has
contraction
the density is increased it shows that
occurred, and chemical combination has probably taken
place between the constituents.
When
c.qmnsion takes
place by the union of the metals, the density will be
below that calculated from the densities of the constituents.
Fusibility.
—In
nearly
all
of an alloy is lower than the
cases the melting-point
mean
melting-point of the
conconstituent metals, and in some instances it is
either of its
siderably lower than the melting-point of
constituents.
bismuth with one part of
temperature of
lead and one part of tin melts at a
An
alloy of
two parts
of
melting-point of
93° C. (200° F.), whilst the lowest
232° C. (449' F-)the constituent metals is that of tin,
the
By the addition of a small quantity of cadmium
melting-point
reduced
is
to
65° C.
(150° F.) (see
Fusible Metals, p. 51).
expansion of alloys is
of
the ratio of the relative volumes
Expansion by Heat.— The
approximately
in
the constituent metals.
Specific
the
mean
capacity for heat of alloys is
which
specific heats of the metals
Heat.— The
of the
compose them.
Conductivity for Heat and for Electricity.—
to
an alloy are found in some cases
powers of the combe the mean of the conducting
have apparently no
ponent metals, and in others to
mean.
relation whatever to such
the
Alloys are generally harder than
These properties
in
Hardness.—
mean hardness
*
of
the constituent metals.*
Calvert and Johnson, PhU.
4tli series, xvii. p.
This
114
is
ALLOYS.
43
especially noticeable in the silver-platinum alloy
as
"Dental Alloy
" (see
p. 174).
contrary, the hardness
lated, tin-zinc alloys
is
known
In some cases, on the
slightly less
than that calcu-
being examples.
Malleability and Ductility.
—These
properties
and sometimes completely deThe brittleness produced
stroyed by alloying metals.
by the addition of lead to gold has already been menare usually diminished
tioned.
Action of Solvents.
alloys
is
— The
sometimes very different from their action on
the constituent metals alone.
uble in nitric acid, but
alloyed with
much
much
is
gold
it is
Thus, platinum
is
insol-
dissolved in this acid
when
silver; silver also
when
alloyed with
not affected by nitric acid, but
completely soluble
excess.
action of solvents on
when present
it
is
in the alloy in large
Generally speaking, however, alloys are readily
soluble in the acids which are solvents of
the con-
stituent metals.
Preparation of Alloys.
adopted to effect the union of
is,
method ordinarily
metals is by fusion
that
—
melting them together, usually in a graphite crucible.
To do
of
— The
this successfully, however, requires a
the properties
Sometimes the
of
the various
metals
knowledge
employed.
mixed
and melted
together, but in other cases one of the metals is melted
first and the others subsequently added to it, sometimes
in the fluid state, but more often in the solid.
A little
charcoal powder should be placed on the surface of the
charge to prevent oxidation, and the lifjiiid metal
constituents are
should be carefully stiiTed with an
ii'on
or fireclay rod
and in sach a manner as to secure
most complete intermixture without liability to in jure it
after each addition,
DENTAL METALLURGY.
44
The molten
an oxidisiag atmosphere.
alloy should be poured at the lowest possible temperaby exposure
to.
ture consistent with the
proper degree of
liqiiidity,
excessive heating always being avoided.
—There
Alloys for Dies and Counter-Dies.
are certain properties which
metallic die
it is
indispensable that a
and counter-die should possess in order
fully the requirements of the dentist.
to
These
answer
may be summarised as follows
hard to resist aiiy
1. A die should be sufficiently
necessary force applied to it in stamping the plate
during swaging without suffering any material change
in the form of
its face.
It should not to
2.
any material extent contract in
the act of cooling.
It should be fusible at a
3.
should not be brittle,
4. It
low temperature.
but should be sufficiently
hammer
cohesive to resist the repeated blows of a heavy
these
without cracking. No metal possesses perfectly
hardness, non-contractibility, fusibility
or two
cohesiveness, although metals possessing one
properties
and
of
of these are readily obtainable.
Much
pended
time and thought have therefore
in the effort to discover
some
alloy
been ex-
which
shall
referred to,
possess more fully the several properties
of metals
but although a large number of combinations
these^ are
of
have been suggested, comparatively few
a die it is
In selecting an alloy to serve as
used.
nature of some
necessary to bear in miad that the
melting, and that their
is changed by repeated
alloys
Thus, an
altered.
physical properties are materially
answer the requirements of a die for a time,
alloy
may
but
very
much
deteriorate
by constant
use.
Some
ALLOYS.
when they
alloys also,
tend to " liquate
" or
solidify
45
from a
state of fusion,
even separate into two distinct
which may
layers of different composition, a property
prove fatal to the
the bottom layer will
die, as
fill
up
the deeper portion of the mould representing the most
prominent part of the
and may be
and
soft
totally
purpose of swaging.
unfit for the
The
die,
most frequently employed for
alloys
counter-dies are as follows
Type Metal. — The
:
better qualities of
this alloy
antimony
consist of three parts of lead with one part of
and one part of
tin.
In different proportions, however,
sometimes with
these metals,
dies or
the
addition of small
quantities of copper and other metals, form
different
grades of type metal (see also p. 211).
This alloy is sometimes used for dies and
less fre-
quently
for
"when used
adding to
counter-dies.
as a counter to a zinc die it
it
states *
Richardson
is
an equal quantity of lead
;
that
improved by
may
it
also
be used in the form of a die in connection with a lead
counter after rough stamping with a zinc die."
Type
metal
is
considerably harder than lead, but a
little
softer
and gives sharp castings. It melts more
readily than zinc, being more fusible than the average
than
zinc,
and the contraction
than one-half that of zinc.
It is somewhat
and therefore needs very careful handling when
fusibility of the constituent metals,
is
less
brittle,
used as a
with the
die.
air
When
lead,
melted in contact
even when
taken, thus the composition
after repeated melting.
*
is
the antimony and tin are oxidised
more readily than the
is
the alloy
When
is
all
much
precaution
very liable to alter
preparing this alloy the
" Mecliiiiiicnl Dentistry," 1S94 edit.
p.
124.
DENTAL METALLURGY.
46
lead
and
then the anti-
tin are first melted together,
added, a layer of charcoal being used to prevent
Excessive heating must be avoided.
oxidation.
mony
Babbitt's Metal,— This
part,
antimouy two
and
parts,
is
an alloy of copper one
tin six parts
;
the propor-
however, vary considerably with different makers.
"iThe melting-point of this alloy is lower than that of
zinc and somewhat higher than that of lead, so that
tions,
counter-dies of the latter metal can be readily
The alloy contracts but
it with proper care."
solidification
brittle,
brittle
and
and is nearly as hard
as zinc, btit
It is
needs care in using.
by the addition
more
of
made
to
little
on
somewhat
rendered
less
tin.
The following proportions of the above metals are
recommended by Fletcher for dental purposes Copper
one part, antimony two parts, tin twenty-four parts.
:
This alloy melts at a little lower temperature than the
is
above, and on account of the larger quantity of tin it
somewhat less brittle than Babbitt's metal of the proportion given above.
Haskell recommends the following alloy for dental
Copper one, antimony two, tin eight. " This
work
:
alloy is nearly as
hard as zinc and has
less shrinkage.
used to finish the swaging of a plate after being
As this alloy
nearly completed on the zinc model.
fuses at a lower temperature than lead, it is necessary
It
is
forms a constituent,
such as lead five, tin one. The die should also be quite
before
cold and covered with a quantity of whiting
to have a counter-die in
inserting
it
tin
in the molten metal."*
Babbitt's metal
is
copper with half the
*
which
best prepared by
tin,
first
melcing the
then adding the antimony and
H. Rose, Brit. Jimm. of Unit. Sc.
1895,
P-
53i-
ALLOYS.
the remainder of
finally
the
tin,
47
stirring well after
each addition and then casting into suitable moulds.
Charcoal powder should be thrown on to the surface
of the metal to prevent oxidation.
to waste
and
alter in
This alloy
is liable
composition by repeated melting.
—
Spence's " Metal." This is not, strictly speaking,
an alloy, but a compound obtained by dissolving metallic
The sulphides of iron,
sulphides in melted sulphur.
lead,
antimony and zinc are usually employed in vary-
ing proportions according to the quality of the product
desired,
which
depend upon the use for
will naturally
The Spence's "metal" usually
employed for dies is " sulphide of iron," made by
melting iron with excess of sulphur. The compound
which
it
is
designed.
melts at i6o° C. (320° F.), expands slightly on cooling
and gives very good castings it is hard although somewhat brittle, and needs care in handling. This " metal "
should be melted in a fireclay crucible and not in an
;
By
iron ladle.
remelting, loss of sulphur
is
invariably
occasioned and the composition of the mass altered.
Alloys of Zinc and
Tin.— These
alloys
are
frequently employed in casting dies for swaging plates,
and are best prepared by melting the zinc and then
adding the tin. According to Richardson, an alloy
suitable for dental purj)oses,
consisting of zinc four
one part, " fuses at a lower temperature, contracts less on cooling, and has less surface hardness
than zinc. This alloy is also more rigid than zinc and
parts, tin
less brittle."
Fletcher
two
and
It
parts,
recommends the following proportions
tin one part, and states that all alloys of
:
zinc
zinc
tin are superior to zinc alone for dies.
may
be remarked, however, that in casting alloys
DENTAL METALLURGY.
48
which zinc predominates there is a
tendency for the metals to separate at the bottom of the
mould, and this tendency increases as the proportion of
of zinc
and
tin in
tin decreases.
The waste
in melting is greater
when
zinc
is
in
All the alloys of zinc and tin give sharp
excess.
and on this account are largely employed for
casting ornamental objects (see also p. 206).
Alloys of Tin and Antimony. Alloys of these
Eichardson gives
metals have also been used for dies.
the following proportions tin five parts, antimony one
castings,
—
:
This alloy has a low melting-point, contracts
but slightly on cooling, is harder than tin, and suffiIt is, however, readily oxidised on
ciently cohesive.
part.
melting, and should be poured as soon as thoroughly
Alloys of tin and antimony are harder than
molten.
tin but less malleable,
brittle
greater
is
and the tendency
the
as
proportion
of
become
antimony
to
increases (see also p. 2 7).
1
Brass.—"
dies, brass,
Before the introduction of zinc for dental
an alloy of copper and
this purpose.
It is generally
zinc,
composed
was used
for
of two-thirds
copper and one-third zinc a small percentage of lead
being sometimes added when used for dental purposes.
;
Brass
may be melted and poured
to ensure
good results
it is
the same as zinc, but
as well to have a good
head
This can be
of metal for the die to contract from.
of sand on
full
effected by placing another casting ring
bell-shaped
the one containing the model, and catting a
comes
cavity in the upper ring, tapering down until it
back of the plaster model. The model is then
removed and the upper ring adjusted to the lower, and
brass can
securely cemented to it by sand the melted
to the
;
ALLOYS.
49
then be poured through the opening on to the sand im-
and when hard and the casting removed and
cooled the bell-shaped piece of brass may be sawn off.
It must be mentioned that the sand impression should
be smoked, and a good carbon surface produced on it
by burning resin. This greatly improves the surface of
pression,
the casting."*
Other Alloys for Dies.
lead with
tin,
—A
of
series
alloys of
bismuth and antimony, having compara-
and possessing other properties
necessary for a die, are given by Austen in a paper on
His results are embodied in the followmetallic dies.f
ing table, in which zinc is introduced for the purposes
tively low melting-points
of comparison.
Alloy.s for Dies.
I
Lead.
Tin.
BisAntimutli. mony.
Zinc.
Contrac-
Haivl-
BHttlc-
tion.
ness.
ness.
.00133
.00200
.00066
.00266
.00566
.00500
2.7
00433
1.4
2.8
McItiiii;'-i)oiiit.
200° F.
200°
250°
300°
320°
340°
420°
440°
779°
93° C.
93°
121°
139°
160°
171°
216°
227°
415°
2-5
2-3
1-7
1.9
2.2
•00633
.01366
I
In the above table the hardness of zinc
is
taken as
and the brittleness as five those alloys having a
hardness below five being malleable, and those above
Kve being more brittle than zinc.
one,
;
*
K. Rose,
t
Am.
/////. .Itmni.
Jimnt.
nf Dciil
11/ Drill. Sr.^
.
Sr., 1895,
xx.wiii.
vol. vi. p. 367.
D
p.
530.
DENTAL METALLURGY.
50
Fusible Metals.
This
uame
is
given to a series of alloys which melt at
very low temperatures, and consist chiefly of tin, lead
and bismuth, with occasionally the addition of cadmium
Many of the alloys obtained by the
and mercury.
union of these metals, in different proportions, melt at
far
a temperature below the boiling-point of water and
below the melting-point of the most fusible metal
entering into their composition.
Tin and bismuth both have low melting-points and
they readily combine in all proportions when fused
together, the resulting alloys being more fusible than
either of the metals taken separately.
very small quantity of bismuth imparts to tin more
hardness, but the alloys become brittle as the pro-
A
portion of bismuth increases.
Alloys of
tin,
bismuth
and lead are more fusible than those containing only
these
two of these metals. It is difficult to obtain
as there is
alloys in a perfectly homogeneous state,
somewhat at the
a tendency for the lead to separate
bottom
of the
mass while solidifying from
a state of
are rapidly tarnished in the air, and
above
more so in boiling water. The alloys of the
addition
the
metals are rendered still more fusible by
readily
being
alloys
of cadmium, some of the resulting
fusion.
They
melted in boiling water.
Cadmium, however, does not
render the alloys so britle as bismuth.
The
following
melting-points of a
table
shows
number
the
composition and
of " fusible metals "
:
1
1
ALLOYS.
51
Fusible Metals.
Hi till"! 11 1
-Li
1
11
nil oy
po \vi t z
4
Wood
s
ulloy
1;
8
Fusible
Jl
Fusible
c
0
3
J
2
I
2
4
2
8
2
10
2
,,
s'
2
8
„
3
,
e
)i
51
)I
1'
!)
i»
:)
n
11
2
3
I
I
3
2
S
I
'3
I
167°
170°
175°
187°
197°
197°
200°
202°
203°
310°
320°
I
I
I
I
I
2
3
2
I
4
4
12
12
IS
I
4
Mi,'ltinf4'-l)0iut.
145° F.
150°
160°
8
lOi
,
CtHliiiiuiii.
1
2
Diilton's.
Newton's
4
3
Fusible
Onion's
Ucll
Lb
Lend.
J
2
0
16
8
ii
Tin.
331°
338°
341°
352°
392°
16
All the fusible alloys are brittle and expand on cool-
ing and are
all more or less
Preparation. Fusible
hard.
—
melting the
are
alloys
prepared
constituents together under a
charcoal and well stirring with a stick of hard
before pouring.
Mercury
is
of one-sixteenth of its
alloy " a
new
alloy
temperature of the
is
formed which
body.
still
Thus, by the addition
weight of mercury to
human
wood
sometimes added to
further lower the melting-point.
by
layer of
"
Darcefs
is fusible at the
The addition
of one
two parts of mercury to "Newton's alloy" also produces a very fusible alloy, and any of the fusible
metals may be rendered more fusible by the addition
of mercury.
The mercury is added after the other
to
metals are perfectly melted.
DENTAL METALLURGY.
52
Uses in the Dental Laboratory.— In
tbe
dental laboratory fusible metals are mainly used for
"fusible plugs" to vulcanisers, the composition of the
alloys being such that the plugs will
"blow
out,"
when the temperature exceeds about 350°
i.e.
melt,
F. or 177" C.
Fusible metals have been used in crowu, bridge, and
vulcanite work, and novel methods have been introduced
for accomplishing in a simple
manner many kinds
dental work with fusible metals.
of
In a very interesting
paper read before the Britiah Dental Association in 1891,
E. P. Lennox of Cambridge drew attention to a number
work.
of uses for these alloys in connection with bridge
Mellotte has introduced the following fusible metal
for
crown and bridge work
:
bismuth
8, tin 5,
lead 3.*
This alloy melts at 100° 0. (212° F.) and expands on
It is harder than tin, but not so hard as
solidification.
For obtaining accurate models with
zinc, and is brittle.
metal he uses a compound of potter's clay
and glycerine known as " moldine," which retains its
it stiffens, however, with constant
plasticity for months
this fusible
:
use,
little
but
may be made
plastic
by moistening with a
glycerine.
Determination of Melting-point of Fusible
Alloys.— A very simple method for determining the
the
melting-point of a fusible alloy consists in melting
burner.
Bunsen
alloy in a porcelain crucible over a
thoroughly melted the flame is removed and a
thermometer held carefully in the molten mass.
When
The temperature
at
which
solidification takes place is
be readily ascertained, as the mercury
stationary for
thread of the thermometer will remain
The
some considerable time when this point is reached.
noted
;
this can
* Efisip:, "
Dental Metallurgy," 1893,
p. 263,
ALLOYS.
53
thermometer, which becomes embedded in the
alloy, is removed by agaiu melting the alloy.
When
due precaution
is
taken there
is
solidified
no risk of
breaking the thermometer, but it is very necessary to
avoid excessive heating of the alloy.
Another method
quantity of the alloy
is
This
of a delicate
the stem
attached to
is
small
placed in a glass test-tube,
and the open end closed with a cork.
tube
A
illustrated in Fig. 6.
is
thermometer just above the bulb by binding
it with thread or fine wire or by means of a
small rubber ring slipped over the larger end
of the
thermometer stem.
The thermometer
and tube are placed in a glass vessel containing water and the vessel gently heated until
the alloy melts the lamp is then removed and
the temperature at which the alloy solidifies
The
accurately noted by the thermometer.
;
mean temperature obtained from
will give
process
several observations
the melting-point of the alloy.
of
heating
During the
should be constantly
the water
For determining the melting-points of alloys
which melt at a temperature a little above that of the
agitated.
boiling-point of water, a liquid with a higher boilingpoint,
such as
glycerine,
may
with
advantage
be
employed instead of water. The alloys should be previously melted and cast on a flat surface in order to obtain
This should be broken up and a small
a thin sheet.
portion only used for determining the melting-point.
The melting-points of alloys which are not sufficiently
fusible to test by the above methods may be approximately determined by placing a fragment of metal of
known melting-point
in
the
locality
of the piece of
DENTAL METALLURGY.
54
and carefully subjecting them to a
uniform heat before the blowpipe, or by other means.
Thus, a small piece of bismuth (melting at 514° F.)
alloy to be tested
may melt
placed beside the alloy
before the alloy
fused, though a piece of lead (melting at 617° F.)
is
may
remain unmelted at the fusing-point of the alloy.
It follows, therefore, thab the temperature at which the
alloy melts
must be between 514° and 617°
Withing recent years very
F.
precise determinations of
the melting-points of metals and of alloys have been
made by means
of pyrometers.
almost universally adopted
when
a junction of
electrical
is
The instrument now
based on the fact that,
two dissimilar metals
equilibrium of the system
the measurement of the
difference
is
is
heated, the
disturbed,
and
of potential thus
produced affords a means of estimating the temperature
In its latest form the instrument conof the junction.*
sists of a thermo-couple of two wires, one of platinum
and the other of platinum alloyed with 10 per cent, of
rhodium, simply twisted at the ends, and connected
with a dead-beat galvanometer usually of the suspendedcoil type. An autographic recorder is used in connection
with the thermo-couple whereby a photographic curve,
of the cooling of a mass of metal or of alloy, is
registeied.
The pyrometer
j
is
unction to certain
calibrated by exposing the thermo-
known
temperatures, such as the
solidifying-points of salts or of readily fusible metals.
a mass of metal passes from the solid to the fluid
state, the temperature remains constant for a short
As
period, hence there
*
For
is
no
a description of tliis
difficulty in
recognising the
pyrometer, see "Introduction to Study
of Metallurgy," Roberts-Austen.
—
ALLOYS.
55
meltiug- or the solidifying-points. By means of this
instrument much vahiable information respecting the
molecular constitution of alloys has been obtained.
Solders.
This term
is
given to alloys used in joining metallic
by fusing them upon the surfaces when in
contact and allowing them to coSl, thus obtaining a
more or less firm joint at the point of juncture.
The alloys used must be necessarily more fusible than
the metal or metals to be united and must possess the
property of flowing readily. They must also consist of
surfaces
metals which possess a strong affinity for the substances
Solders should, if possible, be
to be soldered together.
of the same colour as the metals to be joined, and should
not discolour or undergo decomposition with age.
Solders for dental purposes must also be capable of
resisting the action of the fluids of the
a solder has a high melting-point
heat— it is said to be " hard."
meltiug-point
is
fusible metal, or
i.e.
mouth.
at or
When
above a red
When, however, the
lowered by the addition of an easily
by the addition
of a greater
amount
the more fusible constituents of the alloy, the solder
The term "soft solder"
said to be "easy" or soft.
of
is
is
usually applied to the alloys of tin and lead used for
soldering (see p. 211).
Each metal
kind of solder
requires, to a certain extent, a particular
;
the alloys most suitable as solders are
described under the different metals.
Preparation of Solders,— In making
solders
great care must be taken to secure uniformity of comThey are prepared in the same manner as
position.
other alloys by melting the constituent metals under a
DENTAL METALLURGY.
56
layer of
powdered charcoal and well
stirring the molten
mass before pouring. The metals used must be free
from impurity, and may with advantage be employed
in a " granulated " state.
form
Many
of powder, obtained by
solders are used in the
filing the ingot of alloy;
and gold solders are usually
but
silver
and
" soft solders " are generally sold in sticks.
rolled into sheets
CHAPTER
IV.
THEORY AND VARIETIES OF
BLOWPIPES.
—
The blowpipe is an
Theory of the Bloiopipe Flame.
instrument which is nsecl to direct a stream of air
lamp or coal-gas flame in order to produce a
more intense heat. The introduction of the air within
the flame at once destroys its luminosity for the same
into a
reason that the luminosity of the gas-flame
in the
Bunsen burner
—
viz.
that
with a proper proportion of air
oxygen of the
body
ing
a
it
is
when gas
destroyed
is
mixed
before being burnt the
burns the whole of the carbon in the
air
of the flame,
mak-
non-luminous.
In
well-formed blowpipe
may
flame two parts
distiugaished
Jlame, which
:
is
be
the inner
a.
blue and
and around this
an almost colourless
pointed,
known as the outer
The inner flame
Jlame.
Fig.
7.
flame
reducinfj Jlame, as
it
(Fig. 7, h)
is
often called the
contains excess of carbon, and
is
therefore capable of deoxidising or reducing substances.
The outer flame
(Fig. 7, a) is
known
as the oxidviing
DENTAL METALLURGY.
58
as
flame,
contains excess of oxygen and
it
readily
changes metals into their oxides. The reducing flame
is best obtained by placing the blowpipe nozzle in the
edge of the flame; whilst the oxidising flame
duced,
when the
nozzle
is ptished.
much
is
pro-
further into the
flame and a stronger blast employed.
important in soldering operations to bear in
It is
mind the
properties of the
two flames,
as the object to
be soldered would become unnecessarily
oxidising
flame were
"
dirty " if the
owing to the excessive
used,
oxidation of the base metals present.
Mo^dh Blowpipes. Blowpipes should be
—
either brass or
German
made
of
silver, as these alloys are poor
The simplest form of blowpipe
a plain metal tube, 200-240 mm. long
conductors of heat.
consists of
(8 to
10 inches), larger at
the
end applied
to
the
mouth, and tapering gradually to a point at its other
The tube is curved for convenience in
extremity.
directing the blast to the desired spot (see Fig. 8).
The aperture of the blowpipe nozzle should be quite
circular
and not too
This
large.
adjustment in new blowpipes.
should be slightly
the aperture
;
hammered
When
of the nozzle
be enlarged by thrust-
until a perfectly circular
continued for a long period
the tube and is liable to be
a steady flame
moisture collects in
it,
The end
over, in order to contract
this should again
ing a large pin through
opening is produced.
generally requires
is
THEORY AND VARIETIES OF BLOWPIPES.
59
expelled by the pressure of the air, causing disturbances
To avoid this a hollow chamber is somein the flame.
midway
times constructed about
hold any moisture that
may
in the instrument to
mouth
escape from the
(Fig- 9).
.
Another form of blowpipe for overcoming this diffiIt consists
culty is supplied by Letcher, of Truro.
Fig.
9.
brass tube fitting into a small chamber, which
collects and retains the moisture, and the bottom of
of a
which
is
movable, so that
it
can be taken
off
and the
moisture shaken out at the end of the operation (see
Fig. 10).
Hot-Blast Month £lotu2}ipe.— Fletcher, of Warrington,
has introduced a new form of blowpipe for obtaining
temperatures beyond those attainable
with
ordinary
blowpipes.
The
shown
hot-blast
in Fig.
1
1
.
mouth blowpipe, as it is termed, is
The improvement consists in coiling
Via.
II.
the end of the tube into a light spiral over the point
l^y this arrangement the air becomes
of the jet.
DENTAL METALLURGY.
6o
coil
takes
up the heat which would otherwise be wasted.
The
may
con-
heated iu passing thvongh the tube, as the
moisture
also
which
collect in the
tube
is
verted into steam.
It
is
claimed that by the
much higher temperatures
use of this instrument
are reached than is possible
with the ordinary blowpipe, and- that with the same
amount of blowing a larger amount of work is accomplished, while, if a high temperature
the labour of blowing
The operation
is
not required,
redu.ced in proportion.
blowing
of
is
is
not
always
readily
acquired, but usually a few days' practice removes
the difficulty at
first
all
experienced in producing a con-
tinuous steady blast, and
when once produced
it
may
be continued for a considerable time without fatiguing
even the muscles of the cheeks. The operation is
mouth with air, expanding
the cheeks, and then keeping up a steady pressure
commenced by
filling
the
respiration being allowed to go
with the muscles
on as usual through the nose. To avoid tiring the
muscles of the lips by continual blowing, the trumpet
;
mouthpiece, shown in Fig. lO, which is merely pressed
The
against the open mouth, has been recommended.
curvature of the mouthpiece should, however, correspond
to that of the
mouth and
fit
comfortably, otherwise
it
lips
will require to be pressed very forcibly against the
With this form
in order to prevent the escape of air.
of
mouthpiece an uninterrupted blast may be kept up
fatigue to
for a long period without causing the least
the muscles of the lips.
The length of the blowpipe
(8 inches), but, as
which the flame
it is
is
is
usually about 200
mm.
important that the object upon
directed should be seen distinctly,
1
THEORY AND VARIETIES OF BLOWPIPES.
6
operator
the length must be adapted to the eye of the
short-sighted persons require a short blowpipe, whilst
;
for the long-sighted a longer
one
is
necessary.
Blowpipes.— Ma.ny of the
Bellows
operations
con-
ducted in the dental laboratory require the application
with the
of a higher temperature than that obtainable
mouth blowpipe. In order to effect this, special blowpipe burners are employed, while the necessary blast
obtained by means of a suitable blower.
A
form of burner commonly employed
The burner
in Fig. 12.
is capable of being ad-
angle,
directed
at
any
and when neces-
sary can
in
represented
that the flame
justed so
can be
is
is
be firmly fixed
position by
means
of
at the base.
wing nut
The jet of this blowpipe
a
is
of
removable, so that jets
any
size
as desired.
is
so
can be fitted
The tap
arranged
will turn the
lever
that
light
leave a small pilot
Fig.
12.
it
when pushed backward, and
light when drawn forward, thus
out
avoiding the necessity of relighting for each operation.
The burner is mounted on a heavy bi'ass stand to make
it
perfectly steady
Oinen's
when
Bloiopi'pe is
in use.
also
very frequently used.
It
two peparate brass tubes arranged as shown
inin Fig. 13, thus making the gas and air supplies
Each tube is fitted with an india-rubber
dependent.
consists of
valve,
on which the thumb or fingers are placed in
DENTAL METALLURGY.
62
order to regulate the gas and
ment the blowpipe flame
is
pipe for
many
By
this arrange-
under perfect control.
Fig.
Automatic Blowpipe.
air.
13.
—-A very convenient
purposes in the dental
hand blow-
laboratory
Fletcher's automatic blowpipe, shown in Fig. 14.
is
is
This
a very manageable and effective instrument and
is
capable of producing very high temperatures, and the
intensity of the heat
may be
Fig.
graduated at
will.
The
14.
blowpipe is held in the hand and is provided with taps
as shown, which are under perfect control, so that
the supply of both gas and air can be readily regulated.
Complete mastery over the character of the flame can
be gained after a few minutes' practice. When burning
at full power the blowpipe consumes about ten cubic
feet of gas per hour.
Other forms of automatic blowpipes well adapted for
dental purposes have also been designed by Fletcher.
For soldering operations in
Hot-Blast Blovpipe.
which pure gold is used, as in continuous-gum work,
—
and other operations requiring
a greater intensity of
heat than that furnished with ordinary gas blowpipes,
THEORY AND VARIETIES OF BLOWPIPES.
63
Fletcher's hot-blast blowpipe is sometimes used (Fig. 15).
This blowpipe is so constructed that the air-pipe is
around the gas-pipe
and both are heated by an
independent Bunsen burner,
the gas siipply to which is
coiled
regulated
By
this
by a separate
simple device
the
claimed that
the apparatus
that
of
is
an
tap.
it
is
power
of
about double
ordinary
gas
Fig.
15.
blowpipe.
The advantage of the hot blast is only apparent
when a pointed flame is required having a high temperature
;
under these conditions
platinum wire
may be
The blowpipe
is
it
is
stated
that
thm
fused.
also supplied
with a bench light
attached for convenience in working.
Blowing Apparatus.— The blast necessary for the
production of the flame
with gas blowpipes is obtained by means of a footblower, connected with the
burner by a flexible rubber tube.
s..
A
1^^^
form
Fig.
16.
simple
of
and compact
bellows
for
the
purpose is shown in Fig.
With this apparatus
16.
a
obtained which is
continuous, equable supply of air is
A disc
operator.
completely under the control of the
bellows,
of rubber is fitted beneath the
under the pressure of the
air,
which expands
while the bellows are
m
DENTAL METALLURGY.
64
motion, forming a reservoir which holds the
and
air
thus affords a veiy compact, powerful, and effective
arrangement.
The bellows
are
mounted on
a stand,
thus reducing the risk of injury to the disc, and fitted
with a step for the foot, so that they can be used with
ease,
whether the operator
is
standing or seated.
Oxyhydrogen Blowpipe. — Blowpipes
now
are
dental purposes in which the
means
of compressed oxygen
by
blast is obtained
The blowpipes are very similar in
instead of by air.
specially designed for
construction to those previously described for use with
air blast.
The oxygen
is
supplied from a cylinder of the com-
with
a
regulator for controlling the pressure of gas, as this
is
pressed gas.
The cylinder should be
fitted
more satisfactory than a fine adjustment valve. When
oxygen is not readily obtainable, nitrous oxide may be
employed, but
is
not so suitable as
it
gives rise to a less
steady flame.
Oxy hydrogen blowpipes
are
now being more
exten-
sively used in the dental laboratory than formerly, as
they are well adapted to certain classes of work the
heat obtained, however, is very intense, and care must
;
be exercised in using them.
CHAPTER
V.
MELTING APPLIANCES, FURNACES,
AND FLUXES.
Simple Ingot-Mould.
— When
it
is
required to
melt a small quantity o£ gold or silver, tlie simplest
form of apparatus for the purpose is that shown in
Fig.
follows
A
It
17.
is
very
easily
and
quickly
made
as
:
block of compressed charcoal or carbon
is
carefully
cut in halves lengthways with a saw, in order to obtain
Fig.
17.
two thin slabs, which are rubbed together until perA circular cavity
fectly smooth surfaces are obtained.
cut in one of the slabs for the reception of the metal
At the other end of the slab an ingotto be melted.
is
mould
made
is
carefully carved, the size
and shape of which
to suit the requirements of the case.
A
is
gutter or
then cut to connect the two cavities, after
which the other slab is cut in halves and one half ])laced
over the ingot-mould and secured in position by means
groove
is
DENTAL METALLURGY.
66
of thin iron or copper wire.
The metal
to he melted
is
placed in the cavity and the blowpipe-flame directed
and when thoroughly fluid the charcoal is tilted
so that the molten metal will run into the ingot-mould
upon
it,
prepared for
It is necessary that the charcoal should
it.
be perfectly dry before
use, as the presence of moisture
from the mould.
will cause the projection of the metal
This simple and convenient apparatus
employed
in the dental laboratory
and
is
also
frequently
by jewellers
when only small quantities of metal have to be melted.
similar form of combined melting appliance and
A
ingot-mould made of asbestos
is
obtainable at the dental
depots.
The author has made many
red Windsor brick, which is
and is easily cut and shaped.
Melting Scrap.— When
similar
moulds out of
suitable for
soft
the purpose
melting gold
scrap
for
to prevent
the dental laboratory care should be taken
containing
the admixture of old plates, backings, &c.,
quality, as
portions of solder and scrap of doubtful
and give a
these would lower the standard of the gold
plate of inferior carat to that required.
neglect scrap
this account it is usually safer to
On
and filings
containing solder, and melt only clippings
to prevent
taken
from new plate. Care must also be
the introduction of
impure
filings
:
lead
fragments of dental-alloy or of
is
specially injurious, as
it
renders
the gold brittle and useless.
Melting Apparatus.— A
very convenient and
embodying the same prinuseful form of apparatus,
above, has been devised by
ciples as those described
ingots of gold and silver
Fletcher for quickly obtaining
the
It is shown
without the use of a furnace.
m
MELTING APPLIANCES.
accompanyiug Fig.
18.
A
67
represents a moulded carbon
ii'on side-plate, which
B is an iron ingot-mould
which slide on each other, to
block, siip])Orted in posit on
by an
acts as a shallow crucible.
constructed in two parts,
admit of ingots of any width being cast. By this
arrangement the mould serves for both plate and wire.
Fin.
The apparatus
18.
mounted on a rocking stand for convenience in tilting.
The metal to be melted is placed
in the shallow crucible and the flame of the blowpipe
is
When
adjusted.
apparatus
the
is tilted in
sound ingot
may
metal
order to
is
fill
melted
the
the ingot-mould.
be obtained in a few minutes
use of this simple apparatus.
whole
A
by the
The metal should be
thoroughly molten before being run into the mould,
but excessive heating should be avoided.
The ingot-mould
lieat
of
the flame
is
;
made
it
sufliiciently
hot by the waste
should, however, be
oiled,
or
coated with lampblack by holding the inner surfaces
DENTAL METALLURGY.
68
over the flame of an oil-lamp or gas-jet before using.
When very bulky scrap is to be melted it should be run
into a
mass
placed
in
in a
the
moulded carbon block before being
The melting appliance as
crucible.
usually supplied for dental purposes
ducing ingots of about
3 ozs.
larger size
of
capable of pro-
is
Similar appliances of
may be
producing 20
obtained capable
oz. ingots,
but these
require a half-inch gas supply and a
good blower.
These simple melting appliances
are not adapted to large
of
metal
;
crucibles
are,
quantities
therefore,
usually employed for this purpose.
—
Crucibles. These are made of
fireclay and of graphite (plumbago)
and are of various shapes and sizes
to suit the requirements of the case.
A
dental purposes
is
convenient form of crucible for
shown
in Fig.
Earthen crucibles are made
1
9.
of fireclay
mixed with
fireclay,
other infusible materials, such as sand or burnt
which raw clay
in order to counteract the tendency
The materials
possesses of shrinking when heated.
on heating,
thus mixed with the clay expand slightly
the clay.
and therefore act in an opposite manner to
a
resisting
of
Crucibles of these materials are capable
high temperature without softening.
of varying
Graphite or plumbago crucibles are made
powdered graphite
proportions of fireclay mixed with
Good plumbago crucibles withstand
or with coke dust.
temperature without cracking,
the greatest changes of
by the
relractory and the least corroded
are highly
MELTING AiTLJANOES.
of metallic oxides.
action
Tliey
are,
69
therefore, very
suitable to the requirements of the dental laboratory, as
with due care they
may
be used
many
times in succes-
very important befoi-e using these crucibles
to subject them to a careful preliminary annealing by
sion.
It is
placing them in a
warm
place in an inverted position,
otherwise they will split
when suddenly
The
shown in
heated.
crucibles are usually provided with covers, as
Fig. 19.
and
Gold
plumbago
its
alloys
crucibles,
inside with a
little
particles of metal
When
should
melted in good
be
which when new should be rubbed
charcoal powder, to prevent any
adhering to the sides of the pot.
earthen crucibles are employed for the purpose
they should be glazed inside with a thin coating of
borax.
This is done by placing a small quantity of
borax in the crucible and exposing
ture until the borax
is
it
to a high tempera-
The crucible is
the tongs and carefully
perfectly liquid.
then removed, held firmly in
rotated in an inclined position in order to allow the
molten borax to flow over the entire surface.
When thus glazed the crucible may be
inverted position until ready for use.
By
left in
this
an
means
the pores of the crucible are closed and the retention
of globules of metal during pouring
is
prevented.
—
of Furnaces. Melting operations may
be conducted in any form of fire or furnace in which
Forms
a sufficiently high temperature can be obtained.
The
fire
of an ordinary cooking-stove
is
often
em-
ployed where gas is available, however, the operation
may he more effectually accomplished in a suitable gas
;
furnace, such as those invented by Fletcher, which are
very compact, convenient and effective.
These furnaces
DENTAL METALLURGY.
yo
are easily attended to, and
work can be
them in a very cleanly manner.
The choice of furnace to be used
will
carried ou with
depend
chiefly
on the degree of heat to be obtained, but the following
furnaces will be found perfectly adapted to the require-
ments of the mechanical dentist.
Injector Gas Furnace.
— Fig.
Fletcher's injector gas furnace.
20
represents
The furnace
is
con-
structed of a special refractory material, which is a bad
conductor of heat and very light. It is enclosed by
bands of hoop iron and contains an interior space
Fig.
20.
of
sufficiently large to take crucibles with a capacity
the size
six ounces to twelve pounds, according to
of the furnace.
The necessary temperature
is
obtained
by injecting a mixture of air and gas into the furnace
the
by means of a special burner, constructed on
obtained
principle of the Bunsen burner, the blast being
by a suitable blower, such as that described on p. 63.
the
The burner is provided with a screw check, so that
Extremely high
supply of air can be easily adjusted.
furnaces,
temperatures can be obtained with these
melted
half-pounds of cast iron being completely
twelve minutes, but for rapid working
of gas is
and for high temperatures a free supply
in seven
requix'ed.
to
MELTINU AITLIANCES.
A
thin layer of silver-sand
is
7^
usually placed on the
bottom of the furnace to prevent crucibles adhering
when a white heat is employed.
These furnaces need a special gas supply, varying
from three-eighths to five-eighths inch pipe, and the
india-rubber tubing used for the connections must be
smooth inside, the tubing made on wire not being
suitable.
supply
The burner
to get very hot if the gas
is liable
is insuflicient.
To adjust a new furnace
to its highest power, put the
nozzle of the burner tightly up against tbe hole in the
Fig. 21.
side of the furnace casing, turn
light the gas in the furnace,
on the
full
gas supply,
and commence blowing,
before putting on the cover of the furnace, with the
air- way full
open.
when the cover
If,
i-eplaced, the
is
flame comes out of the hole in the cover about two
inches, the adjustment
is
correct.
If the flame is longer, enlarge the hole in the air -jet
until the proper flame is obtained, or reduce the gas
supply.
Before stopping the blower, draw the burner
back from the hole.
Concentric -Jet
recently
introduced
Gas Furnace.
a
new
series
—
of
h'letclier
haa
concentric-jet
furnaces, which are designed to supersede the injector
These furnaces (Fig. 2i)
furnaces above described.
DENTAL METALLURGY.
72
are very similar
to
the injector furnaces, with the
exception of the burnei-, which
to
avoid any
cutting
is
specially constructed
action or " cold spot " on the
crucible.
no wire gauze in the burner to get choked
or damaged, and the power is limited only by the air
pressure and the gas supply available it is also so conTJie burner and
structed that it cannot light back.
furnace are mounted on an iron stand, so that the former
There
is
;
cannot get displaced when in
Fig.
use.
The furnaces
are
22.
supplied in four sizes with a capacity of from four
superior to the
to twelve pounds, and are in every way
ordinary form of injector furnaces for use in the dental
laboratory, where high temperatures and rapid working
are required.
Injector Oil Furnace.
—When
gas
is
not ob-
lamp
tainable the injector furnace can be fitted with a
a
oil,
for burning ordinary kerosene or petroleum
burner having
been designed by Fletcher for this
purpose.
must be
In using this the wick-holder of the lamp
placed
The
The
close
against the hole in the furnace casing.
blast is supplied
oil
by means
furnace (Fig. 22)
is,
of a blower as before.
however,
iuferioi- in
power
MELTING APPLIANCES.
to the furnaces supplied
wilh gas, but with a
management
experience in
73
little
a half-pound of cast iron
can be melted in about twelve minutes, starting
cold.
Furnace for Coke.
Melting
venient and portable furnace for
—A
very
all
con-
melting operations
where a suitable supply of gas
is
not available
trated
Fig.
in
that illus-
is
made by
23,
Morgan and Co.,
London. The furnace
Battersea,
structed
of
is
con-
suitably
fireclay,
bound with hoop iron, and is
made in two parts for convenience in cleaning and repairing. The necessary draught
is obtained by fixing an iron
tube chimney to the socket a,
and is regulated by means of
the small door
very
d.
convenient
damper,
chimney
for
draught.
An
The
in
iron
a
also
have
a
the iron
regulating
poker
is
Fig. 2^.
the
grate, /,
which
of the furnace,
introducing
is
to
fitted
g,
It
is
fitted at
the
bottom
kept free from clinker by
through
the
stokiug-door
crucibles are introduced through the door h
e.
and
placed on a small fireclay stand resting on the grate.
The fuel usually employed is coke, vvbich should be
broken to
])ieces
the si/e of an egg and well packed
round the sides of the crucible, but not over
furnaces are
made
in
several
sizes to hold
with a capacity of from four to thirty pounds.
it.
The
crucibles
DENTAL METALLURGY.
74
Ladle Furnace.
—Fletcher
has devised
a
new
and substantial form of ladle furnace (Fig. 24) for
melting zinc and lead, which is well adapted for the
dental laboratory.
The furnace
Fig.
is
seven
24.
heated by a special highremovable, and can therefore be
inches in diameter, and
power burner, which
will take ladles
is
used for boiling water and other purposes. The body
and lid are arranged to admit the handles of different-
sized ladles at various heights, to enable
kept perfectly
them
to be
level.
Ladles. The ladles used with these furnaces are
shown in Fig. 25. In order to insure perfect steadiness
fitted with a slide
in pouring, the handles are
]iiished to
and
is,
the cool end while the metal
therefore, always cold.
The
is
which
is
being heated,
ladles are
made
and with mallewith cast-iron bowls for melting lead
MELTING APPLIANCES.
75
able iron bowls for zinc, the handle being so constructed
new bowl can be fixed in a few minutes.
Muffle Furnace, The mufiie furnaces used
that a
—
metallurgical
silver are
poses
;
for
laboratory
assay of
the
in the
gold and
very similar to those nsed for dental pur-
the muffles, however, are
the former case.
The
somewhat larger
in
special feature of this class of
furnace consists in the device for isolating the materials
Fig. 26.
operated upon from both the fuel and the products of
combustion.
The muffle proper
shaped thus
surrounded by the flame on
number
all
chamber
a fireclay
in section, closed at
fixed in the furnace in such a
pei'forated with a
is
one end, and
manner that
The
sides.
of holes or slits
it
can be
sides
ai-e
through which
drawn, the muffle furnace being used chiefly
for operations requiring the passage of a current of
air, as in the processes of cupellation and scorification
the air
is
mentioned under Hilver Assays.
Gas Muffle Furnace.
recently
—A
invented by Fletcher
gas
is
muffle
shown
in
furnace
Fig.
26.
76
DENTAL METALLURGY.
This furnace has been designed specially for gold and
silver assays, and ranks among the best of its kind for
this purpose.
It is
designed to give the best results
and the
uniform from end to end,
at the lowest ordinary day pressure of gas,
temperature of the muffle is
and can be adjusted to any extent.
The
muffle
parts, so that
is
closed
can be
two
extra supply of air is needed.
an
partially opened when
A thin layer of bone ash should be spread over the
by a door arranged
in
it
bottom of the muffle to protect it in case of accident.
A muffle furnace fired by coke somewhat similar
is
in construction to the furnace described on p. 73
and
Morgan
also made by Messrs.
Co.,
and
will
be found useful for
purposes when
assaying
cannot be obtained.
Ingot-Moulds.
coal-gas
— Metals which
are to be rolled into plate are cast
moulds which give a flat ingot
suitable for passing through the
The ingot-mould usually emrolls.
into
shown in
Pio- 07. It is made of cast iron, in two
should
parts, for convenience in removing the ingot, and
compensate
be slightly concave on the inner surfaces, to
ployed for this purpose
is
middle than at
for the greater shrinkage of gold in the
edges of the ingot. Before pouring, the moulds
the
with a
should be moderately heated and rubbed over
by
well-oiled rag, or coated with a deposit of carbon
flauie.
holding the inner surfaces over a gas or oil
Moulds are
also
frequently
rubbed
with
blacklead
must be taken
powder, but when this is
from the mould before
to remove all excess powder
used care
—
.
MELTING APPLIANCES.
the
pouring
Ingot-moulds
metcal.
77
formed
of
soap-
stone are also employed for casting purposes and are
As the metals for dental purposes
preferred by some.
require to be in the form of plate or wire, the ingot is
subjected to rolling, &c., to fit it for the purpose
required.
Rolling, or Laminating.
This
is
accomplished
by passing the ingot rebetween
two
peatedly
cylindrical
Many
polished
highly
strong,
steel
different
rollers.
forms of
flatting mill are used for
this purpose, that
being frequently
in Fig. 28
These are so
employed.
constructed
the
justing
shown
that
by ad-
screws
the
may be brought
rollers
closer together every time
the ingot is passed through
It
is
very
keep the
rollers perfectly
by
parallel
important to
very
careful
Fig.
28.
adjustment of the screws,
otherwise the metal will twist and become unmanageable.
