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DENTAL  METALLURGY:
Manual for the Use of Dental Students
   CHAS. J. ESSIG, M.D., D.D.S.,
            iff
PROFESSOR OF MECHANICAL DENTISTRY AND METALLURGY IN THE DENTAL
    DEPARTMENT OF THE UNIVERSITY OF PENNSYLVANIA.

Or-" (A',
     PHILADELPHIA:

The S. S. White Dental Mfg. Co.

         1882. 
Cxaa^-S-V-
 VvJU
  E7f5u
   I8SZ.
           Copy-right.
The S. S. White Dental Manufacturing Co.
             1882.
ALL RIGHTS RESERVED.
   PRESS OF
PATTERSON &  WHITE,
  PHILADELPHIA. 
PREFACE.
HPIIE object of the author  in the preparation of
     this manual was to  place in the hands of stu-
dents of dentistry an outline of the scientific princi-
ples  involved  in the  reduction of the metals,  their
properties,  the modifications resulting from alloying,
and their application to dental uses.
  While the properties of many of the metals have
been only  incidentally or illustratively referred to,
special consideration  has  been given to those  most
commonly  used by dentists.
  In Chapter V. a resume of the author's experiments
in the formation of alloys for  amalgams is given.
These were made for the purpose of enabling him to
present the subject systematically to the students
who sat under his teachings ;  and, while the chapter
is far from being a complete treatise on the subject,
it is  hoped  that it will prepare the  dental student for
a better comprehension of that" branch of metallurgy,
occupying, as it does,, so conspicuous a place in the
practice of dentistry.
  As the atomic weights, specific gravity, and fusing-
points of the metals are differently stated somewhat
by various authors, the figures given in this manual
                                         iii 
 
CHAPTER I.
METALLURGY.
HPIIE art of separating metals from their ores, or
    from simple combinations with non-metallic ele-
ments, and their application to useful purposes, may
be regarded as a separate branch of chemical science.
It is essential that the student, before commencing
its study, should acquire a good preliminary knowl-
edge of chemistry and mechanics.
  The empirical reduction of the ores of metals seems
to have  been practiced at a very remote period, its
origin  being traced to Tubal  Cain, seventh only in
descent from Adam.*   The remains  of  numerous
mines  have  been  discovered  on the southern  and
eastern borders of the Ural Mountains, in which have
been found hammers and chisels of copper, and other
instruments of  the same metal of which the uses at
present are unknown.f  That these operations  were
conducted by a wandering people would seem to be
evidenced by the absence of any traces of masonry in
the neighborhood; and the fact that no iron  tools
were found near them would indicate their great
antiquity.
  * Fourth chapter of Genesis, Tubal Cain is spoken of as an  " in-
structor of every artificer in brass and iron."
  f Percey's Metallurgy.
                                        (7) 
8
DENTAL METALLURGY.
   (xmelin found  in the  eastern part of Siberia the
remains  of nearly one  thousand  sm el ting-furnaces,
very primitive  in character,  surrounded by heaps
of scoria, broken pottery, and  other evidences  that
metallurgical  operations of considerable  magnitude
had been at some distant period carried  on  in that
locality.*
   The alchemists of the  Middle Ages were the metal-
lurgists par excellence of  that  period, and there  is
evidence  that they were  acquainted with  chemical
processes for  the reduction of metals, which were
brought  to a great state of  perfection, thus showing
that the practical part  of metallurgy  was far in
advance  of the theoretical, j-

  * Percey's Metallurgy.
  f The following experiments, from manuscripts discovered by M.
Ferdinand Hoefer, will serve to convey an adequate idea of  the status
of metallurgy from the third and fourth centuries down to a compara-
tively recent date:
  "Experiment No. 1.—A piece of red-hot iron is placed under a bell,
which rests in a basin full of water.  The water diminishes in vol-
ume, and a  candle, being introduced into the bell, sets fire  at once to
the gas inside.  Conclusion—water changes into fire.
  " Second  Experiment.—A piece of lead, or any other metal except
gold or silver, is burned in contact with the air.  It immediately loses
its primitive properties, and is transformed into a powder or species of
ashes or lime.  The ashes, which are the product of the death of the
metal, are again taken and heated in  a crucible, together  with some
grains of  wheat,  and the metal  is seen rising from its  ashes and
re-assuming its original form and properties.  Conclusion—metals are
destroyed by fire and revivified by wheat and heat.
  " Third Experiment.—Argentiferous  lead is burned in  cupels com-
posed of ashes of pulverized bones; the lead disappears, and  at the end
of the operation there remains  in the  cupel a nugget  of pure  silver.
Conclusion—lead is transformed into silver."  (It is probable that upon
this and analogous facts was founded the theory of the transmutation
of metals.) 
METALLURGY.
9
   To  these early experimenters,  however, must  be
awarded the  credit of great industry.   They knew
nothing  of the metals as ultimate bodies, nor of the
particular force governing their union with the non-
metallic  elements, and finding that an earthy  matter,
such as an ore of iron, became converted by fire into
a metal,  they naturally believed the change of earth
into metals to be possible, and in the search for gold,
the philosopher's stone, etc., they really,  by mere
accident, discovered many valuable chemical  agents.
In this way sulphuric, nitric, and  hydrochloric acids
were produced, and these, made to act upon the metals,
in turn yielded the metalline salts.
   Thus  it will  be seen that from the gradual aggre-
gation of facts  resulting from the pursuits of the
alchemists ultimately sprang an  exact science, and
towards  the  latter part of the  sixteenth  century
appeared a set  of  investigators of a very different

  " Fourth  Experiment.—A strong acid is poured on copper;  the metal
is acted upon, and in process of time disappears, or, rather, is trans-
formed into a green transparent liquid.  Then a thin plate  of iron is
plunged into the liquid, and the  copper is seen to reappear in its ordi-
nary aspect, while the iron in its turn is dissolved.  Conclusion—iron
is transformed into copper."
  Practically the fourth experiment, quoted from Jules Andrieu's paper
on- " Alchemy," written for  the Encyclopaedia Britannica,  is electro-
lysis, the principle by which a compound of a metal with a non-metal
is decomposed by galvanic electricity, but the transmutation theory
was generally accepted as accounting for the phenomena noticed in
this experiment, and it would seem that at least some of the savants
of the period were sufiiciently shrewd and unscrupulous to turn  the
process to profitable account,  since we find that " St. Thomas Aquinas,
in his theological  writings, forbids the sale of ' alchemist's gold,' and,
in a special treatise on the subject unmasks an imposture of the char-
latans of the day, who pretend to  make silver by projecting a sublimate
of white arsenic on copper." 
10             DENTAL METALLURGY.

order, who, instead of wasting their time in the pur-
suit of such fanciful theories as that of transmutation,
etc.,  devoted themselves  to the unraveling of  the
principles that govern the  composition and forma-
tion  of  bodies  already known.   Thus,  Paracelsus*
was  the first to  distinguish the  true  cliaracter of
some of the well-known salts, such as alum and cop-
peras, showing  that they contained metals—a matter
of great importance  at  that day,  inasmuch  as it
eventually led  to the  discovery that many of  the
well-known crystalline salts were  compounds of  dis-
similar elements, as a metal with a non-metallic  body,
and to a knowledge of the particular force governing
their union ; and finally the investigations of Beecher
and  Stahl of Cronstadt,  Klaproth,  Wollaston, Ber-
zelius, Wohler and Deville, and others, have dispelled
many illusions and rendered accurate  the  present
literature of the  subject.   During the latter half of
the eighteenth century the list of metals was aug-
mented  by new discoveries, and the application of
the voltaic current to the decomposition of the alka-
lies by Sir Humphry Davy, in 1807-8, added  a  dozen
or more.  The  employment of the  spectroscope by
Kirchhoff and  Bunsen, in 1860, brought to light so
many new metals that the total number now exceeds
fifty.
  * Paracelsus, though the author of many fanciful doctrines, seems
to have been the first to offer a true chemical explanation of the action
of mercury, lead, etc., upon the human system. 
CHAPTER II.
THE  METALLIC  ELEMENTS.
]y/TODEEN CHEMISTEY assumes that the metals
      are  elementary  bodies,* yet there have  been
other  theories  presented regarding  their  ultimate
character, and it is thought by some that " when man
shall have mastered that great power of nature, elec-
tricity, many of the so-called elements will  be found
probably to be compound bodies."   Others have enter-
tained the theory of but one ultimate element; f while
nearly all agree that as we  advance in knowledge
new elements will be brought to light.
  The old philosophers applied the term element to
imaginary principles  of matter, such  as fire, water,

  *Some authorities on  chemistry do  not strenuously adhere to the
belief that the so-called  elements are  necessarily simple  bodies, and
are careful to teach that what are at  present regarded as elements are
bodies which they are unable to decompose.  Much attention has re-
cently been attracted to the investigations of Mr. J. Norman Lockyer,
F.R.S., as presented to the Royal Society in a paper read December,
1878, in which the theory was presented that " the so-called elements of
the chemists are really  compound bodies."  While the  tendency of
speculative philosophy is  in the direction of Mr. Lockyer's conclusions,
—that all the elements are built  up from a primitive material lighter
than  hydrogen—yet this discovery is too recent and the  experiments
upon which it is based are too imperfectly known to allow us as yet to
count it as one of the assured results of modern research.
  + Prof. Graham's Researches with  Hydrogen, 1869.
                                            (H) 
12
DENTAL METALLURGY.
and air; while the elements of the alchemists were
salt, sulphur, and mercury.  The term is now used
as synonymous with simple body, or one of the  un-
decomposable constituents of any kind of matter, or
that which cannot be divided by chemical analysis.
  The elements known at present number sixty-five,
and are divided into  the metallic and non-metallic.
Of these, fifty-one are metals, as follows:
		COMBINING
NAMES.	SYMBOLS.	WEIGHTS.
Aluminium.	Al.	27-4
Antimony.	Sb. (Stibium)	122
Arsenic.	As.	75
Barium.	Ba.	137
Bismuth.	Bi.	210
Cadmium.	Cd.	112
Cassium.	Cs.	133
Calcium.	Ca.	40
Cerium.	Ce.	92
Chromium.	Cr.	52-2
Cobalt.	Co.	58-8
Copper.	Cu. (Cuprum)	63-4
Davyum.	Da.	(?)
Didymium.	D.	95
Erbium.	E.	168-9
Gallium.	Ga.	68
Glucinum.	Be. (Berryllium)	9-4
Gold.	Au. (Aurum)	197
Indium.	In.	113-4
Iridium.	Ir.	198
Iron.	Fe. (Ferrum)	56
Lanthanum.	La.	93-6
Lead.	Pb. (Plumbum)	207
Lithium.	Li.	7
Magnesium.	Mg.	24
Manganese.	Mn.	55
Mercury.	Hg. (Hydrargyrum) 200	
 
THE METALLIC ELEMENTS.
13
                                         COMBINING
        NAMES.          SYMBOLS.           WEIGHTS.
      Molybdenum.        Mo.                96
      Nickel.             Ni.                 58-8
      Niobium.           Nb.                94
      Osmium.            Os.                199-2
      Palladium.          Pd.               106-6
      Platinum.           Pt.                1974
      Potassium.          K. (Kalium)         39-1
      Rhodium.           Rh.               104-4
      Rubidium.          Rb.                85-4
      Ruthenium.         Ru.               104-4
      Silver.              Ag. (Argentum)     108
      Sodium.            Na. (Natrium)       23
      Strontium.          Sr.                 87-6
      Tantalum.          Ta.                182
      Thallium.           Tl.                204
      Thorium.           Th.               235
      Tin.                Sn. (Stannum)      118
      Titanium.           Ti.                 50
      Tungsten.           W. (Wolframium)   184
      Uranium.           U.                240
      Vanadium.          V.                 51-2
      Yttrium.            Y.                 92
      Zinc.               Zn.                65-2
      Zirconium.          Zr.                 896
  Of these, only about  fourteen are employed in true
metallic condition.  These are:
         Antimony,               Magnesium,
         Aluminium,              Mercury,
         Bismuth,                 Nickel,
         Copper,                  Platinum,
         Gold,                    Silver,
         Iron,                    Tin,
         Lead,                    Zinc.
  Twelve are more or  less extensively used in medi-
cine,  and in the  arts  as coloring  pigments and for
alloying purposes.  These are : 
14
DENTAL METALLURGY.
         Arsenic,                 Lithium,
         Barium,                Manganese,
         Cadmium,              Potassium,
         Calcium,               Sodium,
         Chromium,             Titanium,
         Cobalt,                 Uranium.
  The remaining  twenty-five  are as }Tet  of little or
no practical use in the metallic state.
  Seven of the metals play a more or less important
part in the maintenance of animal and vegetable life.
These are:
         Aluminium,             Manganese,
         Calcium,                Potassium,
         Iron,                   Sodium.
         Magnesium,
  The metallic elements are divided by metallurgists
into two classes—the noble and  base inetals.  The first
are those which are capable of being separated from
combinations with oxygen by  merely heating to red-
ness.  The base metals are those whose  compounds
with oxygen are not decomposable by  heat alone.
  The noble metals are ten in  number, as follows:
      Mercury.           Hg.   '           200
      Silver.              Ag.              108
      Gold.              Au.              197
      Platinum.           Pt.               197-4
      Palladium.          Pd.              106-6
      Rhodium.           Rh.              104-4
      Ruthenium.         Ru.              104-4
      Osmium.           Os.              199-2
      Iridium.            Ir.               198
      Davyum.,           Da.               (?)
  The base metals are further subdivided according
to their affinity for oxygen and other chemical prop-
erties. 
CHAPTER III.
PROPERTIES OP THE METALS.
 A  METAL may be defined as an elementary sub-
     stance, usually solid at ordinary temperatures,*
insoluble in water, fusible by heat, and possessing a
peculiar  luster, commonly spoken of as a " metallic
luster;" an expression sometimes used in describing
the appearance of substances which present a similar
condition of surface.   To these  qualities  must  be
added  those of  conducting  heat  and  electricity,
which  the  metals possess to the greatest extent, and
the power of the metals of replacing hydrogen  in
chemical reactions; as, when zinc .is placed in contact
with hydrochloric acid it displaces the hydrogen and
unites  with the  chlorine to form zincichloride  (chlo-
ride of zinc), thus:
           Zn + 2HC1 = ZnCl2 + H2 liberated.
  Another characteristic of the metals is their basic
properties when united with oxygen.
  Arsenic and tellurium are  by some regarded as  in-
termediate links between the metallic and non-metallic
bodies. Watts, in his " Dictionary of Chemistry," says
of tellurium that "this element, though decidedly
metallic, must be classed as a member of the sulphur

  * Mercury is an exception, being fluid at the ordinary temperature.
It freezes at —40° F.
                                        (15) 
16
DENTAL  METALLURGY.
family," probably in consequence of its bad conduct-
ing qualities and the acid character of its oxides.
  Bloxam does not  regard arsenic as  a metal, and
states that, though " some authorities class it as such
on account of its metallic luster and property of con-
ducting electricity, yet it is lacking in the quality of
forming a base with oxygen,  a  property common to
all the true metals;" and asserts that " the chemical
character and composition of  its compounds connect
it in the closest manner with the phosphorus group."
  On the other hand, we find some of the non-metallic
bodies possessing the chemical  but not the physical
properties of the metals.  Thus, the real nature of
hydrogen has long been an interesting point of dis-
cussion among chemists, some  supposing  it to be a
metal in a gaseous form.  Dumas and others prophe-
sied that '•' if  ever the means of liquefying hydrogen
is found, it will present the  appearance  of quick-
silver," and  their grounds  for this belief are its
uniformly basic properties.  Others contend that it
is a neutral  substance, possessing both  the  basic
properties of a metal and the  chlorous qualities of
a gas.
  In 1869 it was announced that Prof. Graham, an
eminent English chemist, had  discovered the metallic
hydrogen.   " This  new metal, baptized  ' hydroge-
nium,'  was white, magnetic, of a  specific  gravity
about 2, and appeared to have some analogy to mag-
nesium."  This discovery excited much speculation.
Upon verification, however, the new metal was found
to be a compound of  palladium and hydrogen,  in
which  the former had absorbed 700 or  800 times its
bulk of the latter. 
            PROPERTIES OP THE  METALS.          17