As metals become hardened by
rolling, the ingot
should be frequently annealed during the process.
rollers for the pui'poses of
The
the dentist should be from
three to four inches in length.
Thickness of Plate.
is
of attenuation
determined by a gauge-plate,
sometimes circular in shape and sometimes
obtained by rolling
which
—The degree
is
DENTAL METALLURGY.
78
shown
oblong, as
strument
which
is
in Fig.
29.
The edge
provided with a series of
gradually diminish in size
of the
slits
in-
as shown,
and are indexed by
corresj)ond to regular fixed standards,
numbers which
which vary for the different countries. In order to
determine when the plate has been rolled
sufficiently thin it is repeatedly tested by
the gauge during the operation of rolling.
Wire -Drawing. Thick wire or thin
—
metal rods
])assing
may
be drawn into finer wire by
them through
a draw-plate, which
consists of an oblong piece of steel pierced
with a series of conical holes which graOn a small
dually diminish in diameter.
scaio,
strips of
of
metal
rolling, or
wire
off
by
is
readily obtained
by cutting
the rolled sheet in the direction
casting the metal into a thin rod,
and passing it into one of the
holes of the draw-plate, which is firmly held in the
jaws of a vice. The rod is then forcibly pulled through
slightly pointing one end,
the hole by means of a pajr of drawing tongs or pliers,
and the process repeated with smaller holes in succes-
wire of the desired size is obtained. The
or
holes in the draw-plate should be filled with grease
fat to facilitate the operation.
the wire from
It is generally necessary to anneal
sion, until
time to time during the operation, otherwise
it
becomes
after
hard and more or less liable to crack or break,
holes.
having passed through a certain number of
Draw-plates are
also constructed for
round, square, and other forms of wire.
obtaining half-
MELTING APPLIANCES.
79
Fluxes.
—A
added when melting metals and smelting ores, for the purpose of combining with the infusible substances present or formed
Bcjinition.
flux is a substance
fusible
body thus formed
When
air the
The
render them fusible.
during the operation to
termed a
is
slag.
metals or alloys are melted in contact with
oxygen
and converts
flnx is added
fusible slag,
acts on the surface of the
into
it
it
will
oxide
;
molten metal
however, a suitable
if,
combine with the oxide to form a
which protects the surface of the metal
"In many
from further oxidation.
melting of metals
it is
cases of
simple
desirable to remove base metals,
often
it is then
which are present as impurities
advisable to add an oxidising flnx, in order first to
;
oxidise
the
impurities, in
which
state
they readily
combine with other fluxes to form a liquid
is
for this reason that nitre is
impure gold (see
p.
90).
The
in the dental laboratory is borax,
slag."
It
added when melting
chief
which
flux
is
employed
principally
used for soldering purposes, but also used occasionally
when melting
metals.
—
Borm: (Sodium horatc). This substance fuses readily
and is very fluid when in the molten state. In the
crystallised or hydrated form it contains nearly half its
weight of water, which is driven off on heating, causing
When sti'ongly heated it
it to swell up considerably.
fuses into a clear white glass
known
as horax glass.
The
inconvenience sometimes experienced by the swelling
up
of the hydrated borax
fused borax.
may be
avoided by the use of
The commercial material
adulterated with
common
salt
and alum.
is
frequently
DENTAL METALLURGY.
8o
Ammoniuiii Chloride, commonly called Sal-ammoniac,
Several metals when
is also frequently used as a flux.
in a molten state decompose this substance, forming
Advantage
metallic chlorides and liberating ammonia.
frequently taken of this property in purifying gold
and also for purifying zinc which has become impure
is
by frequent melting (see pp. 91 and 200).
A mixture of sal-ammoniac and charcoal is sometimes
employed instead
Sodium
of the former alone.
Chloride, or
common
salt,
is
employed as a
flux in melting operations, as it preserves the substance
beneath from the action of the atmosphere and thus
prevents oxidation. It is also used to moderate the
violent
action of substances such as nitre, which cause
It is for this reason that it is included in
ebullition.
It
the charge for refining " lemel "—given on p. 120.
very
is
and
melts at a red heat in an open crucible
fluid
when
molten.
Potassium Nitrate, also called Nitre and Saltpetre.
agent,
This substance is largely used as an oxidising
yields a large
as it is decomposed on heating and
volume
of oxygen.
It is specially useful
ing gold contaminated with
when
melt-
small quantities of base
metals.
employed to prevent
Flour and resin are
oxidation when melting metals.
Charcoal
Poioder
is
largely
purpose.
also frequently used for the
Soldering.
regarded as a
of soldering is rightly
with
mechanical dentistry, but as it deals
The process
branch of
the
the melting of metals and
use of
fluxes, a
few
MELTING ArPLlANCES.
may be
notes on these points
8l
considered as coming
within the scope of dental metallurgy.
Soldering
is
the process by which two or more pieces
of metal are united
by means of a fusible alloy termed a
" solder " (see p. 55).
It
is
chiefly confined in the dental
laboratory to the use of gold solders, although occasionally " soft soldering" is
is
found useful for several purposes.
In order to facilitate the soldering operation a " flnx
employed, which is usually borax.
"
When
the various parts to be united are heated the
surfaces become " darkened " by a thin coating of oxide,
owing
to the oxidation of the base metals present.
however, borax
is
employed
dissolve the metallic oxides
as a flux
it
which form, and
If,
readily
will
also protect
metal from further oxidation by excluding the
oxygen of the atmosphere. The flux is prepared by
taking a lump of borax and rubbing it on a slab of
the
ground
glass, or porcelain,
wdth clean water, until
attains the consistency of cream, after
to the surfaces to be united
brush.
A
which
by means
saturated solution of borax
for soldering, the piece to be
with solution where the solder
it is
it
applied
of a camel's-hair
may also be
used
soldered being painted
is
wanted
to flow.
The conditions necessary for successful soldering are:
1.
A
2.
Contact of
3.
Avoidance of excess of solder.
Exposure of a clean, bright surface in
over which solder is to flow.
4.
solder which flows freely.
all
the parts to be united.
jjlaces
A
gradual and uniform distribution of heat.
As previously stated, the solders used should be more
5.
fusible than the metals to be united, should
when
fused,
and should possess a strong
How readily
affinity for
I'-
the
DENTAL METALLURGY.
82
metals to be joined, in order that
it
may run
into every
The
part of the joint and thus effect a perfect union.
colour of the
solder
should correspond as nearly as
possible to that of the plate on which
the solder
is
to be exposed
it
is
used.
As
to the action of the fluids
of the mouth, in order that it may resist this action as
far as possible it should be as high in quality as the
plate will admit, without risk of melting the latter
during
i\\e
fuduii of the solder.
form
in
inch)
an
of thin plate (about 0.75 mm. (yVth of
thickness), which is cut up into pieces varying in
size, depending on the extent of the surfaces to be
Solders
for dental purposes should be in the
united.
Very thin plate
is
objectionable, as
it
exposes a larger
surface of base mecal to oxidation, and consequently
retards the flow of the solder and thus tends to weaken
the joint.
When
solder
is
used in the form of
flliugs
mixed with borax of the consistency of cream
form a paste, which is then applied to the parts to
it is first
to
The quantity of
be reduced to the minimum,
have to be removed in the
be united.
excess of solder
place on cooling
teeth.
is
is
solder used should always
as all superfluous portions
finishing process.
When
used the contraction which takes
liable to cause the fracture of the
Care should also be taken to avoid the use of
excess of flux.
oxidising flame should be avoided in all soldering
operations, as this makes the surfaces of the metals
An
unnecessarily " dirty," and renders it diflicult to obtain
It is also necessary that cleanliness be
a clean joint.
to be
observed and care taken to prevent the surfaces
this
as
plaster-of-Paris,
soldered from contact with
—
MELTING APPLIANCES.
substance, on account of
83
iufusibility, greatly inter-
its
feres with the perfect union of the parts.
distribution of heat
The gradual and uniform
great importance in
failure
to
give
all
of
is
soldering operations, and the
proper attention to these points
frequently the cause of
much
is
delay and want of success.
The temperature should be raised gradually
at
first,
to
prevent the displacement of pieces of solder by the
The heating
swelling up of the borax used as a flux.
process for an artificial denture should also be conducted
gradually, as a sudden elevation of temperature will
cause displacement of the plaster owing to the too
rapid expulsion of moisture and will tend to cause the
fracture of the porcelain teeth.
In soldering a large piece of work the flame should
be carefully directed until all parts are uniformly
heated to the
required
temperature, and
then
the
blowpipe-flame directed to the solder and parts to be
united.
The process
of soldering is a delicate oj)eration to
accomplish successfully, and needs to be undertaken
with care and patience.
With
a little practice,
how-
ever, the difficulties at first experienced are soon over-
come, and neat aud successful joints obtained.
—
Soft Soldering. The method of soldering by
means of the blowpipe is known as " hard soldering";
but when
points
The
tin
soft,
solders
i.e.
those with very low melting-
— are used, the process
is
termed "soft soldering."
solders used for this process are usually alloys of
aud lead
" softest " or
in varying proportions (see
\).
21
1),
the
most fusible being those containing the
largest proportion of tin, this being the more fusible
These solders are cast into the form of
constituent.
/
DENTAL METALLURGY.
84
thin,
naiTOW
strips.
The fusion
surfaces to be united
is
of the solder on the
usually effected by
means
" soldering iron," instead of the blowpipe as in
soldering.
employed
sists of a
of a
hard
The blowpipe, however, is in some
The soldering-iron conspecially shaped piece of copper, known as the
cases
for soft soldering.
"bit," which
fixed in a
is
attached to an iron stem and securely
wooden handle.
In soft soldering a flux
and
which is designated " soft soldering fluid " is used,
made by dissolving
consists of a solution of zinc chloride,
a small quantity of zinc in dilute hydrochloric acid.
This solution
is
employed instead
of borax to dissolve
oxides or prevent oxidation of the surfaces to be united,
and
When
also to assist the " flow " of the solder.
surfaces have been prepared the solder
is
the
melted and
applied to the work by means of the soldering-iron. A
novel application of " soft soldering " to dental pur-
poses has been introduced by Mr. Baldwin * in connection with the repairing of bridges and crowns, the
The process
porcelain facings of which are broken.
consists in soldering a " backed " tooth to the preexisting "back," the
new
faces being attached with
For this purpose
a small clockmaker's soldering-iron is necessary, and
soft solder
by soldering in
the mouth.
in easy cases a fine quality of ordinary soft solder
used, while for
more
diflacult cases,
such as
crowns, a solder with lower melting-point
is
Eichmond
is
required,
which contains bismuth
and mercury, in addition to tin and lead, being very
that
known
as "pearl solder,"
suitable for the purpose.
*
Dental Epcuril, i8g6,
vol. xvi. p. 489.
;
CHAPTER
VI.
GOLD.
SYMBOL, An
Occurrence.
(Aiiruni).
— Gold
ATOMIC WEIGHT,
occurs
197.
distributed
very widely
and almost invariably in the metallic state,
the native metal being found disseminated in veins in
some of the oldest rocks. Formerly the most important
deposits were the alluvial deposits, resulting from the
in nature,
disintegration of the ancient gold-bearing rocks by the
atmosphere and running
waters.
The gold occurs in this gravel or sand
detritus in rounded masses, and also in the form of
the masses when of any considerfine grains or dust
able size being termed " nuggets," some of which have
weathering action of
the
;
been found weighing as much as from a few pounds to
two cwt.
Native gold invariably contains more or
less silver
while copper and iron are also frequently present in
The purest specimens of native gold
The Californian
contain about 99 per cent, of gold.
small quantities.
89 per cent., and the
Australian from 96 to 97 per cent, of pure gold.
Preparation. In order to extract the gold from
native
gold
averages
87
to
—
alluvial deposits
The
advantage
auriferous earth
is
is
taken of
washed
in a
its
high density.
" cradle "
or
pnu
DENTAL METALLURGY.
86
whereby the light particles of
rock are carried away, and the greater portion of the
inetallic grains remains at the bottom of the washing
apparatus, from which it is collected and melted into
in a stream of water,
bars.
Gold
is
extracted from auriferous rocks by stamping
the rock to coarse poWder, then causing the powder to
flow; by means of a stream of water, over inclihed
copper plates, the surfaces of which have been amalga^
mated i:e. covered with a layer of mercury. The gold
particles adhere to the mercury, with which they
amalgamate, while the finely crushed rock
The gold amalgam thus obtained
away.
removed, placed in a
off,
retort,
is
is
and the mercury
washed
carefully
distilled
leaving the gold behind.
Another method adopted very
years
treat
and
with a dilute solution of potassium cyanide, which
The gold solution is then
dissolves out the gold.
is
it
readily
largely within recent
to place the crushed ore in large tanks,
run into boxes containing shavings of metallic
zinc,
the precipitate is then
which precipitates the gold
collected, washed, dried and melted into bars.
Parting Gold from Silver.— Gold when ex;
tracted from its ores contains silver, and is frequently
impure and brittle, owing to the presence of small
quantities
of
base
metals.
In order,
therefoi-e,
to
fit
separate these and render the gold malleable and
be
and this may
for use it has to be refined or parted,
efiected either
by
a dry or
wet method.
Miller's Proem.— This dry method, which
is
frequently
crucible,
employed, consists in melting the gold in a
of
current
a
glazed internally with borax, and passing
by means of a
chlorine gas into the molten metal
87
OOLD.
fireclay
tube passing through the
lid of
the crucible.
and other impurities are converted into
partly volachlorides and rise to the surface aud are
The
silver
When
tilised.
is
the operation
allowed to cool, aud
still
molten
when
silver chloride is
is
complete, the crucible
the gold has solidified the
poured
The gold
off.
is
cleaned from adhering chloride, aud then remelted and
cast.
Parting with Acid.
— Gold
is
also purified
from
copper, &c., by the wet process, termed "quart aIn this case the gold is melted with
tion or ])arting."
from two to three times its own weight of silver, the
silver,
molten alloy thus produced being poured into water in
order to
granulate
it.
The granules
are
carefully
acid,
collected, and then boiled with strong- sulphuric
whereby the silver and copper are converted into
sulphates which dissolve in hot water, and the gold is
The
left behind in a pure state as a brown powder.
gold powder
is
washed, dried and then melted and cast
into bars.
obtained by placing sheets of
copper in the solution, which precipitates the silver in
The
silver is readily
the metallic state.
Nitric acid
is
sometimes employed for parting instead
of sulphuric acid.
necessary to have the proportion of silver to
about three to one, otherwise the silver would
It is
gold
only be dissolved from the surface of the alloy, the
large proportion aud density of the gold present i)re-
venting the action of the acid throughout the mass
and the complete removal of the silver when the pro})ortion is less.
Preparation of Pure Gold.
— Gold
of
extreme
88
DENTAL METALLURGY.
purity cannot be obtained by parting alone
therefore, gold
required of absolute puritj^
is
when,
;
it
must be
specially prepared.
Chemicall}'
pure gold
is
parted or standard gold in
the excess of
The gold
by dissolving
prepared
nitro-hydrochloric
acid being driven
chloride thus obtained
is
off
acid,
by evaporation.
dissolved in a large
quantity of water and left at rest for about twenty-four
hours to enable any precipitate of silver chloride to
subside.
The
clear
liquid
then carefully removed
is
from the deposited silvei- chloride by means of a syphon,
and the gold is jarecipitated by passing a current of
gaseous sulphur dioxide through the solution, or by the
addition of oxalic acid or other precipitating agent (see
p. 96).
The gold
precipitate
repeatedly with dilute acid,
obtained
is
washed
then with ammonia and
melted in a crucible with a
potassium bisulphate and borax and poured into
water, after which
little
so
it
is
an ingot-mould.
a small quantity of
If
platinum
is
present in the
gold treated, alcohol and potassium chloride must be
added
to precipitate
it
before diluting the gold chloride
with water.
Properties.
—Gold has a characteristic yellow colour,
but very thin leaves of the metal are translucent and
appear green by transmitted light. It possesses a brilGold is
liant lustre and is susceptible of a high polish.
one of the heaviest metals, its specific gravity being 19.4.
between that of aluminium and silver.
In malleability (see p. 12) and in ductility gold exceeds
a wire
all other metals, its ductility being such that
can be drawn so fine that 500 feet weigh only one
Its
hardness
grain.
lies
89
GOLID.
It is a
electricity,
though
inferior to silver.
It is
good conductor of heat and of
in these respects
it
much
is
welded together in the cold by
It is tenacious, though
the application of pressure.
inferior in this respect to iron, copper, platinum and
also capable of being
the purest gold obtainable having a tenacity of 7
tons per square inch and an elongation of nearly 31
silver,
per cent.
Gold
is
not acted upon by atmospheric
ordinary temperatures or
is it
when
air,
strongly heated
either at
;
neither
tarnished by exposure to the action of sulphuretted
hydrogen.
Gold
is
not acted upon by any single acid
(except selenic), but
it
acid mixture such as
which
evolves
is
dissolved
by chlorine or an
nitro-hydrochloric (aqua regia),
Selenic
chlorine.
acid,
even when
moderately concentrated, has no effect upon gold in
the cold, but the
concentrated
acid
when used hot
(230°-300'' C.) dissolves the gold, forming gold selenate.*
Alkaline solutions have no action on the metal.
and contracts consider"
and though practically a " fixed
It melts at 1061° C. (1942°
ably on solidification,
metal
It
it
may be
will
¥.),
slightly volatilised at a very intense heat.
thus
be seen
that
gold possesses, in an
eminent degree, those general properties which render
it peculiarly fit for the purposes to which it is applied
in dental practice.
Use for Dental Purposes. — On
account of
its
untarnishable nature, gold has long been employed in
In the pure state it is used in
form
the
of foil, as a filling for teeth and for other
purposes.
In combination with copper and silver it is
largely employed for the base of artificial dentures.
the dental laboratory.
*
Liriilicr.
Jdvni. Aiiirr.
Chriii. Sor. 1902.
24 [4]. 354-355.
DENTAL METALLURGY.
90
Effect of Impurities on the Properties of
Gold.— The malleability and ductility of gold are mateiuHueuced by the presence of only small proportions of other metals, such as tin, lead, zinc, antimony, &c.
Gold alloys readily with Und, but a very small quantity
rially
of this metal
and
is
sufficient to
impair the
ductility of gold, rendering
it
malleability
quite brittle, and
generally useless for any of the purposes to which gold
even -.,^t\\ part of lead renders standard
is applied
;
gold
brittle
Having regard
and
destroys
its
working
properties.
to this influence of small proportions of
a
lead on gold, care should be taken, after annealing
coming
gold plate, to prevent the plate while hot from
metal
this
contact with any particles of lead, as
into
would at once be diffused into the plate and probably
quite unfit for further treatment.
Antimony is particularly destructive to the mallea-
render
it
per cent, renders gold quite brittle,
impair its
while quantities not exceeding .05 per cent,
bility of
gold;
.5
malleability.
Bismuth
making
Zinc
alloys with
gold,
hard and brittle.
and Tin both form
and
is
highly injurious,
it
alloys
with
gold,
the
gold more or less
presence of these metals making the
brittle.
become
liable to
In the dental laboratory gold is very
and other
contaminated with particles of lead, zinc,
When, therefore, the gold scrap, &c., is to be
metals.
use, care should be
reconverted into proper form for
as practicable from
taken to prevent the gold as far
metals.
becoming contaminated with base
impure and brittle
Brittle Gold.— Gold which is
little borax in a
may be refined by melting it with a
GOLD.
crucible,
sium
ing
91
and adding a small quantity of nitre (potas-
The
nitrate).
effect
nitre exercises a powerlul oxidis-
on the base metals
in
tbe gold, and the
resulting oxides form a liquid --^lag" with the borax;
sometimes sprinkled on the surface
of the molten gold to remove the lead and tin after
Sal-ammoniac
skimming
Gold
is
the slag;
ofi'
Foils.
— For the manufacture! of
industrial purposes the gold
silver aJid
gold-leaf for
usually alloyed with
is
copper, according to the colour required
the finished leaf
but gold
;
ill
for dental purposes is
foil
beaten from pure gold, on account of its superior welding power, which enables it to be pressed more readily
into a compact form.
The metal
is first
melted and cast into small ingots,
which are thinned by hammering, and then rolled
until a ribbon is produced having a thickness of about
^jiyth of an inch
;
the gold requiring frequent anneal-
The ribbon
ing during this operation.
is
then cut into
pieces one inch square, weighing about six grains, about
150 of which are interleaved with sheets of vellum or
parchment and the whole made into a packet. The
" cutch " thus produced is beaten with a hammer nntil
it has become extended to about four inches square or
sixteen
times
intended for
beyond
the
filling
original
area.
If
teeth the beating
is
the sheets are
not continued
this stage.
For application in the
arts,
however, the beating
is
frec|uently continued until the thickness of the leaves
is
about iTaoVoo^h of an inch.
sheets are cut into four, and ])iled
For this purpose the
again between sheets
of goldbeater's skin, thus forming a " shoder."
beating
is
The
then carried on for some time, after which
DENTAL METALLURGY.
92
the sheets are again cut up into squares, rearranged
as before,
forming a " mould," and the operation of
beating repeated for about two hours until the leaves
have acquired the degree of tenuity required for the
purposes to which they are to be applied.
Prom
the
finished leaves thus produced squares of about three
inches are cut from the central portions by a piece of
bamboo sharpened to a cutting edge. These are then
piled in a book made of soft paper rubbed over with
red ochre or red chalk to prevent adhesion, twentyMechafive leaves being usually placed in each book.
power has in recent years been substituted for
During the earlier
manual labour in gold-beating.
stages of the process the blows are directed mainly
nical
towards the centre, which causes cracks and rents near
the edges of the leaves these cracks, however, become
;
closed up again subsequently, the edges of the cracks
welding together perfectly, so that the finished leaves
exhibit no trace of them.
filling teeth is
Gold for
degrees of thickness, the
according
of
which
60 grains
to
is
the tveiglit
beaten into
foils of
varying
being generally numbered
size
of the sheet, the standard
foils
Each book of foil contains
gold, and the number of the foal
four inches.
ounce) of
indicates the weight of each full sheet.
would contain
three
20 sheets, e^ch four inches square and weighing
sheets,
1
2
a book of No. 5 foil would contain
grains
book
grains;
five
weighiug
inches square, each
For example, a book
of
No.
3
foils
;
four
grains in
10 sheets, four inches square, each six
upwards
weight, and so on. Foils ranging from No. 32
prepared by folding a
are usually employed and are
equivalent to
sheet of No. 4 foil, so that it becomes
No.
6,
GOLD.
93
and then folding it again to make it as thick
as No. 16 foil, and then again to make it equal to
No. 32 foil. When heavier foils are needed several
No. 8
foil,
sheets can be folded together.
Although the foils are generally prepared by beating, yet some of the heavier numbers, averaging from
No. 20 to No. 60, are produced by rolling, and these
are sometimes used instead of thin foils folded to the
required thickness, as they are extremely cohesive and
may be
advantageously employed in extensive contour
operations. The heavier foils, however, are not
worked and considerable practice is required
so easily
in using
them.
The advantages claimed
teeth are that
which
it is
fillings are
for
gold as
a
filling for
able to withstand the attrition to
exposed and that
it
retains its shape,
and, therefore, forms a practically watertight plug
;
it
has no preservative action, however, upon the tooth
substances.
Cohesive and Non-Cohesive Gold.
two
—There are
varieties of gold-foil used in dentistry,
cohesive
and
non-cohesive.
known
as
In the cohesive variety the
characteristic welding property of pure gold
is
each piece of gold-foil introduced into the
utilised,
cavity of
the tooth being carefully welded to the others already
in
position,
principally
by means
of
pluggers
and
mallets, thus consolidating the gold.
In the non-cohesive variety uniou does not take
place between the pieces of gold introduced into the
made to retain
mechanically by wedging and intimately
cavity,
the
the gold
pieces
cavity.
very
being
tightly
between
the
its
position
interlacing
walls
of
the
DENTAL METALLURGY.
94
The
between these varieties of
difference
gold-foil
brought about by a slight alteration in the method
Non-cohesive gold is so prepared
of manufacture.
that there is no possibility of one piece sticking to
is
This appears to be attained by subjecting
the leaves of foil to the influence of certain gases, such
Graham has shown * that when pure
as ammonia gas.
another.
heated
gold
is
ing
gases,
it
has the power of occluding or absorb-
and
notably hydrogen
nitrogen.
"The
hydrogen occluded by gold is sensible, but
most
does not exceed 0.48 of its volume. Probably the
amount
of
gases
interesting point connected with the occlusion of
by gold is presented by the fact tha,t the metal retains
It
0.2 of its volume of nitrogen."
retention
of
which
nitrogen
property of gold.
A
is,
destroys
no doubt, the
the
cohesive
pellet of cohesive gold
made non-cohesive by exposing it
may be
to the atmosphere, or,
more expeditiously, by submitting it to the action
ammonia gas. " If non-cohesive gold is annealed
will
often be noticed that a vapour
then
it
becomes, as a
are a few
so slightly
rule,
is
given
thoroughly cohesive.
off,
of
it
and
There
of non-cohesive gold which become
cohesive on being annealed that this does
makes
These
non-cohesively.
not prevent their being worked
changed
slightly
is only
foils, the character of which
non-cohesive
are often spoken of as 'true
by annealing,
demands
They can be worked cohesively, but it
gold.'
gives
that
is
What it
special care and manipulation.
them
some
this particular
property
is
a trade
secret.
In
probably due to a very slight admixthese true non-cohesive foils,
ture of another metal
cases
it is
;
* Percy's " Metallurgy." vol.
Koberts-Austeu.
i.
p.
by
35; experiments recorded
GOLD.
95
however, seem also to have been subjected to the action
of some vapour, for, as above mentioned, they are not
so absolutely non-cohesive
when annealed, and heating
them causes a vapour to be given off just as with other
makes of non-cohesive gold."* "In using cohesive
gold, care should be taken to avoid touching it with the
destroy
its
grease,
moisture,
hands, since
and exposure
Though
cohesiveness.
foils
are
to
air
sold
as
always best to pass them througli the
flame before working, in order to anneal them and
restore their cohesiveness, and for this purpose a spirit
cohesive,
it
is
lamp should be
A
used.
owing
later to failure,
Bunsen burner
leads sooner or
to the impurities contained in
In annealing, care should be taken not to
overheat the gold, since many varieties become harsh
when exposed to a high temperature. Good cohesive
gold can be annealed to a dull red-heat without becoming
the gas.
The annealing
harsh." f
foil
upon a sheet
is
of mica,
best effected by placing the
which
is
held over the flame
of a spirit lamp.
diversity of opinion exists with regard to the
Much
relative values of the
two
varieties of foil, the advantages
claimed by the advocates of each variety being briefly
as follows
:
For Cohedve
compact
filling,
—That
makes a harder and more
although taking longer to work. That
Foil.
it
adapts itself to the walls of the cavity as well as noncohesive foil.
That in any case exposed to mastica-
it
tion the filling remains
smoother and the edges stand
better.
For Noii-CohcHirr
*
't
Foil.
— That
liUingH are
Grayston, JJcnlal Jtccord, 1896, vol. xvi.
Snuilo
and Colyur,
much more
p. 105.
" Diseiisus oi Teutli," p. 193.
DENTAL METALLURGY.
96
rapidly made, as larger pieces can be used.
adaptation to the walls of the cavity
is
That the
better than with
cohesive gold, thus the preservation of the tooth
That
it
is
better.
can be more thoroughly burnished to the edges
on account of the greater softness which it possesses.
With due care either variety is capable of affording
good results a combination of the two varieties, however, is extremely iiseful and often employed, the
advocates of this combined method claiming that a
;
better joint
cohesive
is
obtained at the cervical edge than with
foil.
Cohesive
foil is
the variety most generally employed,
the gold being consolidated by hand pressure or by
means
of a series of blows struck
by a hand,
electric,
automatic, pneumatic, or engine mallet.
Precipitated and
may be
Spongy Gold. — Metallic
gold
precipitated from a solution of gold chloride in
the form of fine powder, in scales, in a more or less
spongy condition, according to
the nature of the precipitating agent employed, and
also on the strength of the solution and mode of
The gold chloride solution is prepared by
operating.
crystallised state, or in a
dissolving metallic gold in aqua regia as described in
the preparation of pure gold (p. 87).
Owing to the facility with which gold chloride
duced to the metallic
reagents
The
phurous
may
state, a large
most frequently employed are
oxalic acid, and ferrous sulphate.
By Sulphurous Acid.
sul-
—-When an excess of sulphurous
added to a hot solution of gold chloride the gold
precipitated in the form of a brown powder which is
acid
is
of different
be used for precipitating the gold.
reagents
acid,
number
is re-
is
more or
less scaly.
GOLD.
By
O.mlic Acid.
—This
acid
97
is
a vety useful precipi-
tant aud will give gold of several forms, from sponge-
masses to the different crystalline or powdery forms,
according to the strength and temperature of the gold
solution.
Its action, however, is somewhat slower than
like
other precipitants
that of
and the solution requires
heating.
The
crystallised oxalic acid is dissolved in water
and
then added to the gold solution, when carbonic acid gas
is evolved, owing to the decomposition of the acid, and
the gold
By
is
precipitated.
Ferrous Sulphate.
tallic gold, either at
in the form
of
—This reagent
precipitates
me-
once or on heating the solution,
a very finely divided
brown powder.
powder is suspended appears
dark blue by transmitted light aud reddish and turbid
The solution is poured off" after subby reflected light.
sidence has taken place, and the precipitate is washed
first with a little dilute hydrochloric acid and subsequently with water, and then dried.
By other Precipitating Agents. The majority of the
common metals will precijoitate metallic gold from a
The
liquid in
which the
fine
—
solution of the chloride.
Many
metal.
organic substances also readily precipitate the
Thus,
when
a solution of gold chloride
with sugar the gold
is
thrown down
first
is
boiled
as a light
red precipitate, which afterwards darkens in colour.
As sugar
is
similar to oxalic acid in its action, the pre-
cipitation is capable of regulation,
gold
may be
obtained.
"
Lamm's
and various forms of
so-called
'
shredded
somewhat extensively used by dentists for filling
teeth during 1867 and 1868, was produced by the addi-
gold,'
tion of sugar or
gum
arabic to an acid solution of gold."
DENTAL METALLURGY.
98
When
precipitated from
its solutions,
gold assumes a
on being rubbed with a piece
of polished steel, or other hard substance, it readily
assumes its characteristic colour and metallic aspect.
dark-brown
colour, but
and finely divided gold are capable of
being welded and united into a solid mass by the appli-
Precipitated
cation of pressure.
The various forms of sponge and crystal gold used by
dentists are frequently prepared by precipitation, but
other methods are also adopted.
Crystal Gold. When an electric current of
—
through a solution of gold
chloride in which a plate of pure gold forming the
anode is suspended, and a platinum plate, forming the
cathode, the solution is decomposed and the gold defeeble intensity is passed
posited on the platinum plate in the form of crystals,
which vary in size according to the strength of the
solution and intensity of the current.
As the
solution loses gold
by deposition
of the metal,
replenished from the suspended gold plate, which
gradually dissolved. The crystal gold thus formed is
it is
is
generally very pure
and
is
;
then ready for
it is
collected,
washed and
dried,
use.
The beautiful spongy form of gold known as "Watts'
It is a cohesive
Crystal Gold" is produced in this way.
gold,
A
and must be used strictly as such.
an
crystallised form of gold is also obtained when
slowly heated until the whole of the
amalgam
of gold
mercury
is
mass
required, the
is
is
expelled.
When, however, a
amalgam is first
light
spongy
treated with
mercury. The
then heated
aggregate of crystals thus obtained is
thus leaving the gold
to expel the remaining mercury,
of
nitric acid to dissolve out the excess
GOLD.
spongy mass, having a
light
a
as
99
hiptrous
In-ight
appearance.
Assay
of Gold.
— Alloys of gold are usually assayed
by1st.
them with
Alloying
silver
by the process of
cnpellation (see Silver Assay, p. 178).
2nd. Parting the gold from the silver by
means
of
acid.
For this purpose about
grains) of the alloy
is
|-
to
i
gramme (10
to
20
and wrapped
carefully v?eighed
in a piece of lead-foil with pure silver equal in
weight
to 2^ times the quantity of gold assumed to be present
in the
This
weight of alloy taken for assay.
is
then subjected to cupellation, by which means
the lead and copper are oxidised and absorbed by the
and gold remain behind as an
The gold-silver bead is removed
cupel, while the silver
alloy
and
on the cupel.
an oblong
rolled out to
after
which
The
it is
spiral or
glass flask,
and
strip
about 2 inches long,
annealed and coiled into a
"
cornet," as
it is
termed,
spiral.
is
placed in a
" parted "
nitric acid for about
1
5
by heating it, first with dilute
minutes and then with stronger
by which means the silver is dissolved out,
leaving the metallic gold as a brown residue.
The acid is poured off" and the gold washed \vith
water, after which it is dried and then placed in a small
annealed " in a red-hot muffle for a short
crucible, and
time, when the gold acquires the usual yellow colour,
nitric acid,
with a considerable shrinkage in bulk.
The gold
is
allowed to cool, then carefully weighed
and the percentage
of gold present in the alloy calcu-
lated from the weight thus obtained.
After ))arting, the gold retains a very small quantity
DENTAL METALLURGY.
TOO
of silver, so that
when very
great accuracy
is
required a
system of working with " checks " is adopted. In this
case an amount of pure gold (approximately equal
to that in the assay) is very accurately weighed and
alloyed with the necessary quantity of other metals,
in order that the check
may correspond
in composition
then treated simultaneously with the assay and exactly in the same way.
the
If the gold left after parting the cornet from
to the alloy to be assayed.
It is
weighs more than the pure gold taken, the
gold
excess weight is deducted from the weight of the
obtained from the assay of th ? alloy and, conversely,
" check "
;
if it
weighs
less
the deficiency
Assay by the
is
added.
Touchstone.
— This
method
determining the fineness of a gold alloy conbe tested on a small
sists in rubbing the alloy to
resembling slate,
block of hard, smooth, dark stone,
appearance and
called a tonclidone, and comparing the
with those made
colour of the streak thus produced
prepared alloys
series of small bars of carefully
of
by
a
of
definite
composition,
known
as
"touch-needles"
of
and 31). The effect of the action of a drop
regia on these streaks
nitric acid and of dilute aqua
will
the streak from the less pure alloy
is also noted
(Figs. 30
;
production of a
be more readily acted upon, with the
the proportion
more or less green colour, according to
Several series of touch-needles are
alloys of gold and
usually employed, consisting of
gold, silver and copper,
copper, gold and silver, and
of copper present.
the alloys being
made
either
to correspond to legal
the proportion of gold
standards or in series in which
For the sake of
carats or half-carats.
increases
by
are frequently soldered
convenience, the touch-needles
GOLD.
lOI
to the points of a star-shaped piece of metal, as
shown
in Fig. 31.
The vahiation
made by determining
of an alloy is
to
which of the touch-needles the streak it produces most
In order to get correctly the
nearly corresponds.
the alloy to be
streak of
metal should
first
be slightly
have been made
the
tested, the
filed
surface of
away, as this
the
may
than the bulk of
somewhat
by boiling with acid to remove the base
alloy
richer
Fig. 31.
Fig. 30.
or inferior metal
from the surface, as
"
in the " colouring
process used by goldsmiths (see p. 116).
The touchstone is generally used for the approximate
assay of small articles of jewellery, which
it
would be
necessary to destroy in order to obtain samples for a
correct assay
;
it is
also of use to the assayer in deter-
mining the approximate fineness of gold bullion but it
cannot be relied upon for very accurate assay, although
;
it
yields sufficiently useful results for a preliminary test,
and for some purposes is sufficiently exact. It requires,
" The trial
however, a sharp and very practised eye.
is more sensitive for alloys below 750 fine (18 carat)
than for higher standards.
The amount
of
gold in
between 700 and 800 fine (17 to 20 carat) can
be determined correct to 5 parts per 1000." *
alloys
*
T. K. Jlose, " MBtiilhirgy of Gold,"
[i.
459.
DENTAL METALLURGY.
I02
Detection and Estimation of Gold in Alloys.
— Alloys for dental
amalgams are mainly composed of
small quantities of gold and
which
tin
platinum, and sometimes other metals, are added.
-
and
silver, to
—
Detection of Gold. The presence of gold in these
alloys may be detected by treating a small quantity of
the alloy with nitric acid,
undissolved.
As
alloys, it will
acid
when the gold
remain
invariably present in dental
tin is
converted
be
will
by the
into oxide
nitric
and remain with the gold, forming a purple residue
(pu.rple-of-Oassius).
If gold is absent the residue will
be white (metastannic
The
acid).
following are the usual
obtaining a solution in aqua regia
Stannous Chloride containing a
tests
for
gold
after
:
little
stannic chloride
a very characteristic test for gold, giving a beautiful
purple precipitate (purple-of-Cassius), even in solutions
is
containing extremely small quantities of gold.
Ff.rrous SidjyJiatc is also a delicate test, producing
either at once or
on heating the solution a very
divided precipitate of gold
:
the liquid usually appears
by transmitted light, and
turbid by reflected light.
bluish
Sid2)liurettecl
is
always reddish and
Hydrogen gives a brown or black pre-
cipitate of gold sulphide.
Estimation
finely
of
Gold.
—When
tin
is
absent,
the
residue of gold obtained after treatment of a definite
weight of the alloy with nitric acid may be filtered off"
and then heated
to redness
and weighed.
"
" purple-of-Cassins
If tin is present the residue of
caustic potash, which
is filtered off and then fused with
combines with the
tin,
forming a compound (stannate
leaving the gold as
of potash) readily soluble in water,
GOLD.
This
a fine powder.
is
103
collected on a
filter,
then washed,
heated to redness and weighed.
The gold
by
in
amalgam
submitting a
also be
quantity to
small
under Silver,
described
may
alloys
scorification, as
then cupelling and
180,
p.
determined
parting the gold-silver bead with nitric acid in the
ordinary
way
from one-tenth per cent,
in these alloys usually varies
to about 5 per cent.
Alloys of Gold.
— Gold
almost any of the metals,
constituting
The gold present
as previously described.
its
is
its
capable of uniting with
alloys with other metals
most important
uses,
as pure gold is
too soft for application alone.
Gold and Copper,
gether in
all
proportions
—These
when
metals alloy well
fused.
maximum
the hardness of gold, the
to-
Copper increases
degree of hardness
being attained when the copper constitutes one-eighth
The yellow colour of gold is deepened by
of the alloy.
the presence of copper, and when much cop]3er is preThe
sent the alloys become tarnished on exposure.
malleability of these alloys
of gold
if
pure copper
ceed 10 to 12 per cent.
is
scarcely inferior to that
employed, and does not ex-
is
Alloys of gold and copper are
more fusible than pure gold.
The gold coinage of this country
is
made from
22-carat gold, or 916.6 parts of gold to 83.3 parts of
copper, the alloying metal being copper.
termed standard gold (see
An
This alloy
is
p. 105).
and copper of i8-carat standard is
very largely employed for jewelleiy.
Gold and Silver. These metals unite iu all
alloy of gold
—
proportions
when melted
together, the resulting alloys
being paler in colour than pure gold, the presence of
DENTAL METALLUEGY.
I04
oue-twentietli part of silver being sufficient to modify
the colour of gold.
the
alloys
With 27
have a green
to 30 per cent, of silver
but when the silver
tint,
exceeds 50 per cent, the alloys are nearly white. The
effect of silver is to give hardness to the gold without
impairing
more
its
elastic,
and to make it tougher and
the same time sensibly reducing
malleability,
while at
the melting-point.
Gold-silver alloys do not oxidise on exposure to
air,
but are more or less tarnished in the presence of sulphuretted hydrogen.
Gold, Silver, and Copper.
—These
are largely used by jewellers and
by
three metals
dentists for the
production of alloys, v/hich are tougher, more malleable
and more ductile than when copper alone is used as
the alloying metal.
Alloys of these metals, in varying proportions, are
no).
Platinum. These metals unite by
used as gold solders (see
Gold and
p.
—
fusion, but require a high temperature to effect their
combination, in consequence of the high melting-point
The effect of platinum on gold is to
of platinum.
produce alloys which are ductile and
elastic,
but
its
presence makes the colour of gold paler.
Gold and Mercury.— These metals have a great
affinity
for one
another, even
at
ordinary tempera-
Gold-Amalgam, p. 1 34). If a piece of gold
penetrated
is rubbed with mercury it is immediately
and becomes exceedingly brittle care should therefore
be taken to prevent globules of mercury coming into
tures (see
;
contact with gold plate in the dental laboratory.
Gold and Tin.— These metals form alloys which
gold.
are usually brittle and of a paler colour than
GOLD.
Carat and Fineness. —Gold
in
pure
a
but
state,
is
almost
is
never emploj^ed
universally
with a certain j^roportion of copper or of
made
being
alloys
up
definite
to
alloyed
the
silver,
proportions
or
" standards."
Pure gold
fineness
is
described as 24 carats fine, and the
gold,
of
or
proportion in the
its
therefore expressed by stating the
number
alloy, is
of carats
pure gold present in 24 carats of the
The English gold coinage, or standard gold,
(or parts) of
alloy.
consisting of an alloy of 22 parts of gold with 2 parts
of copper, is accordingly described as 22 carats fine.
i8-carat gold
is
an alloy consisting of 18 parts of
gold and 6 parts of copper.
copper
is
In some cases part of the
substituted by silver
thus,
;
the
standard
frequently employed by goldsmiths, though of 22 carats
fine,
contains in the 24 carats 22 of gold with
copper and
metal
for
i
may be
i
of
In special cases the alloying
of silver.
platinum, as in 17-carat gold plate used
bands in dental work.
In England at the present time
exist for gold ware, viz.
18,
15,
12,
17,
and
The
made
16 carat, while
swivels 13-carat gold
is
;
Gold plate and wire
standards of 22, 20,
to
for
gold
springs
and
employed.
fineness of gold is also frequently expressed in
decimals, in which case pure gold
fine.
standards
22-carat, or standard gold
and 9-carat gold.
for dental purposes are
18,
—
five legal
The English standard
would therefore be g 16.6
fine,
is
described as lOOO
for gold coin,
22 carat,
and would contain
this
number of parts of fine gold in lOOO parts of alloy.
The standard of the American, German, and French
gold coinage
is
21.6 carats or 900
fine.
rhe relation
DENTAL METALLURGY.
io6
of the carat to decimals
is
shown
in
following
the
table
Decimal.
Cavat.
Pure gold
English gold coin
24
22
American
21 6
,,
1000
916.6
900
834
750
709
667
62s
542
20
Dentist's gold
18
17
16
IS
13
12
1
— Pure
seldom employed in
the dental laboratory, on account of its softness and
In order to obtain the degree of hardness,
flexibility.
Gold Plate.
gold
is
strength, and elasticity necessary to enable
it
to resist
the wear and strain to which an artiBcial denture is
invariably exposed in the mouth, the gold for dental
purposes
alloyed with other metals.
is
These important properties are usually conferred
upon the gold by the addition of copper or of silver, or
both; or by copper, silver and platinum. Varying
proportions of copper and silver are most generally
gold
employed, but
bands,
&c.,
gold which
not,
is
it
as
that
used for
platinum in
The quahty of
the mouth should
additional elasticity.
to be introduced into
a rule,
as
such
sometimes alloyed with
is
order to give
plate,
be
less
than
18 carat fine or
much
Gold of low standard is much more
proportion of
readily tarnished, owing to the larger
to the
communicates
copper and silver present, and
above 20
mouth
a
carat.
disagreeable
metallic taste,
while
gold of
:
GOLD.
107
high standard will generally be found too soft and
yielding and
not capable of resisting the strain put
upon it during mastication.
Higher grades of gold plate intended
for dental
purposes may, however, have the requisite amount of
and strength conferred upon them by the
addition of a small quantity of platinum.
Gold plate
rigidity
suitable
as
base
a
for
dentures
artificial
may
be
*
the
prepared according to the following formulaa
proportions
relative
;
the various metals added to
of
the pure gold or to the standard gold may, however,
be varied to suit the requirements of the manipulator.
The approximate
preparation
quantities are also given for the
gold plate from
of
English standard gold (coin)
is
the
formulas
when
used, (22 carats fine)
instead of pure gold
Gold Plate.
18
carats fine.
lUvts
Piii-e
gold
Copper
Silver
ihvts. ops.
Standard gold
Copper
18
4
Silver
.
Gold Plate.
Silver
9
2
O
20 carats fine.
(Iwts. grs.
20
.
IS
2
.
(Iwls.
Pure gold
Copper
19
Standard gold
21
19
o
5
2
o
'
.
2
Coppei-
2
Silver
Gold Plate.
22
.
carats fine.
(twts. ni-s.
Pure gold
.
(!opper
*
O
O
I
SilviMI'iMtiniini
22
.
O
o
iS
Kichardaon, "Mechanical Dentistry," 7th edit, 1898,
6
p, Si,
DENTAL METALLURGY.
io8
The addition
amount
of a small
of platinum to high
carat gold, as in the last formula, furnishes an alloy
in
rich
gold, while, as
previously stated,
to the plate a suitable degree of stiffness
and
imparts
it
and
elasticity
does not destroy the characteristic colour of line
gold nor materially impair
its susceptibility
of receiving
The richness of colour of the gold plate
however, more or less impaired as the quantity of
a high polish.
is,
platinum
increased.
is
Gold plate 20 or 21 carats fine, in which the alloying
metals are copper and platinum, is frequently used by
dentists on account of its greater strength and power
of resisting the chemical action
mouth.
With
reference
platinum, Essig remarks*
strength and stiffness a
plate
and
may
of the fluids of the
gold
to
that
much
containing
plates
"owing
to its increased
thinner and lighter
be employed without the additional labour
cost of doubling the plate at
what would be weak
points in partial cases composed of ordinary
or
20-carat gold."
An
objection urged
1
8-,
19-,
against the
employment of gold plate containing platinum is the
increased difficulty of swaging a plate of the alloy so
that
it shall
the die.
perfectly conform to
all
the depressions of
Essig having invariably found,
when the
any considerable percentage of platinum, that the ordinary method of swaging between
zinc and lead was not effective, has for more than
alloy contained
twenty years employed zinc for counter dies as well
for dies, thus entirely overcoming any difficulty
as
in
swaging.
Gold plate and wire used in making bands and
clasps should contain a little platinum in order to
* Essig, "
Dental Metallurgy," 1893,
p. 139.
;
GOLD.
it
tootli.
17-carat
embrace
firmly
to
elastic
sufficiently
render
109
with platinum
gold alloyed
The
quently employed for this purpose.
the
fre-
is
following
formula gives the quantities necessary for the preparation of 20-carat gold plate suitable for clasps, and
whenever
quired
and additional strength are
elasticity
re-
:
Gold Plate.
.
.
.
.
2
Silver
.
.
i
i
.
.
22 dwts.
„
Standard gold
Copper
.
.
o
„
Silver
.
.
i
„
,,
Platinuui
.
.
i
.,
20 dwts.
Pure gold
Copper
Platinum
20 carats fine.
.
„
In France the following alloys are used for " dental
gold plate *
"
:
Xo.
18
Gold
Silver
.
.
Copper
Platinum
Xo.
I.
20
cts.
Xo.
2.
21
cts.
No.
3.
For
cts.
4.
clasps.
20
.
18
...
20
...
21
...
.
2
...
2
...
i
...
i
4
...
2
...
2
...
2
—
...
—
...
—
...
i
.
.
Alloys Prepaeed from French Gold Coin (900 fine).
Xo.
18
Gold coin
Silver
Copper
Platinum
.
.
.
.
.
.
.
.
.
.
.
.
.20
.2
.2
.
No.
I.
For
cts.
—
Preparation of Gold Plate.
2.
clasijs.
20
...
...
0.4
...
C.3
...
0.75
— Alloys
•
for gold
by melting the constituents together
in a plumbago crucible, which should be carefully
A
annealed in an inverted position before use.
small quantity of charcoal powder should be placed
plate are prepared
on the surface of the metal to form a protective
coating and prevent the oxidation of the copper
*
Communicated
to
tli(;
author by Andre
I'.
(irillitliH.
I
DENTAL METALLURGY.
lO
the crucible should also be covered with a
crucible
is
then
heated
a
in
lid.
The
furnace at a
suitable
good bright heat, and when the mixture is melted the
whole should be stirred with an iron rod (previously
made red
hot) in order to promote
between the constituents of the
more intimate union
The alloys of
alloy.
gold should not be over heated but poured immediately
The metal
after complete fusion has taken place.
cast into an ingot-mould (see
rolled
into
sheets
of
the
p.
is
76) and subsequently
required
thickness.
The
mould must be blackened or greased to prevent the
metal sticking, and must be dry and warmed before
Care should be taken to prevent the charcoal
powder from running into the mould with the metal,
use.
otherwise
it
will
up clean scrap
cause a faulty casting.
When
for the production
plate the pre-
of
melting
cautions given on p. 66 should be considered.
Gold Solders. These are alloys of gold employed
—
for effecting the union of the various parts of
composed of pure gold or of gold plate.
To do
this successfully the solder used
articles
must have a
lower melting-point than the materials to be joined
with it the fusing-point of the solder should, however,
;
approach as near as it conveniently can to that of the
material to be soldered, in order that a more perfect
and more tenacious joint may be obtained.
varieties of gold solder of different degrees of
" softness " and " hardness," i.e. of fusibility, are pro-
Many
duced by adding to the gold variable proportions of
the more fusible metals silver, copper, and sometimes
—
zinc.
Gold solders are very frequently made from the same
is
carat gold as that of which the article to be soldered
GOLD.
1 I
composed, the melting-point being lowered by
and
tion of copper
tlie
I
addi-
or of standard silver and
In some cases gold plate of lovs^
standard may be employed as a solder for gold plate of
sometimes of
silver,
brass.
As
a higlier standard.
several standards of gold are
used in dental work, solders of different degrees of
fineness are employed, the solder most suitable for the
work
in
hand
being
selected.
range for gold solders
50 per cent, of
15 to
is
The most
from 20 to 12
carats, or
many
although
alloy,
desirable
from
consider
i2-carat solder too coarse for dental work.
of zinc renders
employed
The presence
more fusible, but when
the solders
make
should only be in quantities sufficient to
the gold flow readily and evenly at a diminished
heat;
when used
it
becomes objectionable.
Gold solders containing zinc are alwaj^s more or less
brittle, and consequently difiicult to roll into plate
in excess it
without breaking into
The following
many
alloys are
pieces.
largely
employed
in this
country as gold solders for dental work. They are
very fluid and flow readily in a state of fusion, and
effect a perfect
combination between the parts united
by them.
No.
I.
Gold
.
Silver
.
Cop[)er
.
No.
"Best Quality."
.15
.
.
.
.
Silver
.
.
.
Standard gold
.
,,
Silver
.
.
4.0
„
5
»
Cop]ier
.
.
3.5
„
24
„
4
.
16.5 dwts.
24.0
"Medium."
2.
(iold
Copper
dwts.
15-cARAT Solder.
ij-carat Solder.
13 dwts.
Standard gold
.
6
,,
Silver
.
.
5
r
Copper
.
.
24
.•
I
.
14 dwts.
6
4
24
,.
I
DENTAL METALLURGY.
12
No.
"Most Fusible."
T..
Gold
i2-carat Sor.nEn.
6
„
Silver
Copper
6
„
Copper
24
,1
The following formula
dwts.
iSUindard gold
12 dwtss.
Silver
6
.
5
24
*
may be used
with 18- to 20-carat gold plate, and
in connection
16 carat fine
is
:
16-CAKAT SOLDEB.
Pure gold
6 purts or 16 dwts. o grs.
Silver
2
))
5
"
^
I
„
2
„
16
24
11
O
Copper
.
„
II
6.5 parts or 17 dwts. 8 grs.
Standard gold
Silver
II
2.0
.
Copper
0.5
,,
5
„
8
„
„
I
„
8
„
24
The following formulae
carat solders
will furnish
15-caratand
18-
:
15-CAEAT Solder.
Pure
gl^
Silver
Copiier
.
15.0 parts
Brass
16.8 parts
36
.,
Copper
2.4
„
„
Brass
1.2
.,
„
4.2
1.2
Standard gold
Silver
3-6
24.0
24.0
18-CARAT Solder.
Pure gold
Silver
.
Copper
Brass
.
18.00 parts
Standard gold
is
2.66
2.66
2.66
1.
,,
Copper
068
„
Brass
0.68
always used as a flux with gold solders.
* Harris, "
Dental Surgery," No.
3, p.
666.
,,
00
24.00
24.00
Borax
19.66 parts
Silver
.,
GOLD.
I I
o
Preparation of Gold Solders.— lu preparing
gold solders the metals are carefully weighed and then
melted together in a plumbago crucible in a furnace at
a bright red heat.
A
little
charcoal powder
is
sprinkled
on the surface to prevent oxidation. When complete
fusion has taken place. the metal is stirred and
then
poured into an ingot-mould to obtain a thin ingot
suitable for rolling.
When
zinc or brass enters into the composition of
the solders it should be added after the other
stituents are completely melted, care
conbeing taken to
avoid excessive heating.
The alloy should then be well
and poured immediately.
The metals employed for the preparation of gold
solders should be free from impurities,
and great
stirred
care
should
be taken to insure uniformity of com-
position.
Calculation of the Carat Fineness of Alloys.
—The
several calculations in connection with the
carat
fineness of various mixtures may be readily
made by
the aiDplication of a simple method devised
some years
ago by Mr. A. Mc William, of the University
College,
Sheffield, for the calculation of all kinds
of steel
tures, and now extensively used by
mix-
students and in the
works.
A
beiug one -^^th part (see
p.
105), the
of ounces (or other unit of weight)
multiplied
carat
number
by the carat fineness gives the number
of 24ths of an
ounce of fine gold present in an alloy,
and this new
unit (^Vth ounce) is termed the
"carat ounce."
This
new
unit will be
found very convenient in
calculating the carat fineness of
gold alloys, for
obvious that in any alloy
.
JI
it
is
DENTAL METALLURGY.
114
ciira t
oimces
^
^.^^..^^^
_
quqcq^.
=
carat ounces.
ounces
carat ounces
cai'ats
ounces x carats
application of this
The
method
will
stood from the following examples
be readily under-
:
Carat Fineness of an
I. To ascertain the
Alloy from a given Mixture
is given for the
Examiilc i.— The following mixture
:
preparation of a gold solder
Pure
:
gold, 6 ozs.
;
silver,
Total, 9 ozs.
produced.
6 ozs.
Ascertain the fineness of the alloy
of gold,
contain 6x 24, or 144 carat ounces
2 ozs.
copper,
;
i
oz.
pare gold
and
as this
is
the
amount
carat fineness of the alloy
liAj^axa^^w^
of gold in 9 ozs. of alloy, the
is 16.
_
J
5 carats
tine.
9 ozs.
solder in the preExample //.-Again, take a gold
standard gold has been used
paration of which English
instead of pure
gold, the quantities
bemg 48
dwts.
dwts. silver 12 dwts.
standard gold (22 carat), 16
48 dwts. standard gold conTotal, 76 dwts.
copper.
tain 48
X
22, or
1056 carat dwts.
i^^gi^^
i-
A^^r^<
(^^Q
carats as the tineness of the
= {'^-^iS
from the given mixture.
Standard
To Reduce Gold to a Required
the
:
II
The standard
of a gold alloy
may be lowered by
these,
of silver, or an alloy of
addition of copper, or
such as silver coin.
/;.;a«^2;ie
4
ozs.
/-Reduce
.
^
, ,
pure gold to i6-carat gold.
,
4
ozs.
pure gold contain 4 X
24, or
96 carat
ozs.
:
GOLD.
g6'
uiu'iit oxti.
1
6
ozs. is
=
t-
6 ozs.
5 carats
the weight of the alloy of i6-carat fine, and
as 4 ozs. of gold are used, 2 ozs. of other metal
must be
added to reduce the pure gold to l6-carat gold.
Mmni'plc II.
— Reduce
2 dwts.
of l8-carat gold to
l6-carat gold.
2 dwts. of
2X
i8-carat gold contain
i8, or
36 carat
dwts.
—
carat dwts.
36
^
7
1
ID carats
Hence
-]
=
,
,
,
2j dwts.
dwt. of other material must be added.
To Raise Gold to a Higher Carat
may
This
be done by adding either pure gold or gold
alloy of a higher standard than that to be prepared.
Example
I.
—Raise
10 dwts. of
gold to
i8-carat
20-carat gold.
The 10 dwts. must be raised 2 carats, and this will
require lO x 2, or 20 carat dwts.
The pure gold (i.e. 24 carats) added must be considered to retain 20 of its own carats, and hence there
are only 4 carats available for enriching.
20 carat dwts.
\
4
5
dwts. of pure gold
=
,
S
,
dwts,
cai-ats
must therefore be added
to raise
10 dwts. of i8-carat gold to 20-carat gold,
EjXLtnple
20-carat
II.
gold
— Raise
10 dwts. of
gold to
l8-carat
by the addition of standard gold (22
carats).
Standard gold has 2 carats available for enriching.
20 carat dwta.
- -
=
.
2 carats
s
,
,
10 dwts.
,.
ol
,
,
,
,
,
,
,
,
,
,
standard sdid
to be added.
"
I 1
DENTAL METALLURGY.
6
Example i//.— Raise 9 dwts. o£ 13-carat gold
gold.
i6-carat gold by the additiou of 20-carat
9 dwts. raised
= 27 carat dwts.
- 16 = 4 available
to
3 carats
20-carat gold has 20
_^7_5f^If^Ldw^^ ^
gn
^^,vts.
carats.
to be added.
4 (available) carats
Colouring of Gold.—This term
process
by which a
obtained on articles
their appearance,
and
superficial
made
is
of
film
is
applied to the
of fine
gold
is
gold alloys to improve
effected by externally dissolv-
with which the gold
ing out the copper or other metal
article to
In conducting the process the
is alloyed.
dull redness in a Bunsen
be coloured is first heated to
and then plunged into
flame or flame of a spirit lamp,
weak solution
which means the
a
acid bath, by
of nitric acid or other
dissolved,
copper, &c., on the surface is
gold of a deep, rich, yellow
leaving behind a film of pure
colour.
T
J
by a
produced
The same effect is also frequently
" dry colouring," which
method known as
consists
m
coloured for a few minutes
placing the article to be
in a paste,
composed of a mixture
of saltpetre,
common
gold
Twelve-and-a-half to thirteen carat
subjected
that can be satisfactorily
is the lowest quality
and unirich
and retain a
to the colouring process,
showing irregularities on" the
salt
and alum.
form appearance without
^''(^Iding
—By
low standard
this process articles of
made to resemble high carat gold
or of base metal are
gold deposited on their surface.
by having a thin film of
The method now
known as "
that when
pmijose is
usually adopted for this
and is dependent on the fact
electro-gilding,"
a current of electricity
is
passed through a
GOLD.
117
suitable solution of a metal decomposition of the liquid
takes place, the constituents of the liquid being liberated
and the metallic constituent deposited.
Large articles are gilded in cold solutions and smaller
A
articles in hot solutions.
small articles
solution for electro-gilding
maybe prepared by
dissolving 15.4 grains
aqua regia and evaporating nearly to
The gold chloride thus formed is dissolved in
of pure gold in
diyness.
water, and a solution of
potassium cyanide carefully
added as long as a precipitate of gold cyanide
The
precipitate
poured
off,
is
allowed to
settle,
is
given.
the clear liquid
and the precipitate dissolved by the addition
The solution is
then diluted with water to one quart. The temperature
of the bath shoald be about 165° F., and the cui'rent
of
more potassium cyanide
solution.
strength 2.0 to 2.5 volts.
The process is conducted by first thoroughly cleansing
the article by immersing it in a hot solution of caustic
potash, and sometimes in an acid bath, and also by
means of a scratch-brush.* The article is then rinsed
in water and transferred to the plating solution.
A
plate of pure gold
suspended in the bath from
a suitable support connected with the positive pole of a
is
battery, while the article to be
plated
is
suspended
by thin copper wire connected with the negative pole.
By this means an electric current is passed through
the plating liquid, which causes the deposition of a
film of metallic gold on the article.
The gold solution is kept hot during the operation
(as above stated), and remains constant in strength.
*
8
This conniHtH
in. loiif;,
left
I'l'i'i'
til
ol;
ii
biindlo of
liiK^, liiird
Ixmiid roimd Vci'v tightly with
ronii
:i
brush.
hniss wiiv; iibont 6 in. or
otli(!r
wire, (lio (mhIs heing
DENTAL METALLURGY.
Il8
owing
to the gradual dissolving
When
sufficient gold has
away
of tlie gold plate.
been deposited, the
article is
removed and well rinsed in water the dull brown surburnishing.
face is then made bright and lustrous by
The electric current employed is usually derived from a
;
and the proportion of gold cyanide,
potassium cyanide, and water in an electro-gilding
Bunsen
battery,
solution
may vary very
greatly without detriment to the
process.
A
process for
making dental bases by
electro deposi-
preparation, was
tion on the plaster cast, after suitable
patented by
Ward
in 1889.
are sometimes gilded
Articles
Fire Gilding.—
old
process,
known
as Jire gilding.
receive the deposit of gold
is
first
The
by the
article
to
cleansed and then
by which
dipped into a solution of mercuric nitrate,
It
means it becomes coated with a film of mercury.
a pasty amalgam of gold
is afterwards pressed upon
(see p.
134), a portion of
which adheres
to
The
it.
behind a
mercury is then expelled by heat, leaving
burnished.
deposit of gold which is subsequently
of Gold from Scrap.— Dental scrap
Recovery
consists chiefly of plate clippings
proper care
platinum,
is
and old
plates.
If
of
taken to prevent the introduction
and to
or particles of base metal,
filings,
scrap
together, the
keep clippings of definite standard
and again converted into
only requires to be remelted
plate or other
form
When, however,
for use.
the
scrap
platinum, and
mixed
filings,
solder,
&c., the gold
contaminated with
fragments containing
is
must be recovered before
it
can
fresh plate.
be worked up again into
first partially refined by
For this purpose the scrap is
119
GOLD.
melting with a
little
with from 2 to
3
borax and
times
its
nitre.
It is then alloyed
own weight
and
of silver
the resulting alloy granulated and parted as described
on p. 87. If platinum is present and does not form
more than 10 per
cent, of the original alloy,
it
will
be
dissolved with the silver after prolonged boiling in acid.
The
silver is precipitated as chloride (see p.
1
69),
platinum subsequently separated with zinc or
and the
ammonium
and converted into spongy platinum.
If more than 10 per cent, of platinum is present the
operations of inquartation with silver and parting must
be repeated, or the gold may be dissolved in aqua regia.
chloride
The
solution thus obtained
evaporated, and potas-
is
sium chloride and alcohol added to precipitate the
platinum.
/ After allowing the platinum precipitate to settle the
clear liquid is poured off and ferrous sulphate or other
added to precipitate
precipitating agent (see p. 96)
the gold.
The
finely divided metallic gold is collected,
washed, dried, and then fused in a crucible, with the
addition of a little potassium bisulphate as a flux, after
which
it is
cast into an ingot
The platinum
is
and
recovered
is
in
ready for use.
a
spongy form in
the metallic state by strongly heating the precipitate
obtained.
—
Sweep
or Lemel. These terms
are applied to the material which accumulates in the
dental laboratory and other places where gold is
Purification of
worked.
It
consists
of
fine
metallic
particles
con-
taminated with dust and organic matter, such as
wax, &c., and varies considerably in composition.
A
magnet is first passed through the filings to remove
any iron which may be present. The lemel is then
I
DENTAL METALLtTUGY.
20
by burning
purified
off
the organic matter, and melted
These neces-
in a fireclay crucible with suitable fluxes.
vary according to the quantity and nature of the
impurity mixed with the lemel, but the following prosarily
portion
may be
conveniently taken
:
5°
Lemel
Sodium carbonate
Borax
5
Potassium bisulphate or nitre
Common
salt
.
.
.
.
.
.
•
.
i
5
to 2
5
•
mixed with the fluxes, with the
exception of the salt, which is kept as a cover for the
mixture, as it prevents the mass rising too much and
The lemel
is
well
which oxidises the
base metals, and potassium bisulphate should be sparThe crucible should not be more than
ingly employed.
half full to commence with, and should be gently
overflowing
the crucible.
Nitre,
heated at first, the temperature being raised gradually.
Towards the end of the operation, when the violence of
the action has nearly ceased, a more intense heat is
employed, and when the whole mass is thoroughly
which
liquid it is well stirred with an iron rod, after
into
the crucible is removed and the contents poured
an ingot-mould, care being taken to prevent the "slag"
running into the mould. The ingot thus obtained will
in
many cases be
brittle,
the alloy
with a
little
in a suitable condition for rolling.
may be
"
toughened
charcoal powder.
When
"
it
If
by remelting
is
desired to
ingot must be
obtain the gold, &c., in a pure state the
and alloyed
cleaned from any adhering slag, weighed,
silver, the
of
weight
with from two to three times its
granulated by
molten alloy being well stirred and then
carefully pouring into water.
aotD.
of alloy are collected, placed iu a
The small granules
aud parted in acid as described on p. 87.
If much platinum is present the alloy is best dissolved in nitro-hydrochloric acid, and the metals resuitable vessel,
covered as described for the treatment of scrap.
Purple- of-Cassius.
—This compound
employed
is
by manufacturers of porcelain teeth for obtaining the
necessary pink tint;
it
is
also
used in the arts for
imparting a rose or pink colour to porcelain, enamel,
and
red or brown, according to
by adding a solution of stannous chloride
It is obtained
(SnCl.,),
from violet to a purplishthe method of preparation.
It varies in colour
glass.
containing also stannic chloride (SnCl^), to a
By this means
dilute neutral solution of gold chloride.
a fine flocculent purple precipitate
allowed to
settle,
is
obtained, v^hich
then collected, washed, and
is
dried.
The exact nature
of this precipitate
understood
supposed to be a combination of
it
;
is
is
not thoroughly
stannic oxide, coloured with finely divided gold or one
of its oxides.
A
very fine product
is
obtained by adding a solution
of stannous chloride to ferric chloride, until the solution
and becomes a pale green. This
mixed solution is then added to the gold solution to
produce the purple precipitate. Many other methods
are also employed.
The purple-of-Oassius used by the
loses its yellow colour
manufacturers of porcelain teeth, in the preparation of
gum-enamel, is sometimes prepared by the following
method.* An alloy consisting of
Silvin-
Gold
Till
....
.
,
*
Kssifi,
.
.
.
.
.
.
40 parts or
85.
1
per
coil
4
„
8.5
„
3
..
6.4
,,
Di'iitMl Mc(:illiir^-y,"
1893, p. 150.
t.
122
DENTAL METALLURGY.
prepared by melting the constituents in a crucible,
under a cover of borax. The alloy is granulated by
is
pouring into water, and the granules treated with nitric
acid and gently heated, until all the alloy has been
acted upon.
The
having thus been entirely dispoured ofE and the purple residue
silver
solved, the solution is
carefully washed, until the last trace of silver solution
is
removed.
After several washings, the purple-of^Cassius is dried
by gentle heating, and is then ready to be incor-
porated with the silicious materials for the preparation
of gum-enamel.
dHAtTER
Vli.
MERCURY,
SYMBOL, Hg
Occurrence.
in the
(Hydrnrgyi-um).
—Mercury
metallic
inated through
state,
is
ATOMIC WEIGHT,
frequently found in nature
almost pure,
usually
globules.
ores in small
its
2Q0.
dissem-
It is also
found in combination with iodine and chlorine, and in
union with gold and
silver, as
native amalgams.
Its
combination with sulphur, constituting cinnabar (HgS),
forms, however, the most important ore of the metal,
and that from which almost the whole of the mercury
of commerce is derived.
Preparation. The method almost exclusively
employed for extracting mercury from the natural
—
sulphide consists in heating the ore in a suitable kiln or
furnace, to which a series of large condensing chambers
By
the action of heat and air the ore
is
connected.
is
decomposed, the sulphur being oxidised to sulphvir
and the mercury liberated and volatilised.
The gases and mercury vapour in passing from the
kiln are introduced into the condensing chambers,
where the mercury condenses. The metal thus obtained
is always more or less contaminated with other metals
derived from the ores treated
it therefore needs
])urirication.
Small (quantities of mercury may be predioxide,
;
DENTAL METALLURGY.
124
pared free from admixture of other metals by operating
upon a pure compound of mercurj^ which is decomposThus, the red oxide readily yields mercury
by simple distillation, while the sulphide (pure vermilion)
is best treated after the admixture of an equal weight
able by heat.
of lime.
—This metal, known
Properties.
difEers
also as quicksilver,
from other metals in being liquid at ordinary
temperatures, but, unlike ordinary liquids,
it
runs
off
non-metallic surfaces without wetting them, while with
many metallic surfaces the mercury unites with the
metal and deposits a film of an amalgam upon it.
a
It has an almost silver-white colour and possesses
not
strong metallic lustre. When pure, mercury is
tarnished by exposure to dry or moist air. If, howtakes
ever, other metals are present, oxidation rapidly
and the surface of the metal becomes covered by
of
a grey powder: this fact forms a ready method
If
detecting any considerable amount of impurities.
place,
mercury be maintained in contact with the atmosphere
the metal
at a temperature just below its boiling-point
Mercury is very
is slowly oxidised to mercuric oxide.
slowly
hydrogen, but
acid.
metal.
is
it
Water and
the
presence
nnaflfected
alcohol
of
sulphuretted
by exposure
are without
to carbonic
action on the
not attacked by hydrochloric acid
the
the concentrated acid is heated with
Mercury
even when
metal.
in
tarnished
is
It is scarcely affected
by
dilute sulphuric acid,
heat acts on
but the concentrated acid with the aid of
Nitric acid is its best solvent, and disit readily.
Alkaline solutions have
solves it with great energy.
Mercury solidifies
or no action on mercury.
little
when cooled
to
-39'
<^'->
and
in the act of freezing it
125
MERCURY.
considerably,
confci-cacts
malleable mass that
hammer
or welded,
out with a knife.
and
forming a tin-white, ductile,
may be beaten out with the
also capable of
it is
boils at 350°
Mercury
being easily
C, producing
a colourless vapour which is very poisonous, giving rise
The density of the metal varies much
to salivation.
with
the
When
high coefficient
mercury is shaken with
triturated
with sugar, lead, and
temperature, owing to
of expansion for heat.
oil,
when
or
it
is
its
obtained in a very finely
divided state in the form of a dull grey powder. This
operation is known as deadening, and is employed in
other bodies, the
metal
is
the preparation of grey mercurial ointment.
Use
for Dental Purposes.
—Mercury
is
chiefly
used ia the dental laboratory for the production of
amalgams for filling purposes. It is also used to a
extent
small
Compounds
as
a
of
constituent
"fusible"
alloys.
mercury are used in the manufacture of
of
dental rubbers.
Testing the Purity of Mercury.— It
is
very
important that the mercury employed for dental purposes should be quite pure, otherwise it will not readily
amalgamate with other metals. All doubtful specimens
Mercury which
should therefore be purified before use.
has been squeezed out in the preparation of amalgams
should not be returned
to
invariably contains small
derived from
merce,
the mercury-holder, as
quantities of
the alloy used.
unless
specially
The mercury
purified,
is
it
other metals
of
com-
frequently con-
taminated with small quantities of the volatile metals.
Zinc and bismuth, which are sometimes present in
mercury
lead,
ores, are distilled over
antimony,
tin,
with the mercury, while
and bismuth are added as adultera-
DENTAL METALLURGY.
The comparative purity of mercury
is readily observed by allowing a drop of it to run
lightly down a slightly inclined surface, when it ought
to roll as a perfect sphere and not elongate or drag a
tions to the metal.
be tested by briskly
shaking a small quantity of the metal in a bottle with
"tail" behind
air,
when
it
may
It
it.
should retain
also
bright metallic lustre.
its
If base metals are present, they are oxidised and form a
grey or black powder upon the surface of the mercury.
—
Purification of Mercury. The method most
frequently employed for freeing mercury from these
impurities
to
is
distil
it,
of
surface
the
the metal
being covered during distillation with clean iron filings
to the extent of about one-sixth the weight of the
The
mercury used.
and
iron filings retain the impurities
also help to prevent the spitting of the mercury,
which, however, cannot be completely avoided.
distilling small quantities of
mercury
used, while earthenware or wrought-iron
The
for large quantities.
retort,
For
a glass retort is
is
employed
about one-third
full
by imbedding it in a
sand-bath, while the neck is inclined and made to dip
beneath the surface of the water, with which the
of mercury,
receiver
is
is
carefully heated
half
filled.
The
receiver
is
still
further
with
cooled by placing it in a large vessel also filled
On the application of heat the mercury boils
water.
while
and distils over, and is condensed in the water,
the other metals are
filings.
retained by the layer of iron
The mercury thus
obtained
is
generally
which is readily
covered with a thin film of oxide,
removed by treating the metal with a little hydrochloric
is well washed and dried
acid, after which the mercury
at a gentle heat.
A
better
method
is
to substitute
;
MERCURY.
coarsely powdered
cinnahar for the
iioii
filings,
the
former being added to the extent of about one-fifth
The cinnabar suffers
the weight of the mercury used.
decomposition during distillation with the liberation of
its mercury, while the impure metals are largely converted at the same time into sulphides, which remain in
In distillation processes a small pox'tion of
the retort.
the more volatile impurities
generally carried over
is
and condenses with the mercury
therefore, when very pure mercury is required, the
separation of the impurities is effected by other means.
The best method of effecting this is to treat the mercury
into
the
receiver
with nitric acid diluted with from six to eight parts of
water and expose
it
to a gentle heat of about 55° C.
(131° F.) for some hours.
impurities and more
very
little
of the
The
acid dissolves out the
readily oxidisable metals, while
mercury
is
dissolved.
In order to
bring the mercury into intimate contact with the acid
it
or
should be exposed in thin layers in a shallow vessel
frequently shaken
method
consists
up with
the
in dropping the
acid.
Another
mercury in a
fine
stream through a high column of dilute nitric acid.
Mercury which has become contaminated with dust,
or from which the impurities have been oxidised by
shaking in air, may be cleansed by filtering through a
cone of paper, the apex of which has been pierced with
a pin.
It may also be filtered by squeezing through
a piece of chamois-leather.
Electrolytic Purification of Mercury.
— Elec-
methods have been recently introduced for the
purification of mercury for dental and other special
purposes, but the details of the processes employed have
not been published.
trical
DENTAL METALLURGY.
128
Mercury may be obtained
from
-by electro-deposition
a solution of the metal in nitric acid or in sulphuric
acid,
with about
per cent, of free acid.
5
In a method devised by Johnson* commercial mercury
is employed as the anode and carbon rods as the
cathodes.
The mercury is placed in a flat basin and
the carbon cathodes suspended above
consisting of
nitric acid
solution
a
and 4 per
the electrolyte
it,
17 per
containing
of
cent,
An
cent, of potassium nitrate.
employed, the current being interrupted at suitable intervals to prevent mercury from
going into solution. As long as the voltage is kept
E.M.F. of
I
volt
below 0.75 very
is
little
mercury leaves the anode, but
the impurities, zinc, cadmium, copper, lead, &c.,
The
currents
weak
very
into solution.
of long
pass
duration, the electrolyte
Six hours were
being renewed from time to time.
found
all
work best with
process is said to
about 2
sufiicient for the purification of
the ordinary commercial mercury.
The theory upon which the process
is
based
lb.
is
of
that
than that of
the ionising pressure of hydrogen
the impurities and greater than that of the mercury
is
the solution of the impurities
the current.
Vermilion.
pound
of
—Mercuric
mercury
is
is,
less
therefore, assisted
sulphide,
This com-
HgS.
extensively used as a colouring
pigment in vulcanisable rubbers and
vermilion of commerce varies
much
celluloid.
quality
*
is
—Vermilion
made by
of fine colour
the Chinese.
The
in tint and purity
its
of colour, slight differences in the details of
facture impairing or improving its colour.
Preparation.
by
manu-
and superior
The process
W. M. Johnson, horn Electric World and Engineer,
of
manu-
37, 634, 1901.
MERCUEY.
129
facture consists in heating a mixture of
one part of
sulphur with four parts of mercury in a shallow iron
pan, the mixture being stirred to effect combination.
The
product, which
a reddish or black powder,
is
is
placed -in iron pans provided with earthenware domes
and strongly heated for eighteen hours to sublime the
The
sulphide.
vessels are then allowed to cool slowly,
found adhering to the
when most
of the vermilion
surface
the dome, that attached to the iron pan
of
finely
is
powdered, then put into a large
vessel containing water
and allowed to
the fine sediment or residue
The powder, which
through muslin and
of the
The purest portion
being of inferior quality.
sublimate
is
is
settle,
when
and
dried.
collected
is
of a very fine colour,
is
then ready for
is
sifted
sale.
by wet
processes, one of the best being that of Brunner, which
It consists in rubbing together
is frequently employed.
for some hours a mixture of 100 parts of mercury
and 38 parts of flowers of sulphur, and then mixing
Vermilion of good quality
is
also obtained
the resultant mass with one part of potash dissolved in
six parts
of water.
After heating this mixture for
about eight hours the mass begins to exhibit a red
colour, and when the right tint has been attained the
mass
is
action,
quickly washed with water to prevent further
and
is
Detection
then dried.
of
Ivipurities.
—Vermilion
is
sometimes
adulterated with red lead, red oxide of iron, and fre-
quently with
gypsum
and
other
impurities.
The
presence of these impurities can be readily ascertained
however, as pure vermilion
is
volatilised
is left it
when heated
in a glass tube
without leaving any residue.
If a residue
denotes the presence of some impurity.
i
DENTAL METALLFRGY.
T30
Fivpcrlics.
—When vermilion
is
bvouglit into contact
and other metals having an aftinity.
for sulphur, it is decomposed with the formation of
metallic sulphides, and it is this fact which renders the
witii silver, copper,
combination of
silver and.vulcanisable
rubbers imprac-
ticable.
unaffected by water, alcohol, or alkalis,
insoluble in nitric, hydrochloric, and sulphuric
Vermilion
and
is
It is readily soluble,
acids.
chloric
is
:
this
however, in nitro-hydro-
mixed acid should therefore not be used
in removing tinfoil applied as a coating for plaster casts
in rubber work, which may adhere so tenaciouslj^ that
cannot be removed without the aid of a solvent.
Hydrochloric acid is the only solvent that will accom-
it
plish the removal of the tinfoil satisfactorily without
injury to the rubber.
"
Pure vermilion
in combination
not likely to produce deleterious effects
when worn in the mouth, nor is it probable that this
compound can be decomposed chemically and converted
with rubber
is
into a poisonous salt of mercury or cause salivation
the saliva." *
by
The discomfort some-
mere contact with
times caused by wearing artificial dentures of vulcanised
rubber is probably due to a certain extent to the
presence of deleterious substances present in the vermilion used for colouring the rubber.
Amalgams. "When mercury is one of the con-
—
an alloy the mixture is called an amalgam.
Mercury unites with most of the metals when brought
metals are in
into contact with them, especially if the
Many of
of foil.
a fine state of division or in the form
metals unite with mercury at the ordinary tem-
stituents of
the
assistance of heat.
peratnre, while others require the
* Essig,
'•
LViital Metallurgy," 1S93
I'dit. p.
223.
MERCITRY.
The
at
with which combination often takes
facility
ordinary temperature
the
li([uid
is
i)lace
jn-obably cine to the
condition of mercury, which facilitates
its
being
brousrht into intimate or molecular contact with other
metals.
is
With most
easily effected
of the metals, union with mercury
but with platinum, iron and nickel
;
combination takes
formation of amalgams
an evolution of
certain
amount
only with difficulty.
.place
The
sometimes accompanied by
is
indicating the existence of
heat,
of chemical affinity
:
in other cases
absorption of heat takes place, but as a rule
little
a
an
or no
thermal disturbance results from the combination of
The formation
metals with mercury.
a
few of the metals
is
of
amalgams of
attended with
considerable
diminution in bulk, while in some cases expansion
takes place, but generally the union of mercuiy with
other metals
volume.
is
accompanied by
The amalgams
little
or no change in
some metals are
of
fluid like
mercury, while others are solid or semi-solid.
solid
amalgams appear
consist
to
of
The
metals united
with mercury in atomic ])roportions, forming what are
regarded by
many
the liquid
amalgams generally
as definite chemical
dissolved in an excess of mercury.
frequently be
compounds, while
consist of a
compound
This excess can
separated by simple pressure through
chamois-leather, the solid
amalgam
many
probably consisting in
behind most
cases of metals united in
The chemical
atomic ])roportions.
left
affinities
between
the constituent metals, however, are only very feeble,
as
many amalgams
atomic proportion
jeoting thpTu
to
in
which the metals are united in
may
))e
partly decomposed by sub-
very great pressure, a part of the
mercuiy being thus forced
out, while
an amalgam con-
DENTAL METALLURGY.
132
taining a larger proportion of the other metals remains
behind.
In many cases liquid amalgams acquire a
form on standing, the excess of mercury
being separated the crystallised body thus formed is
the true amalgam, and, as before stated, probably a
crystalline
;
compound.
Although amalgams are usually obtained by the
direct union of the metals with mercury, other methods
are frequently employed for their production, espereadily.
cially for metals which do not amalgamate
Amalgams may also be produced— (i) by adding mermetal
cury to a solution of a metal (2) by placing the
salt; and
to be amalgamated in a solution of a mercury
definite chemical
;
(3) by the action of a
weak
electric current
produced
by placing the metal in contact with mercury and an
The properties of the amalgams of the common
acid.
metals are as follows
:
Aluminium Amalgam.
minium and mercury cannot be
— The
union of
alu-
effected readily at the
of comordinary temperature, but mercury is capable
the
heating,
bining with finely divided aluminium on
of
beiug attended by a considerable evolution
union
heat.
Although mercury and aluminium are not
oxi-
ordinary temperature,
dised by exposure to air at the
oxidation rapidly
yet after combination has taken place
readily covered
ensues, the resulting amalgam being
very
oxide.
with a thick film of white aluminium
accompanies the
considerable increase of volume also
instruments or
combination. When using aluminium
remember the affinity
apparatus, it is very important to
A
of
and
the
mercury under suitable conditions,
in any form in
to avoid the use of aluminium
The same
contact with amalgam fillings.
aluminium
also
mouth
in
for
MERCURY.
results are
T33
experienced on bringing aluminium into
contact with mercury
salts.
Antimony Amalgam. — Antimony combines with
mercury in the cold with great difficulty, but more
perfectly when heated, producing a soft plastic amalThe amalgamation is also facilitated by the
gam.
addition
of
amalgam
a
dilute
little
is soft,
hydrochloric
or shaken in air the
amalgam
acid.
The
When triturated
white and granular.
gives up the antimony in
the form of powder.
Bismuth. Amalgam.
solving a considerable
—Mercury
is
capable of dis-
quantity of bismuth without
losing its fluidity, the union being readily effected, even
by simply mixing the metals. When heat
is applied combination takes place more rapidly.
With
two parts of mercury and one part bismuth the amalgam
is pasty
it hardens after standing and becomes more
or less crystalline.
Bismuth amalgam, when pressed
iu chamois-leather, passes through the pores like
in the cold,
;
mercury.
Cadmium Amalgam. — Mercury
readily
is,
is
combine
at the ordinary
cadmium
and
temperature
;
the union
however, much more perfectly effected when mercury
added to molten cadmium, When mercury is com-
pletely saturated with
cadmium
a
compound
is
formed
parts of mercury and 21.7 parts of
cadmium, agreeing with the chemical formula Hg.,Cd.
consisting of 87.3
Cadmium-amalgam
brittle mass, heavier
is
a silver-white, crystalline, very
than mercury.
When
moderately
heated it softens and can be kneaded like wax. From its
property of gradually hardening it was formerly used
as a stopping for teeth, but, owing to the action of
the sulphuretted hydrogen in the mouth, the
lilling is
DENTAL METALTATRUY.
134
readily covered with a yellow film oE
Cadmium
easily dissolves in
cadmium
warm mercury,
sulphide.
giving rise
a solid compound, corresponding to the formula
An amalgam of one part by weight of cadHgjCd.,.
to
mium
with six
point of 16' C.
mercury has the low melting-
]iarts of
(60.8^^ F.).
Copper Amalgam.
—This
amalgam may be ob-
tained by the direct union of copper and mercury. It
possesses the property of becoming hard and crystalline
when
left for a
few hours, while
its soft
and
plastic
character can be restored by continued kneading or
pounding of the amalgam.
It also
becomes
and
soft
water,
])lastic when gently heated or placed in boiling
but recovers its hard crystalline character after standCopper amalgam cry stallises readily when hard
ing.
:
it
is
malleable, and can be rolled or
hammered.
It
admits of a good polish and retains its lustre well in
sulphuretted hydrogen.
air, but is readily blackened by
The density of this amalgam is the same in the soft and
does not expand in hardening,
and thus fills cavities, when hard, into which it has been
Copper amalgam is used for
pressed in the soft state.
hard states
;
therefore
it
its
stopping teeth, but is objectionable on account of
Amalgam,
great tendency to blacken (see Dental Copper-
P- 146).
Gold Amalgam.— Gold
iu a fine state of division
is
quickly dissolved by mercury, even iu the cold
if
the mixture
place
is
much more
considerable
slightly heated,
rapidly, the
proportion
of
;
but
amalgamation takes
mercury absorbing^ a
gold without losing
its
liquidity.
The amalgam
is
of
two parts of gold and one
of
mercury
and readily
white in colour, of a pasty consistency
MERCURY.
soluble in mercury, forming
solution
of
.of
It
is
.1
licjnid
Wlieu
mass.
this
strained through chamois-leather, the excess
mercury passes through together with a small quantity
gold, while a white pasty amalgam remains behind.
is probable that definite compounds of gold and
mercury exist. When heated to redness, gold amalgam
is decomposed, the mercury being distilled off', leaving a
residue of gold.
Iron Amalgam.
— An
amalgam
of iron cannot be
obtained by direct union of the metal with mercury,
but by introducing sodium amalgam into a clear, strong
solution of iron sulphate a viscid
which, in small globules,
is
amalgam
is
obtained,
attracted by the magnet.
Liead Amalgam.— These amalgams may be readily
formed by simply rubbing lead filings with mercury or
by pouring mercury into molten lead. The amalgams
they grow more and more pasty
are not entirely liquid
;
as the percentage of lead increases.
By
centrifugalis-
ing them in a chamois bag, crystals are obtained of the
composition Pb.,Hg. When the percentage of lead has
reached 65, the amalgam
tion
takes
place
Contrac-
entirely solid.*
is
during combination, the amalgam
being denser than either of the constituent metals.
Nickel Amalgam. Nickel does not amalgamate
—
when rubbed with mercury, nor can a nickel amalgam
be obtained directly. An amalgam may be obtained
by adding sodium amalgam to a strong solution of a
nickel
salt.
Palladium Amalgam.
—This amalgam
is
obtained
by rubbing finely divided palladium with mercury.
Union takes place at the ordinary temperature, but
not with great facility.
*
l''iiy
Mini Niirdi. Aiiirr
'I'he
('hriii.
combination
is
attended
Jmini.. 1901. vol. xnv- pp- 216 231.
DENTAL METALLURGY.
136
by an evolution of
explosion.
It
is
heat, leading in
some instances
to
therefore probable that chemical union
takes place between the two metals.
amalgam expands
Palladium
This amalgam
is
used as a
filling
probably the most durable of
on cooling.
for teeth, and is
slightly
the amalgams for
all
this purpose, although it is a little difficult to
late.
forms a good watertight
It
filling,
disadvantage of turning quite black.
manipu-
but has the
It does not,
how-
any staining of the tooth substance.
Platinum Amalgam. Platinum in the compact
with
form, such as plate or wire, does not amalgamate
ever, lead to
—
By
mercury.
triturating
spongy platinum (such
as
chloride
that precipitated from a solution of platinic
by means of zinc) with mercury in a warm mortar
amalgam is obtained of a silvery appearance. The
mercury
tion
of
expelled from this amalgam on the applicaleft
heat, and a grey residue of platinum
is
behind.
With
12 per cent, of platinum the
amalgam
greasy
metallic in appearance and possesses a soft,
the proportion of
feel, but it becomes more solid as
is
platinum
is
increased.
An amalgam
of these metals
does not harden well.
Silver
Amalgam.— Mercury slowly dissolves silver
much more rapidly
at the ordinary temperature, but
The more
and perfectly on the application of heat.
finely divided the silver the
mation take place.
more rapidly does amalga-
Silver precipitated from
its
solutions
washed and
of metallic zinc or copper, then
condition for amalgamadried, is in a very favourable
silver thus
tion (see Precipitated Silver, p. 171)-
by means
When
prepared
is
added to hot mercury combination takes
place rapidly.
MERCURY.
mercury for silver is almost etjiial to
that of mercury for gold, but there is a greater tendency
towards crystallisation in the case of silver. The combination of silver with mercury is usually attended by
The
affiuity of
an increase in volume, although in certain proportions
the union appears to be accompanied by a contraction
The amalgam
in volume.
varies in character, accord-
ing to the composition and.
mode
It is readily dissolved in
granular, or crystalline.
soft,
of formation, being
excess of mercury, but the excess can be separated from
the pasty amalgam thus formed by squeezing through
chamois-leather. The soft white amalgam left gradually
becomes hard and brittle, and is generally regarded as
a chemical compound. By adding mercury to a slightly
acid
is
and
amalgam
form, known as a
dilute solution of silver nitrate, the
obtained in a beautiful crystalline
"silver-tree " or
Arbor Diancc.
Silver amalgam,
if
heated
to redness, gives off the mercury, the silver, however,
sometimes retaining traces of mercury.
The union
of these metals in certain proportions is
accompanied by a considerable elevation of temperature.
Littleton has pointed out * that when an amalgam of
silver
and mercury
is
moderately heated, considerable
swelling takes place, and the mass becomes hard, brittle,
and
crystalline in
behaviour was
remarkable
was noted that
It
structure.
most
this
marked when the
and mercury were present in the proportions
corresponding with the formula AgHg^, and that,
silver
when
these metals were brought together, the silver
the state of
in
mercury
*
Ti-itiix,
i8g6,
v()l.
sim])ly
a
line
poured over
Chriii. Sir.. 1895. vol. Ixviii.
(i.
220.
powder, and the
crystalline
it,
|i,
there was v(M'y con239
;
mikI
I'rai'. Chriii. Siir..
DENTAL METALLURGY.
138
amounting to 38 or 40*" C,
so that the amalgam could not be borne on the palm of
the hand without pain. The amalgam, just after its
siderable lise of temperature,
production,
native
is
are
combined
Silver
ai-e
and mercury have been
compounds in which the constituents
of
silver
in atomic proportions.
amalgam has been used
for teeth, bnt
Several
a soft, pasty, semi-fluid mass.
amalgams
found, v?hich
'
it
as a filling material
becomes discoloured
ovi^ing to
the action
of sulphuretted hydrogen.
Tin Amalgam.
even at the
—Tin
and mercury unite
ordinary temperature,
vigorously at the raeltiug-point
of
readily,
but much more
With small
tin.
proportions of mercury the amalgams are brittle and
granular
;
an amalgam of
equal
parts
of
tin
and
mercury is solid, while those with excess of mercury are
more or less soft and plastic. With one part of tin and
ten parts of mercury the amalgam is liquid, like mercury,
but does not flow so readily. Tin amalgam has a tinwhite colour and is more or less brittle and granular,
according to the proportion of mercury present.
the excess of mercury
is
removed from
a fluid
When
amalgam
by squeezing through chamois-leather a flexible mass
remains, which hardens in a few days. The union of
diminutin with mercury is attended by a considerable
Tin amalgam was formerly used as a
in bulk.
tion
hardens slowly and imperceptibly
and also contracts, thus possessing a tendency to draw
away from the edges of the cavity.