  Again, the  existence of a  hypothetic compound
metal called ammonium, and having the constitution
XH4, has  been assumed as the only method of ex-
plaining the perfect analogy that exists between the
salts of ammonium and those of some of the metals,
actual  experiments having already strengthened this
theory, at first founded only on analogy.*
  The metals are all quite opaque, with the single
exception of gold, which, however, is only  transpa-
rent in leaves of a highly attenuated condition, when
it transmits green light.f
  The Color of the metals  ranges from the pure white
of silver to the bluish hue of lead.  Between these
two the major part of  the  others may be found.
About five run from light yellow to deep red. These
are  barium  and strontium,  pale  yellow;  calcium,
somewhat deeper in color, and gold, when pure, of a
rich yellow.   Copper is the only red metal.  It was
at one time supposed that the mineral titanium, well
known to dentists  as  a  dark  red (copper-colored)
crystalline substance, used in a finely-divided  state
as a coloring  pigment in the manufacture of porce-
lain teeth, was a  metal.   It  was so pronounced by
Wollaston.   Wohler and Deville, however, demon-
strated that the red mineral is an oxide, and they
verified their statement  by producing the metal it-
self, which is of a steel-gray color.   The color of the
metals is modified by alloying.J
  * E. Miller, Treatise on Chemistry.
  f It is by some believed that the absence of transparency in the other
metals may only depend upon our inability to obtain them in a sufii-
ciently attenuated condition.
  % See chapter on "Alloys." 
18             DENTAL METALLURGY.
  Luster.—This characteristic of the metals is prob-
ably the result of perfect opacity, by which the rays
of light are reflected from the surface.
  Odor and  Taste are possessed by some few of the
metals. The greater number, however, are destitute
of these  qualities.   Iron,  copper,  and zinc,  when
heated, evolve peculiar odors, and one means of de-
tection of arsenic is the odor of garlic observed when
that metal is exposed to an elevated  temperature.
Odor and taste may depend upon voltaic action.  The
former may be noticed  in a marked  degree  when
holding in the hand a mass of an alloy composed of
gold, platinum, tin, and silver prepared  for use as
amalgam.  The moisture of  the  hand, aided by its
heightened temperature,  seems to promote the elec-
trical action.
  Fusibility.—All metals admit of  being reduced to a
liquid  state by the application of  heat, but the tem-
perature  at which they melt differs widely.  Thus,
mercury retains its liquid form to 39° F. below zero,
and  is  always fluid  at ordinary temperatures.  Po-
tassium and sodium fuse below the boiling-point of
water; tin, lead, and antimony below redness.  Gold,
silver, and copper require bright redness.  Iron, nickel,
and cobalt fuse at white heat, while platinum, iridium,
rhodium, titanium,  etc., become fluid only when ex-
posed  to a powerful voltaic  current or the  flame of
the oxyhydrogen  blow-pipe. 
PROPERTIES OF  THE  METALS.
19
Table of Fusing-points of the Principal Metals.
P3
05  O
rQ *J  61
bD sS  f<
—  a>  o
be
If §tf
bo  ..+=««
bO<U O fl
si
1^ ■
,5* el <u
r
Mercury
Rubidium
Potassium
Sodium
Lithium .
Tin
Cadmium
Bismuth .
Thorium .
Lead
Tellurium, rather less fusible than lead.
Arsenic, unknown.
Zinc     ....    773     412
Antimony, just below redness.
FAHR.	CENT.
—39°	—39-44°
+101-3	+38-5
144-5	62-5
207-7	97-6
356	180
442	227-8
442	227-8
497	258
561	294
617	325
 Silver
 Copper  .
 Gold
 Cast-iron
 Pure Iron
 Cobalt
 Manganese
 Palladium
 Molybdenum
 Uranium
 Tungsten
 Chromium
 Titanium
 Cerium
 Osmium
Iridium
Rhodium
Platinum
Tantalum
FAHR.    CENT.
 1873    1023
 1996    1091
 2016    1102

 2786    1530 
20
DENTAL METALLURGY.
  Capacity for Heat.—The metals, in common with
other bodies, have their specific heat.  This consists
in the amount of heat required to raise equal weights
of different metals from the same to another given
temperature.   Thus, if we express by 1 the quantity
of. heat  necessary to raise a weight of water from
0° C. to  1° C. that which must be supplied to elevate
the same weight of the following metals to that tem-
perature would be as follows:*
Iron				01138
Nickel .			0-1086	
Cobalt .			0-1070	
Zinc			0-0956	
Copper.			0-0952	
Palladium				00593
Silver .				0-0570
Cadmium				00567
Tin				0-0562
Antimony				0 0508
Gold .				0-0324
Lead				00314
Platinum				0-0311
Bismuth				0-0308
  Now, if we should take equal bulks of these metals
and expose them for the  same length of time to ex-
actly the same amount of heat, and then place them
simultaneously upon a  cake of wax, we would observe
those of the above table with the highest figures* such
as iron, instantly melting their way through the wax,
while those of the lowest capacity for heat, such as
bismuth, would remain on the surface.
* Phillips's Metallurgy, p. 13. 
PROPERTIES OF THE METALS.
21
  Expansion by Heat.—Metals expand when heated,
but this property is not uniform, some possessing it
to a greater or less extent than others.  Within cer-
tain limits of temperature this takes place propor-
tionately to  the  amount of heat to which they are
exposed.  Zinc possesses a rather high degree  of ex-
pansibility, and is consequently useful for the purpose
of making dies for swaging metal plates for artificial
dentures. By many mechanical dentists it was for-
merly thought that a metal, to be well suited for this
purpose, should be entirely destitute of this property,
so that  after casting, the die should not, in returning
to its former condition in cooling, be smaller than the
plaster model, the object per se being to have the plate
fit the plaster cast  perfectly; whereas, the real pur-
pose should be to make the plate fit the mouth closely,
the plaster  model  being only a means to  that end.
Plaster  expands  in setting.   From the impression
to the model two expansions are gone through  before
the fac-simile of the mouth  in plaster is obtained;
hence a plate made to fit such a model perfectly must
necessarily be somewhat larger than the mouth—a
condition unfavorable to atmospheric adhesion.  On
the other hand,  a plate made to  fit the  zinc will
not be  found too  small for the  mouth,  but will,
provided the impression is a good one, and represents
perfectly the conformation  of the  mouth, afford a
very  close-fitting plate.  Better results might even
be expected  where the plate  is somewhat smaller
than the mouth, because such a condition  would, in
entire upper dentures, throw an}- undue pressure upon
the alveolar  ridge,  while that  portion of the  plate
covering the  palatine arch would barely be in contact 
22             DENTAL  METALLURGY.

with the tissues; the pressure along the ridge would
quickly promote absorption  of the remains of the
alveoli, and a uniform adaptation of the plate to the
mouth would  soon follow.  On the contrary, if the
plate be  made to fit the plaster cast, and is a trifle
larger than the mouth,  the pressure will be thrown
upon the palatine arch at the back  edge of the plate,
at a region not likely to change by absorption, as is
the case with the alveolar ridge, and hence the margin
of the plate will imbed itself in the tissues, and cause
much discomfort and impair the usefulness of the
denture.   Again, it will usually be found  that the
tissues covering the alveolar ridge are thicker than
upon the palatine arch or roof of the mouth proper;
hence they offer less resistance to pressure, so that the
bony arch, with its very  slight covering of soft tissues.
is called upon to bear the brunt of the force exerted
in mastication, and in consequence  of its unyielding
character tilting of the  plate  and loss of atmospheric
adhesion follow.  This, then, would seem to constitute
a very cogent argument in favor of the value of the
quality of expansibility of zinc as used in  dies  for
swaging  plates.
  Much time and thought have been expended in the
effort to discover some alloy  which,  in connection
with the properties of hardness and fusibility, shall
possess that of non-expansibility when  heated.  Har-
ris's "Principles and Practice of Dentistry "  gives no
less than nine  different  formula?.  I am satisfied that
the property of expansibility in zinc, as used in the
dental laboratory, constitutes one of its most valuable
qualities, as it gives us the means of compensating
for the yielding of the tissues and the  absorption 
PROPERTIES OP THE METALS.          23
along the ridge which nearly always follow the first
insertion of an artificial denture.
Table of Expansion of Metals for each degree from o° C. to ioo° C*
Gold . . .	0-00155155	Lead . . .	0 00284836
Silver . . .	000190868	Tin . . . .	000193765
Platinum .	0-00099180	Zinc (cast)	0-00294167
Palladium	0-00100000	" (ham'r'd)	0-00310833
Copper . .	000171733	Bismuth .	0-00139167
Iron	0-00123504	Antimony	0-00108333
  Power of  Conducting Heat.—The metals  are the
best conductors of  heat  among  the  solid  bodies.
The quality  of transmitting heat is possessed  by
them in variable degrees.   The following table shows
the relative approximate ratio of conductivity of heat
of each of the metals commonly used in the mechanic
arts:
Silver
Copper
Gold
Brassf
Tin
Iron
Steel
Lead
Platinum
German Silver
Rose Fusible Metal
Bismuth .
100
 73-6
 53-2
 23-6
 14-5
 11-9
 11-6
  8-5
  8-4
  6-3
  2-8
  1-8
  Power of  Conducting Electricity.—Metals  conduct
electricity nearly in  the  ratio  of  their  capacity
of transmitting  heat.   Davy, Becquerel,  and  Dr.
* Phillips's Metallurgy,  f Zinc is probably between brass and tin. 
                            i
24             DENTAL METALLURGY.
Matthiesen  have, at different  times, more  or  less
extensively  experimented  upon this characteristic
quality of the metals.   Among the results  of  Dr.
Matthiesen's investigations are  the facts that debas-
ing a metal  or alloying it greatly diminishes its con-
ducting power, and that elevation of temperature*
has the same effect, and that between 32° and  212° F.
(or 0°  and 100° C), great diminution takes place—
not uniformly, however, as some lose it  more in pro-
portion than others.f
  A rough  means of determining  the relative con-
ducting power of metals consists in  connecting the
poles of a voltaic battery  by a wire through which
the current will pass freely.  Now, if the wire be too
small for the transmission  of the electricity supplied
to it, the  obstruction will  be manifested by the wire
becoming red-hot.   Hence the  relative capacity of
metals for this purpose may be observed by employing
equal battery-power upon wires of the same diameter
of different  metals,  and noting the  length  of the
portion of each which can  thus  be heated.
  Conversely, the same  means  may be  employed to
indicate the quantity of electricity, or the capacity
of the battery itself. In this case the wire is made
to demonstrate the power of the battery by the length
of wire which the  battery is capable of rendering
incandescent.
  A good demonstration of the relative conducting
 * This was fully shown in some of the electro-magnetic mallets made
some five or six years ago, in which the wire was too small for the
accompanying battery-power.  They worked very well for a few min-
utes, when they became hot and ceased working.
 I Makins's Metallurgy, p. 17. 
PROPERTIES OF THE METALS.
25
poAver of different metals may be made by construct-
ing a chain of alternate links of platinum and silver
wire. This will show, while the current of electricity
is  passing, alternately  red-hot platinum links with
cool silver ones.  Platinum, being much the inferior
conductor, offers such an impediment to the passage
of the current that great elevation of temperature
results, while the  silver,  being a  good conductor,
offers no check to the free  passage of the electricity.
   The power of  metals for conducting electricity is
shown in the following table from Matthiesen (Phil.
Trans. 1863):
      Silver  ....
      Copper .
      Gold   ....
      Zinc   ...
      Iron   .
      Tin
      Lead       .    .
      Antimony
      Bismuth
   Malleability, Ductility, and  Tenacity.—The qualities
of malleability,  ductility, and  tenacity differ widely
in the metals.  The term  Malleability,  when  applied
to such a metal as gold, signifies that by hammering
or rolling its surface may be extended in all directions,
and that it is capable of being thus reduced to very thin
leaves or sheets without fracture of its continuity at
the edges  during the process  of attenuation; when
applied to other metals, the term should be understood
as expressing this quality relatively.   Gold is the most
malleable of the metals, and is  capable of being made
into leaves of jnnrWo of an inch in thickness,  each
o-rain of which will cover a surface of 54 sqr. inches.
O
                        3
100 at	:J2° F.
99-95 "	a
77-96 »	
29-02 "	
16-81 "	it
12-36 "	"
8-32 "	"
4-62 "	u
1-24 "	a
 