Amalgam.—-Zinc amalgamates slowly with
filling for teeth,
but
it
Zinc
mercury
at the ordinary
and
still
poured into molten
zinc.
readily "if heated,
is
temperature
more
:
but
readily
it
combines
when mercury
MEROTTRY.
The amaliiain
of
one part of zinc with fouv or
is
white, granular, and brittle.
parts of mercury
When
1
39
five
the mercury largely predominates the amal-
gam becomes
pasty.
Zinc
is
occasionally
employed
as
a constituent in dental amalgams.
d(r<tt.^
—
V'
/
•
Ilt^^f -C/VW^
CHAPTER
A^III.
VD^^^A-L ^MAI^AMS.
preioared from
Amalgams
many
different formula' have
The
been used in dentistry as fillings for teeth.
majority of the well-known alloys from which the
dental amalgams are prepared are composed of tin and
It has
with small additions of other metals.
been previously stated that the union of tin and mer-
silver
attended by contraction, and that tin dissolves
very readily in mercury, giving an amalgam which
hardens slowly and imperfectly. On the other hand,
cury
is
expansion generally takes place when silver enters into
combination with mercury, the union being effected
and producing an amalgam
The manufacturers of
which becomes very hard.
tin and
for dental amalgams, therefore, use
with
much
less facility,
alloys
silver
in
different
proportions,
utilising
the
good
one to counteract the inferior qualities
obtaining an amalgam
in the other, with the object of
a filling
which will meet the requirements necessary for
The following qualities are necessary in an
qualities in the
material.
amalgam
1.
to be used for dental purposes
Strength to withstand the force of mastica:
tion.
2.
Sharpness of edge.
DENTAL AMALGAMS.
expand or contract in
3.
It should not
4.
It should retain its shape.
5.
It should
6.
It
setting.
not become discoloured.
should be free from metals liable to form
soluble, injurious salts.
not stain the substance of the tooth.
In the formation of amalgam for dental purposes the
best results will most probably be obtained by uniting
7.
It should
the constituents in atomic proportions to form what are
believed to be definite chemical compounds.
in
amalgams appear for
consist of metals united with mercury
atomic proportions, and capable of being dissolved
in
an excess of mercury.
As previously
the most part to
stated, the solid
an alloy are intimately mixed with
a measured quantity of mercury by thoroughly knead-
When
filings of
ing the mass entirely
mercury combining
has greatest
new compounds
first
with the metal for which
affinity.
slowly
formed.
readily,
If
while with
sufiicient
After
a
short
interval
others
mercury has
been employed, the mass soon becomes of a
consistency.
it
With some metals these com-
pounds are produced very
they are
are formed, the
soft,
pasty
a process
of
commences, which may be accompanied
by a change in volume, the mass thickens slightly, and
when pressed carefully between the fingers emits a
})eculiar grating sound, caused by the rubbing or grating
This mass may
of the crystals against each other.
crystallisation
probably represent a definite chemical
compound
(or
the metals of the alloy in
compounds) of mercury and
atomic proportions and cr\'Stallised, the whole being
dissolved in an excess of
this plastic
compound
mercury.
as a filling
In order to use
inalerial
the excess
DENTAL METALLURGY.
142
must be removed. This can be done to a
certain extent by straining through chamois-leather
by compression with pliers. All the excess of mercury
of mercury
cannot, however, be satisfactorily removed in this way,
and the mass left in suitable working condition.
the most recent experiments* it appears that
Dr. Bonwill's and similar methods t for removing the
excess of mercury are those most likely to give the best
Prom
results with this class of filling.
Tomes has recently shown J the advantage of employing old amalgams for filling purposes these should
;
heated to soften them, and then used alone or
rubbed up with a small quantity of freshly prepared
amalgam. Amalgams which have set and become
hard are softened to a workable consistency by gently
be
first
heating
which
;
is
they harden again on cooling, a phenomenon
ascribed to a state of amorphism, into which
the amalgam passes from the
the process of softening.
crystalline condition in
Old amalgams have the ad-
vantage of having undergone the shrinkage, alteration
which takes place, more or less, when
Although there may be diffifresh amalgam is used.
old amalgams
cnlties with regard to the manipulation of
of shape, &c.,
* "
Notes on Amalgams," C.
S.
Tomes, Brit. Juurn. of Bcntal
Si-ipiwr, 1895, vol. xxsviii. p. 242.
amalgam lan'ly
Bouwill's method consists in inserting tlie
instruments
suitable
with
cavity
the
in
plastic, and squeeiiing it dry
l)ilnilous paper are
of
Pads
pressure.
much
of
l,v the application
the mercury thus pressed
repeatedly placed over the cavity to absorb
of the filling, into whu^h
surface
The softer portions upon the
„ut
t.lso removed from tune
are
s,,uee/.ed,
been
has
the excess of nun-cury
instead of bibulous
Tn some cases gold-foil has been use.l
totin.e.
t
Di-
vol. xxxviii.
''''^"7^nY.-./<wn^ »f Drntal Srirmr, 1895.
1896, vol. xxxix. p. 529.
p.
242; also
DENTAL AMALGAMS.
T43
on accouut of rapidity in setting, there can be no don lit
amalgams tends
to give
watertight pkigs and very satisfactory results.
When
that the use of ready-formed
old
it
amalgam
is
used for the whole operation of
filling-
should be heated in a spirit or Bunsen gas-flame, and
then laid on a hot plate over the flame, in order to keep
With the exception
it soft.
of copper and of palladium
form the basis of all the
These alloys
dental amalgams used at the present da}^
are composed of varying proportions of silver and tin,
ranging from sixty parts of silver and forty of tin to
amalgams,
silver-tin alloys
forty parts of silver
made with
are
alloys
"These
and
alloys in the
sixty of
a larger
form of
Occasionally
tin.
proportion of
filings or
silver.
shavings are
mixed with varjang proportions of mercury, which
generally range in ordinary practice from 30 per cent,
mercury and 70 per cent, of alloy to equal parts of
each by weight, a larger proportion of mercury being
used in exceptional cases." * Silver-tin amalgams vary
of
with regard to working properties, those
most tin being usually
and
soft
and slow in
plastic
setting, while those with excess of
containing
silver are quick-
much harder, " the quickest setting amalgam
being that made from an alloy containing 72.5 per cent,
The amalgam
of silver and 27.5 per cent, of tin." t
setting and
obtained after removing the excess of mercury becomes
more or
less
generally
hard within a few hours, but does not
acquire
the
degree of
full
twenty-four to forty-eight hours.
brittle
It
mass which may be dressed with a
like other metallic bodies.
*
•j-
(i.
V. I'.lnck. Dciitiil
Jh'iil..
1.S9G, vol.
is
file
then a hard,
and polished
The disadvantage
Ciixiiifix.
xxxviii.
hardness for
|i.
.Inly 1S95, vol. .\xx\
9S6,
of this
ii,
DENTAL METALLURGY.
144
material as a filling
in shape
and
is
is
that
liable to
a tendency to alter
As the
discoloured.
lias
it
become
the qualities necesit has
sary for the production of a dental amalgam,
for
been the practice of many manufacturers of alloys
modiof
view
this purpose to add other metals with a
silver-tin alloys
do not possess
all
properties
fying or improving the chemical and phj^sical
The metals usually added
of the resulting amalgam.
occasionally zinc, cadare gold, copper, platinum, and
the
and antimony. The composition of some of
mium
most frequently used
given in the annexed table.
alloys
for
dental
amalgams
The effect of the presence of different metals
the following list.
tin amalgams is given in
is
in silverIt
must
are
individual
be pointed out, however, that the
quantity of metal added
greatly dependent on the
but
addition of gold is usually very beneficial,
efi"ects
thus, the
by experiment* that it is
Dr. Bonwill has ascertained
than 7 per cent, of gold to
not desirable to add more
The ratio between the main consilver-tin
amalgam.
stituents of the
amalgam
is
also of
importance in con-
other metals. The presence
nection with the addition of
of zinc may be beneficial in one
of a small quantity
while a larger quantity of zinc may be
silver-tin alloy,
in this particular alloy, but very
a decided disadvantage
of different composiadvantageous in a silver-tin alloy
of a small
The effect produced by the addition
tion
is frequently very much
quantity of a certain metal
besides silver and tin, are
modified when other metals,
Thus,
constituents of the amalgams.
also present as
silver-tin amalgam appear to be
the properties of a
any
addition of platinum
greatly impaired by the
m
*
IJrnfal Cosmos, vol. xxiv. p. 422.
DENTAL AMALC4AMS.
1^
o
O M
O u-1
>o
o
O
o
O
O
o
o
in
o o
o
IN
<5
7J
-1—
•iffitll
000
o
o
o o
^o
o^nJ^oooooo
lOMVOOOOOOO
000
O ro
o
O
O
o o o O
O O vo
.-n O
o
o
a
0000
0000
CO
^
o o
U-)
NC^ro:l-^^a>or^OO^^•^^o^';^
o
O
^t-o co
U-]
U-1 Tt-
O
00
00
0
"o
roo 000001
0000
o>nooooooooo
OOO'Ol
OOOOroO^rnOiOOONin
O
10
'*-<0
uS 10
r-I
irj
o'
Lovo' oi
^
rood
!>. o'
M
t-I
in »o N
Tt-T^-irjio
IT)
invOirju^'^t^fOfniovo^iniriioininioio
0
d
5
-2
TT
'
'
'
4
'
'
'
-1-
^
3
TT"^
'
S'
1;
a 3
— 3p
Mm
~B
'
3
Si:-
'»
.
>
>"
—
-
"l'*j;ir;^g;::ODS
-
= —
b ^
IS
'
= 5 s
5
-3
.ii
ii
'
3
= = S
-tJ ^-^
> " -
a,
'
:
^
'a-
.
^
P
'
—^—
-F
^1
s
g
'-tj
=->
«
;
i
-0)
-
«
•!-+
1^
'^^.i^
-ri
„
-f^
^
o
'
'
,2'
i?
X
S
-
.
bu
^
"
o = c
I'S o c o
"cs
O -< o
K
-5
DENTAL METALLURGY.
146
considerable (juantity, except
when gold
is also
present,
properties
in which case the platinum confers useful
on the amalgam. The following list must, therefore,
the
be regarded as giving only the general effect of
amalgam.
various metals when added to the silver-tin
The effect of the presence of silver and of tin in the
amalgam
is
also inserted for convenience in reference.
Effect of Different Metals in Amalgams.—
mercury is usually
/S'iVrc/-.— As the union of silver with
with
accompanied by exjMnsivn, and the union of tin
silver
mercury by contraction, the direct influence of
the
lessen
to
upon an amalgam of tin and mercury is
Silver has the
contraction and increase the hardness.
discoloration
disadvantage, however, of increasing the
sulphide
silver
formation of
of the filling, owing to the
hydrogen in the
by the actfon of the sulphuretted
the
also tends to stain the tooth owing to
mouth.
It
formation of soluble silver
Tin
facilitates
discoloration
setting,
and
;
salts.
amalgamation and helps
but
it
causes
to prevent
shrinkage, 'slowness in
loss of edge-strength.
cleaner and easier
Gold in amalgams renders them
produces good edgeto work, reduces the shrinkage,
to maintain a good
strength, and assists the filling
colour.
Its presence affects the
power
of setting.
shrinkage, gives
Copper facilitates setting, diminishes
preservative influence
great edge-strength, and exerts a
largely increases, however,
on the tooth structure. It
the tendency to discoloration.
appears to
Platinum in any considerable quantity
of a silver-tin amalgam,
oreatly impair the properties
slowness in setting, and
causing dirtiness in working,
tendencv to shrinkage.
When, however, platinum
is
DENTAL AMALGAMS.
addeti
to
amalgam containing
silver-tin
a
ai)pears to confer the properties of
gold,
setting
it
quickly,
great hardness, and retention of shape after hardening.
Zinc is occasionally employed as a constituent of
amalgams. It appears to control
shrinkage, add whiteness to the filling, and also helps
the
dental
for
alloys
amalgam
to retain its colour.
But
it
causes rapid
Amalgams
setting and a tendency to change of form.
containing it possess good edge-strength.
Cddmium was
in
at
amalgams, but
that
purpose.
It
it
one time used as a constituent
is
causes
very white and
condemned
generally
quickness
make good
fillings,
for
and
setting
in
Amalgams containing
expansion.
facilitates
now
it
are
but they readdy
owing to the formation of yellow cadmium
sulphide. The tooth substance is also stained an orangeyellow on account of the formation of soluble salts of
cadmium.
Antimony has been occasionally used as a constiIts presence appears to facilitate amalgamation
tuent.
discolour
and control shrinkage, but
and very
it
makes the amalgam
soft
dirty to work.
Fallacliiuii as a constituent
of silver-tin
amalgams
has been condemned, experiments* having proved that
it makes the amalgam very dirty to work, gives leaky
plugs,
that
and
is
blacken
amalgams containing palladium
greater extent than those
stated
It is
altogether unsatisfactory.
from which
it
is
to
a
absent.
(See also Palladium Amalgam, p. 135.)
Bisiimtli
greatly facilitates
amalgamation and the
working properties of the amalgam
But
ex|)ansion.
*
it
;
it
also
reduces
makes the amalgam very dark,
b'letclicr, ///•'/. ./oiini. JJnital
Srinin:
DENTAL METALLURGY.
148
the edge-strength, and
lessens
hardness
:
hence
it is
the
greatly reduces
seldom used as a constituent.
never employed in dental amalgams unless
accidentally present as an impurity in the metals
Lead
is
appears to be similar to that
It facilitates amalgamation, but causes
of bismuth,*
slowness in setting and makes the amalgam very
employed.
Its action
dark.
Aliivdnmm has not been used
as a constituent in
experiments
dental amalgams, but from recent
its
f
presence appears to give a soft pliant mass which is
slow in setting. It also greatly increases expansion
and the tendency
to alter in shape,
the action of the fluids of the
and would
facilitate
mouth on the
filling.
developed in mixing alloys containing it with
(See Action of Mercury on Aluminium,
mercuiy.
Heat
is
p. 132.)
Change
of
Volume. —Much
diversity of opinion
and expansion
exists with regard to the contraction
silver-tin
of
amalgams, some claiming that contraction
takes place,t while others state that the amalgam first
The composition
contracts and then finally expands. §
of the alloys
and the quantity
necessarily influence the
these questions.
of
results
mercury used
of
experiments on
The recent researches
of Dr.
the latter conclusion.
appear to support
that alloys containing
first
*
p.
will
He
Black
than 50 per cent, of silver
shrink and then expand. Alloys with 50 to 62
less
Experiment by G. V. Black, Dental Cosmos,
989.
1896, vol. xxxviii.
t
Hitchcock and Tomes, Trans. New York Odoiit. ,Soo., 1874.
J
Science, July 1888, vol.
Kirby, Brit. Mini, of Dental
§
part
ii.
xxxvui. p. 975.
De7ital Cosmos, 1896, vol.
II
||
found
ix.
DENTAL AMALGAMS.
149
Those with 65 to 75
expand when fresh cut, but shrink
per cent, of silver shrink only.
per cent, of silver
when
fully "
(See
agcdr
p.
1
Alloys containing
56.)
over 75 per cent, of silver expand only.
of Testing Change of Volume.—
The change of volume which takes place more or less
with most dental amalgams constitutes one of the dis-
Methods
The
advantages of this class of material as a filling.
shrinkage or expansion is usually determined by careglass
fully packing the amalgam into a small shallow
tube until
and then making the surface perfectly
contraction has taken place the filling
full
When
level.
will frequently
slide readily
expansion
is
seen
with
projection
of
the
filling
the
out of the tube,
of
a lens
by the
the
mouth
of
aid
above
while
the
tube.
The contraction and expansion of silver-tin amalgams
has been studied by Black,* who examined them under
For this purpose the amalgams were
the microscope.
inserted in Wedelstaedt test-tubes,
made
of hardened
deep and one inch in diameter,
with a cavity three-eighths of an inch in diameter and
The top of the tube is
one-fourth of an inch deep.
ground flat, and the margin of the cavity brought to a
steel
one-half inch
The tubes
perfect edge.
are placed on the stage of the
microscope, and so arranged that every part of the
margin of the cavity is brought under the lens as
the
stage
is
rotated.
A
groove
was
cut
in
the
tube at the bottom to hold the
filling at that point, so that in case of shrinkage
the surface of the filling sinks down into the tube.
inner wall
When
of
the
comparative results are re(|uired the amonnt
*
Dental
(JiiKiiiox,
vol. xxxvii. 1895, p.
648
DENTAL METALLURGY.
of contraction
and expansion
is
measured with a micro-
meter.
Several forms of apparatus have also been constructed
by different investigators for studying the change of
volume in amalgams. One of these, devised by Kirby,
consisted of a V-shaped metal trough (Fig. 32) having
a movable end, to which a delicate screw micrometer
was attached, and so constructed that any change of
and accurately measui'ed. The
be tested was made up in the way generally
volume could be
amalgam
to
easily
Fif!.
adopted for
filling teeth,
"52.
then placed in the trough and
means of this
allowed to remain for some time. By
of expansion
apparatus the most minute change, either
was readily indicated.
adjustOther forms of apparatus, with micrometer
principle, have also been
ments, embodying the same
or contraction,
devised.
the
"The advantage of the tube test over that
of doing a
amalgam micrometer is the possibility
time, as tube
number of experiments in a limited
ot
aside for results,
tube can be packed and set
each packing has to remain
while with the micrometer
the result is obtained. This
in the instrument until
many months for each
requires from several days to
after
^5^
DENTAL AMALGAMS.
experimeut
;
but while the tube test
is
imtdical, reliable
*
more accurate."
ascertained by taking
The change of volume is also
amalgam.
the specific gravity of the
alloy or
stated, when the density of an
micrometer work
is
As previously
amalgam is less than
that of the
mean
of the constitu-
place during
shows that expansion has taken
density denotes
combination, while an increase in the
the union of the
that contraction has accompanied
ents, it
in amalgams
For ascertaining the change of volume
exceedingly delithe specific gravity method f an
by
must be used and a large number
cate balance
precautions taken, in
of
obtain accurate and
order to
important being
concordant results, one of the most
heat is given out
the consideration of the fact that
during the setting of some amalgams.
with
Alteration of Shape.— Much has been said
" spheroiding " of
reo-ard to the so-called
* Fliio-g, " riastic Filling Materials," p. 72.
fallacious rule is freciueatly given for
+
A
amalgams
or
computing the specihc
alloying of given quantities ot
-ravity tliat should result from the
no condensation or expantwo metals of known densities, supposing
Thus, it is said that iC gold_ and
sion of volume to take place.
the computed specific gravity is
eoiiper be united in equal weights
numbers denoting the
HHireiy the arithmetical mean between the
the computed
incorrect
is
however,
This,
gravities.
two
specific
;
obtained by the following rule
siiecific gravity of the
by the product of the two
weights
the
sum
of
Multiply the
and multiply each speciftcsi)ecitic-gravity numbers for a, numerator
weight of the otluM- constituent, and add the
alloy
:
is
;
gravity
number by the
denominator. The (luotieut obtained
tlie truly
by dividing the said numerator by the denominator is
On comiiariug with
specific gravity of the alloy.
two products
togetiier for a
computed mean
that density
the
whether expansion or condensatiou
bination."' —lire's Diet., vol.
i.
11.
l)c
seen
lias ;i(ti'iidc'd (lir
com-
by experimeut,
density found
of voluiuf
92.
it
will
DENTAL METALLUEGY.
tendency to assume the spherical form. "The phenomenon from which this term splieroiding has been
mostly derived appears to be the tendency of some
amalgam fillings to rise in the middle and assume a
convex form on the surface." *
This alteration of
shape, or tendency of some fillings to assume a convex
form on the surface, after having been dressed flat, is
probably due to a change of volume. The amalgam being
down on all sides but one during expansion
tend to flow towards the point of least resistance,
firmly held
will
thus causing the surface
Kir by
that
is
become
slightly convex.
of opinion, as the result of his experiments,
" is
it
to
due
to
unequal distribution of mercury
throughout the mass, and that the alteration
is
pro-
duced by the passage of the mercury from one part of
the filling to the other, causing contraction in the
portion containing excess and expansion in the drier
When
mercury is distiubuted equally
throughout the filling, no change in shape takes place,
since there will not be any passage of mercury from
portion.
tlie
one place to another.f
The alteration of sbape will be appai'ent in making
tests for
of a
change of volume, and may be seen by the aid
good
lens.
Change of Colour. — Dental amalgams
differ con-
by
exposure in the mouth copper and palladium amalgams
being those which darken most rapidly. The addition
of gold is an advantage in helping amalgams to retain
siderably with respect to their liability to darken
:
'
their colour, while copper greatly facilitates discoloration.
*
Fillings containing an
Brit. Jm/ni. of
t Smale and
fJc/itiil
Srip.iirr,
excess
of mercury are
1895, vol. xxxviii.
Colyer, " Diseases of Teeth," p. 186.
i).
901.
DENTAL AMALGAMS.
more
liable
when
inserted.
to
T53
blacken than those which are drier
Discoloration
is
largely dne
to
the
formation of sulphides, resulting from the action of
sulphiaretted hydrogen in the mouth, produced by the
Silver
decomposition of the oral secretions.
and mer-
cury, under the conditions in which they exist in the
Dismouth, both have a great affinity for sulphur.
coloration is also due to the presence of vegetable acids
to the action of drugs
in articles of food, such as fruit
;
taken as medicines
fluids of
fillings
:
or to
The
the mouth.
may
abnormal conditions of the
surface of
be kept bright by friction, whether pro-
duced by mastication or by a brush
will
probably blacken
if
they are protected from
On
fillings
friction.
fully preserve the
the other hand, an
but such
;
they occupy positions in which
An amalgam may become
and yet
many amalgam
discoloured at the surface
teeth from further decay.
amalgam ma}^
retain its original
colour and surface brightness and yet not protect the
tooth, the
tooth-substance being darkened, thus in-
dicating chemical action at the edges.
of the substance of the tooth is
The darkening
due to the formation of
soluble salts, resulting from the action of the oral fluids
upon the metals composing the amalgam.
Imperfect adaptation
is
frequently the cause of the
discoloration of the tooth, as this favours the ingress of
the oral fluids which form the eroding agent.
Change
by packing a small quantity
of the amalgam into a small glass tube and covering it
with a dilute solution of sulphuretted hydrogen water
of colour is usually tested
(about one part of strong solution with about four parts
of^water).
In this way the
filling is
of sulphur in the foi'm in which
it
exposed to the action
exists in the
mouth.
DENTAL METALLURGY.
154
Gradual discoloration
is
seen better in dilute solutions
than in strong.
Leakage.
— One
of
the disadvantages experienced
the
using amalgams as fillings is
getting absoliTtely watertight plugs.
in
The leakage
packing used.
is
difficulty
largely dependent on the
Amalgams
method
are tested for leakage
of
of
by
packing them into small circular holes, about one-eighth
in
of an inch in diameter and a quarter of an inch
depth, bored right through slips of bone or of ivory,
which are clamped to a flat surface of ivory whilst being
then plunged into ink, Draper's
for
dichroic being frequently employed, and are left
On being removed the plugs are split and
time.
filled.
The
slips are
some
of the
the surfaces carefully examined for the ingress
fluid used.
Human
same
teeth have also been employed for the
pui-pose.
Edge-Strength.—This
term
is
used to denote the
mass
degree of resistance the edge of an amalgam
amalAn
fracture it.
offers to a force which tends to
suffigam used for filling purposes should always be
edge under the
ciently strong to retain its integrity of
" The stress in the ordinary use
force of mastication.
to be from sixty to
of the teeth has been shown
molars of medium
eighty pounds upon the area of two
would give from seven
size. This, if evenly distributed,
occupying oneand a half to ten pounds on a filling
This would be a
fourth the area of one of these teeth.
frequently happens
of ordinary size; but it
filling
that the miing must bear
edge-strength of amalgams
* Black, Dcivtal
all
is
of this stress."*
The
sometimes approximately
Comox, July
1895, p. 554-
DENTAL AMALGAMS.
determined by mixing the amalgam in the ordinary
" button " and testing
way, then forming it into a small
it with the
the strength of the edge by breaking
This,
thumb-nail when the specimen has hardened.
method
however, cannot be regarded as a satisfactory
For accurate and reliable
for comparative testing.
work some form of dynamometer or instrument
measuring force
is
for
This usually consists of a
used.
and graduated metal beam upon
which a sliding weight is placed. A chisel-shaped steel
rod is also fixed to the balanced beam and so arranged
carefully balanced
of
that the pressure necessary for testing the strength
the amalgam filling can be applied to the chisel by
moving the sliding weight along the graduated scale.
The instrument is also provided with suitable screws
The amalgam to be tested is
ordinary fillings and made into small
for accurate adjustment.
mixed
as
for
blocks in order to obtain the greatest edge-strength of
After allowing the
which the specimen is capable.
amalgam to harden it is carefully secured in position
upon the instrument, so that the point of the chisel rests
The sliding weight
upon the edge of the specimen.
then slowly pushed out along the graduated scale on
the beam until the pressure produced is sufficient to
is
In this way the
break the edge of the specimen.
position of the weight indicates the point at which
"crush" or fracture occurs, and the relative edgestrength of
various samples, with the accompanying
toughness and brittleness,
is
determined.
Permanence in the Mouth. —The permanence
of
amalgam
largely
in
fillings
dependent
on
the
the
mouth
care
is
necessarily
bestowed
on
the
manipulation of the material, on the proper prepara-
DENTAL METALLURGY.
156
tion
of
the
cavity,
tooth in which
it is
the condition
on
and
placed.
the
of
dependent on
It is also
the metals present in the amalgam used, as each of
these materially affect the character of the amalgam
Careful observation
of which it forms a constituent.
and experiment with each amalgam can only satisfactorily solve the question of permanency in the
mouth.
Amalgams
containing large
metals possessing an
silver,
affinity
for
proportions
of
such
as
sulphur,
copper, and cadmium, are more liable to waste
or wear away, and
containing
those
are usually less permanent than
only
small
proportions
of
such
metals.
Metals which are more or less readily acted upon
by alkaline and acid fluids under ordinary conditions
are sometimes protected from action when alloyed with
other metals.
Copper and
zinc, if
used alone, would
mouth, but when added
in small quantity to other metals employed for amalgams
they are largely protected from corrosive action.
The tendency of some amalgam fillings to shrink and
be attacked by the
fluids of the
draw away irom the edges would be favourable
to the
thus
ingress of the erosive fluids of the mouth, and
possibly reduce the permanency of the filling.
Possible Action on other Metals in the
Mouth.— When amalgam fillings come into contact
usually
with other metals in the mouth, galvanic action
Galvanic action
takes place, as described on p. 30-
tends to facilitate the
filling.
of
the amalgam
given to a peculiar change
in the working
takes place with the lapse of time
after being
silver-tin alloys for amalgams
Ageing.
tl.at
—This term
"wasting"
properties of
is
DENTAL AMALGAMS.
cut.
In some cases amalgamation
" ageing"
;
in other cases it
of alloys for dental
is
facilitated after
is
The
retarded.
"
ageing"
amalgams has been attributed
to the
being
formation of a film of oxide, the silver-tin alloys
particularly susceptible
Although
to oxidation.
this
would greatly tend to retard amalgamation, the recent
subject
experiments of Black* in connection with this
in
have demonstrated that the changes that occur
the temperaa cut alloy are largely dependent upon
He showed that the change
ture at which it is kept.
known
as
the
in
"ageing" was universal
silver-tin
different formute
alloys, but varying in degree with
the temperaalso that it could be produced artificially,
;
was effected varying with the composiThe explanation offered by Professor
tion of the alloy.
Black for the changes which occur in a silver-tin alloy
ture at which
it
by subjecting it to heat is that in cutting the alloy it is
hardened and undergoes a molecular change. Heating
normal
the alloy anneals it and causes it to return to its
condition.
That certain alloys undergo molecular change when
subjected to mechanical treatment or to change of
temperature has long been known and has been the
subject
much experimental
of
Some
investigation.
kinds of brass wire become extrejnely brittle in the
course of time, at ordinary atmospheric temperatures,
especially when kept in a state of tension or subjected
An
to vibration.
alloy of tin
and
lead,
which
is
com-
used in pattern-casting for
brass foundry work, becomes after a time so soft as
paratively
to
hard,
be no longer
*
fit
and
is
for use.f
Dental
O1.111WK, vol.
xxxviii.
t Percy, " Mutallurgy," vol.
i.
\).
p.
976.
21.
DENTAL METALLURGY.
158
Quantity of Mercury needed.
—The
quantity
merciuy used with aa alloy to form an amalgam is
very variable and necessarily differs with every alloy.
The proportions usually vary from 30 to 50 per cent,
Sufficient mercury must be used to satisfy
of mercury.
the chemical affinity of the metals present and thus
of
form a true amalgam.
If insufficient is added the mass
will consist of a
mixture of amalgam with particles of un amalgamated
The two inethods most frequently employed for
alloy.
obtaining the right quantity of mercury are
—
i.
To
Fiti. 33-
shavings of alloy to a globule of mercury
produced.
until a mass of proper working consistency is
excess of mercury and then remove the
add
2.
filings or
To add
with the
excess by straining through chamois-leather
By the first method there is no indicaaid of pliers.
when the proper amount of filings has been
tion as to
added
to
the
exactly satisfy the chemical affinity of
second method is
quantity of mercury employed. The
of alloy is
objected to by some, as a small quantity
squeezed through
removed in solution by the mercury
This method is also open to
the pores of the leather.
remove all the mercury in
the objection that it does not
most satisThe methods which appear to give
excess.
DENT A L AM A LG AMS.
mercury is
factory results are those in which sufficieut
mixed with the filings to give a fairly plastic amalgam
and
and the excess forcibly squeezed out in the cavity
removed by means of bibulous paper or gold-foil.
in
In order to obtain the right quantity of mercury
correct
preparing amalgams, after ascertaining the
emproportion to be used, balances are sometimes
represents a balance designed by
Pig.
ployed.
33
which turns to the fraction of
The small metal pin acts as the weight and
a grain.
balanced beam
is inserted in the different holes on the
according to the quantity of mercury required.
Kirby
for this purpose,
Fig.
34.
Another balance designed by Fletcher
is
represented
The filings are placed in the large cup and
in Fig. 34.
the mercury in the two small cups, according to the
quantity required.
Mixing Amalgams, — Different
methods are em-
ployed for effecting the union of the filings or shavings
That most frequently
of alloy with the mercury.
adopted
consists in simply rubbing
the
filings
and
mercury together in the palm of the hand. This is
perhaps the most expeditious way of eff"ecting union,
but it is open to the objection that the moisture or any
film of dirt on the hand may retard amalgamation and
possibly
bring
about
failure in the
result
desired.
Amalgamation is also effected by means of small porcelain Wedgv/ood mortars, but owing to the attrition of
l6o
DENTAL METALLURGY.
the pestle the particles of alloy become more or less
burnished, and union is thus liable to be retarded.
Amalgamation
heating
greatly facilitated,
is
however, by
and effective
appliances have been introduced for promoting amalgamation by percussive force. Fletcher has introduced
the
mortar.
Several
simple
the glass mixing-tube shown in Fig. 35. The required
weight of filings is put into the tube, the
mercury added and the tube well shaken for
a few seconds, the open end being closed
with the thumb.
By the jiercussive force
thus produced union readily takes place. If
necessary, the tube
facilitate
shown
be gently heated to
Another form of
mixing, introduced by Kirby,
Fig. 36.
It consists of two
amalgamation.
apparatus for
is
may
in
tubes provided with a handle for convenience
in shaking, each tube being closed
by means
of a rubber stopper.
Preparation of Alloys for Dental
Amalgams. Alloys for dental amalgams may be
—
readily prepared
by melting
the
constituents
in a
graphite crucible heated in a suitable furnace, any of
the forms previously described being well adapted for
As previously stated, the metals entering
the purpose.
into the composition of alloys for
silver
and
amalgams
are mainly
tin with small additions of gold, platinum,
and copper.
All these metals possess an affinity for
one another, but they vary considerably with regard to
the temperature required to melt them the alloys
produced are very easily oxidised, care is therefore
needed in preparing them.
The constituent metals are placed in a crucible and
;
•«3
DENTAL AMALtJAMS.
l6l
a little charcoal added to prevent oxidation.
The cru-
and the temperature raised
sufficiently high to thoroughly melt the metals and
obtain a uniform alloy, but excessive heating should be
cible is placed in the furnace
avoided as
The molten
tion.
into
leads to loss,
it
a
suitable
employed
alloy is
owing to unnecessary oxidathen well stirred and poured
mould.
ingot
Borax
to prevent oxidation, but
is
frequently
when using
it
care
must be taken to prevent the molten "slag" from
running into the mould with the alloy on pouring. If
zinc is a constituent of the alloy it should be added in
Fig. 36.
needed in the alloy, in
by oxidation, which invariably
slight excess of that actually
order to allow for loss
The ingot should be
takes place.
required for use, a coarse
purpose.
It
may be
file
freshly filed off as
being employed for the
pointed out that, owing to
segregation which invariably takes
alloys during
solidification, it is
very
the
place with these
difficult to
obtain
ingots which agree exactly in composition or correspond
to a given formula,
Qualitative
Amalgams. — it
know how
even when every precaution is taken.
Examination of Alloys for
is
important that the dentist should
to ascertain the composition of the alloys
used in the preparation of amalgams
scheme
is
;
the following
therefore given for detecting the presence of
the various metals usually present.
A
small c[uantity,
L
DENTAL METALLURGY.
l62
about one gram (or lo to 20 grains),
nitric acid, gently
heated until
all
is
treated with
action ceases and
all
red fumes are expelled, then diluted with water, the
insoluble residue allowed to settle and filtered
Residue.
—May contain
tin, srold, or phitinuni.
A
lohite rexidve denotes
the presence of t'ui, which
is oxidised to niutastanuic
acid.
—
Solution. May contain silver,
platinum, copper, nine, cadmium
add liydrochloric acid a white precipitate denotes the presence of
:
xilvnr.
evaporate the clear soluFilter
add some
tion nearly to dryness
potassium chloride solution, tlien
A yellow
alcohol, and stir well.
precipitate denotes tlie presence of
:
A
purple rcsidnc denotes
the presence of ijuld, which
is insoluble and forms purple-of-C'assius
with
off.
when present
plafiimm.
tin.
Black
:
pmtirlc'f in
the
residue denote the presence of plat iiuniij which is
only partially dissolved in
some cases. When present
in small iiuantities, howit is completely dissolved and should be tested
for ueparately in the solution as given.
Allow the precipitate to settle,
pour oil' the clear liquid, boil to
espial alcohol, and then dilute.
Divide the solution into two portions.
ever,
First Fortiuii.
excess of
ammonia: a deep
blue coloration
denotes the presence of copper.
— Add
Add to theblue
PorSecond
Pass a current of sulphuretted hydrogen,
filter oil' the precipitate of cadnuum sulphide,
solution a solu-
then
tion of potassium
cyanide until
monia
colourless, pass a
current of sul-
phuretted hydroA bright
gen.
precipiyellow
tate denotes the
presence of cad-
mium.
Note.— It am-
monia gives
nu
blue colour, copper is absent and
sulphuretted hydrogen may be
passed at once.
add
am-
the
to
clear solution.
white precipitate
denotes the presence of zinc.
A
DENTAL AMALGAMS.
Wheu
old
amalgam
fillings are tested
they should
be heated to redness to remove the mercury, the
residue crushed to ]iowder in a mortar and then treated
first
with acid as previously directed.
Dental Copper Amalgams.
Sullivan's
Amalgam.
—This
is
prepared by mixing
pure precipitated copper with mercury, but there are
slight differences in the methods of manufacture.
The copper
is
generally pi-epared by placing rods of
zinc or of iron into a hot dilute solution of copper
sulphate and allowing the action to go on until
copper
is
The
precipitated.
the
all
dull red flocculent precipi-
tate of copper thus obtained is thoroughly
washed with
and sometimes finally with alcohol or ether.
It is next ground in a mortar with mercury, the combiuation being facilitated by the addition of water
cold water
slightly acidulated with sulphuric acid.
is
then washed with
dilute
ammonia
The amalgam
to neutralise traces
rubbed in the mortar, and
subsequently washed with hot distilled water and dried.
of acid, again thoroughly
It is finally rolled into small pellets or lozenge-shaped
pieces
to set for about twenty-four hours
and allowed
before
using.
remove
all
Care should be taken to thoroughly
moisture from the pellets before allowing
them to set.
The precipitate
is
sometimes
first
moistened with a
whereby it receives a thin
coating of mei'cuiy, and then mixed with the required
The amalgam usually consists
quantity of mercury.
solution of mercuric nitrate,
of
3
It
is
parts
of
stated
copper
that
to
copper
6 or 7 parts of mercury.
precipitated
by
iron
is
DENTAL METALLURGY.
164
more
serviceable
and durable
with zinc, and iron
is
than
obtained
that
usually employed for the
now
purpose.
.
_
The
copper should be freshly prepared
when
required,
on exposure to air and becomes
This amalgam,
practically useless for amalgamation.
the
in common with all copper aumlgams, possesses
hardening
property of softening with heat and again
as it readily oxidises
This phenomenon, as previously stated, is
which the
ascribed to a state of amorphistn, into
passes from the crystalline condition in the
on cooling.
amalgam
When
one of the small pellets of
heated, small globides of mercury ooze
process of softening.
amalgam
is
then, more suddenly, a greater
by a hissing
(juautity is set free, sometimes accompanied
mercury
If the heating is carried too far the
sound.
"
burnt."
be driven off and the copper oxidised or
slowly to the surface
;
will
When
employed as a
hlling,
one of the pellets
is
gently
flame of a
heated in a small iron spoon or ladle over the
into a plastic,
spirit-lamp, and then crushed and rubbed
workable mass in a mortar.
With some
varieties of this
amalgam
it is
recom-
rubbing in a mortar, to clean with water
then wash with
acidulated with sulphuric acid and
mended,
after
Much
diver-
salt.
water or dilute solution of commbu
the point at which to stop
sity of opinion exists as to
some discontinue the heating
the application of heat
on the
when globules of mercury begin to appear
;
surface
;
others continue
till
the excess
is
driven out.
shown* that the strength of the filling
removed from
affected when the amalgam is
Dr. Black has
is
seriously
appearance of globules. Great
the source of heat on the
'
Dental Cusiim. 1S95,
p. 738-
DENTAL AMALGAMS.
165
diversity of opinion also exists in regard to the merits
and demerits of copper amalgams as a filling material.
All copper amalgams, however, have the disadvantage
that they discolour readily and stain the tooth sub-
undergo a process of "wasting,"
resulting from the combined action of the acid and
alkaline fluids of the mouth and of the sulphuretted
They
stance.
also
hydrogen always present in the mouth to a greater or
Copper amalgam is also said to possess
less extent.
therapeutic properties and thus arrest decay.*
Other copper amalgams
are
also
used for
filling
purposes, but these only differ in slight alterations in
the method of manufacture and in the addition of
small quantities of other metals, mainly tin and silver,
with a view to helping the amalgam to better retain its
colour.
Filings of silver coin (alloys of silver and copper)
employed for preparing amalgams for
are also
filling
purposes.
*
For
fiirthpi- details
regnTtling the advantages
and disadvantages
the studenl is referred to
of coiiper
an interesting paper on the subject by Badcock, read before the
Odontological Society of Great l?ritain (see Pn>(\ Odonf. Sue. (1S97),
amalgam
vol. xl. p. 295).
as a
tilling material,
CHAPTER
IX.
SILVER.
SYMBOL, Ag
Occurrence.
—
(Avgentuin).
Silver
ATOMIC WEIGHT,
in
occurs
nature
io8.
in
the
metallic state, occasionally in masses weighing several
hundredweight, and usually alloyed with small quantities of
other metals.
It
is
also
frequently found
in combination with sulphur and chlorine.
present in most
Silver is
ores of lead, notably with rjalcna (lead
sulphide), argentiferous lead ores constituting one of
the main supplies of
silver.
Preparation.— The methods employed
for
the
very
separation of metallic silver from its ores are
three
varied; they may, however, be classed under
heads, namely
1.
Amalgamation processes involving the use
2.
mercury.
Smelting processes involving the use of
3.
Wet
of
lead.
processes.
Amalgamation Processes.— "^he
finely
ground ore
is
then well
formed into a thin mud with water, and
amalgam
mixed with mercury, by which means a silver
mercury
This is collected and the excess of
is formed.
squeezed out; the residual amalgam
is
then heated in
167
SILVER.
a retort to
distil
off'
the mercury, leaving J^ebiud the
melted and cast into bars.
smelted with lead
Smelting Processes.— Sihev ores are
lead and silver is obtained,
ores, whereby an alloy of
silver,
which
is
from which the
silver is extracted
by a process known
which the alloy is melted in a furcalled a cupel. ^ A
nace on a porous bed of bone-ash
which oxidises
of air is blown over the surface,
as cupel kdion, in
blast
partly absorbed
the lead and the oxide fuses and is
whilst the silver
by the cupel and partly flows away,
remains behind.
by
considerable portion of silver is also obtained
produced
smelting argentiferous galena, the lead thus
A
concentration of
being subjected to a process for the
from the
the silver which is subsequently extracted
enriched lead by cupellation.
convert
Wet Processes. The ore is roasted with salt to
out of the
the silver into chloride, which is dissolved
such as hot
roasted ore by means of a suitable solvent,
The silver is then precipitated either by placing
brine.
—
copper in the solution or by some other means,
dried and
the "spongy" silver thus obtained being
strips of
melted.
Properties.
— Silver possesses
a pure white colour,
of taking
has a very high metallic lustre, and is capable
It is not acted upon under ordinary
a good polish.
temperature,
conditions by exposure to the air at any
the
hydrogen
sulphuretted
l)ut in the presence of
the formasurface becomes rapidly tarnished owing to
Water is withtion of a black film of silver sulphide.
dilute
out action upon silver, and hydrochloric acid aud
metal.
the
sulphuric acid have little or no action upon
Hot concentrated sulphuric
acid converts
it
into silver
DENTAL METALLUEGY.
sulphate, while nitric acid
readily
silver
at
the
is its
best solvent, dissolving
ordinary temperature.
It
is
In malleability
only exceeded by gold, and is
slowly attacked by alkaline solutions.
and
in ductility silver is
capable of
than
not more
being hammered into leaves of
thickness, which
^^'^^
TTTcTooo-*^^
are
capable of transmitting light giving a bluish or bluishBy hammering and wire-drawing the
green colour.
and requires more
frecjuent annealing than gold under the same conditions.
metal becomes more or
The presence
less brittle,
of small quantities of other metals, such
as antimony, bismuth, tin, zinc,
silver brittle
and
liable to crack
harder than gold and softer
considerable tenacity.
Of
and
when
arsenic, renders
Silver
rolled.
is
than copper, and possesses
all
the metals
it is
the best
It fuses at a
conductor of heat and of electricity.
temperature of 960" 0. (1760" ¥.), a little below that
required to melt gold and copper, and
when
liquid
possesses the power of absorbing oxygen from the
which
it
gives
up on
solidification.
When
it
air,
silver is
quickly cooled after fusion it solidifies on the surface
before the oxygen has escaped from the interior this
;
gas then bursts through the crust, the evolution being
attended with the projection of small portions of the
metal into a number of protuberances on the surface
" spitting "
constituting the phenomenon known as the
or vegetation of silver.
If,
however, silver be melted
beneath a layer of borax or of charcoal powder, the
absorption of oxygen is prevented and the spitting
Silver contracts on solidification, the decrease
avoided.
in volume being about equal to that of zinc
to volatilise at a white heat.
poured into water
it
When
;
molten
it
begins
silver is
becomes "granulated," and
is
169
SILVER.
usually employed in this condition for the preparation
of alloys.
The
specific gravity of
than that of lead
;
Uses
and
it
= -H
.00193
;
while
its
— Owing to the
nature of pure silver and
seldom used
is
expansion per
.
Dental Purposes,
for
flexible
sulphur,
is
lower
specific heat is nearly equal to
its
that of palladium, being .0570
unit of length
10.5, a little
silver is
the
in
soft
affinity for
its
dental
laboratory
other
metals.
hardened by the addition of
When alloyed with platinum it is employed as a base
for artificial dentures; it also forms an important
unless
constituent in the alloys used for dental amalgams.
Preparation of Pure
Silver.
— Scrap
and when
dis-
hot water.
If
silver is dissolved in dilute nitric acid,
solved
the
solution
is
any gold or platinum
diluted with
present *
is
it
dissolved as a fine black powder;
remain un-
will
the solution after
diluting should, therefore, be allowed to stand
the residue has completely subsided.
is
then carefully poured
or old
The
until
clear solution
heated nearly to boiling-
off,
and an excess of a solution of common salt or
hydrochloric acid added to precipitate all the silver as
point,
On
chloride.
stirring the hot
solution
very briskly
for a few minutes, the precipitate will readily settle,
leaving the supernatant liquor perfectly clear.
*
If
sci-ajis
of
(liiiital
(which
alloy
consists
of
After
silver
and
platininn) arc also present with the material treated, the nitric ar\d
will
dissolve
platiiinni
will
6iit
the silver in the alloy, hnt a part only of the
he dissolved, the
residue which iinist he filtered
(with hydrochloric acid) and
may
remainder
oil'.
filterinfi,
he recovered hy introdticiuj;
n
T)yiiij;
h^ft
as
a lilaek
AfU'.v pnicipitatinfi' the silver
tli(!
platinum
in
the solution
clean strip of x.iuc which pr(!cipi-
tates the i)hitinnni in the metallic state as a hiack si)onge.
DENTAL METALLURGY.
170
and
the
with repeated quantities of
hot
subsidence the acid liquor
chloride well washed
water to free
is
from copper
it
poured
solution.
off,
It is
then dried
and mixed with four times its own weight of anhydrous
sodium carbonate, and the mixture placed in a crucible
and heated in a furnace, first at dull redness, and then
gradually raised to bright redness. The reduction is
complete in about thirty minutes, and when tranquil
the contents of the crucible are poured into a suitable
mould and allowed to cool, after which the coating of
sodium chloride, produced by the reaction, is removed
from the button of silver by means of a hammer, and
As carbonic
the silver finally cleaned in hot water.
acid is given off freely during the reduction, care should
be taken not to have the crucible more than three parts
full,
and to avoid a high temperature
otherwise the charge
may
boil
at the beginning,
over and occasion
The silver thus obtained is practically pure.