26
DENTAL METALLURGY.
  In the following list, by Begnault,* the metals are
arranged in the order of their malleability:
    1. Gold.         6. Lead.       11. Potassium.
    2. Silver.        7. Zinc.       12. Sodium.
    3. Tin.          8. Iron.       13. Frozen Mercury.
    4. Copper.       9. Nickel.
    5. Platinum.    10. Palladium.
  Ductility signifies that property which renders a
metal capable  of being drawn into  rods or  wires,
usually accomplished by passing an elongated piece
of metal through a series  of gradually diminishing
holes in a steel drawT-plate; the granular particles of
the metal are thus extended into fibers.  One grain of
gold has been drawn into a wire 550 feet long.   To
accomplish this result the  gold to be operated upon
must first receive a coating  of silver.  It is then
carried to the smallest hole in the draw-plate, after
which it is immersed in nitric acid, which dissolves
the silver, leaving a gold  wire 5 ^ 0 of an inch in
diameter.
  In the following table  the metals  are arranged
according to their ductility :
    1. Gold.           5. Nickel.       9.  Lead.
    2. Silver.          6. Copper.      10.  Palladium.
    3. Platinum.       7. Zinc.        11.  Cadmium.
    4. Iron.           8. Tin.
   Tenacity is the  power possessed by metals of sus-
taining weight, or of resisting rupture, when a bar
or rod is exposed to tension.  As the fitness of metals
for certain purposes in the industrial  arts depends
largely upon this  property, it is of the utmost  im-
portance to  know  the relative tenacity,  not only
* Phillips's Metallurgy, p. 412. 
PROPERTIES OP THE METALS.
27
of the different metals, but of different alloys.  This
is usually ascertained by preparing wires  of exactly
equal diameters.  These are suspended by one end
from a fixed bar, and to the other extremity weights
are gradually  and  carefully  added until the wire
breaks.   The weight which causes the fracture rep-
resents, when compared with others similarly treated,
the relative tenacity of the metal.
  Elevation of temperature, even within  rather cir-
cumscribed limits, affects the tenacity of metals to a
marked degree, generally diminishing it.   There are
some exceptions, such as iron and steel. On the other
hand, malleability and ductility are only developed
in some  of the metals by an elevated temperature.
Thus, it was found that  zinc, which had  previously
been of no use in an unalloyed state, was rendered
perfectly malleable and capable of being rolled into
very thin sheets merely by heating to between 248°
and 302° F. (=120° and 150° C), and it has  conse-
quently come very largely into use.  If carried much
beyond this point, however, say to 400°  F. (=205°
C), it becomes  very brittle, and may even be reduced
to powder in an iron mortar.  A rather unsatisfactory
demonstration  of this fact sometimes occurs  in the
fracture  incident to the falling upon  the hearth or
floor of a hot  zinc  die, carelessly removed from the
molding sand in the  laboratory, its brittleness  being
so extreme at 500° F. that it might be broken into a
number of pieces.
  Magnesium,  aluminium, and  some  other  metals,
which at ordinary temperatures are nearly destitute
of ductility, have that quality greatly increased by
heating, and  are then readily drawn into wire. 
28              DENTAL METALLURGY.

  In alloys these qualities are diminished by heating.
Thus, the  great' tenacity and ductility of brass are
entirely destroyed by simply heating to dull redness.
Again,  while it is claimed that in pure gold tenacity
is increased by heating,  it is  quite certain that 18-
carat gold is rendered brittle at red heat.
  The following table gives the results of experiments
on this  subject by Baudrimot (An. de Ch. et de Phys.
1850):*

Tenacity of the Principal Malleable Metals at the Temperatures of o° C,
   ioo° C, and 2000 C,  as found by  Experiment, with the Tenacity
   calculated for i sqr. Millimetre of  Sectional Area (0.0155 sqr. inch):
	2> II " u -• rt *• 0 u a u c .5 on to C •-* CT* ta 2: 0 _i Q"° . Milli-metres	TENACITY.	Tenacity calculated for 1 sqr. Millimetre of Sec-tional Area.		
METALS.		At 0° C Atioo°C At2oo°C	At o° C	0 0 8 Grms	8
		Grms Grms Grms	Grms		Grms
Gold . .	.0-41250	2459 2035 1722	18400	15224	12878
Platinum	.!o-41000; 2987 2546 2281		22625	19284	17277
Copper .	.;0-48000, 4542| 3958 3296		25100	21873	18215
Silver .	. 0-39825 3528 2898 2314		28324	23266	18577
Palladium	.0-39750 4527 4031 3360		26481	32484	27077
Iron .	. 017500	4940; 4611 5057	205405	191725	210270
  The following  table  shows the order of relative
capacity of the metals for sustaining weight:
* Percey's Metallurgy. 
PROPERTIES OF  THE METALS.
29
    !• Iron.             4. Silver.        7. Tin.
    2. Copper.           r>. Gold.         8. Lead.
    3. Platinum.         6. Zinc.
   It has been observed that students and others very
 often fail at first to appreciate the difference between
 these properties, and  they not infrequently fall into
 the mistaken idea that the three qualities of malle-
 ability, ductility, and tenacity  are possessed to  an
 equal extent by each metal.  If,  however, we  take
 gold,  for example, the most perfectly  malleable and
 ductile  of the  metals, we shall find that in tenacity
 it ranks considerably below some of the others, and
 the greatest care is necessary to enable the operator
 to draw a piece of  pure gold into even a moderately
 fine  wire,  and  beyond a  certain  limit, past  which
 platinum or copper may be carried with safety,  gold
 would not possess sufficient tenacity to overcome the
 resistant force to which it would be exposed in passing
 through the smaller holes of the draw-plate, and  frac-
 ture would result.
   Iron, on the other hand, which exceeds all the other
 metals in tenacity, is in malleability inferior to gold,
 silver, copper, platinum, palladium, lead, zinc, tin, and
 cadmium.
   Crystalline metals, such as bismuth, antimony, and
 arsenic, do  not  possess these properties.   They are
 easily broken by even slight blows of a hammer, and
 the two latter may be reduced to powder in a mortar.
  It is  stated that brass which has been drawn into
 wire will  often  after a certain lapse of time become
 crystalline in  texture and brittle by slow  change of
molecular arrangement.*
               * Making's Metallurgy, p. 10.
                        3* 
30
DENTAL METALLURGY.
  Crystallization.—It  is stated that, under  favorable
circumstances all  the metals will assume a crystalline
form.  It is known that some of them, as gold, silver,
etc., are found native as cubes or octahedra, or in
slight modifications of these forms;  and metals in a
crystalline  form  may be obtained by electrolysis.
For example, silver may be obtained in the form of
crystals nearly pure by introducing strips of copper
into a solution of argentic nitrate.   A piece of zinc
introduced into a  solution of plumbic  nitrate will
precipitate the lead in the form of feathery crystals.
Gold may also be deposited in this form from solution
by the introduction of a stick of phosphorus.   Nearly
all  the metals 3'ield  crystals when  deposited from
their solutions by electric currents of feeble intensity.
The beautiful preparation known as Watts's Crystal
Gold  is formed in this  way.  Gold  so prepared is
generally in a high state of purity.
  Elasticity and Sonorousness may be conferred upon
the metals by alloying.   Thus, iron does not possess
these qualities  until combined with the proper pro-
portions  of carbon, when by subsequent tempering
the highest  degree of elasticity  is  developed, and
pieces of steel of  different lengths, as arranged in the
dulcimer, responding to percussion by a small wooden
hammer, are capable  of giving off the most musical
sounds.
  Again, a very great amount of elasticity is obtained
by the admixture of  copper and zinc in the form of
brass, from which a spiral spring may be made, equal
to that from any  other alloy.
  It is curious to observe how this  quality may be
developed by the admixture of two metals, both of 
PROPERTIES  OF THE METALS.
31
which, examined separately, are soft and destitute of
anything like springiness.  Thus, gold and platinum,
both soft metals, when combined in the proportions
of, say,  1 grain of the latter to 1 dwt. of the former,
of 20-carat fineness,  will  afford a  decidedly elastic
alloy suitable for clasps as attachments for artificial
dentures.
  A tolerably elastic alloy may be formed by combin-
ing platinum with  a small amount of iridium.   This
alloy is  frequently employed  in the  construction of
artificial dentures.*
  Sonorousness  is obtained to the greatest extent in
alloys of copper and tin, known as bell-metal.
   Volatility.—All metals are probably more or  less
volatile, although  only a certain  number admit of
being converted with any degree of  facility into a
state of vapor, even  at the  highest temperatures.
Some of the conspicuously volatile metals are  zinc,
cadmium, mercury, arsenic, tellurium, potassium, and
sodium; while  a few others  have the  property of
communicating  characteristic colors to flame, and are
probably "volatile to a limited extent.
  Metals are sometimes characterized as " fixed," as
gold, copper, nickel,  etc., and "volatile"  (during
fusion), as cadmium, zinc, etc* Arsenic may unques-
tionabl}T be regarded as belonging to the latter group,
passing as it does without fusion from the solid to the
gaseous state.
  Gold  has been known to volatilize under certain
conditions.   Makins states that it is doubtful whether
it is at all volatile per se, but if alloyed with copper
* See chapter on " Platinum and its Alloys." 
32
DENTAL  METALLURGY.
it  has  been shown b}T Napier to be considerably vol-
atilized, so that quantities amounting to  4£ grains
could be collected during the pouring of 30 pounds'
weight from  a crucible.   According to Makins, the
conditions  under which gold  has been known to vol-
atilize  are,  when it is mixed with silver and lead and
cupelled together,  he having  collected considerable
quantities  of  each  metal from the chimney of an
assay furnace after only a few weeks' use.
  Agents which may  Volatilize a Metal.—Concentration
of solar rays in the focus of a lens;  the  Voltaic cur-
rent; the oxyhydrogen blow-pipe flame.
  M. Despretz employed  the three in conjunction, by
which  means he volatilized magnesium, and by the
action of a  powerful Bunsen battery alone he reduced
carbon by  volatilization to   the state  of a black
powder.*