The silver may also be obtained from the
loss.
chloride by
covering it with water acidulated with a few drops of
hydrochloric acid, and then adding two or three pieces
of clean sheet-iron,
hours until
all
and allowing
the chloride
is
it
reduced.
to stand for
some
The undissolved
then removed, and the spongy mass of silver
parwashed with hot hydrochloric acid to dissolve any
acid
the
After standing a few minutes
ticles of iron.
iron
is
and the silver washed several times
then dried and
with hot water by decantation. It is
Plates of
melted in a crucible, and cast as required.
is
poured
off,
used instead of iron to
case the spongy
reduce the silver chloride, but in this
more washing, in order to free it from
copper or of
zinc
may be
silver requires
the copper or zinc solution.
:
171
SILVER.
Precipitated Silver.— This
is
prepared
by
dis-
with hot
solving pure silver in dilute nitric acid, diluting
or of zinc in
water, and then placing a strip of copper
Silver is thus precipitated in the metallic
the solution.
form of a spongy mass, which is washed
when it is
several times with hot water and then dried,
" Precipitated silver has long been
use.
state in the
ready for
^
known as forming an excellent
colours the teeth greatly."*
Alloys of Silver.— Silver
with most of the
common
is
filling,
though
dis-
it
capable of combining
metals by direct fusion of
The
alloys.
the constituents, forming a series of useful
laboratory are
alloys of silver chiefly used in the dental
as follows
Silver
and Copper.— These
proportions
metals combine in
all
together, the resulting alloys
when melted
comparatively homogeneous, though ingots of
composition
are not absolutely identical in
being
^
the alloys
many
throughout;
of
them undergo
a
of
process
molten
liquation " on cooling, however perfectly the
In some cases the interior of the
alloy may be mixed.
"
exterior
richest in silver, while in other cases the
These alloys are white in colour until
contains most.
ingot
is
the copper amounts
alloy
;
beyond
to
nearly 50 per cent,
this limit the tint
the
of
becomes yellowish,
with the increase in the amount of
The density of these alloys is less than the
copper.
mean of the constituent metals, owing to the expansion
which takes place during combination. The effect of
finally red
and
cop])er is to increase the hardness
of the alloys being harder and
more
the hardest alloy consisting of about
*
Tomes,
"
and
elasticity,
elastic
than
most
silver,
parts of silver
5
Notes on Anmlgmiis," Odont. Soc, of G.
B.,
and
1896.
DENTAL METALLURGY.
172
1 1
The
of copper.
ductility is also very considerable,
but slightly inferior to that of pure
silver.
Although
not oxidise on
copper alloys are subject to change when heated in
the application of heat, silver-
silver does
owing
to the oxidation of the copper.
The coating
oxide formed on the surface of standard silver
annealing
may
air,
of
during
the silver whitened
be removed and
by heating the metal and plunging it while still hot
The most important appliinto dilute sulphuric acid.
cations of silver-copper alloys are for the purposes of
which uses pure or
fine silver is too soft to withstand the necessary wear
consequently copper is added to obtain the required
coinage, plate, jewellery,
&c., for
;
hardness.
—
British silver coin and plate conof silver and copper regulated
proportions
tain definite
Standard
by law.
Silver.
The
alloy for
silver
coin contains
1 1
ozs.
2 dwts. of fine silver per lb. Troy, or 925 parts of
silver per 1000, the remaining 18 dwts. or 75 parts
being copper. This alloy is designated sterling or
standard
silver,
and has a fineness
merce the purity of
silver is
of
925.
In com-
referred to this standard,
other specimens of different composition being reported
in terms of pennyweights letter or ivorse than the stan-
Thus, the French and American coinage, which
contain 24 dwts. of copper per lb. Troy (900 parts
dard.
of silver per
1000), are stated to be
worse
6
dwts.
(24-18 = 6); while the Indian rupee, containing only
12 dwts. of copper in the Troy lb., is described as better
In England all sterling silver goods are
stamped, at offices appointed for that purpose, with a
" Before the
special mark known as the " Hall Mark."
6 dwts.
introduction of vulcanised rubbers as a base for
artificial
SILVER.
dentures, standard silver was employed in the United
an
States for temporary dentures, where cheapness was
important consideration." * Standard silver, however,
cannot be regarded as a suitable alloy as a base for
dental substitutes, on account of the affinity which its
constituents possess for sulphur and the readiness with
which it is tarnished under the conditions which exist
in
the
mouth.
Filings
of
sometimes employed for dental amalgams.
Silver and Gold.— (See Gold Alloys,
and Platinum.— Alloys
Silver
are
alloys
silver-copper
p. 103.)
of these metals
obtained by fusion of the constituents, small
proportions of platinum rendering silver harder but
may be
greyish-white in colour.
As the proportion
become
melt.
num,
of
platinum increases the alloys
malleable and ductile, and more difficult to
Owing to the very high melting-point of platiless
it
alloys is
be thought that the preparation of these
When, however,
a matter of great difficulty.
may
a small quantity of platinum-foil or
to an excess of the
condition,
it
more
added
fusible metal silver in a molten
melts without
furnace temperatures.
are
is
readily combines with the silver, producing
an alloy which
num
"sponge"
much more
The
difficulty
at
alloys of silver
ordinary
and
fusible than platinum itself
plati;
they
are also less readily tarnished than silver or ordinary
silver alloys.
In preparing these alloys there is always a tendency
for the two metals to separate ou cooling according to
it
their densities, the platinum settling to the bottom
stir the molten alloy
is very essential, therefore, to well
;
before pouring.
*
Essig, "
In preparing "dental alloy"
Don till Mutalkirgy,"
p. 182,
jrd
cil.
it
is
DENTAL METALLURGY.
174
necessary to remelt the alloy in order to obtain as
uniform a product as possible.
An
alloy of silver
and
platinum, containing only 2 per cent, of the latter
but if the
metal, completely dissolves in nitric acid
;
platinum much
exceeds that proportion, part of it
remains undissolved. With sulphuric acid the silver
only dissolves.
Dental Alloy.
—This name
is
given to an alloy of
and platinum used by dentists which contains
silver
from 20 to 30 per cent, of platinum according
to the
Two "qualities" of this alloy are in general
([uality.
use in England, the " first quality " consisting usually
of 2 parts of silver
"
second quality
platiniun,
but
" of
the
stronger
rigid
part of platinum, and the
3 parts of silver
artificial
and
i
part of
composition varies slightly with
than standard
largely employed.
ing,
I
Dental alloy
different makers.
and more
and
denture,
The
for
alloy is
is
much mo re du rable
silver,
and makes a
which purpose
it
is
hardened by hammer-
and requires annealing during swaging.
much less tendency to blacken than
when exposed in the mouth, although
It
has
silver-copper alloys
the presence of
platinum does not wholly protect silver from the action
Dental
of sulphuretted hydrogen and the oral fluids.
alloy comes into the market in the form of wire, sheet,
and perforated sheet, the last named being used as a
base for strengthening vulcanite pieces.
Nitric acid attacks this alloy, and dissolves a considerable quantity of the platinum along with the
Concentrated sulphuric dissolves out the silver,
leaving the whole of the platinum in the metallic state
silver.
and dipping it
On
heating a plate of dental alloy
into dilute sulphuric acid, the silver on the
as a black residue.
SILVEE.
surface
of silver
"An
dissolved, leaving the platinum.
is
alloy
for pivots
and platinum was used by dentists
*
of artificial teeth before 1835."
The union of two or more pieces of dental alloy is
effected
by means
Von
of gold solders (see p.
Eckart's Alloy.—This
an
is
1
10).
alloy consist-
ing of silver 3.5; platinum 2.4; and copper 11.7;
dentures.
which is used in France as a base for artificial
which latter
It is hard, malleable, and very elastic,
property it retains after annealing. It is less tarnished
by the atmosphere than silver-copper
Owing
capable of receiving a high polish.
proportion of copper
it
ened in the mouth
contains,
by the
it is
and
alloys,
is
to the large
gradually black-
sulphuretted hydrogen
present..
metals combine readily
when fused together to form alloys which have about
They are more or less
the same colour as pure silver.
and Tin.— These
Silver
brittle or semi-ductile
tion
a very
of
small
The
and in general hard.
quantity of tin renders
addisilver
brittle.
Experience has shown that different portions of a
mass of any of the solidified alloys of the silver-tin
except the eutectic alloy, exhibit a want of uniformity in composition. This is no doubt due to the
series,
Heycock
presence of the eutectic alloy (see p. 39)and Neville t have ascertained that the eutectic alloy,
which is mechanically homogeneous, consists of 3.53 per
cent, of silver
and 96.47 per
cent, of tin,
and
solidifies
at 220'" 0.
They have
*
also
shown that the
Percy, " MetiilLurtjy of Silver,"
p.
initial
solidifying-
668.
vol. cLt-Kxix. (1897), pp. 25-70.
t Prac. Roy. Soc,
DENTAL METALLURGY.
176
point of an alloy containing 60 per cent, silver aud
40 per
cent, tin
is
about 500"
0.,
consisting of 40 per cent, silver
about 450" C.
It is evident,
and that of an alloyand 60 per cent, tin
therefore, that, in
.
the
range of temperature between the
points of these alloys and that of the eutectic alloy
initial solidifying-
abundant op poi't unity
afforded
is
mass to
hence
the
for
arrange itself as previously indicated (p. 40),
the divergency in composition.
On
These alloys are very oxidisable.
heating theui
with bichloride of mercury (corrosive sublimate) the tin
is
volatilised in the state of chloride, while the silver
left
behind in a comparatively pure
state.
is
Alloys of
these two metals are, as previously stated, largely em-
ployed in admixture with mercury for stopping teeth.
The density of the silver-tin alloys is l^s than the
mean
result of the densities of the
two constituents,
thus showing that chemical combination has probably
taken place and that expansion has occurred during
the union of the raetals.
and
Silver
Mercury.
— Silver
amalgams
are
white, soft, granular or crystalline bodies, accordiug to
the composition aud
mode
They harden
of preparation.
slowly, and expansion takes place during combination.
The properties of silver amalgams are given under
Mercury,
p.
136.
Silver Solders.
—The
articles of silver are usually
alloys
used for soldering
composed of
silver,
and zinc in variable proportions, with
sometimes of
tin,
the latter metal being added to the
silver to increase the fluidity
when
fused.
copper,
the addition
and cause
Several qualities
of
it
silver
to
run well
solders
are
employed according to the nature of the work upon
1/7
SILVER.
to
which they are
various degrees
The
be used.
of
using
the silver solders are obtained by
which enter into
different proportions of the metals
Alloys of silver and copper form
their composition.
difficult to melt.
the hardest solders— ir. those most
while the
The addition of zinc gives a medium solder,
a
are prepared with the addition of
fusibility of
easiest or softest
certain proportion of tin.
dental depots is
silver solder frequently sold at
The
composed
fine silver
3 parts
of
and
part of brass.
I
This represents a percentage composition of
Fine silver
Copper
Zinc
.
.
•
•
.
.
•
.
.
.
•
•
:
7S-00 per cent.
16.66
„
8-33
99-99
Kichardson* gives- the following formulte for solderino- articles
No.
Fine silver
Copper
Zinc
.
of standard silver
made
:
No.
I.
.
.
.
.
.
.
-
.
66 parts
30
10
2.
.
•
60 parts
.
.
.
20
„
-
.
lo
.
„
Fine silver
Copper
Brass
employed in the form of
however, are sometimes used.
Silver solders are usually
plate;
thin
filings,
generally soldered with gold solder, as
too readily in the
silver solder would blacken much
Dental alloy
is
mouth.
borax, as
flux used with silver solders is always
during soldering, but also
it not only prevents oxidation
required
greatly facilitates the flow of the solder into the
The
places.
Preparation of Silver
*
Uichanlson,
may be
>S'o/(/«'S.— Silver solders
" Mei-li!iniciii
Dnitistry," 1894,
p.
1 1 1,
6th ed.
M
DENTAL METALLURGY.
178
and copper together
under a layer of charcoal powder in a plumbago
The zinc, which
crucible heated in a suitable furnace.
slight
excess of that
in
heated
and
should be previously
required, is cautiously added after the silver and copper
prepared by melting the
silver
and the whole well stirred with an iron rod
and then poured into a flat ingot mould to obtain a
are melted,
plate of alloy suitable for rolling.
When
rolled into a sheet of
Brass
thickness.
is
and zinc separately
is
removed from the mould and
about one-sixtieth of an inch in
cool the ingot
;
is
invariably used instead of copper
it
should be added after the silver
Silver coins are sometimes used instead of
melted.
and copper separately, in which case the solders
are prepared by adding to the coin from one-tenth to
silver
one-sixth
its
weight of
Assay by
zinc.
Cupellation,
The operation
or
Dry Method
of cupellation has for
removal of base metals in a gold or
oxidation and by
its
of Assay.
object the
silver
alloy
by
the aid of fused litharge (lead oxide).
based upon a property which characviz. that they
terises the precious metals
It is
—
are not oxidised
a
condition to
metals,
oxidised.
Lead
or silver, as
it is
when
is
when exposed
current
of
air,
in a Tuolten
while
similarly treated, are
base
readily
always added to the impure gold
readily converted into litharge (lead
which fuses and dissolves the oxides (formed
during the operation) of base metals in the alloy. The
"
operation is conducted in a small vessel termed a " cupel
porous,
(Vig. 37), made of bone-ash, which, being very
oxide),
absorbs the molten oxides, leaving the unoxidisable
metals gold and silver on the cupel.
—
—
T79
SILVER.
The assay
is
of silver alloys
by the cupellation method
conducted as follows
fair sample of
1. A
:
2.
the
alloy
accurately
is
weighed in a delicate balance.
This weighed portion is then wrapped in
thin sheet-lead and cupelled, to remove the
base metals present.
3.
The button
is
of silver
remaining on the cupel
weighed.
In conducting the assay I gramme (or 10-15 grains)
of the alloy is usually taken and carefully wrapped in a
weighed quantity of lead-foil. The amount of lead to
be added to an alloy of silver and copper varies in
accordance with the composition of the alloy, and is
greater in proportion as the quantity
creases.
copper in-
of
English standard silver (925
fine)
requires
weight of lead for cupellation.
After wrapping the alloy in the required weight of
heated
lead-foil it is charged into the cupel, previously
If the
in a muffle furnace kept at a uniform red heat.
about six times
its
right temperature
is
attained the charge quickly melts
and cupellation begins, the metallic globule steadily
diminishing in size until, after the expiration of a,bout
twenty to thirty minutes, the lead and base metals
have become completely oxidised and absorbed by "the
cupel, leaving a bright globule of pure silver.
as the cupellation
is
finished the muffle
is
As soon
allowed to
down, in order to avoid the spitting of the silver,
and the cnpel withdrawn when the silver bead is solid.
The bead is then detached, brushed, and weighed.
Tlie weight of the silver bead does not, however, give
cool
the true proportion of silver in the alloy, as there are
always small losses of silver due to volatilisation and
i8o
DENTAL METALLURCtY.
by the
absorjDtion
These are determined by
cupel.
placing in the muffle with each batch of assays one or
more proof
same weight and of
similar alloy but of knoion composition.
The checks
are prepared from pure silver and copper, and when the
or check assays of the
approximate composition of an alloy
is
not known a
preliminary cupellation must be made to ascertain this
before suitable " checks " can be prepared. When these
checks are cupelled side by side with the assay piece
is
concluded that the
same.
loss of
silver
on each
will
it
be the
In order, therefore, to obtain the true per-
centage of silver in the alloy submitted to assay, the
calculated loss sustained
by the check
added as a
is
correction to the weight of the silver bead from the alloy.
When
gold or platinum
is
present in the alloy
remains on the cupel in combination with the
and must be subsequently separated
(see
it
silver,
Gold Assays,
P- 99)-
Silver alloys, such as those used for dental amalgams,
containing
tin,
or zinc, must be subjected
fication " before
first to
" scori-
metals produce
cupellation, as these
oxides which are not absorbed by the cupel.
Scorifica-
tion consists in mixing a weighed quantity,
usually
5
grammes
(or 50 grains), of
the alloy with about 10 times
its
weight of
granulated lead in a small saucer-shaped
vessel of
fire-clay,
termed a
" scorifier
''
this in a muffle furnace at a bright
(Fig. 38),
and placing
red heat.
By this means the base metals are oxidised and
form a fusible " slag " by combining with molten lead
oxide, produced by the oxidation of a part of the lead,
while the unoxidisable metals remain in combination
with the metallic lead present in excess.
As
the scorifier
l8l
SILVER.
" slag " floats
not made of absorbiug material, the
is comabove the excess of lead. When the operation
is
the scorifier are poured into a"
" slag " detached, and the
suitable mould, the glassy
lead " button " cupelled in the ordinary way.
plete the contents
of
Wet Assay of Silver. — Silver is usually estimated
A
in the wet assay by precipitating it as chloride.
weighed quantity of the alloy
is
dissolved in
nitric acid with the aid of a gentle heat.
solved (see note) the solution
is
dilute
When
diluted with
dis-
boiling
hydrochloric acid added to
The solution is well
precipitate the silver as chloride.
completely
stirred, and when the silver chloride has
water and an
excess
separated, leaving the
of
supernatant liquor clear,
it
is
and washed well with hot water. It is then
of
carefully dried and weighed and the percentage
chloride
One hundred parts of silver
silver calculated.
filtered off
contain 75.27 parts of silver.
treated
_yy^e_Aiiy gold, tin, or platiiumi present in the alloy
oil'
liltered
be
must
wlduli
residue,
insoluble
would V)e left as an
before precipitating the silver.
Electro -plating.—This term is applied to the
is
process by means of which a film of metallic silver
deposited on the surface of articles made of German
give them
silver, copper, brass, and other base metals, to
the appearance of silver, and
is
similar to electro-gilding.
be plated is first thoroughly cleaned,
It is next dipped
as described for gilding on p. 1 16.
into a solution of mercuric nitrate, whereby it receives
The
article
to
a thin deposit of mercury, then
rinsed in water, and
immediately suspended by means of thin copper wire
ot
in the plating li(|uid, which consists of a solution
silver
cyanide in potassium cyanide.
'Phe
article
is
m
DENTAL METALLURGY.
l82
of
then couuected to the negative pole
battery,
while a strip of pure silver
the positive pole and
An
is
a suitable
connected to
suspended in the plating liquid.
electric current is thus
passed through the solution,
a coherent form, to be precipitated
upon the article, while the silver plate is gradually
dissolved, forming silver cyanide, thus maintaining the
causing
silver, in
The deposit of silver is
the solution.
usually dull or " frosted," but the addition of a few
drops of carbon disulphide to the solution causes the
strength of
silver deposit to
form with a bright surface.
Recovery of Silver from Scraps.— The
of dental alloy are treated with
nitric
acid,
scraps
and the
platinum removed as described on p. i8g. Strips of
copper or of zinc are then placed in the solution to
precipitate the silver.
is
The spongy
washed, dried, and then melted.
silver thus obtained
CHAPTER
X.
PLATINUM.
SYMBOL,
Pt.
ATOMIC WEIGHT,
Occurrence.— Platinum
is
always
i95-
found
in
tlie
or flattened grains
metallic state, generally as rounded
metallic lustre, occurof a lio-ht steel-grey colour and
and gold-bearing
ring in alluvial deposits, detritus,
contains iron
It is never pure, but invariably
sands.
found in platinum
osmium, and
ores— viz. palladium, iridium, rhodium,
The
group:'
ruthenium, known as the "platinuvi
from the Ural
largest supply of platinum comes
districts.
Mountains, but it is also found in other
The mettJ is first separated, by
and a group of rare metals
chiefly
Preparation.—
sandy,
washing operations, from much of the
ore, the residue
earthy, and lighter portions of the
careful
with gold, &c.
consisting of grains of platinum, along
residue with
The platinum is extracted by treating the
associated copper, lead, or
nitric acid, to
remove any
hydrowith water, and treating with
heating with
chloric acid to dissolve the iron, and then
The solution thus obtained
aoid.
silver,
washing
it
nitro-hydrochloric
chloride),
then mixed with sal-ammoniac (amnionic
of
whereby a yellow precipitate of the double chloride
is
platinum and
ammonium
is
obtained.
The
precipitate
DENTAL METALLURGY.
washed, dried, and ignited iu a plumbago crucible,
when the metal is obtained as a grey spongy mass
is
known
ammonia
as spongy platinum, the
The
chlorine being expelled.
whiteness, and
hammered
fine
until
chloride and
powder
it
is
is
heated to
welded into a
homogeneous mass, or it is melted in a crucible of
lime or gas-coke by means of the oxy-hydrogen ilame.
Properties. Platinum is a white metal with a
greyish tinge, and when polished it has a very high
It does not become tarnished by exmetallic lustre.
posure to the atmosphere at any temperature, even in
—
presence
the
the
resists
agents
nitric,
hydrogen.
sulphuretted
of
action
water and
of
of
most
Platinum
chemical
not attacked by hydrochloric, sulphuric,
or any single acid, except wheu alloyed with a
;
it is
large proportion of silver, in which case it is soluble in
It dissolves slowly in nitro-hydrochloric
nitric acid.
acid,
which
is its
This property of with-
best solvent.
standing the action of chemical agents, coupled with
its non-oxidisability at all temperatures, makes it a
valuable material for dental purposes.
The pure metal is slightly harder than silver and
is
very malleable and ductile, being only inferior to gold
and silver in ductility, while in tenacity it is only
Platinum is
surpassed by iron, steel, and nickel.
hardened by rolling and mechanical treatment, but
may be
five to
softened by heating to a bright red heat for
ten minutes and allowing
inferior to both gold
and
for electriciiy.
stances in nature,
is
and
its
it
to cool.
It is
much
silver in conductivity for heat
It is
one. of
specific
the heaviest sub-
gravity being 21.5.
attainable
infusible at the highest temperature
ordinary furnaces, but
may be
fused by the
It
in
electric
185
PLATINUM.
by the oxy-liydrogeu blowpipe flame. It
much
becomes soft and workable at a temperature
the
below its meltiug-poiut, and at high temperatures
Like
metal can be welded by pressure or hammering.
oxygen when
silver, large masses of platinum absorb
to
molten but expel it on cooling, causing the mass
curreut, or
"spit."
When
heated
platinum
the
possesses
re-
markable property of absorbing considerable quantities
a
and other gases, especially when it is
of
m
hydrogen
fine state of division.
Use in Dental Laboratory.— Platinum
is
used
continuous gum-work; for pins for
attaching teeth for backing and other minor operaAlloyed with silver, it
tions of the dental laboratory.
as
a
base
for
;
is
largely used as a base for artificial dentures.
Brittle Platinum.— Experience having proved
that the platinum pins attached to mineral teeth are
frequently brittle and very liable to break, an investigation into the composition of brittle platinum
* with
pins was undertaken by Prof. Hartley of Dublin
a view to ascertain the cause.
For this purpose fragments of
brittle pins
were sub-
mitted to a very careful spectroscopic examination.
The results of the experiments showed that the brittle
and crystalline character of the platinum was in all
probability due to the presence of minute quantities of
phosphorus or of carbon, and by remelting in a limecrucible under the oxy-hydrogen tiame its malleability
was greatly improved, thus confirming the accuracy of
the conclusion arrived
Platinum
beaten
out
*
at.
Foil.— IMatinum
into thin foil,
l>i;w. Cliriii.
Sue,
may be
and can
be
vol. xviii. (1902),
11.
rolled
used
30.
in
or
this
DENTAL METALLURGY.
form
for filling purposes.
of platinum adhere
In order to make the leaves
when pressed
together the surface
covered with a film of pure gold by electro-deposition.
The foil must be thoroughly annealed when used in
is
order to
make
it
work
work compared with
easily.
gold.
The metal
—
harsh to
Fillings of platinum have
the advantage of being almost white
Platinum Black.
is
when
finished.
Platinum in an extremely fine
forms a black powder known as " platinum black," which resembles lampblack in appearance
and soils the fingers in the same way. This finely
state of division
may be
divided platinum
obtained in various ways.
A common
method of preparing it is by precipitation
with zinc from a solution of platinic chloride containing
an excess of hydrochloric acid, or by adding an excess
of a mixture of sodium carbonate and sugar to a solution
of
platinic chloride
and then boiling
until the
formed becomes perfectly black and the
supernatant liquor colourless. The soft black powder
precipitate
washed, and dried at a gentle
It is also prepared by fusing platinum with
heat.
twice its weight of zinc, powdering the alloy thus
produced, and dissolving out the zinc with sulphuric
is
collected
acid,
when
on a
filter,
the platinum remains in the form of a black
powder.
Platinum black possesses remarkable and powerful
chemical properties; it absorbs and condenses gases,
that the
especially oxygen, within its pores so rapidly
becomes red hot. When exposed to a red heat
mass
assumes the
the black substance shrinks in volume and
and no longer
metallic appearance of spongy platinum,
soils
the
fingers.
When
platinum with zinc and
prepared
from
otbei' n.etals, the
alloys
of
black powder
PLATINUM.
1
87
an opeu vessel to a temperature couwith a hissiug noise,
sLderably below redness deflagrates
sometimes detonating like gunpowder.
when
LeaLecl iu
Spongy Platinum.—This name
is
applied to the
metallic platinnm
spongy, slightly coherent form of
the double
obtained by heating to bright redness
latter
platinum and ammonium. This
chloride
of
formed as a yellow precipitate when
to a solusal-ammoniac (ammonic chloride) is added
by dissolving
tion of platinic chloride, obtained
compound
is
platinum in aqua
regia.
The yellow
precipitate
is
gives
decomposed on the application of heat and
spongy
of
chlorine and sal-ammoniac, leaving a residue
off
By the application
spongy mass when at a bright
may be welded together, when
platinum.
of
pressure
the
to
^
red heat
its particles
assumes the form
Like the
and appearance of commercial platinum.
of inducing
other forms of platinum, it is capable
combinations in the mixture of certain comit
chemical
bustible gases.
Detection of Platinum in Alloys.— Platinum
described
usually detected in alloys for amalgams, as
on p. 162. The
in the qualitative examination of alloys
exceeds
(quantity of platinum in these alloys seldom
is
I
per cent., and
the alloy
is
is
usually completely dissolved
when
treated with nitric acid.
platinum in gold plate may be
regia,
detected by dissolving a few chippings in aqua
The presence
of
removing excess of acid by evapoi'ation, diluting and
filtering off any residue of silver chloride, then concentrating by evaporation and adding ammonium chloride
and alcohol as before.
Ill
silver alloys (such as dental alloy) the
presence of
DENTAL METALLURGY.
i88
platinum may be detected by treating the alloy with
nitric acid, when the platinum is partly dissolved, the
remainder being left as a black insoluble residue. The
platinum in solution may be detected by adding ammo-
nium
chloride
and alcohol
as before, after precij)itating
the silver with hydrochloric acid and
filtering.
Estimation of Platinum in Alloys. — i. In
Dental Amalgams.
proportion
of
— Owing
tin
to the comparatively large
present in alloys used
for
amal-
somewhat difficult to accurately estimate
the small amount of platinum usually present. The
most satisfactory method consists in scorifying (see
gams
it
is
80) 5 grams, or 50 grains, of the alloy with from lO
to 1 5 times its weight of granulated lead, whereby the
p.
tin
1
is
removed and the
retained
in
gold,
the resulting button of
The
cupelled.
silver,
silver
button
and
lead,
platinum
which
(containing also gold
is
and
platinum) obtained by cupellation is treated with dilute
nitric acid to dissolve out the sUver and platinum.
The residue
of
gold
(if
any)
is
filtered
off
and
After
the silver precipitated with hydrochloric acid.
filtering off the silver the solution is evaporated to very
small bulk, then
ammonium
and alcohol are
chloride
added to precipitate the platinum, the precipitate thus
obtained being dried, heated to redness to obtain
metallic platinum, and weighed.
The small quantity of platinum usually present in
amalgam alloys will probably all go into solution with
but when large quantities are present a
the silver
;
part of
it
will
remain with the gold
;
the residue left
any), after being treated with nitric acid, should
therefore be dissolved in acpia regia and the platinum
(if
precipitated and weighed as previously directed.
PLATINUM.
alloys
Platinum may also be estimated in amalgam
alloy in a small crucible
by melting the
and gradually
the tin is
adding mercuric chloride, by which means
This must be done in
as a volatile chloride.
removed
a draught cupboard
it is
left
to carry off the
fumes produced,
as
silver
dangerous to inhale them. The button of
present).
behind contains the platinum (and gold if
above described.
may be conveniently
2. Platinum in dental alloy
alloy
estimated by treating a weighed quantity of the
It is treated with nitric acid, as
with nitric
which dissolves
acid,
On
of the platinum.
all
the silver and part
introducing a sheet of zinc into
precipitated,
the solution the silver and platinum are
and on treating this precipitate with nitric acid the
silver only is dissolved.
The two
quantities of platinum
and
are then put together, washed, heated to redness,
weighed. The platinum precipitate may also be dissolved in aqua regia, the metal precipitated with
nium
chloride
and weighed
as
ammo-
spongy platinum
as
previously directed.
The
silver
may be
recovered from the solution in
way by precipitation as chloride (see
Alloys. Platinum will alloy with most
.the usual
—
other metals
under the influence of
bodies which
are
than platinum
itself.
usually
heat,
considerably
Platinum and Gold.
—These
p: 169).
of
the
producing
more
metals
fusible
combine
with the formation of alloys which are more fusible
than platinum, the melting-point being lowered as the
quantity of gold increases.
The
alloys are elastic
and
ductile,
approaches more or
less to that of
tion of the latter
increased.
is
and their colour
gold as
tlie
])rupor-
I
DENTAL METALLURGY.
go
Platinum and
tinum by
fusion,
malleable, ductile,
Silver.
—
Silver unites with pla-
forming alloys which become more
and
fusible
as the
proportion of
silver increases.
Dental Alloy.
—This
alloy of silver
and platinum has
been described under Silver Alloys (p. 174).
Platinum and Iridium. These metals unite in
different proportions, but the union is only effected by
—
the use of the intense heat of the oxy-hydrogen flame.
The presence of iridium gives increased stiffness, hardness and elasticity to platinum. An alloy consisting
of nine parts of platinum and one part of iridium is
extremely hard, as elastic as
It
to fuse than platinum.
exceedingly beautiful
polish
steel,
and more
is capable of
and
difiicult
taking an
unalterable
is
on
Alloys with 20 per cent, of iridium
worked.
are malleable, ductile, and capable of being
Platinum containing a small quantity of iridium is stated
exposure to
by Essig*
gnm-work
air.
to be of value for strengthening continuous
by forming the backing of it, especially in
partial lower sets.
It is also of value in
combination with
It
cases.
vulcanisable rubber for either entire or partial
countermay be perfectly swaged by the use of a zinc
used as a solder with these alloys.
Platinum and Copper.— Platinum unites with
a high temperacopper in all proportions by fusion, but
of these alloys.
ture is required for the production
require the oxyThose containing excess of platinum
The alloys
hydrogen flame to effect combination.
die.
Pure gold
is
ductility, and tenacity,
possess considerable malleability,
and are
less tarnished
by the atmosphere than
copper with base metals.
*
"
Dental Metallurgy,"
p. 201.
1S93
i-dit
alloys of
.
THIDIUM.
—
Recovery of Platinum from Scraps. Platinum
may be conveniently recovered from scraps of dental
alloy
by the method described on
p.
189 for estimating
platinum.
Solder for Platinum.— Pure gold
alloys.
joint,
for
solder
suitable
platinum
and
is
the only
platinum-iridium
Ordinary gold solders do not make a strong
and are not suitable for the purpose. For con-
tinnous-gum and porcelain bridge-work "platinum
solder," composed of gold 4 parts and platinum I
part, is supplied * for use with an oxygen blowpipe.
IRIDIUM.
SYMBOL,
Ir.
ATOMIC WEIGHT,
193.
found in the form of grains, which
consist essentially of an alloy of platinum and iridium,
called " platin-iridium," and are usually associated with
Small particles of alloy
the grains of platinum ore.
of osmium and iridium (called " osmiridium ") are also
This metal
is
found.
Properties.
—Iridium
is
a white, lustrous,
steel-
metal slightly heavier than platinum, its density
being 22.4. It is not acted upon by air at the ordinary
like
temperature
oxidised,
heating.
but
it is
heat.
at a red heat, however, it is superficially
:
but regains
its
metallic
lustre
on further
extremely hard and brittle when cold,
rendered somewhat malleable at a bright red
It is
by the oxy-hydrogen blowpipe
not acted upon by ordinary acids or aqua
It is fusible only
llame.
It is
regia.
When
alloyed with
much
platinum, however,
dissolves in a(pia regia.
*
C. Asli
.'i;
Sons, Ltd., IJst
M
it
DENTAL METALLURGY.
192
Alloys.
— Iridium
alloys
creasing their hardness, but
gold.
With platinum
it
with
it
most
metals,
in-
cannot be alloyed with
forms alloys remarkable for
and hardness. (See Platinum Alloys.)
Dentistry. Alloys of platinum and
their strength
Use
in
—
iridium are sometimes used as a base for
also in the
form of wire
for pivoting,
dentf-,1
plates,
and occasionally
for the manufacture of nerve instruments.
CHAPTEE
XI.
PALLADIUM.
SYMBOL,
Occurrence.
ATOMIC WEIGHT,
Pd.
— This
metal
found in the
chiefly
is
io6.
nature in small quantities associated
metcallic state in
with platinum and gold.
Preparation. In order to extract the metal the
ore is heated with aqua regia, which dissolves the
—
Ammonium
metals as chlorides.
added
precipitate
to
chloride
then
is
the platinum present.
This
is
filtered off and the solution neutralised by the addition
solution of mercuric cyanide
of sodium carbonate.
A
is
added to
of palladium
then
form
whitish,
insoluble
washing,
drying,
palladium in the
precipitate the
which
cyanide,
heating
redness,
to
metallic palladium in a spongy state,
welded
into
solid
a
mass
as
a
This compound, after
substance.
and
separates
the
in
yields
which may be
same manner
as
platinum.
Properties.
— Palladium
sembling platinum and
is
is
a
white
capable of
metal,
re-
being highly
upon by atmospheric air
at the ordinary temperatures, but when heated to
dark redness it assumes a violet or blue colour, owing
polished.
It
is
not
acted
to a superficial film of oxide
•,
at a higher temperature
DENTAL METALLURGY.
'94
the oxide
lustre.
is
It
hydrogen,
it
It
is
also
ever,
by hot
acid
acid.
and
acid
and
slowly
is
boiling
in
also
best solvent,
Its
which
regia,
acids than platinum.
nitric
sulphuric
aqua
is
upon by
hydrochloric
in
concentrated
metallic
sulphuretted
of
action
its
not attacked by water, but
is
easily acted
dissolved
soluble
the
resists
l^alladium
more
is
reduced and the metal regains
readily
dissolves
howthe
metal.
Palladium
fairly
malleable,
hammered
it
is,
rather
platinum,
viz.,
it
is
drawn
than
ductile
less
into fine wire
;
platinum.
somewhat lower temperature
a
at
;
and tenacious, and can be
ductile,
into thin plates or
however,
Palladium fuses
than
platinum
slightly harder than
is
1500"
C.
(2732"
cannot be fused in an ordinary furnace.
in the oxy-hydrogen flame
When
volatilises
it
but
F.),
in
it
heated
greenish
vapours.
When
is
the melal
evolved
is
melted
when the metal
"spit" as in the case
of
it
absorbs oxygen, wliich
solidifies,
silver.
sesses the property of absorbing a
hydrogen.
900 times
At
its
a red heat
own
it
cavising
Palladium
large
it
to
pos-
quantity of
absorbs, or occludes, about
volun\e of hydrogen, while even at
ordinary temperatures
it is
capable of absorbing over
absorption of gases
300 times its
forms one of the most characteristic properties of
volume.
This
palladium.
Palladium
is
specific gravity
only one-half as heavy as platinum,
being
its
12.
Although palladium resembles platinum it ma}' be
readily distinguished from this metal by placing upon
it a drop of tincture of iodine, which upou evaporation
PALLADIUM.
by heating produces a black stain with, palladium, while
platinum is not acted upon by this substance.
Use for Dental Purposes. Palladium in a
finely divided state is used for the preparation of
palladium amalgam, but this forms its only use in
The unalterable nature of palladium in the
dentistry.
—
air, its fine
which
silver-white colour,
it
does not lose
on exposure to sulphuretted hydrogen, and
ness
make
dentistry,
its
light-
a very suitable metal for use in prosthetic
it
and
it is
for this purpose
quite probable that
if
its
it
would be used
high price did not exclude
from the dental laboratory.
Palladium Precipitate.
—This
is
it
the form in
which the metal is employed for the preparation of
palladium amalgam. It is usually prepared for dental
by placing strips of zinc in a solution of
palladium chloride, whereby the palladium is precipitated as a fine black powder, which is then carefully
washed and dried. The powder appears to lose its
purposes
mercury after long exposure to the air.
Palladium and Silver. These metals unite by
affinity for
fusion in
—
all
proportions.
An
alloy of three parts silver
and two parts palladium is white, hard, elastic, and
malleable, and it is not blackened by sulphuretted
hydrogen. Even when alloyed with as much as three
times
its
weight
of
silver,
palladium retains
in the presence of that gas.
of a high polish
silver
to
An
dentists.
Palladium and Gold.
is
brilliant surface.
per cent, of palladium and 62 of
was formerly used by
palladium
colour
These alloys are capable
and retain their
alloy containing 38
its
—The
effect
of
gokl on
produce alloys that are usually white
or grey in colour, hard and ductile.
DENTAL METALLURGY.
196
Palladium and Mercury. — Palladium amalgam
may be formed by rubbing the finely divided metal
with,
mercury.
tion of heat.
The union is accompanied by an evoluThe properties of palladium amalgams
have been given on
p. 135.
CHArTER
XII.
ZINC.
SYMBOL,
Occurrence.
ATOMIC WEIGHT,
Zn.
—Zinc
stated
is
65.
have been found
to
in the metallic state in small quantities in Australia,
chief forms of occurrence are in combination
with sulphur as zinc-blende, and with carbonic acid as
but
its
calamine, these being by far the most important and
abundant ores
The metal
of zinc.
is
found in
also
combination with oxygen.
Preparation.
— In
extracting
zinc
from^
its
ores
taken of the volatility of the metal at a
bright red heat. The metal is chiefly prepared from
the carbonate and sulphide, these minerals being tirrt
advantage
is
powdered and roasted to expel the carbonic acid and
The zinc
sulphur, and convert the zinc into oxide.
oxide is then mixed wirh powdered coal and heated
to bright
oxide
oxide,
redness in earthenware
when the
carbon mon-
retorts,
reduced with the formation of
which escapes, while the metallic
is
liberated distils over
and
is
/.inc
thus
collected in clay or iron
receivers.
The metal thus obtained
zinc oxide, from which
before
it is
it
is
is
contaminated with a
little
separated by re-melting
ready for the market.
Zinc ores frequently
DENTAL METALLURGY.
198
contain small quantities of cadmium, but as this metal
is
more
the
readily volatilised than zinc
it
passes over in
portions of the distilled product, and can thus
first
be collected.
(See p. 224.)
Properties.— This metal,
mercially
possessing
as
"spelter,"
when
polished
which
is
known com-
bluish-white
is
bright
a
in
colour,
metallic
lustre,
and when freshly broken a crystalline surface.
It is not acted upon by exposure to dry air
at the
ordinary tempei-ature, but at a red heat it rapidly
oxidises and burns with a bluish-white flame, with
the production of a white floccalent powder of zinc
If exposed to a moist atmosphere at the
oxide, ZnO.
temperature
ordinary
coated
its
surface
with a grey layer or
film
rapidly
of
becomes
oxide,
which
does not, however, increase by exposure, but protects
the metal from further oxidation. When carbonic acid
is
present the coating
sists
is
formed more rapidly and con-
then of zinc carbonate.
not attacked by pure cold water, but it is
slowly oxidised by hot water and by water containing
Zinc dissolves readily in hydrochloric
carbonic acid.
Zinc
is
and sulphuric acid it is also soluble in nitric
and is slowly acted upon by alkaline solutions.
acid
;
At ordinary temperatures zinc is
when heated to between 100' and
acid,
a brittle metal, but
150' C. (212" and
becomes both ductile and malleable, and
may be rolled or hammered, after which treatment it
302" F.)
it
retains its malleability
when
cold.
When
the heat
is
again
increased to about 205" C. (401° F.) the metal is
in an iron mortar.
brittle, and may be readily pulverised
hardened by rolling and hammering, and recjuires
malleaannealing at a lo'io temperature to restore its
Zinc
is
199
ZINC.
It melts at
bility.
C. (779° ^')
415
volatile at
^^'"^
the
It contracts on solidification,
a bright red heat.
with that
shrinkage being considerable when compared
or
It is a harder metal than gold
of other metals.
silver, and has a density of nearly 7.
of the
Zinc has the property of precipitating most
metals from their solutions.
galvanised iron,
It is extensively used for making
dipping
of iron plate coated with zinc by
which consists
Iron thus
the iron into a bath of the molten metal.
of air
treated is better able to withstand the action
or
moisture, the zinc preventing its corrosion
and
rusting.
Use
for
Dental Purposes.— The
zinc in the dental laboratory
is
chief use of
in the formation of dies
is
used in swaging metal plates, for which purpose it
the
almost the only metal employed, as it possesses
extent
properties required for this purpose to a greater
Several of the compounds of
preparation of
zinc are also largely employed for the
than any other metal.
"
cement"
fillings.
Zinc Dies.— The use of /inc for dies has been objected
to
by some on account of the shrinkage which takes
place
when
sally
employed
plates,
as
it solidifies,
it
for the
but this metal
is
almost univer-
formation of dies for swaging
possesses
the
properties
of
hardness,
toughness, and malleability, and melts at a comparaExperiments by the late
tively low temperature.
Professor iVusten * have demonstrated that an averagesized
contracts
*
die
zinc
Tw^th
••Mutiillic
l)i(;s.''
measuring
of
two
inches
transversely
an inch from the extremities of
Aiiirriniii
Jiiiirii. i[f
DriiUil S'-ir^icr, vol. vi.
200
DENTAL METALLURGY.
the alveolai- ridge, being
equivalent in
thickness to
about three or four ordinary leaves of a journal.
In a moderately deep arch (about half aa inch in
depth) the shrinkage between the level of the ridge
and the
floor of the palate
would be nearly yoVoth of an
inch, or rather thicker than one leaf of a journal.
question of shrinkage
arches
most serions in the deepest
is
in the case of shallow arches
;
rtTTTTrth
or
When
^oljTrtli
is
it
only about
of an inch.
melting zinc for the preparation of dies
necessary to remember that zinc castings
high temperature are more or
when
Hue, but
The
less brittle
made
and
it is
at a
crystal-
cast at a temperature only a little above
the melting-point of zinc they are comparatively malleable
care should always be taken therefore to avoid
;
Zinc dies which are cast at a high
excessive heating.
temperature
In some
will re(|uire
annealing by gentle heating.
the die will
cases
be
sufliciently
annealed
during the process of taking the counter-die.
Zinc
may
is
also occasionally
che zinc die, provided
taken.
render
the metal
If
it
fluid
without fear of
the
thin film
Adhesion may
with a
little
cold the die
if
used for counter-dies, which
be obtained by pouring the metal directly upon
the
only heated
is
may
it
be cast
adhesion,
this
to
sufficiently
upon the zinc
die
being prevented by
on the surface of the die.
also be avoided by rubbing the surface
of
oxide
blacklead powder before casting.
and
Purification of Zinc.
— The
zinc of
pure for ordinarv- purposes
dental laboratory
When
conntei--die will separate as readily as
lead had been used.
sufliciently
necessary precautions are
it
;
commerce
but
in
is
the
becomes deteriorated by constant
20I
ZINC.
melting, owing to
tlie
fact tliat a small <]aantity of zinc
by the metal. It also becomes contaminated with iron from the ladle. If a small (juantity
of charcoal is placed on the surface of the metal when
oxide
dissolved
is
oxidation
meltino-,
The
minimised.
i«
may
zinc
be
by placing a few lumps of ammonium chloride
(sal-ammoniac) on the surface of the molten metal, then
When
stirring well with a stick of wood and pouring.
melting zinc in an iron ladle care should be taken to
purified
avoid excessive heating, as zinc forms an alloy with iron
under favourable conditions. A malleable iron ladle
more readily attacked,
some cases penetrating the ladle and escap-
should be used, as cast iron
the zinc in
is
coating the inside of the ladle with whiting
or a wash of clay and heating carefully, accidents of
When zinc has become
this kind may be avoided.
ing.
By
accidentally contaminated with lead
from the
latter
slowly.
On
it
may be
by melting and allowing
account of
the bottom and
its
of zinc are those
to solidify
density the lead will
fall to
may then be removed by means
chisel.
Compounds
it
separated
of Zinc.
—The
following compounds
most frequently employed by
Zinc Oxide (ZnO).
Known
known compound
of a
dentists.
also as Zinc White.
This
oxygen and
and
of
is
the only
is
the chief ingredient in the plastic filling-materials
known
zitic,
and oxy-phosphates.
It is prepared on a large scale by the combustion of
metallic zinc in air, the fumes produced being led into
as oxy-chlorides
a series of
condensing chambers where the oxide
is
deposited.
For pharmaceutical and dental jiurposes
it
is
usually prepared by adding sodium carbonate to a
solution of
ziuc sulphate.
The white
precipitate of
DENTAL METALLURGY.
202
is washed and dried, and
then heated to expel the carbonic acid and water, leaving
zinc carbouate thus obtaiuecl
the zinc oxide as a powder.
Zinc oxide
when
a pure white, soft substance, which,
is
heated, becomes yellow, but
becomes white.
carbonic acid
is
It is insoluble in
by
and strong solutions
again
water except when
present, in which case
It is unaffected
it
dissolved.
is
dilute alkaline solutions, but acids
The
the oxy-hydrogen flame, and
of alkalies dissolve
oxide does not fuse even in
it
on cooling
readily.
it
possesses the advantage of not being blackened by
exposure to sulphuretted hydrogen.
Zinc
Chloride (ZnCl,,).
—This
compound
usually
is
prepared by dissolving metallic zinc in hydrochloric
acid and boiling down the resultant liquid, until on
cooling
it
becomes
by the
It is also prepared
solid.
direct combination of zinc with chlorine gas.
Zinc chloride
is
a soft, greyish -white, easily fusible
substance, which resembles
It is extremely deli(|uescent
is
Dry
as a caustic,
employed
and a
distilled.
on exposure to moist
very soluble in water and in
powerfully caustic.
is
wax and may be
alcohol, its
zinc chloride
is
air,
and
solution being
used in surgery
dilute solution of the salt in water
as an antiseptic.
(ZnSOJ or White Vitriol.— Zmc sulformed when zinc is dissolved in sulphuric
Zinc Sulphate
phate
is
on a large scale by roasting the
natural sulphide (blende), whereby the oxygen of the
air partially converts it into sulphate, which is then
acid.
It is obtained
dissolved out with water and allowed to crystallise.
of
It is extremely soluble in water, with evolution
heat, but only slightly acted
temperature of about
300'^
C.
upon by
alcohol.
(572° F.)
it
At
a
loses water
203
ZINC.
converted iuto the anhydrous comj)oiind, a white
is converted
friable substance, which at a white heat
Zinc sulphate, in common with all
into the oxide.
taste and is
the soluble zinc salts, has an astringent
and
is
poisonous.
These three compounds of
zuic, viz., the oxide, chloride
and sulphate, when mixed together or
with other substances, form the basis
class
known
materials
of
are
Three varieties
fillings.
as
in
combination
of the valuable
osteoplastic
commonly
cement
or
under
used,
the names of oxy-chlorides, oxy-phosphates, and oxysulphates.
The cement used as a filling for teeth should be
capable of being worked easily and should not set too
It should also possess the following qualities.
rapidly.
It should
:
and harden under water (2) be
(i) be dense
;
unaffected by contact with saliva
(3) be devoid of irritating chemical action
(4) be free from shrinkage or
;
;
expansion; and (5) adhere firmly to the walls of the
cavity.
The materials used for the preparation of the cements
consist of a powder and a liquid, which are different for
the several varieties made.
Oxy-Chloride.
—The
paration of this cement
is
powder used for the prefinely powdered zinc oxide,
which has been heated almost to whiteness for about
two hours, whereby it loses neaily half its original
bulk.
to
The
liquid
which borax
is
is
a dilute solution of zinc chloride,
sometimes added.
A
paste
made by
moistening zinc oxide with zinc chloride rapidly sets to
Each special preparation of oxy-chloride
a hard mass.
naturally differs a little in detail of manufacture, but
the powder in
all
consists of zinc oxide with a small
DENTAL METALLURGY.
204
admixture of other ingredients,
glass or silica,
sucli as finely
for tlie purpose of
mechanically con-
ferring greater hardness on the mass
mixture in
common use*
gether in a mortar
(silica),
and 30 parts
mixed these
This
is
i
is
powder by grinding.
A
to-
part of fine silex
When
thoroughly
and heated
called the " frit,"
mass
set.
prepared by grinding
of zinc oxide.
cool the semi-coherent
three times
when
are placed in a small crucible
to bright redness.
fine
is
parts of borax,
2
powdered
and when
again reduced to very
It
is
mixed with
The
then
its weight of calcined zinc oxide.
liquid usually
employed with
deliquesced zinc
chloride
following proportions
—
I
this
powder
diluted with
consists
of
water in the
ounce of zinc chloride dissolved
drachms of water.
Oxy-chloride cements as a class are readily acted
upon by the alkaline and acid fluids of the mouth,
They are, therefore,
especially at the cervical edges.
They usually set
valueless as permanent fillings.
in 5 or 6
and a notable shrinkage generally takes place.
Oxy-Phosphate. In this cement the powder is
zinc oxide and the liquid is one of the varieties of
The oxy-phosphate powders are
phosphoiic acid.
slowly,
—
similar mixtures to the oxy-chlorides, and, like them,
only in minor details of
manufacture. The liquid used is frequently prepared
by dissolving glacial phosphoric acid (ortho-phosphoric
the various preparations
acid) in pure water
until
differ
and then evaporating the
solution
attains the syrupy consistency of glycerine,
which a crystalline mass is deposited on standing.
it
from
Phosphoric acid
is
extremely soluble in water
a pleasant, purely acid taste, and
* Essig,
••
Deiitiil
is
;
it
has
perfectly free froiu
Metallurgy," 1893, p 241.
205
ZINC.
When
smell.
phosphoric
oxide, the latter
is
acid
is
mixed with
zinc
dissolved and zinc phosphate formed.
Crystals of pyrophosphoric acid are sometimes employed
They
instead of the liquid, and are preferred by some.
are carefully melted in a platinum or porcelain spoon
the
over a spirit-lamp, ebullition being avoided, until
liquid attains the consistency of glycerine.
Oxy-phosphates are soluble in the alkaline secretions
cements
of the mouth, the period of duration of these
They are
varj-ing from two to about seven years.
chlorides.
antiseptic, though less strongly so than the
a class the oxy-phosphates are considered preferable
As
to the oxy-chlorides, as they are
more permanent and
less irritating.
Oxy- Sulphate.— The powder
sists of
phate
;
for this
cement con-
a mixture of zinc oxide and calcined zinc sulthe liquid consists of a solution of gum arabic.
The following proportions are frequently employed:*
part of calcined zinc sulphate with
2 or 3 parts of zinc oxide ; for the liquid, 15 grains of
gum arabic in oz. of pure water, to which when completely dissolved i grain of sulphite of lime is added.
for the
powder,
i
-|-
The
solution
In
is
then
purest form
its
substance, which
is
through absorbent cotton.
filtered
gum
is
a yellowish-white
soluble in cold
water, forming a
arabic
viscid, adhesive, tasteless solution.
These cements usually lack hardness, but they are
The oxy-sulphates are
acted upon by the alkaline and
non-irritating and set rapidly.
all
more or
less readily
acid fluids of the mouth.
,
Alloys of
alloys, to
Zinc— Zinc
forms a number of
i^seful
which when present in certain proi)Oitions
*
Fliigg, " I'lastiu FilliiifrH,"' p. 156.
it
2o6
DENTAL METALLTT-RGY.
gives hardness without impairing the malleability of
the alloy
while in larger proportious
;
brittleness.
Zinc
lowers
the
it
often induces
melting-point of
the
metals with which
it is alloj^ed, and for this reason is
added to gold solder
it also renders the metals with
which it unites less liable to be affected by exposure to
;
the atmosphere.
Zinc and Copper.
— These metals nnite
in all pro-
portions to form the numerous varieties of brass, which
are the most important alloys of zinc.
p. 222.)
— Alloys
Zinc and Tin.
readily prepared
by
of these
(See Copper,
two metals can be
forming combinations that
fusion,
are generally softer than zinc, harder and less malleable than tin, and
The
alloys
more or
contract
less crystalline in structure.
than
less
zinc;
the amount of
shrinkage varies, however, according to the proportions
of the constituent metals, those containing excess of
zinc contracting most.
ployed in the arts for
patterns
;
emcasting ornamental objects and
Zinc-tin alloys are chiefly
they have also been used as a substitute
zinc in preparing dies for swaging plates.
in re-melting is greatest
cess of ziac.
all
alloys
(See Alloys for Dies,
Zinc and Lead.
in
in
— Zinc
may
for
The waste
which contain ex-
p. 47.)
be melted with lead
proportions, but on cooling the mass does not
remain homogeneous
;
the lead on account of
its
greater
density sinks to the bottom, leaving a layer of zinc on
top.
zinc,
The
lead will, however, retain a small quantity of
which has the
effect of
impairing its malleability.
hardening the lead without
(See Lead,
p. 212.)
Zinc and Bismuth. — These two metals
alloy
when
molten, but on solidification two layers are foruied, the
207
zrN(
zinc with about 2 per cent, of bisnuifch rising to the
top, while the bismuth on account of its density settles
at the bottom,
and contains about 8 to 14 per
cent, of
/inc.
Zinc and Mercury.— (See Zinc Amalgam,
p. 138.)
Zinc unites readily with gold, silver, platinum and
the alloys produced are described in the
palladium
;
chapters dealing with these metals.
Zinc enters into
the
composition
of
the English
bronze coinage to the extent of about one per cent,
and is also present in varying proportions in the
different qualities of
German
silver.
(See
p. 252.)
CHAPTER
XIII.
LEAD.
SYMBOL, Pb
ATOMIC WEIGHT,
(Plumlnini).
Occurrence.
— Lead
quantities in
tlie
lias
been found in nature in small
The
metallic state.
the metal, however,
is
207.
chief source of
combination with sulphur as
in
sulphide,
Galena PbS, this being the ore from which
the metal
is chiefly
bination with
obtained.
oxygen,
It is also
found in com-
carbonic acid and
phosphoric
acid.
Preparation.
galena
;
the ore
with free access of
is
—Lead
is
is
very readily obtained from
roasted in a reverberatory furnace
air,
whereby a portion
of the sulphide
oxidised to sulphate, whilst in another portion of the
sulphide the whole of the sulphur is burnt off as sulphur
dioxide,
and lead oxide formed.
The
and the
temperature
air excluded,
lead react
giving
off
of
the
furnace
when the
is
then
raised
sulphate and oxide of
upon the undecomposed sulphide of lead,
sulphur dioxide and leaving metallic lead
behind.
Galena almost invariably contains a small quantity of
silver, which will remain alloyed with the lead after
smelting, and is subsequently extracted by the process
of cupellation described
on
p.
167.
LEAD.
Auofcher
sists iu
method
209
of extracting lead froui galeua con-
heating the ore in contact with metallic iron
;
the iron combines with the sulphnr, and the lead thus
liberated isinks to the bottom of the furnace, while the
sulphide of iron or rcrjulm collects above
Properties.
— Lead
is
it.
a bluish-grey metal which,
may
be cut with a knife or scratched by the finger nail,
being the softest metal in common use.
freshly cut
A
surface possesses a bright lustre, which, however, be-
comes rapidly tarnished on exposure to the air.
Lead is both malleable and ductile at the ordinary
temperature, possessing the former property to a considerable degree.
It can easily be rolled out to thin
which form
sheets or
foil,
used as a
filling for teeth, as it also
in
perty of welding
when two
it
has occasionally been
possesses the pro-
clean surfaces are pressed
together.
Its tenacity is inferior to that of all the other ductile
cannot be drawn into fine wire. It
is tlexible and non-elastic, and may be bent backwards
and forwards repeatedly without fracture. On account
metals, so that
it
and the readiness with which
of its flexibility
made
to
it
may be
flow," thin sheet lead is frequently em])loyed
for obtaining patterns, &c. in the dental laboratory.
It is a very
tricity.
bad conductor of both heat and
Lead fuses
at 325" 0. (617" F.),
sensibly volatile at a red heat
on
solidiKcation.
When
;
it
elec-
and becomes
also contracts sliffhtlv
heated to a temperature just
below ita melting-point it becomes brittle, a property
which accounts for the fact that lead counter dies are
liable to be broken if they are accidentally dropped
immediately after casting.
If lead is kept in a state
of fusion in contact with the air, rapid oxidation
takes
o
DENTAL METALLURGY.
2IO
melted repeatedly it beof a
comes hard and brittle owing to the formation
metal.
small quantity of oxide which dissolves in the
soft and
This oxide may be removed and the lead made
place on the surface.
When
powder
malleable again by placing a layer of charcoal
stirring it
on the surface of the molten metal or by
Commercial lead is frewith a stick of green wood.
and malleable
(juently almost pure and extremely soft
quantities of other metals are sometimes
yet small
whiter and less
present, the impure lead being usually
Metallic lead, on account of its
soft than pure lead.
and the
softness and pliability, its low melting-point,
of water and many
fact that it withstands the action
common metals, is
acid liquors better than most of the
great variety of
largely employed in the arts for a
purposes in the form of sheets and pipes.
Use
for
Dental Purposes.— Lead
ployed for the
form
with
is
chietly
production of counter-dies and
em-
in the
When
alloyed
of thin sheets for cutting patterns.
important purother metals it is used for several
poses in the dental laboratory.
of the
Alloys.— Lead may be alloyed with most
The general
common metals by melting them together.
to lead is to harden
of the addition of other metals
effect
it
.
and impair
its malleability.
Lead and Antimony.-The
alloys
of
lead
and
than either metal
antimony are harder and more fusible
than lead, but if antialone and also more oxidisible
proportion the alloys
mony is present beyond a certain
which
and brittle. Alloys
are very crystalline, hard
imthe
exceed 15 percent, have
the antimony does not
on cooling, a property
portant property of expanding
castings.
makes them well adapted for
m
which
LEAD.
Mdid.
Ti/pc
—
I
I
one of the chief alloys
Tliis constitutes
and antimony.
of lead
2
For large types
it
consists of
lead with about one-fourth to one-eighth of its weight
of antimony, while for small types tin is invariably
added, and for
small quantities of
special purposes
other metals such as copper and iron.
harder than lead, and brittle
dies,
and
dies.
also,
though much
;
it is
Type metal
less frequently, for
(See also Alloys for Dies,
—
is
sometimes used for
counter-
p. 45.)
Tin, These metals when fused together
readily unite in any proportions, the resulting alloys
having a somewhat darker colour and less brilliancy
than tin. They are generally harder than tin and contract less on cooling than either of the constituent
uietals_, but they are not so fluid when melted, and
Lead and
castings
alloy of
made with
4 or
5
these alloys lack sharpness.
parts of lead
and
i
The
part of tin burns like
charcoal at a red heat, producing a " cauliflower "-like
niass.
Lead-tin
alloys with the
addition
of a small
proportion of other metals are used for dies instead of
'/sine.
(See Alloys for Dies,
p. 49.)
4 parts of tiu with i part of
lead, but small (juantities of other metals are somePcivter is an alloy of
times added.
Soft Solders.
—These
are alloys of
lead aud tin
in
various proportions, the fusibility of which generally
increases
with the
amount
of
tin.
Goiiiiiloh.
Su/dcr
two metals Fine Solder
is composed of i
part of lead and 2 of tiu; while
I'li'inherH Solder is made by melting together 2 parts
of lead and I of tin.
Alloys of these metals are remarkable for the facility with which they ignite and
burn when raised to a red heat.
consists of e(iual parts of the
;
2
I
DENTAL METALLURGY.
2
Lead and
proportions
Zinc.
—
l^hese
two metals
when molten, but
their densities on solidification.
alloy in all
separate according to
(See
p.
206.)
Lead which has become contaminated with zinc may
be " softened " by melting it and exposing the surface
of
the molten
metal
to
oxidation
with
occasional
In this way the impurities are oxidised and
form a scum on the surface which may be readily
removed.
Lead and Mercury. (8ee Lead Amalgam, p.
stirring.
135-)
CHAPTEE
XIV.
TIN.
SYMBOL,
ATOMIC WEIGHT,
Sn (Stnnnnm).
Occurrence.
—All
commercial tin
tin-fitonc or cassiterite,
oxide of
tin,
is
iiS.
obtained from
SnO,, this mineral
forming practically the only ore of tin. Tin ore is not
very widely distributed, only occurring in large quantities in comparatively few localities.
Preparation.— To
crushed
with
is
which
oxide
is
being
after
ore,
matters,
the
metal
washed
from
obtain
roasted to expel any sulphur
may
it
The
be associated.
then mixed with
the
finely
all
earthy
or
arsenic
purified tin
powdered anthracite and
smelted in a suitable furnace
;
the
carbon
of
the
anthracite combines with the oxygen to form carbon
monoxide and thus
obtained
with
is
billets
separation of
liberates
purified
of
green
a
scum
by
the
stirriug
wood,
tin.
the
The
tin
so
molten metal
which results
or dross carrying with
in
it
the
the
impurities.
The
known
pecnliar
structure
of
the
commercial
metal
produced by heating ingots of
the metal to a temperature at which they become
brittle and breaking tliem
by dropping Croni
a
height.
as urain-tin
is
DENTAL METALLURGY.
214
Properties.
—Tin
is
one of the whitest metals, but
possesses a peculiar faint yellow tinge
in
and
]ustre
polish.
its
surface
undergoes
It
;
it
rivals silver
capable of taking a fine
is
change in dry or moist
little
at ordinary temperatures, but
it
air
tarnishes slowly in the
presence of sulphuretted hydrogen owing to the formaIf heated in air it rapidly
tion of a film of sulphide.
which forms the
well-known polishing putty powder, but the i^ure metal,
if melted at a low temperature and poured out, retains
Tin has
its resplendent lustre for a considerable time.
oxidises
to
stannic
oxide
(SnO.,),
becomes evident when
the metal is warmed by being held in the hand for
It is a little harder than lead but softer
a short time.
a characteristic odour which
than gold.
Water has no
action on the metal, but
soluble in hot hydrochloric acid
acid
sulphuric
acts
violently
the action of the dilute acid
nitric
acid acts violently
is
upon
it
is
readily
boiling concentrated
;
on
the
metal,
less energetic.
it,
while
Dilute
liberating nitrous
fumes, and converting the tin into metastannic acid,
which settles at the bottom of the vessel as a white
powder.
Tin
bar of tin
known
is
when
also soluble in alkaline solutions.
as the cry of tin, caused
crystalline particles.
Tin
of the metals, only lead,
inferior to
it
A
bent emits a peculiar crackling sound,
is
by the
friction of the
one of the least tenacious
antimony and bismuth being
in this respect
;
it is,
however, very malle-
able and can be easily rolled out to thin
foil of less
than yyVsyth of an inch in thickness. Tin may be
welded by the application of pressure, when two clean
It |iossessPS little
surfaces are brought into contact.
At a
be
drawn
into wire.
ductility, but with care may
,
TIN.
215
temperature of 392" F. (200° C.) it becomes so brittle
that it may be readily powdered.
It melts at a temperature of 232" C. (449 F.) and
'
contracts slightly on solidification.
Tin
conductor of heat and of electricity
;
it
an inferior
is
has a density
of 7.3.
Tin
is
by treating the
sulphuric and nitric
easily crystallised superficially
surface with a mixture of dilute
the ornamental appearance seen on tin boxes, &c.
known as " moiree metallique," is obtained in this way.
acids
;
Tin
is
also
obtained in a crystallised
deposited from
by
solutions
its
electrical
when
state
agency, the
prepared by this means being in the form of
metal
brilliant elongated needles.
Uses in Dental Laboratory. — Tin was
used as a base for
artificial teeth,
formerly
and more recently
it
has been introduced as one of the constituents in the
alloys used for the " cheoplastic " process.
It is some-
times used for counter-dies and occasionally for dies.
"
When
.
employed for dies
in connection with a lead
counter the latter should not be obtained directly from
the die,
as
the
comparatively high temperature of
molten lead would produce, when poured upon the tin,
partial fusion of the latter and consequent adhesion of
the
As
two pieces."*
its
affinity
for sulphur
is
so
swaging operations, for
supplied in thick and thin sheets
tin is largely used in
slight,
which purpose
it
is
as " Soft Metal."
Tin as before stated enters into the composition of
.alloys used for dental amalgams, and for dies.
Clean surfaces of pure tin
by
compression,
*
and
on
Eichardson, " Mechiinicnl
may be made
this
account
to cohere
tin
in
Dt'iitistry," 1894. p. 125.
the
DENTAL METALLURGY.
form of thin
foil
frequently used as a
is
filling for
" Tin-foil
teeth.
is very little employed as a filling
by itself, being generally used in combination with gold.
The advantages claimed for it are that (i) it is easy
to work
(2) it has a preservative action ujjon the
—
;
For the latter reason it is generally
used as a lining to cavities and at cervical margins.
It has one distinct disadvantage in the fact that it
tooth substance.
becomes black." *
Tin-foil. Pure
—
tin-foil
is
made by
casting the
metal into slabs about one inch thick and reducing
these to foils of the desired thinness by passing
repeatedly through a rolling mill.
soapsuds are allowed to flow on the
sticking to the
rolls.
Ordinary
During the
foil
them
rolling
to prevent its
about
tin-foil is
-pfyLy^th
of an inch thick, but for dental purposes foils of vary-
ing degrees of thickness are made and are numbered
in a
manner
(See p, 91.)
similar to that
employed
for gold foils.
—
Tin-plate. The material Ivnown in commerce as
Lin-plate is composed of thin plates of iron coated with
tin by dipping them into a bath of molten tin, the
object of the coating being to prevent the formation of
which takes place when iron plates are exposed
unprotected to the action of air and moisture.
Alloys of Tin. Tin enters into the composition
rust,
—
number
of a large
of useful alloys,
many
of which are
of considerable impoi'tance,
—
—
Tin and Silver. (See p. 175 and also chapter viii.)
Tin and Zinc. These metals alloy readily when
fused together.
(See p. 206 and
Alloys for
P- 47-)
*
Smale and Colyev,
" Diseases of Teeth."'
p. 183.
.Dies,
TIN.
Tin and Copper,
— Tin unites readly with
co]>per,
the most important alloys being the various bronzes, &c.,
described under Copper Alloys, p. 222.
Tin and Mercury.
— Tin
(See Tin. Amalgam,
mercury.
readily combines
with
p. 138.)
Tin and Antimony.— These
metals unite when
antimony being to harden
the tin and generally to impair the malleability and
ductility, making it more or less brittle.
The brittlemelted together, the
effect of
An
ness increases with the proportion of antimony.
alloy of
4 parts of
and
tin
ciently malleable to be
I
part of antimony
hammered and
—This
is suffi-
rolled cold.
an alloy of tin and antimony in very variable proportions, to which small
Britannia Metal.
is
quantities of other metals are also frequently added.
and ductile alloy, and can
and
be
stamped into various shapes.
It
takes a high polish and is largely employed for the
manufacture of impression trays and other articles used
An inferior kind of Britannia metal
by dentists.
"
known as Queen's Metal " consists on an average of 75
It is a hard, very malleable
rolled out
per cent, of
tin, 8.5
cent, of lead,
per cent, of antimony, with 8.5 per
cent, of bismuth.
and 8 per
Meter ilfe/a/.^This
is
composed
of
tin,
antimony,
and lead it is used in the dental laboratory for making
matrix and polishing plates. It possesses certain valu;
it to be worked up in a
steam swager, a thin diaphragm of the alloy being-
able properties that enable
made
to give accurate copies
and adapt
itself
to the
Owing to its fusibility
may be melted over a good Bunsen burner.
Detection of Tin in Alloys.— To detect the
surface of the model with ease.
it
presence of tin in an alloy advantage
is
taken of the fact
DENTAL METALLURGY.
2l8
that the metal
is
converted
into
a
white
insohible
powder (metastannic acid) when acted upon by
nitric
acid.
A small
quantity of the alloy to be tested
is
heated
with dilute nitric acid until the whole of the material
is
acted upon.
white residue of
The
solution is then diluted
tin, if present,
allowed to
and the
settle.
If gold is also present in the alloy, the residue will
be purple in colour, owing to the formation of a small
([uantity of
"purple of Oassius."
CHAPTER
XV.
COPPER.
SYMBOL,
Occurrence.
Cii
(Cuprum).
— Copper
ATOMIC WEIGHT,
63,
found in the metallic state
is
in various parts of the world, notably in the neighbour-
hood of Lake Superior, where
occurs in enormous
it
masses which are frequently several
found
It is also largely
oxygen and carbonic
Preparation.
in
tons
in weight.
combination with sulphur,
acid.
—From
ores containing no
such as the oxides and carbonates, the metal
by smelting the ore with
or
coal
whereby the copper
monoxide formed.
furnace,
Ores containing sulphur are
is
is
sulphur,
obtained
coke in a blast
liberated and carbon
first
subjected to a pro-
cess of concentration in either blast or reverberatory
furnaces to obtain a
known
as "regulus."
compound
of sulphur
This "regulus
whereby a portion of the copper
is
" is
and copper
then roasted,
oxidised to copper
oxide, which, as the temperature rises, reacts
upon the
undecomposed copper sulphide, giving metallic copper
and sulphur dioxide, which last escapes. The copper thus
obtained is impure and is subjected to a refining process.
Properties. Copper possesses a peculiar red colour
and a bright metallic lustre. At ordinary temperatures
—
220
DENTAL METALLURGY.
this metal is uot altered by
when heated
oxidises
it
temperatures ia moist
acid, it
air,
rapidly
;
while
at ordinary
becomes coated with a green layer or
known
rapidly tarnished in the
also
retted hydrogen
owing
copper sulphide.
but
air,
in the presence of carbonic
copper carbonate, commonly
is
exposure to dry
scale of
as " verdigris."
pi'esence
It
of sulphu-
to the formation of a film of
Water and
cold hydrochloric acid
have no action upon copper, and
it
only slowly
is
soluble in strong hydrochloric acid.
Strong and dilute
when heated, but its
nitric acid slightly diluted, in which acid
sulphuric acid acts on the metal
best solvent
is
soluble.
Copper is highly malleable,
and tenacious, and can be hammered or rolled
into thin sheets or drawn into moderately fine wire, but
it
readily
is
ductile
b}^
these operations the metal
is
hardened and requires
frequent annealing or softening during the processes.
When
wrought
it
ranks next to iron in tenacity
;
sur-
passing platinum and silver in this respect.
Copper is
one of the best conductors of heat and of electricity,
being inferior only to silver.
The melting-point of
copper
is
lower than that of gold but a
than that of
silver,
being 1050°
contracts slightly on solidification.
temperature just below
its
C.
little
(1922*^
When
higher
F.)
;
it
heated to a
melting-point copper becomes
may be readily fractured.
" granulated " by pouring the molten metal
very brittle and
Copper
is
into water,
metal
is
and
is
frequently sold in this form.
The
largely used for a great vai'iety of technical
and domestic purjooses.
Effect of Impurities on Copper.
— The
physical
properties of copper are materially impaired by
presence of even small proportions of impurities.
the
The
22
COPPER.
1
most common impurities in commercial cop]ier are iron,
arsenic, silver, and copper oxide, and occasionally
bisnnitli, tin, antimony, snlphnr and lead.
Of these arsenic, sulphur, and antimony are the most
injurious, as they harden the metal and impair its
malleability and tenacity.
Molten copper has the property of dissolving copper
The effect of
oxide, which makes it more or less brittle.
iron is to render copper harder and paler in colour.
Bismuth
lessens the toughness of the metal.
Use in Dental Laboratory.
bined state copper has very
dental laboratory, but
in small quantities
forms a valuable constituent in alloys
other
metals,
conferring
upon
the uncom-
application in the
little
when added
— In
it
of gold and
them many
useful
with most
other
properties.
Alloys.
— Copper
unites
easily
metals, and forms the basis of a large
number
of im-
portant alloys.
Copper and Gold.
metals alloy in
all
— When
proportions,
melted together these
and when the copper
does not exceed lO to 12 per cent, the malleability is
thus 21 carat gold and higher qualities
little altered
—
are practically as malleable as pure gold.
Gold Alloys,
p.
103.)
Copper and
all
Silver.
— These
(See also
metals combine
in
proportions, the resulting alloys ranging in colour
copper through yellowish tints to the
white colour of silver. These metals form a series of
most valuable alloys, having a great variety of applica-
from the red
of
tions in the arts.
(See also Silver Alloys,
Copper and Zinc. — Copper
zinc,
unites
forming alloys generally known as
p. 17 i.)
readily
brass.
with
2
DENTAL METALLURGY.
22
Alloys of these metals, however, are
known
in commerce by a variety of names, such as Tombac, Muntz's
metal, Mosaic gold, Pinchbeck, Mannheim gold. Prince's
metal, &c.
Ordinary brass (commonly called composition) consists of 2 parts of copper with i of zinc.
Certain varieties of brass are exceedingly malleable
and
but these properties vary with the composition and the temperature.
Some varieties are only
ductile,
malleable
when
temperature.
rolled hot, others can be rolled at
Brass
is
fore better adapted to
any
harder than copper, and there-
wear and
resist
melted these alloys alter somewhat in
tear.
When
composition
owing to the readiness with which zinc is oxidised.
The easy fusibility of brass, and its fluidity when melted,
render
it
valuable for casting purposes, as
very fine impressions from
of
receiving
On
this account it
was
dental laboratory.
Cast brass
tin,
the mould.
is
generally more or less
being very pronounced in the
containing excess of zinc.
Copper and Tin.
with
capable
at one time used for dies in the
crystalline, this property
brittle varieties
it is
— Copper
in combination
is
extensively alloyed
with which
it
forms many
valuable bodies generally termed " Bronzes."
The
effect of tin
wise modify
on copper
its properties.
is
to
The
harden
it
or other-
alloys are capable of
taking a high polish, and present a beautiful metallic
They melt at a moderate temperature, and
when melted, thus forming excellent alloys
lustre.
fluid
casting.
Bell-metal
variable projiortions.
and
I
Metal.
is
is
for
an alloy of coj^per and tin in
With about 2 parts of copper
of tin an alloy is
This
are
produced known as SpcciUam
a very hard, brittle, steel-like alloy,
capable of receiving a very high and uniform polish.
OOPPEll.
Gun
il/r/^/^.— This
is
22.^
a variety of brouze formerly
used to a large extent for ordnance, hence its name.
It consists of copper, alloyed with from 8 to lo per
cent, of tin
;
the term "
exclusively confined to
gun metal," however, is not now
alloys of copper and tin, as small
proportions of other metals are very frequently added.
Vulcanising flasks for dental purposes are made largely
of
gun
metal,
as
it
is
a hard alloy and gives good
castings.
Ck)pper
and Aluminium.— These
when melted
metals unite
together, forming alloys which are
more
or less golden-yellow in colour.
With lo per cent, of aluminium it forms the alloy
known as aluminium-bronze. With excess of aluminium
the alloys are hard, brittle and crystalline.
Copper and Nickel.
these metals unite in
all
—When
melted
proportions.
together
The resulting
with the addition of zinc and sometimes of other
metals, are largely used in the arts under the name pf
alloys,
German
silver, &c.
Copper and Mercury. — In
a fine state of division
copper readily amalgamates with mercury, the resulting
amalgam becoming hard and cr\-stalUne after the lapse
of a
few hours.
as a material for
p.
1
34-)
Copper amalgams have long been used
(See Copper Amalgam,
filling teeth.
CHAPTEE
XVI.
CADMIUM.
SYMBOL.
Cd.
Occurrence.—This
metallic
state
in
ATOMIC WEIGHT,
metal
nature.
is
It
112.
never found
is
usually
combination with sulphur, associated
the
in
found
with
tlie
in
ores
of zinc, in small quantities not exceeding two or three
per cent.
Preparation.— Being more
than
zinc,
cadmium
distils
fusible
over with the
and
volatile
first
portions
of zinc during the smelting of the ores of that metal.
The product thus obtained consists of a mixture of
cadmium and zinc, contaminated with oxides of these
mixed with charcoal and ag-ain distilled,
when the metal which passes over first contains a larger
proportion of cadmium.
To obtain pure cadmium the
mixture of cadmium and zinc from the last distillation
metals.
is
It
dissolved
is
in
hydrochloric acid
and metallic zinc
placed in the solution, which precipitates the cadmium
in a spongy crystalline form.
When melted, this is
cast into small cylindrical rods about half an inch thick,
which form it is usually sold.
Properties. Cadmium resembles tin in colour and
appearance and takes a high polish. It is slowly oxidised on the surface by exposure to the atmosphere, and
in
—
CADMIUM.
when heated in
cadmium oxide.
hydrogen
it
air it
burns with a brown flame to
presence of sulphuretted
In the
gradually becomes coated with a yellow
cadmium
film of
225
sulphide.
The metal
is
not acted
upon by water, but is soluble in hydrochloric acid
and in sulphuric acid. Its best solvent is nitric acid,
in which it is readily dissolved.
Acetic acid (vinegar)
also acts
on the metal, and
tions of the alkalies.
it is
slowly soluble in solu-
These tendencies to corrosion make
unfit for use as a filling material, as it
would not
withstand the action of the fluids of the mouth.
Cad mium is malleable and ductile and may be rolled
into thin sheet or foil or drawn into wire at the ordinary
it
temperature, but at 80° C. (176° F.) it is very brittle
and may be readily powdered in a mortar. It melts
at the low temperature of 320° C. (608° F.) and may
be
distilled
Cadmium
knife.
is
harder than
tin,
but
may
C.
heavier,
its
specific
(1418" F.).
be cut with a
It also possesses greater tenacity
somewhat
is
at a temperature of 770°
than
tin
gravity being
and
8.7.
Cadmium
has no direct use in the arts, but is of value
as a constituent of certain alloys, especially those with
bismuth and lead,
Use for Dental
tin,
cadmium
Purposes.—The
only use for
in the dental laboratory is in combination with
other metals as "fusible metals" and other alloys.
It
has also been employed as a constituent in alloys for
dental amalgams, but its employment for this purpose
now been abandoned. The advantages and diradvantages of cadmium in amalgams and alloys may be
has
classified as follows
:
AiJVANTA(fKH
J.\
Amal(;am,s.— Cadmium was at one
time employed as a constituent of alloys for dental
I'
DENTAL METALLURaV.
226
amalgams, as its presence gives whiteness to the fillings
and tends to produce a good ping. On account of its
affinity for mercury it also facilitates amalgamation and
dauses quickness in setting.
In Alloys.
— Cadmium,
like bismuth, has the valuable
property of lowering the melting-point of
some of which are
many
alloys,
readily fusible in boiliog water.
It
therefore a useful constituent in the so-called "fusible
metals " described on p. 50 and is occasionally used for
is
dental purposes.
—
Although cadmium
amalgams pi'oduced from
alloys containing it, it has been generally condemned
It is readily acted upon
as a constituent of these alloys.
by the joint action of sulphuretted hydrogen and the
alkaline and acid fluids of the mouth with the formation of an orange-yellow film of cadmium sulphide and
the production of soluble salts which stain the tooth
Disadvanta(;es
in
Amal(jams.
confers useful properties on
substance.
—
In Alloys. When present in alloys in
cadmium tends to make them more or
many of
its
large quantities
less brittle,
but
combinations are capable of being hammered
and rolled. Owing to the affinity of cadmium for
oxygen when molten, a considerable loss is liable to
take place
when
excessive heating
taken
to prevent
alloys
is
containing
it
are melted,
if
not avoided and every precaution
oxidation.
On
this
account
it
is
extremelj^ difficult to obtain an alloy of definite composition.
XML
CHAPTER
BISMUTH.
SYMBOL,
Occurrence,
metallic
state
Bi.
ATOMIC WEIGHT,
—Bismuth
and
occm-s
iu
207.5.
nature
in
the
combination with oxygen,
sulphur and other elements, but the bismuth of commerce is chiefly obtained from the native metal.
also in
Preparation.— To
extract
the
metal
from the
taken of its
matters accompanying
it,
advantage is
low melting-point, namely, 268° C. (514" R).
The
crushed ore is placed in a series of iron tubes or retorts
set in an inclined position in a brickwork chamber
provided with a fire-grate, by means of which the retorts are heated externally.
The upper end of each
retort,
through which the ore
charged,
is closed by
an iron door; the lower end is also closed witii an iron
plate provided with a small aperture.
On the appliis
cation
of heat the bismuth melts
and the liquid
metal soon begins to flow through the small apertures
in the lower ends of the tubes and falls into iron
bowls, in which
ladles
a
collects
and cast into ingots.
metal has
and
it
entirely
fresh
the retorts.
and
is
dipped out
As soon
ceased the
with
as the flow of
raked out
once introduced into
The metal thus obtained is refined by
charge of
ore at
residue
is
DENTAL METALLURGY.
228
various methods to obtain bismuth of good commercial
quality.
Properties.
^
— Bismuth
greyish-white
a
is
metal,
having a decided reddish tinge and a bright metallic
It is not sensibly altered by exposure to the
lustre.
atmosphere at the ordinary temperature, even in the
presence of sulphuretted hydrogen, but when heated in
air
bismuth
is
readily oxidised
and
at a high temperature
burns with a bluish flame and gives
known
yellow colour,
without
little
it
its
effect
off
fumes of a
Water
as Jl.oircrs of hisimtth.
Sulphuric acid
when hot and concentrated
;
onl}^ attacks
while nitric acid forms
Alka-
best solvent, attacking the metal vigorously.
is brittle
is
on bismuth and hydrochloric acid has but
action on the metal.
line solutions
light
have no action on bismuth.
and can be
easily pulverised
;
This metal
when broken
it
Bismuth fuses
presents a highly crystalline surface.
at a comparatively low temperature, 268° C. (514° F.),
and at a high temperature may be volatilised or distilled.
It expands very considerably on solidification, the solid
more space than the liquid
metal occupying about
metal, so that bismuth is denser in the liquid than in
the solid state; the density of solid bismuth being 9.8.
When a large quantity of bismuth is melted, allowed to
cool slowly until the surface begins to solidify, the crust
broken and the
still
liquid metal
poured
out, fine crystals
are obtained.
Bismuth
is
the poorest conductor of heat and
amongst the common metals.
The brittleness of bismuth renders it unfit
of
electricity
for use
itself,
but in combination with other metals
alloys
which are frequently employed in the
it
arts.
by
forms
The
BISMtlTH.
salts of
229
bismuth are somewhat extensively used
iii
mecliciue.
Use
Dental Purposes.
for
bismuth in the dental laboratory
certain alloys,
more
— The
is
only use for
as a constituent of
especially those
known
as fusible
metitls.
Alloys of Bismuth.
—The
alloyed with other metals
which are readily
fusible,
bismuth when
usually to form bodies
is
effect of
hard and expand on
solidifica-
tion after fusion.
Bismuth and Antimony. — These
metals
when
united yield alloys which are hard and brittle and
expand considerably on
Bismuth and Tin.
cooling.
— These metals readily combine
in all proportions
when
fused together.
A
very small
proportion of bismuth imparts to tin more hardness,
and fusibility. The alloys of bismuth and tin
are more fusible than either of the metals taken
lustre
separately.
Bismuth and Lead. — These metals unite in various
proportions by melting
them
together.
If the propor-
tion of bismuth does not exceed that of lead the alloys
and more tenacious than lead.
These properties, however, are diminished with an inare ductile, malleable
crease of bismuth.
Fusible Metal.— Bismuth
and lead by
fusion,
forming a
unites readily with tin
series of alloys
as fudhla imtah, a full description of
which
known
will
be
found on page 50.
An
alloy of etpial parts of
bismuth and
with 2 parts of
tin, is
account of
low melting-point.
its
lead, alloyed
used as a solder by pewterers on,
Bismutli
is
also
an
DENTAL METALLURGY.
occasional coustitueut of Britannia metal and Queen's
metal.
—
Bismuth and Mercury. Bismuth readily amalgamates with mercury at the ordinary temperature, the
amalgam
without losing
Mercury
amount of bismuth
(See Amalgams, p. 133.)
retaining a considerable
is
its fluidity.
frequently adulterated with bismuth, but
the presence of this metal
be detected by shaking
air, when, if bismuth be present, a
powder separates out.
(See Purifica-
the mercury with
crystalline black
may
tion of Mercury, p. 126.)
CHAPTER
XVIII.
ANTIMONY.
SYMBOL,
Occurrence.
ATOMIC WEIGHT,
Sb (Stibium).
— Antimony
120.
found in the metallic
is
state in nature in various parts of the world, notably in
Borneo.
siibnitc
It also occurs in
combination with sulphur as
and with oxygen, the former being the chief
source of the metal.
Preparation.
—To obtain the metal from the native
sulphide the purified ore
is
broken up and heated in
a large crucible along with scrap iron.
As
the charge melts the antimony
is
liberated and
bottom of the crucible, while the sulphur
combines with the iron, forming iron sulphide, which
remains on the surface of the molten antimony. The
settles at the
antimony
is
cast into suitable
moulds and subsequently
refined.
Properties.
bluish-white
surface
when
— Antimony
metal,
fractured,
readily powdered.
is
possessing
It
and so
is
a
a
comparatively hard
highly
crystalline
brittle that it
can be
not sensibly altered by ex-
posure to the atmosphere at ordinary temperatures,
and
is
only slightly tarnished by sulphuretted hydrogen,
but when heated
in air it burns with a bluish-white
flame, producing thick
white
fumes
of
antimonious
DENTAL METALLURGY.
Water and
oxide.
dilute sulphuric acid
action on the metal,
trated
sulphuric
sulpbate.
acid
as
but when heated with concen-
acid
it
converted into antimony
is
It is easily dissolved
well
by cold aqua
as
are without
by hot
regia.
hydrochloric
It
is
rapidly
oxidised without solution upon treatment with nitric
white oxide formed collecting at the bottom
acid, the
of the vessel.
Alkaline solutions have no action on the
metal.
It melts at a
temperature a
little
above that required
to melt zinc, its melting-point being 632'' C. (l 170° F.),
and
is
volatilises
the air at a bright red heat.
in
the next lightest metal to aluminium,
being
its
It
density
6.8.
Uses
for
Dental Purposes.
—The
antimony in the dental laboratory
of aboys for dies and counter-dies.
Alloys.
—The
effect of
metals with which
it is
is
antimony
chief use of
as a constituent
is
harden the
to
alloyed and generally to impair
the malleability and ductility of the malleable metals,
in
some cases rendering them
brittle.
Antimony and Lead. — The
metals
is
readily
antimony the
of
effected
-
crystalline.
With
on cooling.
(See
alloys
union
by melting.
are
hard,
of
these
With excess
brittle,
and very
than 15 per cent, of antimony
lead alloys have the important property of expanding
less
]).
210.J
Antimony and
Tin.
—These
form alloys which are hard and
tin,
metals
less
unite
to
malleable than
and become brittle as the proportion of antimony
These metals when united form the basis
increases.
termed Britannia metal, many vaiieties of
This
which coiisist of tin hardened with antimony.
(,f
what
is
ANTIMONY.
alloy
and
is
is
233
used for the mauufacture of impression trays,
described on p. 217.
Antimony and
Gold.
— Antimony alloys
readily
with gold, but has a very injurious
effect upon it, the
presence of 0.5 per cent, of antimony rendering the
gold quite brittle.
Antimony and Copper. — Copper
and antimony
combine well together, producing a crystalline, brittle,
alloy, known as " Eegulus of Venus," which,
however, has no practical use in the arts.
violet
CHAPTER
XIX.
IRON.
SYMBOL, Fu
Occurrence.
(tV'iTuiii).
—Irou
is
ATOMIC WEIGHT,
56.
one of the most abundant and
widely distributed elements, being found in nature in
the metallic state in small quantities as vietcoric-iron of
ultra-teiTestrial origin
;
also in combination with
forming the minerals magnetite and red
oxygen
hajinatitc,
with oxygen and water the brown hasmatites, and with
carbonic acid, the spathic
ore,
these minerals forming
the chief sources of the metal.
Iron
and
found largely in combination with sulphur
but these compounds are not employed for
is also
arsenic,
the extraction of the metal, owing to the difficulty of
completely separating these substances from the iron,
and
theii-
]n'esent.
deleterious effect on the final product
The
when
commerce exists in three distinct
iron, wrought iron and steel, each
iron of
forms, namely, cast
of which exhibits different projjerties.
Cast Iron,
or pig iron,
is
the j)roduct obtained by
and besides iron
usually contains from -2 to 4 per cent, carbon from
0.2 to 3 per cent, silicon and varying proportions of
smelting iron ores in the blast furnace,
manganese (generally under
2 per cent, in
ordinary-
cast irons); with small proportions of sul])hiir
and of
IRON.
phosphorus.
Cast iron varies in composition according
to tlie materials operated
this
upon
and
for its product ion
varying composition with differences in the method
of treatment (mainly the rate of cooling) causes
it
to
vary considerably also in appearance and mechanical
properties, giving rise to three
main
varieties
known
as
and grey, from the appearance of the
white, mottled
White
fractnred surfaces.
iron has practically
carbon in the combined form, and
while grey iron
is
comparatively
is
soft,
hard and
the
all
brittle,
having the carbon
mainly present as graphite, scales of which may often
be picked off the fractured surface with a penknife,
and mottled iron as its name implies is a mixture of
grey and white.
In
ii'on
all its varieties,
and
steel
however,
it
does not admit of being welded,
iron.
Owing
melts
at a lower
but
it
from wrought
by being almost void of ductility
not so tough, and
steel,
differs
to
is
it is
also
more
harder than
usually
the presence
of carbon,
;
it
brittle,
malleable
cast
iron
temperature than wrought iron or
requires a bright yellow heat to melt
Grey iron contracts very
little
it.
on solidihcation, and gn
that account has been proposed as a suitable metal for
dies,
as
it
is
also hard
and
runs perfectly in open
sand in the usual manner of casting dies for dental
purposes.
however,
is
The high temperature required to melt it,
a considerable drawback to its use for this
purpose.
Wrought
Iron, or malleable iron, represents the
nearest approach to pure iron which can be produced
by manufacturing processes upon a large scale, and
generally contains from 0.05 to 0.3 per ceut. of
carbon.
Its
mechanical properties are totally distinct
DENTAL METALLURGY.
236
from those
malleable
of cast iron
for while the latter
;
not
is
and has a low tenacity varying from 7
to
15 tons per square inch, wrought iron
is comparatively
very malleable and ductile with a tenacity in its
soft,
purest form of 20 tons per square inch.
is
very
difficult of
Wrought
fusion (1600° C.) and before becoming
liquid passee through a soft or pasty condition.
in
this state
iron
clean surfaces
pressed or
if
When
hammered
together cohere and weld into a single mass.