                * Percey's Metallurgy.
« 
CHAPTER  T\T.
                  ALLOYS.


"A/TOST of the metals are capable of uniting with
      one  another, forming  a class of compounds
termed alloys, in which may be observed to a greater
or less extent the properties of the several constituents
entering into the union.
  From 41 purely scientific point of view, the study
of the alloys is an interesting one, as they are not
only mixtures  of metals possessing certain  distinct
qualities, but in reality are true chemical compounds.
In the appearance which often accompanies the union
of the metals, and in  the properties of the resulting
alloys, we  may frequently  observe the  phenomena
which characterize chemical affinity, such  as heat
and incandescence, resulting in the formation of sub-
stances having a definite composition, distinct crys-
talline form, and properties  different  from those  of
the constituents.
  When a piece of clean sodium is rubbed in a mortar
with dry mercury, the former dissolves, and a peculiar
seething sound, resembling that caused by the immer-
sion of a hot body in water, is produced, due to the
evolution of heat which accompanies the combination.
the mercury rising rapidly in temperature as the pieces
of sodium  are added.   As the mercury  cools, the
                                       (33) 
34
DENTAL METALLURGY.
resulting alloy, which is brilliantly white, crystallizes
in long, needle-like forms from the middle of the liquid,
and the excess of mercury may be poured off.
  Alloys are generally harder and more fusible than
the metals of which they are formed, and as many
metals are unfit  in the pure state  for use in the me-
chanic arts, owing to extreme softness or high fusing-
points, these properties are modified to suit various
requirements by the admixture of other metals.  Thus,
as a base for an artificial denture, pure gold would be
too soft to withstand, without bending, the force to
which the fixture would be exposed during mastica-
tion, but by the  addition of 4 grains of copper and 2
of silver  to  the dwt.  of pure gold the necessary
rigidity may be obtained without materially affecting
the other properties.  Again, it is often desirable to
unite several pieces of the same metal or of different
metals.  This is  accomplished by means of a class of
alloys called solders, generally formed of the metal
upon which they are to be employed, with the addition
of some other metal which will  materially reduce
the fusing-point  without affecting the color,  as it is
desirable that the place of union should not be notice-
able.   For example,  a solder suitable for use in pros-
thetic dentistry should fuse at a much lower temper-
ature than the plate  upon which it is to be used.   Its
color should be  as nearly as possible the same, and,
what is even more important, it should withstand  the
action of the fluids of  the  mouth nearly as well.
These properties may be obtained by the addition of
small amounts of silver,  copper, or brass.
  The value  of many  of the  metals for  industrial
uses is very greatly enhanced by alloying.  Thus, 
ALLOYS.
35
copper, which is unfit for casting and too tough for
turning, may, by the addition of zinc, be rendered
not only harder and more elastic, but the fusing-point
of the resulting compound will be so much lower than
that of the copper alone as to render the  casting of
it  a matter of no great  difficulty, while at the same
time it will be found susceptible of being turned in
the lathe with facility.
   The tendency  on the'part of metals to unite in
definite  proportions may  be studied in  connection
with  platinum,  iridium, gold, rhodium, ruthenium,
and silver, when fused with tin.  If the latter metal
is  in excess after cooling, a metallic ingot is obtained
resembling closeby the original substance; but by the
action of strong hydrochloric acid the excess  of tin
may be dissolved, leaving crystals of a definite alloy
of the tin and the noble metal, which cannot be further
dissolved by the same acid, but  are solvable-in nitro-
hydrochloric acid, even when the precious metal con-
tained, whether rhodium, ruthenium,  or iridium, is in
the free state absolutely insoluble.
   It must not, however, be assumed that all the alloys
employed in the  industrial arts  are the result of defi-
nite combination, dissolved in  an excess of one of
the metals.  Many combinations  are capable  of co-
existing in the same alloy.  This may be demonstrated
in an alloy of tin, lead, and bismuth, which melts
below the boiling-point of water.   Heated to 25° C,
and then permitted to cool, it will be observed, by the
assistance of the thermometer, that the fall of temper-
ature  is twice  distinctly  arrested.   The cause of
this phenomenon has been assumed to be the produc-*
tion in the  compound of a  less fusible alloy, which 
36
DENTAL  METALLURGY.
in solidifying evolves heat, and thus for a time retards
the gradual cooling of the mass.  It may, therefore,
be assumed that true  chemical combinations may
occur between two metals, notwithstanding the fact
that such union may be masked by excess of one of
the constituents.
  Matthiesen, in an elaborate paper on the subject,
states that " an alloy may be, first, a solidified solution
of one metal in another; second, a chemical combina-
tion;  third, a mechanical mixture;  or, fourth, a solid-
ified solution or mechanical mixture of two or all of
the above."  In simple mechanical mixture  of two
metals there is often a tendency to separate.  This is
noticeable in some alloys of silver and copper by an
absence of perfect homogeneity in the ingot.  Again,
some of the metals form mixtures so decidedly mechan-
ical that on being allowed to stand  after fusing they
will separate, the one possessing the highest specific-
gravity settling to the bottom.   This may be observed
when lead and zinc are mixed.   Matthiesen, however,
found that the lead retains 1-6 per  cent, of the zinc,
while the zinc retains 1-2 per cent, of  the lead.*
  Density.—Theoretically, it might  be supposed that
the density of an alloy would be the mean  of its con-
stituents.   Such, however, is not always the case, as
the resulting number is sometimes equal to, or greater
or less than, the theoretical mean.  The alloys of gold
and silver are less than the mean density of the com-
ponents in consequence of expansion, while brass and
the alloys of lead and antimony vary in the opposite
direction through a condensation of their constituents.