Wrought
iron
may be magnetised by
bringing
it
contact with a magnet, but
it
the removal of the magnet.
plunged into cold water, it
If heated to redness
original
its
Steel
about
o.
is
I
flint
into
this property
on
and
not hardened, but retains
thus differing from tool
softness,
which become
is
loses
steels,
hard when similarly treated.
a malleable alloy of iron (containing from
to over 2 per cent, of carbon with small pro-
portions of other elements), which has either been cast
direct into a malleable mass, or
becomes
flint
hard when
heated to a bright red heat and cooled rapidly as by
quenching in cold water or brine. This definition excludes wrought iron, which will not become flint hard
and has been formed in a pasty condition, and also
cast iron
mass.
like
which has been
It includes all
wrought
become
cast
but not into a malleable
commercial
iron, has
steels, for
Shear Steel,
never been molten as such, but
hard on quenching, while structural or
mild steels do not become flint hard on quenching, but
have been cast direct into malleable ingots. Carbon is
the element which has the greatest effect in modifying
will
flint
the properties of iron.
amount
Steels containing only a small
of carbon, say about O.
sometimes termed mild
steels,
i
to 0.5
per cent, are
and have a tenacity
moN.
237
and the better
qualities when fractured by a tensile stress, show a fine
silky appearance on the edges of the broken surface.
varying from 2^ to 50 tons per
These
sq. in.,
from 0.4 to
steels generally contain
manganese and small proportions of
phosphorus, usually less than
o.
silicon,
per cent,
i
sulphur, and
per cent, of each.
i
Tool
from about 0.8 per cent, of carbon, upwards
with from 0.05 to 0.4 per cent, of manganese, and generally less than 0.2 per cent, of silicon, and 0.03 percent,
steels contain
each of sulphur and phosphorus.
Preparation.
compounds.' The
—Iron
readily reduced from
is
its
ore, as oxide, together with carbon in
the form of charcoal, coal, or coke, and with suitable
fluxes to
combine with the earthy matters of the ore and
render them fusible at the temperatures employed,
charged into a blastfurnace, whereby the ore
is
is
reduced
by the gaseous carbon compounds produced by the action
The iron thus set free takes up carbon and
of the blast.
other elements during
its
becoming
nace, and thus
passage
down
the blast fur-
temperature
fusible at the
of the furnace, gradually sinks to the hearth,
At
accumulates.
intervals
it
moulds, and constitutes what
is
is
where
it
tapped into suitable
known
as
cast
or
pig iron.
Wroufjht or MallcaUe Iron.
—This
is
obtained by
melting the cast iron in a reverberatory furnace and
gradually removing the impurities by oxidation the
;
iron "
coming
to
nature
" in
small pasty particles, which
are gathered into a spongy ball of iron particles and
cinder, which
by hammering and rolling
a solid mass, the great
expressed.
is
welded into
bulk of the cinder being thus
The purest forms, however, always contain
some entangled
cinder,
which may be clearly seen under
DENTAL METALLITRGY.
^3^
the microscope, thus forming a convenient
distinction
between wrought irons and mild steels.
may
be produced either from wrought iron by
the addition of carbon or from cast iron by removing
the carbon. In the former process, known as " cementaSteel
tion," small bars of
and heated
thus
made
wrought iron are buried
for several days to a red heat.
is
blister-steel is piled, welded,
required form of bar,
is
Carbon
is
to pass into the iron, which presents a blistered
appearance, and on that account
When
in charcoal
it
is
known
termed
Uister-steel.
and worked
to the
as shear steel,
which
a favourite hardening steel for some tools.
When
broken up and melted with suitable
additions (of manganese, &c.) in a crucible, cast into
an ingot, and hammered or rolled into bars of various
blister-steel
is
sections, the product is
known
as crucible cast steel,
and
mostly used for tools required to harden and keep a
cutting edge. The mild steels are generally produced
is
either
by the Bessemer
or
Siemens processes.
The Bes-
semer process consists in oxidising the carbon and some
of the other impurities by blowing air through molten
pig iron, adding manganese to remove excess of oxygen
and carl)on according to requirements, by means of
suitable alloys of iron rich in
carbon and manganese.
In the Siemens process the impurities are oxidised by
the addition of iron oxide as iron ore to the molten bath
of pig iron, and the process finished in a similar manner
to the
Bessemer process.
The metal in each case is
generally tapped into a ladle and thence into ingot
moulds.
Properties
(see also Wrought Iron, p. 235).— Iron
a white metal with a bluish-grey tint.
It undergoes
no cliange in perfectly dry air, or in water free from
is
IRON.
aiv,
but
it is
rapidly coated with a scale of oxide or mist
exposed to the action of moist air. When heated
to redness it oxidises rapidly with the formation of a
if it is
It is soluble in dilute nitric acid (i-i),
scale of oxide.
hydrochloric, and dilute sulphuric acids, but
much
affected
by strong sulphuric
acid.
it
is
not
Alkalies have
no action on the metal.
Effect of Impurities on Iron. The properties
of tenacity, malleability, and ductility in iron are power-
—
fully influenced
by the presence of only small quantities
of certain impurities.
As
the carbon content of iron
city increases in a general
of 1.2 per cent,
is
way
is
increased, the tena-
until a carbon content
reached, but the malleability and the
ductility steadily decrease.
From
will
0.9 per cent, of carbon and upwards the steel
harden and temper (see next paragraph), but
manganese
is
if
also present, the steel will take a cutting
than 0.9 per cent, of carbon.
Very small quantities of sulphur render steel red-
edge with
less
short or unworkable at a red heat, while phosphorus in
makes the steel cold-short. Manganese
is found to counteract to some extent the evil influence
of sulphur, and a certain proportion of phosphorus has
more effect in high-carbon than in low-carbon steels.
Until recently arsenic has been considered somewhat
small (juantities
similar to phosphorus as to its mechanical
but recent research has shown that
moderate quantity,
is
its
efl^ect
on
iron,
influence, even in
almost negligible.
Silicon,
when
present up to 4 per cent, imparts hardness and brittleness with a gain of tenacity.
Copper in small quantities has little effect.
From these remarks it will be seen that the influence
DENTAL METALLURGY.
240
of iuipnrities on iron is a very complicated matter, owing
to the considerable influence they exert on one another,
and for several other reasons, but the statements above
will give a fair
general idea of the facts.
Hardening and Tempering.— When
steel
is
heated to redness, and then plunged while red hot into
cold water, or is otherwise suddenly cooled, it acquires
great hardness and brittleness.
hardened
steel, which is very hard and brittle,
re-heated to redness and allowed to cool slowly it
again becomes soft and malleable, or if it is re-heated
below redness and allowed to cool it is also partly
If this
is
made
softened and
and
less brittle, the decrease in
hardness
depending on the temperature employed, the higher the temperature the softer and less
brittle the steel is made.
in brittleness
This re-heating to different temperatures to obtain
the compromise between hardness and brittleness necessary for the tool being made is called tempering.
The
steel is first
tempered or
hardened
let
in the
down by
manner described and then
re-heating
it
to a definite
tem-
perature, varying according to the degree of hardness
and then cooling it quickly. The temperature
necessary is usually judged by the colour of the thin
film of oxide which appears on the polished surface of
required,
the steel
when
heated, the tint of the film varying with
the temperature, being yellow
when
heated, then passing gradually to
and
the steel
is first
brown and purple,
deep blue as the temperature increases.
The temper necessary for various steel articles depends
finally to
upon their application thus, most surgical instruments
and razors are tempered at 232" 0. (450" F.), indicated
by a pale straw tint, while the temper given to fine saws,
;
IRON.
241
indicated by full blue, correspouds to a temperature of
293
0. (560^^
The following
corresponding
table indicates the temperatures
colours
necessary
various articles used in dentistry
and
"tempering"
for
:
Tc'iuiiLTiitiirt'.
'l'(Mii)iL'r ol'
Colour.
vai'ioiis
artick's.
Kalir.
Cunt
430"
221'
Very pule yellow
450°
232'
Piile
470"
243"
254°
Full yellow
490="
510
265^
55°^
2SS'
Lancets
/'Enamel chisels and niosi,
surgical instruments
Excavators
Pluggers
strnw
Brown
Brown dappled
/'
twitli
purple spots/
blue
Bri,i;-ht
In "tempering" or letting
.Saws,
L*cc.
Watch-springs
down
dental instruments
be employed, the instrument after hardening being held in the flame and
carefully rotated to ensure uniform heating. The
flame
should strike the instrument at some distance frota
the
cuttiug end, and when the end attains the desired
colour
it should be
instantly quenched in cold water and
the flame of a spirit lamp
may
allowed to remain in the water until cold, to
jirevent
" letting
down
The same
" further.
result
may
also be conveniently effected
by
heating a small
block of iron to dull redness and
placing the instrument to be tempered
upon it, then
removing it as soon as the desired tint appears
and
plunging into cold water.
It is advisable to continually rotate the instrument in order
that it may be
uniformly heated.
DENTA.L METALLURGY.
242
Annealing.
—
Iron and sfceel which have become unduly hard or brittle by hammering, rolling, or otherwise
working the material, may be softened and made malleable by annealing, i.e., heating the metal to about a
cherry-red heat and allowing
This
it
to cool very slowly.
frequently done by withdrawing
is
it
from the
source of heat and then immediately covering
it
with
ashes or other bad conducting material such as sand,
lime, &c.,
under which
it is
allowed to cool
ordinary temperature before
it is
removed.
p. 12.)
Burning of Iron and
iron or steel
air,
is
down
Steel.
to the
(See also
—When malleable
heated to redness and exposed to the
oxidation proceeds veiy rapidly with the production
of a "scale" or layer of oxide of considerable thick-
By
ness.
excessively long or intense heating the iron
" burnt," is friable, incapable of being welded,
becomes
and cannot be restored completely to its original state.
Steel requires much more precaution in heating than
iron,
and does not bear the same degree of heat as iron
Steel which has been slightly over-
without injury.
heated
may
be restored to a certain extent by judicious
hammering at a lower temperature, but the improvement effected in bui'nt steel by this treatment is very
slight.
CHAPTEK XX.
ALUMINIUM.
SYMBOL,
Occurrence.
dant of
ail
of clay, but
Al.
ATOMIC WEIGHT,
— Aluminium
is
27.
one of the most abun-
the elements, being found in every variety
it
has never been found in the metallic
state.
In combination with oxygen it constitutes the minerals
coruncluvh or emery
is
and
batoxite,
mainly extracted on a large
from which the metal
scale.
Some
of its
com-
binations with oxygen are of great beauty and hardness,
such as ruby, sapphire, and garnet.
Another mineral from which aluminium sometimes
is obtained is cryolite, which is foiind in abundance in
Greenland, and consists of aluminium in combination
with sodium and fluorine.
—
Preparation. Aluminium is almost exclusively
obtained by means of the electric furnace, which consists of a large iron
forming the
electrode
is
box or crucible lined with carbon,
negative electrode,
while
a bundle of carbon plates.
the
positive
The
crucible
contains a bath of readily fusible compounds, to which
the aluminium oxide (alumina)
time, and dissolved.
is
When
is
added from time
to
a powerful electric current
passed through the bath the alamina
is
decomposed
DEXTAL METALLURGY^
244
and the metallic aluminium thus liberated falls to the
bottom, whence it is drawn off at intervals.
The
oxj^gen set free combines with the carbon to form carbonic oxide, which escapes and burns in the air formingcarbonic acid.
It is only within recent years that
alnminium has
been prepared in sufficiently large quantities and at a
sufficiently low price to enable it to be classed with the
other metals in
common
use.
—
Properties. Aluminium is a white metal possessing a colour between that of silver and zinc.
It is
remarkably light, being only about two and a half times
as
heavy as water
it is unaffected by air, even in the
presence of sulphuretted hydrogen, and consequently
;
preserves
its colour in an atmosphere in which silver
would rapidly become black. It is extremely malleable
and ductile, the pure metal being regularly rolled into
sheets one-thousandth of an inch in thickness, and also
drawn into very fine wire. Aluminium is most malleable between lOo" 0. (212'" I\)and 150" C. (302" F.)and
can be worked some time at that temperature before
becoming hard. When rolled and worked cold it needs
more frequent annealing. It is highly sonorous, and is
a good conductor of heat and of electricity.
The melting-point of aluminium
being a
that of silver;
it
(i 157'' F.),
melts somewhat slowly and
is
viscous
for casting purposes.
The vegetable
acids exert no perceptible action on
aluniinium, consequently
vessels.
625° C.
higher than that of zinc but lower than
little
when poured
is
it is
well adapted for culinary
It is readily dissolved in either'dilute or strong
hydrochloric acid and also in solutions of caustic potash
or soda.
'
ALUMINrrTM.
Use
Dental Purposes.
for
245
—
()u account of the
aluminium and the
facility with which it retains its colour, attempts have
been made for several years to employ it as a base for
artificial dentures, both by swaging a plate of the metal
lightness, strength,
in the ordinary
and whiteness
way and by the
these attempts
of
cheoplastic process, but
have only been partially successful.
Although some of the physical difficulties encountered
in the effort to render aluminium available in prosthetic
dentistry have been overcome,
its
great susceptibility
by the action of alkaline solutions is the
The diffichief obstacle to its use for this purpose.
culty of obtaining a suitable solder by which pieces of
to corrosion
the metal
may be
vented
use in the dental laboratory.
its
securely united has also largely pre-
Experiments in casting the metal for dental purposes
have not been entirely successful on account of the
amount of contraction which takes j^lace on cooling and the somewhat high temperature required to
" At the present time the use of
melt the metal.
large
aluminium
is
rarely attempted except as a base in con-
nection with rubber or celluloid, the latter substances
being employed as a means of attaching the teeth."*
When combined
with copper
it
forms an alloy which has
been used to a limited extent in Germany as a base for
artificial dentures. (8ee p. 248.)
Impression traj'^s and
now made of aluminium.
Plate for Dentures. When alu-
other dental appliances are
Aluminium
minium
is
—
used for the construction of
an
denture the method most frequently a,dopted
artificial
is
to
swage
a plate of the metal in the ordinary way.
During the swaging the metal becomes
*
Ricluirdsdirs " Meclianiciil
Ueiitisti\\',''
1S94
I'd.
rigid
|i.
120.
and
DENTAL METALLUEGY.
246
hard, but
it
may be
softened by heating. to dull redness
and cooling quickly by dipping into cold water. Thin
slieets may be softened by putting into boiling water
and letting them cool with the water. After swaging
.
the plate the teeth are attached with rubber or celluloid
in a
manner
a gold plate
similar to that sometimes emplo3fed
is
used.
forated with a
Por
number
this
purpose the plate
is
per-
of countersunk holes along the
part covering the top of the alveolar ridge.
to Essig * " sets of teeth
known
when
made
in this
According
way have been
to do good service for eight or nine years, but
they showed unmistakable evidence of the action of the
oral fluids."
Casting
Aluminium
application of
aluminium
several difficulties are
very
met
for
to
Dentures.
the
the cheoplastic process
aluminium contracts
witb, as
much on solidification and
— In
requires a high tempera-
it.
For casting in closed moulds the best
have been obtained by the application of a slight
ture to melt
results
pressure to the
artificial
still
liquid metal in the
mould
immediately after pouring.
The addition
of a little copper to
aluminium causes a
decrease in the contraction and renders
it less liable
to
corrode in the mouth, but the presence of copper increases the hardness of the aluminium.
Essig
that " aluminium
t states
may
be cast upon
plain teeth with comparative safety, provided the metal
is
prevented from overlapping the necks of the teeth.
But when gum teeth
are employed, either singly or in
sections, their fracture is almost certain to follow the
contraction incident to the cooling of the metal."
*
.
Essif;-,
"
Dental MetiiUurgy,"
f Ihid. p. 252.
3r(l ed. p.
253.
ALUMINIUM.
Solders for Aluminium.
247
—The
difficulty of sol-
dering aluminium has prevented a more extensive appliIt
cation of the metal for dental and other purposes.
obtain a clean, bright surface owing to the
is difficult to
rapid formation of a very thin film of oxide which
cainnot be
removed by the ordinary fluxes used
in solder-
ing operations, such as borax, &c., as these are liable to
attack the surface of the metal and prevent union taking
place.
It has also a very high conductivity for heat and
A
thus chills quickly at the joint.
large
number
of
aluminium have been patented within recent
yea.rs, but comparatively few have given satisfaction.
Two solders containing aluminium are recommended
solders for
by Schlosser* as being specially suitable
dental
laboratory on
use in the
for
account of their resistance to
chemical action.
Platimm-Aluminium
Gold
.
Platinum
Silver
.
.
.
.
.
Aluminium
.
Gold
Copper
'
i
.20
.
Aluminium
Solder.
|
30 parts
.
dolil
Solder.
100
Silver
..
.
.
...
AluminiTin:
,
.
Another solder consists of zinc 22.5
50 parts
.10
.
.
.
.
parts,
10
20
„
aluminium
With regard to these solders
Richardson remarks f that "none of them are suitable
copper
1.5 parts,
i
part.
for attaching artificial teeth."
Two
pieces of
aluminium may
also
be united with
ordinary solder, with silver chloride as a flux, by means
of which a film of metallic silver is deposited on the
silver chloride is
The
powdered fused
spread along the lines of contact and
surface of the aluminium.
finely
the soldering completed in the usual
Das Lothen,"
|-
•'
way with the blow-
p. 103.
Mechanical Dentistry," 7M1 cd. 1898,
p. 109.
DENTAL METALLURGY.
2^8
pipe or otlier device.
The uuiou thus obtained
is said
to be perfectly strong and reliable.*
Aluminium Bronze.—This is an alloy of copper
with aluminium, and usually contains lo per cent, of
the latter metal.
—
Preparation. Aluminium bronze is prepared by
simply melting the constituents in a crucible or by first
melting the copper and then adding the aluminium.
The union
heat,
white heat
attended by a considerable evolution of
is
which
raises the
it is
;
temperature of the whole
to a
therefore necessary to use crucibles of
good quality when preparing the alloy. The alloy is
brittle when first prepared, but when re-melted two or
three times the brittleness
point of aluminium bronze
silver,
is
is
The meltintrnearly the same as that of
removed.
being about 950' 0, (1742° F.). It shrinks on
about twice as much as brass.
solidification
Pkopkrties.
that of gold
:
—It has a
fine yellow colour
scarcely tarnished
it is
sulphuretted hydrogen.
or
It
by exposure
The
alloy
is
to air
the action
resists
chemical agents to a large extent and
a high polish.
resembling
is
of
susceptible of
malleable at the ordinary
temperatures, but far more so at a red heat. It becomes
very hard and
when worked and
stiff
requires frequent
done by heating the alloy at a
hright-ml heat for sometime, then cooling to redness
and plunging it into cold water to temper it. Alumi-
annealing.
This
is
nium bronze may be swaged
but
it
requires fi'equeut annealing during the process.
When the
is
as readily as 20-carat gold
alloy is placed in dilute nitric acid the copper
dissolved from the surface, leaving the aluminium,
thus changing the colour of the alloy on the surface.
*
Chemiciil yeicx,
iv. Si.
:
:
ALUMTNTUM.
Aiumiuium bronze
Crermany as a base
used
is
to
i8-carat gold.
on the
alloy, it
extent
limited
a
in
for artificial dentures, as it is strong,
and capable of resisting
hard,
249
as
as well
attrition
As chemical agents do not readily act
is only slowly discoloured by exposure
month.
in the
Aluminium Bronze.— Eighteen-
Solders for
carat or fourteen-carat gold solder with the addition of
a little copper is sometimes used as a solder for alumi-
nium bronze, the union of the pieces being effected
without difficulty. The following alloys are recommended * as effective and convenient solders for o per
i
cent,
aluminium bronze
Nh.
Xo. U.
IJavd SoUlev.
r.
Mf<}inm linn]
2T.s-ciivat.
(jold
Silver
....
....
Copppr
.
.
Ciold
SS.88
.
....
.
.
4-68
Silver
6.44
Copper
.
Xo.
Copper
Till
.
.
.
.
II f.
5440
.
.
27.00
18.60
.
.
100.00
100.00
.
Sniilcr.
i3-c.ai-iit.
Snfl Solilcr.
yolwrcent.
y
30
....
_
J
Gold
.
.
Silver
.
.
Copper
.
.
14-30
.
.57-10
14-30
.
100.00
Alloys of Aluminium.
— Dr. Carroll has used
casting
following
n alnmiiiinm alloys for
tures
9°
Aluniiiiiniu
Silver
5
Copper
o
* liichards,
'^Aluminium," 3rd
artificial
93
I'i"'''^
••
9
"
,.
1
,.
ed. p. 569.
th(
den
DENTAL METALLUEGY.
These alloys when cast under slight pressure
give
good castings, are very white, and easy to work.
The
addition of the copper
mum
is said to decrease to a minithe shriukage of the alloys and also to give
a
closer grain.
CHAPTEE
XXI.
NICKEL.
SYMBOL.
Occurrence.
ATOMIC WEIGHT,
Ni.
—Nickel
59.
occurs chiefly in combination
with arsenic and sulphur, and
its
ores almost invariably
contain small quantities of cobalt.
Preparation. Nickel is extracted from
—
first
concentrating
arsenic or
the metal
in
its
ores
by
combination with
The product
sulphur in blast furnaces.
then roasted to expel the arsenic or sulphur,
and the nickel oxide thus formed reduced to the
metallic state with carbon at a high temperature.
obtained
is
Properties.
—Nickel
a lustrous metal, approach-
is
almost to a silver whiteness in colour, but possessing
It is very hard and takes a fine
a slight yellow tinge.
It does not readily tarnish by exposure to the
polish.
atmosphere at ordinary temperatures, but when heated
in o-
in air
to
it is
The metal
slowly oxidised.
any appreciable extent
retted hydrogen.
Water
is
not tarnished
in the presence of
sulphu-
without action on the metal,
is
only slowly soluble in hydrochloric acid or
dilute sulphuric acid or even in concentrated sulphuric
and
acid.
it
is
On
the other hand,
nitric acid or in
aqua
it
regia.
dissolves readily in dilute
The metal
by alkaline solutions or vegetable
acids.
is
not attacked
-52
DENTAL METALLURGY.
It is very malleable
and
and may be
ductile,
rolled out into thin plate or
drawn
very tenacious, in which quality
into wire;
easily
it is
also
only exceeded by
steel. It is magnetic like
iron, but possesses this quality
to a much smaller degree, and
loses its magnetism by
heating to 250^ C. (481^ F.), recovering
the quality
again, however,
temperature
it
is
upon cooling.
to
fuse
it,
being 1600' C. (29 1 ^
2
It requires a very high
the melting-point of nickel
F.),
and
it
may be welded
at a red
heat.
Use
the Dental Laboratory.— Oast and
sheet nickel muffles are now extensively
employed for
dental furnace work the metal appears
in
to
;
first
have been
introduced for this ])urpose in 1886.
Alloys of Nickel.—The
chief alloys of nickel are
those in combination with copper and zinc in
varying
proportions, producing a series of alloys of much
value,
and
to denote
which different manufacturers employ
fanciful names.
German Silver, or nickel silver, consists of nickel,
copper, and zinc in proportions varying with the
uses
to
which
applied, the best qualities containing a
larger proportion of nickel than the inferior qualities.
German
it
is
silver, as
made by good makers,
of one part of nickel,
one part of
consists usually
zinc,
with two or
three parts of copper.
Prepakation.— Various
methods are
pursued for
the manufacture of
German silver, but that generally
adopted at the present time consists in first alloying the
zinc with one-half of the copper, the brass so formed
lieing cast
into thin plates, so that
it can be easily
broken up, while the nickel is melted with the remaining portion of the copper in another crucible, to
NICKEL.
which, after thorough mixing, the brass is added in
small pieces nntil the necessary composition has been
high temperature required for
the fusion of the nickel and the low melting-point and
oxidisabie nature of zinc, the preparation of this alloy
Owing
obtained.
to the
attended with a considerable loss of zinc
care is accordingly required in its production.
is
re-melting the alloy
zinc to
add
it is
When
loss,
and
it is
advisable to
zinc after the' fusion of the alloy has been
On
effected.
amounts
special
necessary to add a portion of
compensate for the
this
;
account of this oxidation the relative
of the constituents are altered
:
it is
therefore
In
difficult to obtain an alloy of definite composition.
all cases a layer of charcoal should be placed on the
surface to prevent oxidation as far as possible.
Properties. ^German silver is greyer in colour and
—
harder than
ductile,
the
and
is
capable of receiving a high
and
and works well under the hammer or between
It
polish.
silver,
is
also
tough,
tenacious,
malleable,
rolls.
and requires careful
annealing before rolling or hammering, but after the
crystalline character has been thus overcome the alloy
It is
crystalline
after casting
be rolled and hammered into a variety of shapes.
Sound castings are secured by the use of borax, glass,
may
or other good flux.
German
When
exposed to the atmosphere
silver acquires a yellow tint
due
to the presence
of sulphuretted hydrogen, and in acid solutions, such as
vinegar, with access of air, it becomes gradually coated
with
a
layer of green verdigiis.
oxidised
when heated
in air,
and
It is
superficially
at a bright red heat
the alloy fuses, a pro])ortion of the zinc burning away.
The
alloy
is
readily soluble in nitric acid.
Impression
DENTAL METALLURGY.
254
trays, matrices,
and a number of other dental aiDpliances
made of German silver.
Nickel and Iron.— These metals unite when
are
melted together to form a series of alloys which are
very
hard and tenacious and little affected by the atmosphere.
The
alloys
more
are
than ordinary steel when
melted, set more rapidly, and can be readily hammered
and rolled. Nickel steels are extensively used for
fluid
armour-plates.
Nickel Plating.—This
articles of iron, copper,
the process by which
and other metals are coated
is
with metallic nickel by means of an electric current in
a manner similar to gold and silver plating.
The
solution usually employed
of nickel
is
the double sulphate
and ammonia.
It is of great
importance that the
articles to be coated
should be absolutely clean and that any existing film of
nickel should be entirely removed, the cleaning of the
article being even more important in nickeling than in
silvering or
Small
gilding.
articles
are
frequently
cleaned by rubbing with fine emery cloth, but a chemical
method is more often employed, which consists in
dipping the articles for a brief period into an acid bath.
On account of its extreme hardness the nickel deposit
cannot be burnished like deposits of gold and
is
before immersing in the plating solution.
ing every
in
a
trace
solution
rinsing
in
a
of
water,
plating bath
of
silver
:
it
essential, therefore, that the articles be well polished
suitable
of
grease
potash
the
;
is
removed by
then,
article
After polish-
ia
after
a
dipping
thorough
transferred to
the
and connected with the negative pole
battery, a plate of pure nickel
connected with the positive pole.
being
Generally speaking.
NICKEL.
to four hours
from half an hour
will
suffice
for the
deposition.
When
the thickness of coating
is
sufficient the article
removed from the solution and thoroughly washed in
water, dried in hot sawdust or a small stove and then
is
finally
Articles of
polished.
cast
iron
are
usually
covered with a film of copper before being suspended in
the plating solution.
Nickel-plating
articles of all
the metal
is
is
now
largely
employed
for coating
kinds on account of the brilliant polish
capable of taking and
its non-liability to
tarnish under ordinary atmospheric conditions.
A
thin coating will also resist the wear and tear of
hard use owing to the hardness of deposited nickel.
PART
II.
EXPERIMENTS RELATING TO THE PHYSICAL
AND CHEMICAL PROPERTIES OP METALS
AND ALLOYS.
Ix order that the student
may
acquire a more practical
knowledge of the properties of the various metals given
in Part L, the following simple experiments hcwe been
which may be readily conducted in a
moderately well equipped dental laboratory. In addiarranged,
all
of
tion to the following experiments,
it
would be well
for
students to perform also the various experiments mentioned in the text of Part
I.
The
quantities of metal
necessary for the various experiments are given in
grammes,
as the metric
ployed for
iisually sold
all
system
now
is
experimental work
;
universall}^
em-
but as the weights
with scales for dental purposes are Troy, the
((uantities are also given in grains for convenience.
In
most cases larger quantities of material may be taken
with advantage, but with due care satisfactory^ results
can be obtained with the <[ uantities given.
The experiments
may be j)er~
anvil when a
relating to malleability
formed with a hammer and bright
rolling-mill is not available.
steel
—
;
GOLD.
,
Material Required.
GOLD.
— About
5
grams, (or 75 grains)
of 22-carat or other carat gold.
Experiment
i.
— Dissolve the gold alloy in aqua regia
;
evaporate nearly to dryness to expel excess of acid
add a solution of
dilute with about a pint of water;
iron sulphate
and gently
precipitated as a fine
filter
paper,
heat,
when the gold
brown powder.*
will
be
Filter through a
wash the precipitated gold repeatedly
witli
and warm till perfectly dry. Carefully rub a
brown powder with some hard smooth
surface, such as a steel or agate burnisher, and note
that the characteristic yellow colour and metallic lustre
water,
of the
little
of gold appear.
of the
powder
Reserve about
.5
gram, (or
5
grains)
Experiment 14. Transfer the rea suitable support and melt into a globule
for
mainder to
by means of the blowpipe, heating gently at first to
avoid loss.
Note that it requires a bright red heat to
fuse
it.
suspending
fine silk,
—
Determine the density of the gold by
from the arm of a balance by means of
and accurately weighing it in air. Then place
E.C2)erimcnt 2.
it
a small vessel of water in such a ]30sition that the gold
completely immersed while still suspended, carefully
remove air bubbles by means of a camel's-hair brush,
and then note the weight in water.
The gold will appear lighter than before, the loss in
is
weight being exactly equal to the weight of an equal
volume of the water.
Calculate the specific gravity of the gold as follows:
*
\\\y of
till)
n;iif;oiits
procipitiiting tho gold.
muiilioiiud uii luigu 96
iiiiiy
bo used fur
DENTAL METALLUEGY.
Weight
ill
air
between weight in
and weight in water
-Difterence
3.— Strongly
J^xperiment
aii-
_
"
^'^^^
heat the globule of
" fine "
gold before the blowpipe for a few minutes and observe
that no oxidation takes place, the surface remaining
perfectly bright
there
;
allow to cool in
air,
and notice that
no alteration of the surface due to the liberation
of oxygen, as in the case of silver when similarly
is
treated.
(See
Uxperivicnt
its softness.
p. 168.)
4.— Cut the gold
Eoll or hammer
with a knife to ascertain
it out into a strip, and
great malleability, the edges remaining perfectly smooth.
Note that mechanical treatment tends
prove
to
its
make
it
ness, allow
hard and " springy."
it
Heat the strip to redto cool, and observe that it is soft and
pliant after thus
JExpcj-iiiteut 5.
annealing."
— Cut
off
two small pieces of
one on top of the other on an
anvil,
gold, place
strike with
a
hammer and notice that the two pieces weld. They
may also be welded by passing between the rolls.
Kiperivient 6.
— Place
the strip of gold in dilute
sulphuretted hydrogen water and observe that no discoloration takes place, proving that gold has no affiuity
under these conditions.
Uxperiment 7. Melt i gram, (or 10 grains) of gold in
for sulphur
—
a small crucil^le with the addition of .005 gram. (-Vth
of a grain) of lead, and roll or hammer out as before.
now
Notice that the edges
small
crack,
showing that
amount of lead has rendered the gold
lias also altered
Experiment
brittle
this
;
it
the colour.
—Melt
gram, (or 10 grains) of gold as
beforo. with the addition of antimony instead of lead,
8.
i
.
GOLD.
259
and in the same proportion. Observe that the same
effect is produced as with lead.
Uxpcrimcnt 9. Re-melt the gold from Experiments
7 and 8 in a small crucible, and when fusion has taken
place cautiously add a few crystals of nitre (potassium
—
nitrate).
solidifj-,
Pour the gold into a suitable mould, or let it
and then break the crucible. Roll or hammer
out and note that
Experiment
it is
10.
now
malleable after being refined.
— Dissolve
.5
gram, (or
5
grains) of
pure gold in aqua regia as before and dilute to about a
Reserve a small portion of the solution
pint.
Experiment 1 1
Heat the solution
oxalic
acid
" spongy "
bottom.
to
slightly,
precipitate
for
then add a solution of
the gold and observe the
mass which settles at the
wash with water, then diy
nature of the
Filter off the gold,
and examine with a lens. Notice that the spongy mass
is made up of minute crystals.
Beautiful spangles of metallic gold are obtained by
The
using a more 'dilute solution of gold.
may
precipitate
not appear until the solution has been standing for
a short time.
Experiment
11.
tion prepared for
—Take
a small quantity of the solu-
Experiment 10 and further
dilute with
water to obtain a very dilute solution of gold.
solution of stannous chloride,
mixed with a
little
Add
a
stannic
chloride, shake well
and notice the purple precipitate
(purple of Cassius).
This forms a very delicate test for
gold.
Experiment
12.
—Melt
.5
gram, (or
'5
grains) of gold
in a crucible or before the blowpipe, with the addition of
two and a half times
its
weight of
silver.
resulting alloy into a thin strip, place
it
Roll out the
in dilute nitric
26o
acid,
DENTAL METALLITEGY.
and heat.
Observe that the silver is dissolved,
leaving the. gold behind as a brown residue.
Pour off
the silver solution, wash and dry the gold thus "parted,"
and then heat to redness. The gold assumes its characteristic yellow colour
—
and
also contracts in volume.
Note.
The silver may be recovered as directed
Experiment i6.
Experiment
—Melt
in
gram, (or 10 grains) of gold
in a crucible with the addition of .2 gram, (or 2 grains)
13.
i
of copper, using a thin layer of charcoal
powder and
also a cover to prevent oxidation.
Allow the resulting
and turn out when cold.
with sand and water and notice that the
alloy to solidify in the crucible
Clean the alloy
colour of the gold
and prove
is
deepened.
malleability
its
Roll out into a strip,
and hardness
as
compared
Anneal it at a red heat and notice the
discoloration which takes place owing to the oxidation
with pure gold.
of the copper jiresent.
Plunge the
strip while still Lot
into dilute nitric or sulphuric acid, and observe the
" colouring " which takes place owing to the dissolving
of the copper on the surface.
Experiment
— Place
14.
about
.5
gram, (or
5
grains)
of finely divided gold (Experiment i) in a clean glass
add a few drops of mercury, warm gently
and shake for a few seconds, closing the top of the tube
with the finger. Notice that amalgamation takes place
readily.
Squeeze the resulting amalgam in chamois
test-tube,
leather with a pair of pliers and observe the nature of
the amalgam
left.
Allow
it
to rest for
some days and
note the "hardness."
Experiment
15.
— Heat the amalgam in a small porce-
mercury is expelled. Notetbe
character of the residue and weigh.
lain crucible until all the
261
SILVER.
This experiment sliould be perfox-med iu connection
with a suitable tliie for carrying off the mercury fumes,
as these are poisonous if inhaled.
SILVER.
Material Required.
— About 10 grams, (or 200 grains)
of standard silver or silver scrap.
— Dissolve
the silver in dilute nitric
acid in a glass beaker of about one pint capacity, then
add distilled water until three parts full heat nearly to
Experiment
16.
;
boiling
and carefully add a strong solution
salt to precipitate
common
of
Stir briskly
the silver as chloride.
with a glass rod for a few minutes, allow the precipitate
to settle, then carefully pour off the clear supernatant
add hot water to the precipitate, stir, allow to
again decant the clear liquid, and repeat this
settle
operation three or four times in order to remove all the
liquid
;
;
copper solution.
Wash
the precipitate into a basin,
sodium carbonate, well mix,
transfer to an earthenware crucible, and fuse at a good
red heat for about twenty minutes then pour into an
ingot mould, cool, and detach the slag, the last portions
of which may be removed by dissolving in hot water.
dry, add twice the bulk of
;
The heat should not be
the charge
raised too suddenly, otherwise
may boil over owing
to the rapid escape of
carbonic acid.
Experiment
17.
—Melt the
silver
on a cupel or suitable
support by means of the blowpipe flame, and keep in
the molten condition for a few minutes.
it
requires less heat to fuse
metal does not tarnish
in
it
Observe that
than gold, and that the
contact with the
the silver to cool quickly iu contact with
air.
air,
Allow
when the
262
DENTAL METALLURGY.
oxygeu, which has been mechanically absorbed
by the
molten metal, is disengaged on the metal
solidifying,
causing a number of small excrescences on
the surface.
This action is called " spitting."
Experiment 1 8.— Re-melt 2 grams, (or 20 grains) of
the silver with the addition of one-fifth of its weight
of
copper, cool in air as before, and notice that the
presence
of copper prevents " spitting."
Erpcriment ip.^Melt the remainder of the
with sufiicient
silver
common
salt to cover the metal, so that
the metal cools under a layer of salt, to prevent absorption of oxygen, and notice the smooth surface.
Eaypcriment 20.
— Determine the density of the
as directed for gold in
Experiment
2,
silver,
after carefully
removing the salt adhering to the metal.
Experiment 21.— Roll the silver into a thin strip,
noting its malleability and elasticity heat to redness,
allow to cool, and note that it is now pliant and " soft";
;
cut with a knife to ascertain
its
"hardness."
22.— Place
Experiment
the strip of silver in dilute
sulphuretted hydrogen water, and observe that it readily
blackens owing to the formation of a film of silver
sulphide.
Experiment 23.
—Melt
the silver in a crucible under
a layer of charcoal powder,
fifth
of
When
and when molten add oneweight of platinum in the form of foil.
thoroughly melted, pour out and roll the alloy
its
into a strip
observe its hardness and toughness compared with pure silver anneal at a red heat and note
the effect by bending.
;
;
Ex23erimcnt
24.— Place
and cover with dilute
num
is
left
the strip in a glass beaker
nitric acid.
Observe that
plati-
undissolved as a black residue, while the
263
SILVER.
silver (with a small
quantity of platinum)
is
dissolved.
water,
Pour o£E the solution, wash the residue with hot
burnisher
dry and heat to redness when cold rub with a
and notice the bright metallic surface of platinum.
ExperiExperiment 25.— KoU the button from
and
ment 18, observing that it is malleable, tough,
and
than pure silver. Heat the strip to redness
;
harder
notice that discoloration takes place
owing to the pre-
Ee-heat the strip and plunge while hot
Notice the "frosted"
sulphuric acid.
sence of copper.
into
dilute
" in acid, and
appearance produced by thus " pickling
lustre is restored
also observe that the bright metallic
by burnishing.
Experiment 26.— Dissolve
i
gram, (or
1
5
to 20 grains)
about oneof pure silver in dilute nitric acid, dilute to
a strip of
third of a pint with hot distilled water, place
crystalline
copper in the solution and observe the grey
precipitation
precipitate of silver produced. Allow the
on for about half an hour, remove the copper,
allow the
carefully wash off all silver adhering to it,
and
precipitate to settle, pour off the copper solution,
with hot
then wash the precipitate two or three times
to go
water.
dry,
Eemove
small portion
a
and examine with a
lens.
the precipitate,
of
Notice
its crystallised
character.
Experiment 27.— Place the precipitated silver in a
takes
mortar, add mercury, and rub until amalgamation
place.
Remove
excess
product in a piece of
character of the
soft
mercury by pressing the
chamois leather; observe the
of
amalgam
left
behind.
Reserve
the remainder
a portion for Experiment 28, and allow
harden, then break and examine with a lens, noting
to
its crystalline stfite
and
brittleness,
264
DENTAL METALLURGY.
Experiment
28.-Carefully pack a small quantity of
the amalgam into a small
glass tube until full, level the
surface, and allow to rest
until hard. Ascertain whether
expansion or contraction has taken
place by examining
carefully with a lens.
(See p. 149.)
Experiment 29.—Heat a small portion of the amalgam
in a porcelain crucible (in a suitable
draught) and expel
the mercury.
Examine the product left behind and
note
^
its
character.
Experiment 30.— Dissolve
Sliver in dilute nitric acid,
Heating,
with
dilute
.5
gram, (or
5
remove excess
grains) of
of acid
by
hot
water; then pour a small
quantity of mercury into the vessel containiug
the
and allow it to stand undisturbed for
Observe the crystallised amalgam or
which is formed.
silver solution,
several hours.
'•'silver tree "
MERCURY.
Material lieqidred.
— 20 grams, (or 300 grains)
of pure
mercuiy.
Experiment
—Take a small
31.
quantity of mercury
:
observe that
it
has a silvery-white colour and bright
lustre;
it
is
that
.
and that it is liquid at
Pour a few globules of mercury
tasteless
ordinary temperatures.
;
on to a clean sheet of glass, notice that the globules
and leave no "tail," and that the sur-
are spherical
face of the glass
liquids.
not " wetted," as with ordinary
Heat a very small quantity of mercur}^, preis
ferably in a muffle, and observe that
volatilised.
No
oxidation
takes
it is
place
at
completely
the
ordi-
nary temperature, or on gently heating, but at the
boiling-point of mercury (350° C.) the metal begins
to oxidise.
MERCURY,
mercury into dilute
hydrogen water, and observe that no
Expe^'iment 32.
sulphuretted
— Pour
265
a little
discoloration takes place.
Experiment
— Place about 4
33.
mercury in a mortar, add a
of
grains, (or
little
50 grains)
lead and either tin
or zinc, but not sufficient to destro}^ the liquidity of the
mercury, and rub until amalgamation takes place. Then
cause the globule of impure mercury thus obtained to
roll
down
a slightly inclined surface.
Observe that the
mercuiy does not maintain the spherical shape, as
in
the case of pure mercury, but that the globule elongates,
carrying a
with
tail
Place the globule in a small
it.
glass tube, shake well,
and
obsei've the thin film of
oxide which forms on the surface, impairing the lustre
of the mercury.
Experivient 34.
— Introduce a small
quantity of mer-
cury into a long glass tube closed at one end.
until the metal
Heat
has volatilised, and observe that the
mercury is condensed at the cold end of the tube in
the form of very minute globules, which adhere to the
surface of the glass, thus proving that mercury
may
be.
readily distilled.
—
Experiment 35. Pour a little mercury into a mortar,
add flower of sulphur and well mix, when black mercury
suljihide will be formed.
Transfer this to a small porce-
lain crucible, cover with a close-fitting lid, heat gently
for
some time; allow
to cool,
and observe the small
red crystals of vermilion.
Place a
when
little
of the sulphide in a glass tube
and heat,
the vermilion will be completely volatilised with-
out leaving any residue.
vermilion add a
little
To another portion
red lead or oxide of iron, heat in
a tube as before, and notice that the impurity
a residue.
of the
is
left as
266
DENTAL METALLUEGY.
PLATINUM.
—
Material Required. About
5 grams, (or 100 grains)
of platinum plate or wire.
Experiment
— Determine the density
36.
of the metal,
as directed in
Experiment 2. Observe that it is heavier
than any of the other metals in common use.
Experiment 37. Roll a piece of platinum to ascertain
—
its
malleability
and
" stiffness."
Heat
it
strongly in the
blowpipe flame for five to ten minutes allow to cool
and observe that annealing has made it soft and
;
flexible.
Experiment 38.— Heat a strip of platinum at a bright
red heat for some minutes, then cool in the air. Notice
that the surface remains b?ight, no oxidation taking
place.
Experiment 39.
sulphuretted
untarnished,
—Place
hj^dz'Ogen
as
a clean strip of platinum in
water.
has
it
The
metal
no
practically
remains
affinity
for
sulphur.
Experiment 40.
suitable support
possible
—Place a small piece
and heat
temperature
for
of platinum on a
some time
attainable with
to the highest
the
blowpipe.
Observe that the metal does not melt or even show
signs of fusion at the sharp edges.
—
Experiment 41. Take two small pieces of platinum
with clean surfaces place one on the toj) of the other,
:
and heat to a white heat for five minutes, then squeeze
quickly and hard with a pair of pliers. Notice that
the pieces have welded and cannot be readily separated.
Experiment 42.
— Heat a piece
of clean platinum to a
white heat, and while at this temperature place a small
PLATINUM.
upon
piece of pure gold
it.
267
Observe that the union of
the metals takes place at once.
Experiment 43.
—Repeat
A
instead of gold.
Experiment
similar result
cold place the strip of platinum
and
is
42, using lead
When
obtained.
thus treated in the vice
hammer. Notice that the presence
lead makes platinum brittle.
strike with a
of very little
—
Experiment 44. Dissolve i gram, (or 1 5 grains) of
platinum in aqua regia cautiously evaporate nearly to
dryness re-dissolve the residue in a small quantity of
;
;
water
;
divide the solution into
one portion
for
of a solution of
Experiment 45
ammonium
;
two portions reserve
to the other add excess
;
chloride (sal-ammoniac), then
about an equal bulk of alcohol allow to stand in a
warm place for a few hours until all the platinum is
wash the yellow precipitate with
Filter
precipitated.
;
;
alcohol;
dry and ignite,
metallic platinum
is
left
A
grey spongy mass
behind (see
the sponge to a white heat for
place on a bright anvil and
five
p. 187).
of
Heat
minutes, quickly
hammer
mass, which will have the appearance
into a
compact
and metallic
lustre of platinum.
Experiment 45.
— Further dilute the solution
of i)]ati-
from Experiment 44 with a
small quantity of hot water, add a few drops of hydro-
num
chloride reserved
chloric acid, place a clean strip of zinc in the solution,
go on until the liquid is colourRemove the zinc, wash off any adhering pre-
and allow the action
less.
to
spongy
and then
cipitate of metallic platinum, allow the black
precipitate to settle, pour ofE the clear liquid,
wash the residual platinum first with a little hydroPlace the
chloric acid, and then with hot water.
platinum in a heated mortar, and add a little mercury
2
05
DENTAL METALLURGY.
and rub well for some time. Amalgamation is readily
effected by continual mixing, producing a
more or less
unctuous mass. The amalgam may also be obtained
by using finely divided platinum, such as that produced
by heating the precipitate of double chloride of am-
monia and platinum, as described in Experiment
44.
After removing excess of mercury by squeezing in
ch amois leather, allow the amalgam to stand for some
days, and note that it hardens very imperfectly.
TIN.
Material Required.
pure
— 150
grams,
2500 grains)
(or
of
tin.
Ex2Jeriinent 46.
— Melt 50
grams, (or 1000 grains) of
tin in a small crucible or ladle,
and notice that
it
melts
at a very low temperature, the melting-point of
tin
being lower than that of any of the other metals in
common use. Allow the tin to cool and cast into a flat
open mould at as low a temperature as possible (i.e.,
just before solidification takes place).
dross from getting into the
placed across the
lip
mould a
To prevent any
stick should be
of the crucible
when pouring.
Allow the
tin to cool without disturbance, and observe
the clear, white, and bright surface of the metal when
cold.
If the tin is too hot when cast the surface will
be discoloured owing to oxidation.
Commercial tin often contains small portions of other
metals, and when impurities are j)resent they impart to
the tin a more or less dull and frosted appearance.
Hold the ingot
close to the ear
peculiar crackling sound,
will
be heard.
known
and bend
as the
it,
"cry"
when
a
of tin,
269
TIN.
Kvjm'iriicnt 47.
by weighing in
ment
air
density of the metal
and in water as directed in Experi-
Notice that the specific gravity of tin
2.
hio;her
—Ascertain the
than that of
Experiment 48.
is
slightly
zinc.
— Cut the
metal with a knife, noting
Test the malleability of pure tin by
Cut a strip of sheet tin about one-eighth of
rolling.
an inch wide, fix one end firmly in a vice, hold the
other end securely in the pliers, and observe that little
softness.
its
force
is
required to produce rupture, the tenacity of tin
being very low.
—
Experiment 49. Melt 50 grams, (or lOOO grains) of
cool and then fracture
tin, cast into an ingot mould
by placing in a vice and bending backwards and
forwards with a hammer. Notice the toughness of
;
the metal.
Ee-melt,
cast
into a
warm mould, then
Notice
remove quickly when solidified and break.
readily.
that the metal is more or less brittle and fractures
Experiment 50. Melt 50 grams, (or lOOO grains) of
—
tin,
and
raise to a red heat
;
the surface of the metal
be speedily covered with a layer of oxide. Allow
the metal to cool somewhat, then cast into a warm iron
mortar and pound with the pestle as soon as solidificawill
Observe that the metal is readily
powdered, tin being brittle at a temperature near its
tion takes place.
melting-point.
Experiment
sheet
tin,
through
51.
—Take
place one
the
rolls
two perfectly clean
on top of the other,
or strike several blows
strips of
and pass
with
a
hammer. Observe that the two pieces become welded.
The strips should be scraped with a knife to clean
them, as any dirt or film of oxide on the surface tends
to prevent union taking place.
270
DENTAL METALLURGY.
Experiment 52.— Place a clean strip of tin
in
sulphuretted hydrogen water, and notice that no
black
film is formed, as in the case
of silver when thus
treated.
ExpcHvunt 53.— Put about
of tin in a glass beaker,
and warm.
The
gram, (or 10 grains)
.5
add a little dilute nitric acid,
upon with the formation of
tin is acted
a white residue (metastannic acid).
Experiment 54._Melt 2 grams, (or 20 grains) of
with a little charcoal powder to prevent oxidation,
\t
tin
add
20 grains) of lead, then
4 grams, (or
40 grains) of bismuth stir and then cast the resultingf
alloy into a mould, and note its brittleness.
Place the
2
grams, (or
;
alloy in boiling water, observing that
it melts readily.
Determine the melting-point
p. 52,
^
Part
of the alloy as directed
on
I.
Experiment 55._Melt 6 grams, (or 60 grains) of
add 4 grams, (or 40 grains) of tin, using a layer
silver,
of charcoal to prevent oxidation.
Clean the surface of
the resulting alloy with emery, then heat it and
observe
that it is easily oxidised.
Out with a knife or file
it to determine the hardness;
place in a vice and
fracture, noting its brittleness. Eepeat the
experiment,
using 6 grams, (or 60 grains) of tin and
4 grams, (or
40 grains) of
silver.
Note the
characteristics of the
alloy as before.
Exjjerimeut
by placing
56.— Test
the affinity of tin for mercury
tin foil in a
mortar and adding mercury.
Observe that amalgamation is speedily effected. Mix
well with the pestle, place in chamois leather, and
remove excess of mercury by squeezing.
portion of the plastic
amalgam
for
Eeserve a
Experiment
57,
and
allow the remainder to stand for a few days until
it
271
ZINC.
colour, fracture with a
Note its white
hardens.
aad observe
hammer,
its brittleness.
Experiment 57.— Pack the plastic amalgam into a
glass tube, as directed in Experiment 28, and note
whether expansion or contraction takes place.
Expcrimeni
58.
—Take
pared in Experiment
55
;
filings of
each of the alloys pre-
add a little mei'cury to each, and
observe that amalgamation takes place with less facility
in the case of the alloy containing excess of silver.
zmc.
Material Beci'mred.
— 100
grams, (or
1
500 grains) of
zinc.
Eo:pcrimcnt 59.
—Melt 50
grams, (or
1000 grains) of
zinc, cast into
an ingot mould (similar to that described
on
I.) to
Part
obtain a
Observe that
zinc requires a slightly higher temperature to melt it
p. 76,
than lead.
flat
ingot.
Place the ingot in a vice and strike with a
hammer, when the metal will break off short, thus
showing its brittleness at the ordinary temperature,
and its crystalline structure. Cut the metal with a
knife, and ascertain its hardness.
Take one-half of
the ingot, heat to about 150 C, place it on the anvil
and hammer, observing that it is now malleable. Heat
again if necessary, and roll into a thin sheet. The
ingot
may
require annealing once or twice during the
operation by heating to about
50 C.
Heat the other
200°
half of the ingot to a temperature of
to 300° C,
i
'
and prove the brittleness of zinc at this temperature by
hammering or powdering in an iron mortar.
Experiment 60.
—Melt
10 gx'ams. (or 200 grains) of
zinc in an open crucible with free access of air
;
observe
^72
DENTAL METALLURGY.
that the surface of the metal
is readily covered with
a
film of oxide.
Raise the temperature to a bright
red
heat notice that the zinc is
volatile aud burns with a
brilliant bluish-white flame,
forming a very light white
powder, which is zinc oxide.
;
E.pcrimcjit 6x.—V\i,ce the strip of sheet
zinc from
Experiment 59 into dilute sulphuretted
hydrogen
water observe that no discoloration takes
place.
;
Er2m-imcnt
62.— Take
or 500 grains) of zinc
equal parts (abont 30 grams,
aud
lead, melt well together, and
pour into ail upright ingot mould. When
cold remove
from the mould and carefully inspect the
surface of the
a line will be observed where the
two metals
have separated on cooling. Place the
ingot in the
vice, as near as possible at the line
of junction of the
ingot
;
two metals, and
strike with a
break
off short.
Hammer
anvil;
notice
which
hammer, when
it
will
each half separately on the
that the
upper half consists of zinc,
hard, crystalline, and brittle
while the lower
lead, being very malleable and
soft.
is
;
half
is
63.— Place a little mercury in a mortar,
add zinc filings, and rub with tbe pestle until
amalgamation takes place.
Obsei've the character of
Mjj^erimerit
the
amalgam produced
effected.
;
also
Amalgamation
that
union
is facilitated
of water slightly acidulated with a
is
not readily
by the addition
few drops of
acid.
LEAD.
Material Reqaircd.~ioo grams, (or
1
500 grains) of
lead.
Erperimcnt 64.—Melt 50 grams, (or 1000 grains) of
Observe tbat it melts at a
lead in a crucible or ladle.
LEAD.
comparatively low temperatiive and that oxidation takes
Pour into an upright
place when the metal is molten.
ingot mould, remove
when
one end in the
cold, place
backwards and forwards with a hammer
brealcs, thus proving the toughness of the metal.
vice,
bend
until
it
it
Cut with a knife and notice that it is very soft roll
Take two
into a thin sheet and prove its malleability.
pieces of the sheet lead, clean the surfaces by scraping,
place one piece on top of the other and pass through
;
the rolls or
hammer on an
have welded.
Experiment
6'^.
anvil.
Notice that the pieces
— Prepare an ingot
of lead as in
Ex-
periment 64, remove at once from the mould when set,
place the ingot across two iron supports about i finches
apart
;
heat the centre by means of
held in the hand.
melting,
When
a'
shows
the lead
remove the burner
at
Bunsen
flame,
signs
of
once and strike the
centre of the ingot one sharp blow with a hammer,
when the metal will break, showing the brittleness
of
lead
at
this
Examine the
temperature.
verse columnar structure of the
compare
it
broken
with that obtained by fracturing lead
cold.
Experiment 66.
—Melt 50 grams,
trans-
surface
and
when
(or lOOO grains) of
gram, (or 20 grains) of antimony, stir well
and cast into an ingot mould. When cold remove,
Notice that the presence
place in a vice and fracture.
lead,
of
add
i
antimony has made the lead
brittle
;
cut with a knife
and observe that the alloy is much harder than pure lead.
Experiment 67. Determine the density of lead as
described in Experiment 2, observing that it should be
classed with the heavy metals.
—
Ecperimcnl 68.
— Place a clean
strip
of sheet lend in
s
DENTAL METALLURGY.
dilute sulphuretted
metal
is
hydrogen water
cand notice that the
tarnished.
I!xperime7it 69.— Clean a piece of sheet lead, place it
in a vessel with a little vinegar, and allow it to stand.
Observe that the metal
acted upon somewhat readily.
is
COPPER.
Material Required.
— 50
grams, (or 750 grains) of
sheet copper or thick copper wire.
—
Experiment 70. Cut a piece of copper with a knife
and notice its hardness test the malleability of the
metal by rolling or hammering observe that mechanical
;
;
treatment renders
it
hard.
Heat the
redness, observe'that the metal
contact with the
into
cold
;
notice
pliant
after
dilute
sulphuric acid
oxide
is
readily tarnished in
is
Plunge the metal while
air.
water
slip of cojjper to
that
Ee-heat
annealing.
;
the metal
observe
and
that
is
and
soft
plunge
the
hot
still
into
coating
of
removed from the surface by the action of the
acid.
—
Exim-iment 71. Take a small coil of copper wire
and determine the density of the metal as directed in
Experiment 2.
Eayperiment
72.
—Place
dilute sulphuretted
a clean strip of copper in
hydrogen water.
Notice that
coloration of the copper rajoidly takes place
dis-
owing
io
the formation of a film of sulphide.
Clean a piece of copper, place
it
in a vessel with a
few drops of vinegar, and allow it to remain for a day or
two.
Observe that the copper is acted upon, with the
formation of a green coating of " verdigris."
Erpeiiment 73.
— Hold
a piece of copper in contact
COPPER.
with the tongue and notice that
it
possesses a peculiar
faint, nauseous, metallic taste.
grams, (or 50 grains) of copper
on a cupel or charcoal support by means of the blowNotice that the temperature required to fuse it
pipe.
melt gold. Keep in
is a little below that required to
B.q)cnmcnt 74.— Melt
5
the molten condition for some minutes, allow to solidify,
then roll or hammer. Observe that the metal is more
owing to the presence of dissolved copper
The copper is more readily melted in a small
or less brittle
oxide.
crucible in a suitable furnace.
Exfcriment 75.
—Melt 30
grams, (or 500 grains) of
copper in a crucible with the addition of a little charcoal
powder and add i gram, (or 20 grains) of metallic arsenic.
When mixed pour into a suitable mould. EoU or
hammer the resulting alloy and observe that the
presence of the impurity causes brittleness.
—About half
the quantity of arsenic will probably be lost
by volatilisation when conducting the experiment.]
l^Xote.
—
Experiment 76. Melt 30 grams, (or 500 grains) of
copper and add .5 grams, (or 10 grains) of antimony.
Roll or
hammer
antimony
is
as before,
and notice that the
effect of
very similar to that of arsenic.
[JYute— Home of the antilnony will be lost owing to oxidation.]
Experiment 77.
— Place
a
strip
of
bright metallic
copper in a solution of mercuric chloride (corrosive subA silvery white deposit of metallic mercury is
limate).
obtained, which,
metallic lustre.
Experiment 78.
when gently rubbed, shows
— Dissolve
i
a bright
gram, (or 20 grains) of
copper in a small quantity of dilute nitric acid when
all fumes are expelled dilute with water and place a strip
;
of iron plate into tbe solution.
Allow
it
to stand for
DENTAL' METALLURGY.
276
some time
until the copper
the iron, pour
Eemove
precipitated.
is
the solution, wash the spongy copper
off
precipitate well with repeated quantities of cold water,
then transfer to a mortar,
a,dd a little mercury and rub
well with the pestle until amalgamation is complete.
The union may be
by the addition of a little
hot water and a few drops of sulphuric acid, or by adding
facilitated
a solution of mercuric nitrate to the precipitate before
the introduction of the mercury.
Eemove the excess
of mercury, if necessary, by squeezing through chamois
leather,
and allow the resulting plastic amalgam
for about twenty-four hours.
quite hard.
Hammer and
Notice that
observe
jDOund or knead in a mortar until
it
to stand
becomes
it
its malleability,
acquires
its
then
original
Allow to stand for a few hours, and notice that
recovers its hard crystalline character.
Experiment yg. Prepare a small quantity of copper
softness.
it
—
precijjitate
as directed in
.
Experiment
78, allow
stand exposed' to the air for a short time
it
;
it
to
observe that
becomes rapidly coated with a film of oxide and
is
unfit for amalgamation.
CADMIUM.
Material Required,
—40
grams,
(or
500 grains) of
cadmium.
Experiment 80.
crucible
readily
;
observe
oxidised
;
—Melt
its
cadmium
the
mould.
heat to bright redness,
Test
its
— Place
small
it
is
when the
Cast the metal into a
toughness, softness, malle-
and welding properties
Experiment 64.
ability
Ex'im'imcnt 8i.
a
low melting-point and that
metal burns with a brown flame.
suitable
in
as described for lead in
a clean strip of
cadmium
in
bismuth;
sul]ihuretted
hydrogen water.
277
'
Notice that the metal
is
sulphide.
soon covered with a yellow film of cadmium
Mix together in a mortar mercury
Exferiment
and cadmium observe that combination readily takes
82—
;
producing a soft tin-white mass. Allow it to stand
brittle mass
for some time, when it hardens and forms a
which softens when moderately heated and can be
place,
kneaded
like
wax.
BISMUTH.
Experiment 83.— Prove the brittleness of bismuth by.
Heat the metal in a crucible
crushing in a mortar.
a
observe its low melting-point and that it burns with
;
blue flame
when heated
to a high temperature.
the metal into a mould, and notice that
Cast
expands in
it
the act of solidifying.
Experiment 84.— Prepare an amalgam of bismuth by
shaking powdered bismuth with mercury in a tube.
Notice the liquid character of the amalgam obtained.
ANTIMONY.
Experiment 85.— Crush a little antimony in a mortar
Melt the metal,
to prove its extreme brittleness.
notice
noting its melting-point, raise it to a red heat;
burns with a white flame, forming the white oxide.
Experiment 86.— Place a little powdered antimony
and mercury in a glass tube, shake well and observe
that
it
that union does not take place readily even
when heated.
IRON AND STEEL.
Experiment
notice that
it
87.— Take
a
piece
of
soft
bends readily without breaking
iron wire;
;
heat
it
to
2
DENTAL METALLUEGY.
7^
redness and plunge while hot into cold
water
that it still retains its softness and
;
observe
bends readily.
Exim-imcnt 88.— Take a piece of
wn-e)
;
observe that
it is
eteel wire (pianoforte
" stilT" and hard, but
can be
bent;
heat to redness and plunge into cold water;
notice that the wire is now very hard
and brittle and
breaks readily,
Heat another piece
water to harden
of the wire to redness, plunge into
clean the
surface carefully with
emery, heat gently over a Bunsen flame until it acquires
a blue tint, then plunge at once into cold water.
Observe
that the wire has lost its brittleness and can
now be bent
it,
after thus tempering.
Experiment 89.— Heat a piece of soft iron wire at the
temperature attainable with the blowpipe;
observe that it does not melt.
Continue heating for
notice that the metal is oxidised and
5 or 10 minutes
" burnt " and becomes more or less
brittle.
^
highest
;
Ejjjcriment 90.
pieces,
place
— Cut
some hoop
iron
into
small
about
50 grams, (or 500 grains) in a
crucible, raise to a red heat and add small pieces of
sulphur at intervals. When the whole is melted pour
when
into a mould, and
and notice that
it is
bronze-like colour.
cool fracture the iron sulphide
more or less brittle, and has a
(See Spence's "Metal," p. 47.)
hard,
ALUMINIUM.
—
Experiment 91. Take a sheet of aluminium and
determine its density as described in Experiment 2.
Observe that it is the lightest of the common metals.
Melt a small piece of the metal before the blowjMpe
observe that it requires a bright red heat to melt it and
that
it
is
somewhat ''pasty "when molten.
Eoll the
NICKEL.
metal to prove
and toughness, heat
malleability
its
279
redness and drop into cold water, thus proving that
(See p. 246, Part I.)
softened by annealing.
— Place
Experiment 92.
sulphuretted hydrogen water
tion takes place.
Experiment 93.
strip
a
— Prepare
;
of
notice that no
is
it is
metal
in
discolora-
a solution of sodium car-
bonate, put a strip of aluminium into
that the metal
the
to
it,
and observe
acted upon.
—
Experiment 94. Remove the aluminium from the
solution in the preceding experiment and rub a little
mercury on the surface the plate will soon become
;
covered with a white film of oxide,
the surface and
may be
detached in
which swells up on
flakes.
NICKEL.
—
Experiment 95. Take a piece of nickel wire or plate,
clean with emery, observe that it is white, malleable
when hammered
and
difficult to
or rolled, very tenacious, hard, tough,
break.
Heat
it
at the highest
tempera-
ture obtainable with the blowpipe, and notice that
does not melt, and that it is oxidised on the surface.
it
Experiment 96.— Place a clean strip of metal in
sulphuretted hydrogen water observe that no discolora;
tion takes place.
THE BLOWPIPE FLAME.
Experiment 97.
charcoal, place in
— Make a
it
small cavity in a piece of
a piece of lead foil
and heat before
the oxididmj flame of the blowpipe (see p. 57, Part I.).
Notice that the lead is gradually converted into oxide.
28o
DENTAL METALLURGY.
Enperivicnt 98.
— Clean a piece
of copper
before the oxidising flame, observing that
"
and Leat
it is
it
quickly
blackened " or oxidised.
Kqwrwicnt
99.
—Place a
little
lead oxide (red lead)
in a cavity in charcoal
of the blowpipe (see
is "
reduced
" to
and heat with the reducing flame
The lead oxide
p. 57, Part T.),
the metallic state in the form of
little
globules.
Mqjerirnent 100.
— Heat
a clean sheet of copper before
the reducing flame, and notice that the metal
readily tarnished than in the oxidising flame.
is
le?s
7S
2
)
APPENDIX
Common
List of the
Elevients, toiih their
Symbols
and Atomic Weights.
[
V„^,,._The words in brackets are the Latin names of the elements
from which
t\ie
symbols have been derived.]
Atomic
c>
Xavuc.
Wciylits.
111 yjyjKt
Aiiiiroximate
Values.
Al
Aluminium
Antimony {Stibium)
Sb
As
Arsenic
Bismuth
Bromine
.
•
.
27
120
Bi
75
207.5
Br
80
More Exact
Values.
27.04
iig.6
74-9
—
79.76
Carbon
Cd
C
Chlorine
01
35-5
35-37
Cu
F
Au
63
63.
Cadmium
Copper
.
.
(CKjJrviii)
Fluorine
.
Gold [Auruiii)
.
H
Hydrogen
Iron (Fcrruni)
.
Lead (I'ii(iiihiiw)
Mercury {Ihjdruriiy.
V in
12
III.
n7
i.y/
1
T
1 T
19
197
1
19.06
196.8
I
Ir
127
192.5
Fe
Pb
56
207
Hg
200
Ni
59
14
I
Iodine
Iridium
1
.126.54
5788
206.39
199.8
5S.6
14.01
15.96
106.2
Nickel
Nitrogen
O.xygen
Palladium
Phosphorus
Platinum
Potassium {K(tliuni)
Pd
P
106
Pt
Silver {Art/rn(niii)
Ag
Na
19s
39
108
30.96
194-3
39-03
107.66
23
32
118
22.99
31.98
117-35
.
.
Sodium
{N(itrium)
Sulphur
Tin (Stannviii)
Zinc
0
K
S
.
.
N
.
Sn
Zn
16
31
90.4
DENTAL METALLURaY.
282
CONVERSION OF CENTIGRADE AND
FAHRENHEIT DEGREES.
The thermometric
scales in use in this country are the
Centigrade and Fahrenheit
;
the former of these
is
rapidly
becoming universal for scientific purposes. The two
ai-e mutually convertible by the following rules
scales
:
1°
C.
=
1.8° F. or 4° ¥.
—
To Convert Centiynide into Fahrenheit. Multiply by 9,
5, and add 32.
To Convert Fahrenheit into Centigrade. Subtract 32,
multiply by 5, and divide by 9.
divide by
—
ENGLISH WEIGHTS.
APOTHECARIES' WEIGHT.
Ounces.
I'oiiiitl.
fb
=
I-
Drncliiiis.
=
12
51=
=
=
96
8
Grniiin.
Hcriijilis.
=
=
=
=
288
24
51=
3
3
I
5760
480
60
Gr. 20
AVOIRDUPOIS WEIGHT.
tt)
1
Drachms.
Ounces.
I'ouiul.
=
16
oz.
I
'J'l'oi/
=
=
=
256
-
=
16
dr.
I
Grains.
7000
437.5
27.344
RELATIVE VALUE OF TROY AND AVOIRDUPOIS
WEIGHTS.
PouihL
I
Troy
I
Avoirdupois
I'ound.
I'onnds.
=
=
0.822857 Avoir.
1. 215277
Troy
=
=
Ounces.
o
...
I
..
13
2
Grains.
72.5
..
.
.
280
APPENDIX.
283
IMPEKIAL MEA,SUltE.
Flu id
Pints.
(liiltoii.
=
I
Fluid UiiKccs.
.
8
:=
160
=
1280
I
=
20
=
=
160
I
I
gallon
I
fluid
.
.
.
ounce
(j'o
I
gallon
I
fluid
JJrachms
.
pint)
=
=
—
437-5
„
-i
277.280 cubic inches
—
ounce
S
70,000 grains of water
1-733
n
!:
METMC SYSTEM
OF WEIGHTS AND
MEASURES.
In the French or decimal system the smaller denominations are obtained by taking a tenth, hundredth, thousandth,
&c., of the unit chosen, and are designated by the Latin
the higher denominations are 10 times, 100 times, 1000, &c. times the unit,
and are named by the Greek prefixes deca-, hecto-, kilo-, &c.
examples of this will be found in the tables given below.
prefixes deci-, centi-, milli-, &c., whilst
;
The
of
I
of
iinit
cubic
the gkamme, which
loeight is
centimetre of water, and
is
is
the weight
equal to 15.432
grains.
The unit of
length
is
the
metke, and
is
one ten-
millionth of the distance on the earth's surface fi'om the
equator to the pole.
The unit
It is 39.37 inches.
mPMSure of capacity
oj
cubic decimetre, and
is
the litre, which
is
equal to 1.7 61 pints.
The chief
convenience arising from the use of the metric system is
that the difl'erent denominations can be written as one,
I
is
since they are either multiples by 10 or are decimal frac-
tions of the
decigramme.«,
gmmmes.
Tlius 6 decagrammes, 2 grammes, 5
milligrammes would be written 62.503
unit.
3
DENTAL METALLURGY.
METRICAL MEASURES OF WEIGHT.
I
gram.
=
the weight of
i
cubic centimetre
GiMius.
(c.c.)
of water at 4° C.
Cir;iius.
Avoirdupois.
1
1
1
Milligram.
Centigram.
Decigram.
.001
54323
0.0
100.0
000.0
10000.0
1
oz.
I
lb.
I
lb.
Avoir. =28.3675 grams.
=437.5 grains
Avoir. = 16 ozs. Avoir.
.
.....
....
Troy =12 ozs. Troy
Troy
A voirdupois
I
oz.
I
lb.
I
cwt.
I
ton
Jrms.
0
0
3
5.65
8.5
22
I
2
235
154323 48800
grain
_
gram. = 15.43235 grains = 0.032151 oz. Troy =
oz. Troy = 3 1. 1
04 grams. =480 grains
I
oz.
0
lljs.
15-43235
154-32349
1543-23488
15432.34880
1
Mjriogram.
1
1-
1.0
Kilogram.
I
0-
.1
Gram.
Decagram.
Hectogram.
I
0.01543
15432
.01
0.0649 gram.
0.0352736
1.
=
-
097 1
oz.
oz. Avoir.
Avoir.
0.91 14 oz. Troy.
7000 grains.
5760 grains.
31.1035 grams.
453-593 gi-ams.
50.8024 iiilograms.
(Icilos).
The
.
1016 kilos.
followiijg
approximate relations
G raiiiiiies.
I
5
10
20
may be found useful
Grains.
.
-
77i
.
155
.
310
28A
100
.
142
.
.
I
oz.
32 oz.
5 oz.
10 oz.
285
APPENDIX.
METRIC MEASURES OF LENGTH.
Millimetre
\_
(mm.)
J
Centimetre
Decimetre
Metre
Decametre
Hectometre
Kilometre
Myriometre
0.001
=
=
=
=
=
=
o.oi
0.1
1.0
lo.o
100.0
1000.0
10000.0
=
=
yard =
mile =
=
=
=
=
=
=
=
03937=
•
3937079=
393.70790=
3937.07900=
39370.79000=
393707.90000=
inch
.0254 metre
I
foot
.3048
I
39371=
3.93708=
I
I
Mile.
Ins.
Motrc.
„
.9144
=
=
=
Fl't;-.
Ins.
Yds. Ft.
- — - — — — —
— — — J
— —
— —
— 4
6
I
10
109
2
213
4
156
0
•°3937
.39371
3.937X
3-371
9.7
I
I
10.2
6
2.5425 centimetres.
3.048 decimetres.
9-144
"
1.609 kilometre.
METRIC MEASURES OF CAPACITY.
I
litre
=
Liti-c.
Millilitre
=
=
=
=
=
=
=
Centilitre
Decilitre
Litre
Decalitre
Hectolitre
Kilolitre
Myriolitre
-ooi
-oi
-i
'-o
lo.o
100.0
1000.0
Tints.
Cubic Indies.
1
or'i
Cubic centi- V=
metre (c.c.) J
1
cubic decimetre.
I
=
.06103
=
=
=
=
=
=
.61027
6.1027
61.027
610.27
6102.7
10000.0
-
=
0.00176
=
=
0.01761
0.17608
1.76077
17.60773
176.07734
1760.77341
17607.73414
=
61027.0
610270.0
=
:
1
I
cubic inch
=
=
=
.01639 litre
=
16.39 c.c.
2S.31531 lifes-
I
cubic foot
I
gallon
I
litre
=1000 cubic cm. = 61.02705 cubic inches =1./ 6
I
pint
=
4-54336
34-66 cubic inches.
.
,
^
pin
DENTAL METALLURGY.
of Substances which are knoion by
Names, with
their
Coiuuiou Name.
Alum
Chemical
Common
Names ami
or Popular
Formula}.
Chemical Nauio.
Foriiiul.v.
/Double sulphate of]
aluminium and po-
A1.,(S0,)3,K,S0,
1
[
Aqua
fortis
Aqua
regia
|
calcium hypochlo-
I
rite
Calomel
or
Corrosive sublimate
salts
or
)
spirits of salt
Plaster of
gypsum
\
Ca.lPOj).,
HgXl.,
NallO
Calcium carbonate
CaCO.,
KHO"
Sodium chloride
NaCl
Mercuric chloride
Magnesium sulphate
HgCl,
MgSO„7H20
Sodium sulphate
Lead oxide
NaoSOj
Silver nitrate
AgNO;,
VhO
Hydrochloric acid
HCl
Calcium sulphate
CaSOj
/
Paris or
Ca(OCl)Cl
Potassium hydrate
Sodium hydrate
J
salt
Glauber's salt
Litharge
Lunar caustic
Muriatic acid
HN63
3HCI + HNO3
J
/"Nearly pure calcium')
phosphate
\
j
Mercurous chloride
Bono ash
Caustic potash
Caustic soda
Chalk, marble
limestone
24H.,0
I
1
Epsom
J
Nitric acid
f Mixture of nitric and")
hydrochloric acids J
(
^Compound of cal-'j
cium chloride and
Bleaching powder or
chloride of lime
Common
tassium
j
Prussic acid
Hydrocyanic acid
Putty powder
HCy
Tin oxide
Quicksilver
Mercury
Oxide of iron
SnOo
Hg'
Rouge or colcothar
Sal ammoniac
Salts of
lemon
Saltpetre or nitre
Spirits of
Ammonium
/Citric acid and po-)
\ tassium oxalate
j
Potassium nitrate
wine
Tartar emetic
Alcohol
Vermilion or cinnabar
Vitriol (oil of)
„
blue
green
white
„
Washing soda
White lead
f
1
tartrate
Mtrcury sulphide
Sulphuric acid
Copper ^ulphate
Iron sulphate
Zinc sulphate
Sodium carbonate
(crystallised)
Lead carbonate
KNO^
C.HoO
/"Potassium antimony^
\
„
FCoOt
Am"ci
chloride
/
4(SbO)K(C4H,0„)
HgS
H.,S0,
CuSOj
FeSOj
ZnSOj
"1
/
Na^COnioHoO
PbCO.T
INDEX.
Acids, action on
„
mct:il8,
alloys,
n
Aluminium bronze, 248
34
preparation, 248
„
43
properties, 248
„
„
Ageing- of araalg:im alloys, 156
solders,
„
on metals, 33
Alkalies, action on metals, 35
Air, action
249
Amalgams, 130
Alloys, 37
colonr, 41
„
„
contraction, 131
„
dclinition,
expulsion, 131
130
„
condnctivity, 42
„
„
constitution of. 38
„
preparation, 132
„
ilefinition,
„
properties, 131
„
density, 41
„
dental, 174
.,
entcctic, 39
37
Amilgams, Dental, 140
action in muutli,
„
„
156
ageing, 156
for amalgams, T43
„
„
dies,
shape, 151
solders, 55
fusibility of,
„
fusible,
42
50
baUnccs for, 158
change of colour,
„
„
„
„
„
„
„
,,
152
176
„
li(|uation, 41,
„
preparation, 43
„
properties, 41
„
Von Eck irt's,
175
composition, 145
copper, 163
248
„
alloys,
„
amilyam, 132
„
annealing, 246
„
casting,
„
„
detection of gold
„
„
detection of pla-
„
„
discoloration, 152
,,
„
edge
in, 102,
„
246
effect of mercury, 132
exijcriments with, 278
„
for d(!ntnres, 245
„
in dental
prepiration, 243
„
])roperties,
„
solders,
„
swaging plates
161
tinum, 161, 188
strength,
154
amalgams, 148
„
„
vol-
change of
ume, 148
Aiuininium, 243
„
of
alteration
„
„
44
„
(HVectof dilVerent
„
lo;ikag(!,
melals,i44,T46
244
154
mixing, T59
247
of,
245
uses of In dentistry, 245
licriniincnci'
tlie
in
mouth, 155
288
INDEX.
Amalgiinis, Dental, pveparation, 160
"
"
proiioi-ties,
><
1,
finalitativc
1.
<,
(luilities
1,
„
(inaiitity of uicr-
ing
of,
sary,
„
161
iiopus-
oxyhydroyen, 64
iSnr ix, 79, 8t
222
Hr.iss, 48,
158
Sullivan's
Uritiiiinii metal,
217
Brittle! H'old,
ciiji-
por, 163
tnbos
mouth, 58
Owen's, 61
„
test-
140
ciiry,
IJlowpipcs, theory of,
57
143
f ir uiixiM'4-,
90
iiriti le platinum, 185
Brittleness of met Us, 12,13
Bronze, 222
Buruiut;- steel, 242
Anno iluiL;',
242
12,
Antimony, 231
.'liloys,
„
Cadmium, 224
232
advant
anialiiani,
133
oxperinuMits willi, 277
ill dental am ilyams,
147
UMtion, 231
lire))
„
proiiertios,
„
solvents for, 36, 232
use in dentistry, 232
„
!.
refii
Ass i,v of
„
,.
1.,
231
„
IJase metals, i
liellows for blowiiipe, 63
,1
„
alloys,
amalgam, 133
229
50
amilgam,
,,
cxperiment.s, 277
in dental anial-jam,
„
])rep iration,
„
projierties,
227
228
„
solvents for, 228
„
UBC
dentistry, 229
Hlast-fnruace, 3
147
prei)aration, 224
„
projierties,
„
solvents for, 36, 225
uses in dentistry, 225
224
alkalies on, 203
,,
for lining, 20T
of
volume
in metals.
Constitution of alloys, 38
Contraction of dies, 45, 199
„
„
met:ils,
30
Copper, 219
action of
.acids,
air,
«
220
220
58
alkalies,
automatir-. 62
snlphuri!! ted
35
hydrogen, 220
57
liot-ljlast, 59.
29
„
„ metals, 7
Colcmring gold, 116
„
238
llanie,
147,
Colour of alloys, 41
„
ill
alli).v.s,
„
Change
„
„
„
in dental
C'liiTt and fineness, 105
Cast iron, 234
Cements, action of acids on, 203
Bismntli, 227
lllowiiiju'S,
fusible
„
.^6
Balance, Fletcher's amalgam, 159
Kirby's amalfiiim, 158
„
r.lister steel.
„
225
178
liAliniTT METAI,,
:'.m il-
226
experiments with, 276
99
silver,
133
H'.un,
36
ijold,
ilgMii,
dis idviMitase of, in
Appendix, 281
A<iii
amalgam,
in
alloys, 51
am
„
„
'.ge of,
225
62
„
„
watei',
220
289
INDEX.
Flame, blowpipe,
221
CoppL'i- alloys,
„
„
cffoct o£ Impuvitic's,
FlotcUer'a balance, 159
220
oxpoi'iiuouts witli, 274
ill
„
doutal amalgams, 146
iivcpai-ation,
„
propcrtios, 220
solvents, 36,
liot-blast
„
mixing-tube, 160
Fi-actnre of metals, 20
of metiils, 14
Fluxes, 79
Foil gold, 91
220
uses in ilcntistvy, 221
,,
blowpipe, 59, 62
„
Flow
219
„
tliuory of, 57
Flatting mill, 77
amalgam, 134
dental amalgam, 163
platinum, 185
„
tin, 216
Furnace, blast, 3
„
Crucibles, 68
Crystalline ch'.iraeter of metals, 20
crucible, 5
„
Cupellition, 167, 178
fusion,
Cupels, 167, 178
5,
69,
73
muffle, 5
Density or alloys, 41
metals, 9
„
„
oil,
Dental alloy, 174
Fusible met.Us, 50, 229
„
amalgams, 140
copper amalgiims, 163
„
gold plate, 106
„
72
reverbcratory, 4
„
determining melting-
„
point
,,
Detection of gold, 102, 162
„
.,
„ tin, 162,
„
„
52
preparation
pliitinnm, 162, 188
Dies, alloys for,
of,
Melotte's, 52
of,
51
use in dental labora-
„
218
tory, 52
Fusibility of metals, 18
44
properties ol, 44. 199
Draw-plate, 15, 78
Galvanic action,
Ductility of alloys, 43
„ metals, 15
„
German
Edge sthenctii of amalgams,
154
alloys, 42
Electrical conductivity of
„ metals, 25
„
of
purification
silver,
252
Gilding, 116
mercury,
air.
„
alkalies, 89
„
„
sulphuretted
gen, 89
Electroplating, 116, 181
water, 34, 89
Eutectic alloys, 39, 17S
„
Expansion of amalgams, 148
28
witli metals,
Extraction of mctuls, a
FrNF.NF.SS OF flOLO, IO5
Fire gilding,
n8
89
„
127
Experiments
156
Gold, 85
action of acids, 89
„
Elasticity of metals, 17
„ metals,
30,
Galvanised iron, 199
Gauge-plate, 77
256
alloys,
103
„
amalgam, 134
„
assay,
„
beating, 91
„
Ijrittle,
„
carat,
„
colouring, irO
,.
CI
99
90
105
ysl 11,98
T
bydro-
290
INDEX.
Gold, detection of, 102, 162
eft'ect of iminirities,
„
90
„
estimation, 102
„
„
experiments with, 257
fineness, 105
„
foil,
„
„
„
93
„
liarduess, 11, 88
„
impiu'ities in,
„
in dental
„
Lamm's shredded, 97
„
„
meltiug-point, 19, 89
occnrronco, 85
„
parting-,
„
plate,
„
precipitauts, 96
precipitated, 96
„
solvents for, 36, 239
„
wrought, 235, 237
„
Lamm's snnEDDEn gold,
97
pniTDle-of-Cassius, 121
raising standard, 115
recovery from scrap, 66. It8
reducing standard, 114
Ladles, 74
Lead, 208
„
air,
,>
!.
no
solders,
„
solvents for, 36, 89
II
„
spongy, 96
„
„
standard, 105
sweep, 119
„
„
„
tests for,
„
Gun
action of acids, 34, 210
11
„
„
experiments, 150
mixing tiiho, 161
„
106
„
„
„
Kihby's balance, 158
„
„
234
239
experiments with, 277
preparation, 237
properties, 238
86
„
„
cast,
effect of impurities,
„
preparation, 85, 87
properties, 88
pnro, 87
„
„
„
„
90
amalgams, 144, 146
234
amalgam, 135
annealing, 242
burning, 242
„
cohesive, 93
non-coliesive,
I,
„
Iron,
„
„ prepanition, 91
gilding, 116
»
Iridium, use in dentistry, 192
33
alkalies,
35
sulphuretted hy.
drogeu, 33
to ascertain fineness of,
113
„
water, 34, 210
210
amalgam, 135
experiments with, 272
in dental amalgams, 148
preparation, 208
uses in dentistry, 89
„
properties, 209
„
sheet,
„
102
Watt's crystal, 98
metal, 223
Habdening steei,, 240
Hardness of metals, 10
Heat conductivity of metals,
INOOT-MOULD, 76
simple, 65
,,
Iridium, 191
„
alloys,
209
solvents for, 36
uses in dentistry, 210
„
Lemel, pm-iflcation of, 119
„
Limit of
elasticity, 18
Lustre of metals, 7
25
Liqu.ition of alloys, 41, 176
Malleability of metals,
„
43
„
alloys,
„
properties, igr
192
12
effect of alloying
Melotte's fusible metal, 52
Melting appliances,
INDEX.
MeltiDg-points
„
Metals, fracture, 20
42
iilloys,
oJl
„ metals, 18
„
scrap, 66, 118
„
Mercury, 123
„
action of acids, 124
124
air,
„
124
„
„
alkalies,
„
„
sulphiu-cttcd
„
„
water, 124
liy-
drogeu, 124
„
adulteration ot, 125
„
(listillat'on of,
„
electrical
„
127
experiments with, 264
126
purification
of,
127
„
filtration of,
„
for dental amalgams, 125
„
impm-ities
,,
in,
preparation
fusil)ility,
„
„
galvanic action, 30, 156
hardness, 10
„
lustre,
„
malleability, 12
„
„
methods of extracting, 2
micro-structure, 24
123
7
„
native, 2
„
noble, I
„
occurrence
„
physical properties,
„
solvents for, 36
„
„
specific gravity, 9
heat, 27
„
„
taste, 8
„
tenacity, 16
„
useful, 5
used in dentistry, 6
125
of,
i8
„
2
of,
Sleter metal, 217
„
properties
„
purification of, 126
Micro-structure of metals,
„
solvents for, 36, 124
„
stilpliide of,
Moldine, 52
Moulds, ingot, 65, 76
Muffle furnace, 5, 75
of,
124
128
Motallui'gy, definition of, 2
Metals, 7
action of acids on, 34
„
33
„
„
„
„
alkalies,
35
sulplmrctted hy-
Native metals,
„
drogen, 33
water, 34
„
alloying, 37
appliance* for melting, 65
„
base, I
„
brittlencss in, 13
„
capacity for heat, 27
„
change of volume, 29
colour, 7
„
conductivity
aiiS
„
alkalies,
„
„
of,
alloys,
251
sulphuretted hydro-
densily, 9
ductility, 15
„
ehisticity,
17
„
„
expansion by heat, 28
„
cxperluieuts
colli,
cxposMn'
„
How
ill
14
„
experiments with, 279
„
preparation, 231
„
properties, 251
„
solvents Cor
Noble metals,
cllect of
.,
amalgam, 135
plating, 254
f_
„
252
„
25
crystalline character, 20
of.
251
»
„
gen, 251
„
„
action of acids, 251
„
water, 251
„
„
2
Newton's metal, 51
Nickel, 251
i
19
witli,
256
the moulli, 35
Occurrence or metals,
2
Ores, 2
(
(
203
)xy-hydroyou blowpipe, 64
(xy-cliloride, niuc,
292
INDEX.
Oxy-phoBphato,
zinc,
Oxj-.suliiliatc, zinc,
204
Platiunm, properties, 184
205
solvents for, 36, 184
sponge, 187
uses in dentistry, 185
welding-, 187
„
„
I'ALLADrUM, 193
„
action of acids, 194
„
"
air,
»
alkalies,
..
"
194
Polishing- putty, 214
Precipitated gold, 96
35
sulplim-etted
»
„
Piu'iflcation of lemel, iig
liydi-ogeii,
194
"
«atei-,
..
alloys,
M
„ mercury, 126
„ sweep, 1T9
Purple-of-Cassius, 121
194
Pyrometers,
c-4
195
amalgam, 135
i>
„
„
(iUICICSILVER, 124
in duutal amalgams, 147
precipitate, 195
(inoen's metal, 217
)i
preparation, 193
Keitnino gold, 86
»
properties, 28, 193
Kevcrboratory furnace,
4
Rolling mill, 77
»
solveuts for, 36, 194
use for dental piiriioses,
11
»
Hose's fusible metal, 51
195
I'artiug: gold,
I'ott ter,
I'liysical
II
Scrap, melting,
86
211
properties of alloys,
37
II
„ dental amal-
gams, 141
„ metals,
i:
I'iiis,
brittle platiunm,
7
11
II
Silver,
185
„
action of acids, 184
184
„
air,
»
,1
alkalis,
)i
11
sulpliiu'etted
„
-miter,
II
,,
alloys, 189
amalg:am, 136
black, 186
„
brittle, 785
„
dental alloy, 174
detection, 187
estimation, 188
„
„
.,
„
„
„
„
184
experiments with, 266
foil, 185
from scrajis, 118
gronp, 183
iu dental amalgam.-i, 188
preparation, 183
182
166
action of acids, 167
167
II
„
air,
11
I,
alkalies,
II
II
sulphuretted hy-
11
„
water, 167
168
drogen, 167
35
liydrogeu, 184
11
silver, 119,
i>
Scorilication assay, 180
Platinum, 183
„
66, 118
recovery of gold from, 118
platinum, 118
„
„
„
alloys, 171
„,
amalgam, 136
„
assay, 178, i8i
„
chloride, 169
„
cupellation, 167, 178
„
experiments with, 261
amalgams, 143, 146
in s(j-ap, 182
„
„
in dental
181
„
plating-,
„
precipitate, 171
„
preparation, 166
„
i)roperties,
„
pure, 169
167
solders, 176
II
„
preparation
nf,
177
iNDEX.
Tin, action of air, 214
Silver solvents, 36, 167
168
„
spittins^ of,
„
stiiiulai-il,
„
uses in duntistry, 169
172
alumminm, 247
249
for dies, 47, 206
„
amalgam, 138
„
detection
„
no
216
„
„
„ platinum, 191
„
„ silver, 176
„
,,
of,
experiments
foil, 216
grain, 213
„
prepiiriition of, 55, 113,
„
soft, 55,
witli,
„ fusible alloys,
„
177
218
268
amalgams, 140, 146
in dental
hard, 55
„
50
216
„
plate,
„
preparation, 213
Solvents for metals, 36
Specific gravity of alloys, 41
„
properties, 214
„
solvents for, 36, 214
„
uses in dentistry, 215
211
metals, 9
heat of metals, 27
„
Speculum metal, 222
welding, 214, 216
T6uchstone, 100
Type metal, 45, 211
„
Spelter, 198
Spence's metal, 47
Spongy
„
gold,
96
Vermilion, 128
platinum, 187
impm-ities
Standard gold, 103, 105
silver, 172
„
in,
„
aunealiug, 242
properties
„
A'arieties of blowpipes, 57
„
burning, 242
Von
„
definition of, 236
„
hardening, 240
Water,
,,
tempering, 240
Watt's crystal gold, 98
Welding gold, 91
Sullivan's
of,
238
amalgam, 163
Sulpluiretted
hydrogen, acliou
on
metals, 33
Swaging- metal plates, 12, 108, 174
Sweep, purlHeatiou of, 119
129
preparation, 128
„
Steel, 236,
liyilro-
water, 214
„
„ g-old,
sulphuretted
alloys,
„
Soldering-, tlioory of, 80
-bronze,
„ aliiiniui urn
alkalies,
„
gen, 214
Soft-soldcviug, 83
Solders, 55
for
„
2x4
„
130
Eckart's alloy, 175
action ou metals, 34
209
„
lead,
„
ijlatiuum, 187
„
tin, 214,
2i6
Wn-e-ilriiwing, 15, 78
Wood's metal, 51
Tastk of metals,
8
Wrought
iron,
235
Tempering, 240
Zinc, 197
Tenacity, 16
Testing amalgam, 149, 161
Tests for gold, 100, 162
„
„
jdatinum, 162, 187
„
tin,
218
„
„
.
action of acids, 198
„
alkalies, 198
„
sulphuretted
gen, 198
Tin, 213
action of acids. 214
„
w-ator, 198
liy.lro
294
iiSTDEX.
.
Zinc alloys, 205
I,
ti
„
Zinc, melting-
amalgim, 138
brittle, 13, 200
chloride
of,
202
„
compoiiuds
of,
„
contraction
of,
„
counter
„
dies,
),
dies,
199
experiments with, 271
fusibility of, 19, 198
hardness of, n, 199
in dental
„
oxy-cbloride, 203
„ -phosphate, 204
„
199
108, 200
-sulphate, 205
preparation
„
properties, 198
puriiioation, 200
of,
197
„
solvents for, 36, 198
„
sulphate, 202
uses in dentistry,
„
amalgams, 147
London
„
„
„
white, 201
Printed by Ballantynu:,
200
oxide, 201
„
2or
of,
„
Hanson
Edinburgh
6)^ Ci
199
No.
J.
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