              * Makins's Metallurgy, p. 62. 
But in the formation of some alloys there is no altera-
tion of volume, and the density of such will correspond
to that obtained by calculation as the mean of their
constituents.
   The following table,* by Thenard, gives the alloys
in  which  the specific gravity of  the compound  is
superior,  also those possessing an inferior density  to
the mean  of the combined metals :f
Alloys Possessing a Greater Spe-
  cific Gravity than the Mean of
  their Components.
Gold and Zinc.
  "   "  Tin.
  "   "  Bismuth.
  "   "  Antimony.
  "   "  Cobalt.
Silver and Zinc.
  "    "  Lead.
  "    "  Tin.
  "    "  Bismuth.
  "    "  Antimon}'.
Copper and Zinc.
   "    "  Tin.
   "    "  Palladium.
   "    "  Bismuth.
   "    "  Antimony.
Load and Bismuth.
  "   "  Antimony.
Platinum and Molybdenum.
Palladium and Bismuth.
Alloys Having a Specific Gravity
  Inferior to the  Mean of their
  Components.
  Gold and Silver.
    "   "  Iron.
    "   "  Lead.
    "   "  Copper.
    "   "  Iridium.
    "   "  Nickel.
  Silver and Copper.
  Copper and  Lead.
  Iron  and Bismuth.
    "   "  Antimony.
    "   "  Lead.
  Tin and Lead.
   "   "  Palladium.
   "   "  Antimony.
  Nickel and Arsenic.
  Zinc  and Antimony.
  Color is always modified 1 >y alloying.   It is generally
such as might be expected to result from the mixture
  * Phillips states that it is doubtful whether some of the mixtures
included in this table should be regarded as alloys.
  f Phillips's Metallurgy.
                           4 
38
DENTAL METALLURGY.
of the metals entering into the formation of the alloy.
There are a few instances, however, where  it is  dif-
ferent.  Thus, three  parts  of  silver  to  seven of gold
yields a green alloy,  and nickel, added  to  brass, pro-
duces an alloy of silvery whiteness.
  Malleability, Ductility, and  Tenacity.—These prop-
erties are generally much changed in metals by alloy-
ing ; malleability and ductility being diminished, and
in some cases entirely destroyed, even in the combina-
tion of two very ductile metals,  as  is the case with
gold  containing a small  amount of lead, ductility
being completely lost.  Again, gold and  platinum, two
exceedingly ductile metals, are rendered much harder
and somewhat elastic by admixture.
  The union of a brittle and a ductile metal yields a
brittle alloy.  According to Mr. Makins, antimony, a
metal so brittle that it may be broken up in a mortar,
when added to gold  to the extent of y-^r Vai% w^
make the gold quite unworkable.
  Tenacity is generally increased by alloying. The
following results were  obtained  by Matthiesen.  by
employing wires of the same  gauge and noting  the
weight which caused their rupture  before and after
alloying:
                  MS.                          LBS.
Copper, unalloyed. 25 to 30;  alloyed with 12per ct. Tin, 80 to 90
Tin,            under 7;    "   with 12 per ct. Copper   7
Lead,      "       "7;    "   with Tin.....7
Gold,      "     20 to 25;    "   with Copper   ...  70
Silver,     "     45 to 50;    "   with Platinum,   75 to 80
Platinum,  "     45 to 50.
Iron,      "     80 to 90; Steel (or Iron alloyed with Car-
                          ton) ......above 200
  Generally  speaking,  the  hardness   of  metals  is 
ALLOYS.
39
increased by alloying them.   A familiar  instance is
standard  gold  or  silver.   Neither  of these  when
unalloyed is sufficiently hard to resist attrition to the
degree, required for currency;  but the addition of one-
tenth of its weight of copper to either metal increases
its hardness to the  required point.  Ninety-four parts
of copper with six  parts of tin form an alloy so brittle
that it may be  broken with a hammer.
  Fusibility.—This is always greater than that of,the
least fusible metal entering into the composition of the
alloy, and is sometimes greater than  in  any of the
components.  Thus, an alloy composed of five parts of
bismuth, three of lead, and two of tin, melts at 91° C,
less than the boiling-point of  water, while  tin  alone
fuses at 227-8° C, and lead at 325° C. and the addition
of a small amount  of cadmium to the above alloy will
further reduce the fusing-point to 140° F.,  or G0° C.
Lead containing a small  amount of silver is more
fusible  than  the former in a  state of purity, and an
alloy may be formed of  potassium and sodium which
remains fluid at ordinary temperatures  of the air.
  This phenomenon has been explained by Matthiesen.
He says that " matter in the solid state exhibits excess
of attraction over  repulsion, while in the liquid state
these forces  are balanced, and in the gaseous  state
repulsion predominates  over  attraction,  and similar
particles of matter  attract  each other more powerfully
than  dissimilar particles do.   The attraction subsist-
ing between the particles of a mixture will  be sooner
overcome by repulsion than will the  attraction  in the
case of a homogeneous body;  hence  mixtures should
fuse more readily than their constituents."*
*Makins's Metallurgy, p. Cj. 
40
DENTAL METALLURGY.
  Composition of Alloys.—A statement of the average
proportions in which metals enter into the best-known
alloys, the  composition  of which  is generally very
variable, is given in the following table:
Coinage of Gold . .	rGold . . . 1 Copper .	. . 90 . . 10
Gold Jewelry and Plate < t Copper .		75 to 92 25 to 8
Silver Coinage . .	J Silver 1 Copper . .	. . 90 . . 10
Silver Vessels . . .	( Silver . . 1 Copper .	. . 95 . . 5
Silver Jewelry	f Silver . . 1 Copper . .	. . 80 . . 20
Aluminium-Bronze .	fCopper . 1 Aluminium	90 to 95 10 to 5
Specula of Telescopes	J Copper . ' I Tin . .	. . 67 . . 33
	J Copper . IZinc . .	. . 90 . . 10
	/ Copper . 1 Zinc . .	67 to 72 28 to 33
	rCopper .	. . 50
German Silver . .	J Zinc . .	. . 25
	1 Nickel .	. . 25
Type-Metal....	/ Lead . . 1 Antimony	. . 80 . . 20
	t Copper .	. 94 to 96
Bronze Coins and Meda	Is J Tin . .	4 to 6
	1 Zinc . .	1 to 5
Bronze Cannon . .	fCopper . '1 Tin . .	. . . 90 . . . 10
Bronze Bells . . .	f Copper " I Tin . .	. . . 78 . . . 22
Bronze Cymbals . .	( Copper " I Tin . .	. . . 80 . . . 20
 
ALLOYS.
41
                          | Tin.....100
      t?  v i  nr * i          Antinionv ...   s
      English Metal .  .   .   \
                           Bismuth . '.   .  .   1
                           Copper  ....   4
      Pewter.....i Tin.....u-
                          t Lead.....8
      Liquid .Measures .   .  . {Tin.....*-
                          I Lead.....IS
      Plumbers'Solder.   .  . ■ Tin.....,i7
                          t Lead.....33
  Alloys used as plates for artificial dentures and those
constituting solders will he described with the metals
forming their bases.
  Decomposition.—When the  alloy contains a volatile
metal, like zinc or mercury,  heat decomposes it, but
the temperature required to expel the  last trace  of
the volatile metal must be considerably higher than
that metal's normal temperature of ebullition.  If the
alloy is composed of a noble metal and  zinc, lead,  or
tin, and it is  desired  to free it of the impurity, this
may be accomplished  by exposure to a high tempera-
ture, and the addition, while the metal is fluid, of some
substance rich in oxygen, such as potassium nitrate.
By this means  the  base metal is converted into an
oxide, and is then dissolved and held in solution by the
borax, which should be used as a flux in the  crucible.
.Metals in combination with mercury may be separated
by  the application  of heat,  mercury volatilizing  at
600° F.  In  the case  of particles of amalgam, how-
ever, the temperature to which the pieces are exposed
should he at least a  bright-red heat.
  Influence of Constituent Metals.—Mercury, bismuth,
tin, and cadmium give fusibility to alloys into which
thev enter;  tin also  gives hardness and tenacity;  lead
                         4* 
42
DENTAL METALLURGY.
and iron give hardness; arsenic and antimony render
alloys brittle.
  It has been observed that phosphorus and arsenic,
when added to alloys of copper and tin, have the power
of deoxidizing or eliminating metallic oxides, which
are invariably present.   The well-known  phosphor-
bronze owes its closeness of grain and superior tenacity
to the  addition of phosphorus, and it is claimed that
" when  arsenic or arsenical compounds are made to
unite, under suitable conditions, with alloys of copper
and tin, known as bronze or  gun-metal, it imparts to
them several remarkable  and,  for many purposes in
the arts, desirable properties—among others and prin-
cipal of which are homogeneity, hardness, elasticity,
greatly increased tensile strength and toughness, and
a peculiar  smoothness, rendering it a  valuable  anti-
friction metal for journal-bearings," etc.
  The  arsenical compounds of alloys  of copper and
tin are also more fluid when molten than are other
known  alloys  of copper and  tin—a property which
renders them capable of filling out sharply and with-
out flaws the most intricate molds.
  Liquation.—The  constituents of an alloy  heated
gradually to near its point of fusion frequently  unite
to form newT compounds,  and if the fluid  portion  is
poured off, there remains a solid alloy less fusible than
the original.  Copper is separated from silver  by this
process.  In  bars of silver  alloyed with  copper, a
curious tendency on  the part of the latter to separate
and aggregate at the edges, as the fused mass assumes
the solid form, has been observed.  Mr. Makins states
that, as a  result of  careful examination of Mexican
dollars  and crown  pieces, he found  the  variation 
ALLOYS.
43
between the center and edges to range in the former
from  one  to six, and in the latter from one to four
milligrammes.   He gives as the average of a number
of experiments on twenty-four  crown pieces a mean
variation of two milligrammes,  and as the quality in
which the greatest tendency to separate is shown that
of 900 parts of silver to 100 of copper.*
   Temper.—Modified conditions of hardness and elas-
ticity of a metal, it has been shown, may be obtained
by admixture with other metals and b\- sudden varia-
tions  of temperature, as in  the case of the alloy of 94
parts of copper and G of tin, which forms a bronze so
brittle that it may. when slowly cooled, be pulverized
with  a  hammer; but if, on the  contrary, it is  cooled
rapidly, by  immersion in cold  water,  it  becomes
malleable.   The treatment of iron mixed with carbon
(steel)  is  just  the opposite,  the same  result being
attained by slowly cooling the heated mass.
   Preparation.—When  the  alio}- is to be formed  of a
noble and one or more  of the base metals, the former
should  be thoroughly  fused first ; the  latter is then
added, and the whole covered with charcoal, to prevent
oxidation, and  then thoroughly mixed  by stirring or
agitating.
   When it  is designed to  lower the fusing-point of
gold  or silver  for  use  as solders,  by the addition of
brass, etc.,  the precious  metal should first be thor-
oughly fused with  a  sufficient quantity  of borax;
the brass, in the convenient form of wire, should then
he quickly thrust into  the  melted gold or  silver.   It
will almost instantly mix with the melted mass,  and
* Makins's Metallurgy, pp. 379, 380. 
44
DENTAL METALLURGY.
the borax, if in sufficient quantity, will cover  the
liquid alloy, and thus protect from oxidation by con-
tact with the atmosphere.
  The action of acids  upon alloys is generally more
energetic than upon  a simple metal,  but it varies
according; to the relative amounts of their constitu-
ents.  Silver alloyed with a large quantity of gold is
protected from the action of nitric acid.  Sometimes,
however, the reverse   of this is  seen,  and metals
which  are totally  insoluble  in certain  menstrua  are
made to  dissolve in them by the  addition  of a metal
on which they have the power of acting.  Thus, plat-
inum, although of itself insoluble in nitric acid, may
be dissolved by it when sufficiently alloyed with silver.
  Alloys consisting of two metals, one readily oxi-
dizable, the other  possessing less affinity for oxygen,
may be readily decomposed by the combined  action
of heat and air.  In this case the former metal will be
rapidly converted into an oxide, excepting perhaps
the last portions, wilich may in some degree be pro-
tected from further action by the oxide already formed.
This increased affinity  for oxygen exhibited by alloys
is probably an electrical phenomenon, the stu<hT of
which belongs rather to the  science of chemistry than
to metallurgy.   For further light on this subject  the
student may refer to  Fownes's,  Bloxam's, or other
standard works on chemistry. 
•


              CHAPTER V.
                 AMALGAMS.


 A  MALGAM—the name given to an alloy of mer-
     cury  with  one or  more  other  metals.  The
amalgams are a very numerous class of compounds,
and many of them are used largely in the arts.
  Some amalgamations are formed merely by contact
of the  metals, and  are accompanied by evolution of
heat; others are obtained by the action of mercury
on a salt of the metal, or the action of the metal on a
salt of mercury, thus developing in some cases a weak
electric current.
  Some amalgams  are  solid;  others liquid.   They
are,  generally speaking,  weak compounds, many of
them being  decomposed  simply by  pressure, and  all
b}' high temperatures.  Tin amalgam is used for "sil-
vering" mirrors; gold and silver amalgams in gilding
and silvering ; while amalgams containing gold, silver.
tin,  platinum, and,  in  some  cases,  cadmium, zinc,
copper, and other of the base metals, compounded
according to many different formula?, have been used
very extensively in dentistry.  An  amalgam of zinc
and  tin is employed for the  rubbers of  electrical
machines.
  An alloy  for dental amalgams should possess the
qualities of strength and sharpness of edge, and
                                       (45) 
46             DENTAL METALLURGY.

freedom from admixture with any metal favorable to
the formation of soluble salts of an injurious character
in the mouth.  It should be capable of maintaining its
color, although in  an alloy composed of several  dif-
ferent  metals  absolute  freedom from  discoloration,
under the conditions to which an amalgam  filling is
exposed, cannot readily be obtained.  It should also
be capable of retaining its shape, as the tendency on
the part of many  amalgams  to assume  a globular
form after their introduction, thus leaving the edges
of  the  cavity  unprotected, is  probably a  frequent
cause of failure in  this class of fillings.
  Undue expansion, although not so  likely to occur
as some other changes, would  be equally  a  source
of failure.  According to Mr. Fletcher, amalgams of
silver and mercury expand, sometimes sufficiently to
split a tooth;  and  Mr. Kirby states that "amalgams
of pure silver,  either the precipitate or filings, expand
greatly."  With a  suitable instrument  for  measure-
ment, he was  able  to  determine the  change in bulk
of such an amalgam, in which he found  the  extent
of expansion to reach one-fortieth of its diameter.
  Many old amalgam fillings have the appearance of
projecting from the edges of the cavity, as though
there existed some force behind or beneath  sufficient
to push them out.   There seems to be some diversity
of opinion respecting the  cause of this, and  while by
some it is attributed to expansion, others believe it
to be due to contraction.  Favoring the latter theory,
Mr. Fletcher states that he has found  it to occur only
with  those amalgams which are  known to shrink,
and he suggests that the plug may be raised or forced
out by the "decomposition  of tooth-substance  and 
AMALGAMS.
47
formation of gas under the loosened plug, the driving
flown and accumulation of food underneath, or some
similar cause.'-  It is evident that an amalgam liable
to contract or expand  to a marked extent is not to
he relied upon as a filling-material.
  Discoloration of dental amalgams depends largely
upon the  formation  of sulphides.  The fluids of the
mouth,  in every  case  where  the most scrupulous
cleanliness is  not observed, may  be said to contain
sulphur in combination with  hydrogen, as dihydric
sulphide (II.,S\ resulting from  decomposition of par-
ticles of food having a lodgment between or adhering
to the teeth.  The affinity of sulphur  for both silver
and  mercury  is so  active that we  may reasonably
assume  that not only the discoloration of amalgam
fillings, 1 mt in many cases their failure  to prevent a
recurrence of decay, is due to the action of that
element upon the alloy.  Nor is it safe, in compound-
ing alloys for  dental  amalgams, to depend  upon the
protecting influence of metals  which do not possess
the  same affinities,  such as gold and platinum;  for
while these metals  individually may remain  wholly
unaffected by contact with sulphur, it does not neces-
sarily follow  that  their presence in  an  alloy will
secure the same  immunity to  such  metals as silver
and  mercury.
  There are doubtless other causes for the discolora-
tion of amalgams, some of them purely adventitious.
depending upon the  administration of certain reme-
dies  in diseased, abnormal conditions of the fluids of
the  mouth, or  the   presence  of  vegetable acids in
articles  of food, such as fruit.
  An amalgam filling   may  retain its integrity of 
48
DENTAL METALLURGY.
surface, while, at the same  time, the darkening of
the tooth-substance unmistakably indicates chemical
action at its peripheral portion, doubtless due to im-
perfect adaptation, favoring the ingress of the eroding
agent.  It  appears  that almost  any amalgam filling
may be kept bright by friction, whether of the brush
or from mastication, and it seems equally certain that
any amalgam  will blacken if the position which the
filling occupies  protects it  entirely from  friction.
Again,  an  amalgam filling may retain  its  original
color  and brightness  of surface, and yet not protect
the tooth;  and, conversely, a filling of this class may
exhibit a great degree of surface-discoloration,  and
yet fully preserve the tooth  from  further decay,
peripheral  discoloration being much  the worst con-
dition of the two.
  In  a number of  experiments made with  some of
the well-known  amalgams, such as Townsend's, Ar-
rington's,  " Standard  Alloy," Lawrence's, Walker's,
etc.,  as well  as with  some of  a higher  grade, it
was found  that with care in  using the proper quan-
tity of mercury, and  in packing the mass into clean
glass tubes, subsequently filled with colored fluid  and
closely sealed,  there was after several weeks  not  the
slightest apparent leakage; and yet, when the same
tubes  were thrown  into a solution of  sulphureted
hydrogen, the  edges were attacked, and marked  dis-
coloration  occurred at  the periphery of the fillings,
while  the surface directly exposed to the action of
the sulphur, and not  in contact with the  glass, was
but slightly clouded.  The edges had the appearance of
having been eroded, as by an acid.  This experiment
is not merely speculative, as it is simply filling a cavity 
                     AMALGAMS.                 49

 with amalgam and then exposing it to sulphur in the
 form usually found in the mouth.  The  result is pre-
 cisely similar to that which is observed in the  great
 majority  of amalgam  fillings in actual service. It
 would seem, however, that the purely theoretical test
 of covering the plug with colored fluids, such as indigo,
 blue  ink, etc., known as the "color-test," is not to be
 relied upon in testing peripheral adaptation, for all
 the  plugs used in these experiments had apparently
 excluded  the passage of a solution of indigo or ink.
 Yet,  that they  did  not  perfectly  seal  the tubes,
 although  introduced  under veiy favorable conditions,
 is plainly shown by the result, which indicated  that
 solution of one or more of  the constituents of the
 alloy had taken place, resulting in the  formation of
 new compounds, consisting of sulphides  of silver and
 mercury,  and in some instances probably of copper.
  Influence of Different Metals in  Dental Alloys.—Tin
 dissolves veiy easily in mercury, but the  alloy hardens
 slowly  and imperfectly.   Without admixture  with
 other metals it is unfit for use in the form of an amal-
 gam in the mouth.  It is also wrell known to possess
 a tendency to drawr away from the edges  of any cavity
 into which it may be packed, and to assume a globu-
 lar form,  and it  never becomes sufficiently hard to
 answer the requirements of a filling-material.  Mixed
 with other metals, tin serves  to facilitate amalgama-
 tion and  to  afford different  degrees of plasticity.
 Between mercury arid silver the affinity  is but slight.
 By the addition of tin, however, union is facilitated.
  Silver apparentl}T unites very readily with mercury.
 Yet it will be found, upon close examination, that com-
plete solution of pure silver filings will not take place
                        5 
50             DENTAL METALLURGY.         %

until after long contact, unless the silver is in a finely
divided state and the mercury heated.   Under these
circumstances, amalgamation will be more readily ac-
complished.  Amalgams of silver and mercury alone
are said to  expand.
  Silver with tin added forms an alloy very white in
appearance, but more  easily oxidized  than  either of
the constituents; mixed  with mercury, an exceed-
ingly unctuous and plastic amalgam is obtained,  but
it  is somewhat slow in hardening.  There  is much
diversity of opinion in regard to the contraction and
expansion  of this  alio}'.  Dr.  Hitchcock  and  Mr.
Tomes both claim contraction* for it, while Mr. Kirby
states  that an "amalgam of an alloy of 3  parts of
silver  and  2 of  tin contracts slightly  at  first,  but
finally expands about j^." f  These variable results
may depend upon the quantity of mercury employed.
I am satisfied that  when an alloy of silver and tin is
used no excess of mercury should be present, and when
this precaution has been carefully observed I  have
found the results to be quite as good as those obtained
with  alloys of the  higher grades.  Thus, 500 milli-
grammes  of  Arlington's  amalgam,  composed | of
silver 40 per cent., tin 60 per cent., mixed with  160
milligrammes of mercury, withstood the sulphureted
hydrogen test quite as well as those containing gold
and platinum.  It should be borne in mind that alloys
composed of tin  and silver only, require much  less
mercury to render them plastic than those containing
gold and platinum in addition.

      * Transactions New York Odontological Society, 1S74,
      f Ibid.
      J Hitchcock,  Ibid. 
AMALGAMS.
51
  Probably the  most unfavorable property observed
in an alloy of silver and tin is slowness in hardening,
which  favors  the ingress of fluids by capillary force.
The direct influence  which  silver  exerts upon an
amalgam of tin and mercury is to lessen the tendency
to assume  the spheroidal form, and  to facilitate set-
ting.  In this respect its action is  similar to that of
gold;  but while the  latter  further  lessens  these
injurious tendencies, and confers similar properties,
it cannot be made to supersede silver.  In my experi-
ments  with these curious  compounds I formed an
alloy consisting of

     Gold .....    500 milligrammes.
     Platinum ....    o00      "
     Silver    ....   2000      "
     Tin.....2.">00      "

 An  amalgam of this alloy hardened  almost instantly,
 so that a filling of it might be inserted and  finished
 at one sitting.  For the sake of experiment, another
 ingot  was made, from which  the silver was  omitted.
 The result was an exceedingly brittle alloy,  which
 could  only be made to unite with  mercury  by heat-
 ing, and  even  then with  difficulty, and  it did not
 harden  sufficiently to  be of any use as a filling-mate-
 rial.  Thus it will be seen  that silver fills an import-
 ant place  in dental  alloys, since without its presence
 amalgamation becomes difficult, and rapidity in hard-
 ening  is not secured.
   Cold  combines with mercury at  all temperatures.
 but for rapid amalgamation an elevation of tempera-
 ture is required, and the process is  accelerated if the
 o-old is  in a  state of fine  division.  AVith  mercury 
52
DENTAL METALLURGY.
alone it does not harden well; added  to  tin, it to a
certain extent facilitates setting, but does not harden
sufficiently for use in the mouth, though it prevents
the tendency to draw away from the edges.  But  it
is when added to an alloy of tin and  silver that the
greatest benefit is derived from its presence.  I found
that an alloy consisting of

     Cold .    .'   .    .       500 milligrammes,
     Silver    ....  2000      "
     Tin.....2500      "

when mixed with  mercury  in the proportion of 500
milligrammes  of  the alloy  to  250  milligrammes  of
mercury,  retained  its sharpness of edge,  hardened
well in a  few minutes, and apparently filled all the
requirements of a dental amalgam.  I am aware that
it has been stated  that  gold  added to an alloy of tin
and  silver retards hardening, but I  suspect this to
be an error, and the presence of an excess of mercury
to be the real cause of the tardiness in setting.
  Platinum, in the usual form of plate or wire, does
not readily unite with mercury.  A very smooth and
plastic amalgam may, however, be formed by rubbing
some finely-divided platinum, such as is obtained by
precipitation, with mercury in a heated mortar.
  An amalgam composed of platinum  and mercury
alone does not harden  well.  The  properties of an
alloy of tin and silver  are also greatly impaired  by
the addition of platinum in any considerable quantity.
The author found an  alloy consisting of tin. 2500
milligrammes, platinum 500  milligrammes, to be ex-
ceedingly  brittle, and with so little affinity for mercury
that amalgamation Mas only accomplished by elevation 
AMALGAMS.
53
of temperature and much rubbing, while the property
of setting was almost entirely lost.
  If platinum be added to an alloy of gold and tin,
the same negative results  are observed.  When com-
bined with  tin, silver, and gold, however,, the  influ-
ence of platinum becomes apparent.  With the right
amount of mercury, it  seems to confer upon such an
alloy the property of almost instantly setting, as well
as much greater hardness.  Thus, it will be seen that
the qualities claimed for  platinum per se  belong in
reality to the combination of tin, silver, gold, and plat-
inum, with mercury, since if either one of the others
is omitted the platinum does not even remain passive,
but actually by its presence causes marked  deteriora-
tion of the qualities essential in a dental amalgam.
  Alloys containing platinum amalgamate less readily
than those wherefrom  it is  absent; yet when union
has once begun the}" seem to require a greater amount
of mercury to render  them plastic.  By careful ex-
periment, I  found that with an alloy of

     Platinum  ....   500 milligrammes,
     Gold.....500
     Silver.....2000
     Tin.....2500      "

the smallest amount of mercury which could be em-
ployed without  impairing the strength and general
working qualities of the  amalgam, was  300 milli-
grammes  to 500 milligrammes  of the alloy; while
with another ingot  composed of
     Gold.....500 milligrammes,
     Silver.....2000
     Tin.....2500
                        5* 
54
DENTAL  METALLURGY.
160 milligrammes of mercury to 500  of  the alloy
afforded a perfectly good result.
  The proper quantity  of mercury should be ascer-
tained by careful  experiment, as  the  statements of
manufacturers or venders are not always reliable.
  In  order to ascertain the amount of mercury re-
quired by different  alloys, a  small quantity  of the
latter should be taken, say one gramme,  and,  after
weighing, the mercury  may be  carefully added and
mixed by rubbing until the  mass assumes  a semi-
coherent state.   It should then be weighed again, to
determine accurately the amount of mercury present.
It may then be introduced into a glass tube and con-
densed by means  of instruments slightly warmed.
Should the proportions  not be correct,  another  trial
may be made, and  the quantity of mercury increased
or diminished as indicated by the results of the first
experiment.
  The quantity of mercury required by each alloy is
probably definite, so that a tolerably accurate approxi-
mation of the composition of an alloy may  be arrived
at by carefully noting the required proportions of one
to the other.
  Different means  are employed in the attainment of
this object.  Probably the most common is  to mix the
alloy  with a large excess of mercury, and then to ex-
press the surplus  of mercury either by compression
with  the fingers or through  the pores of a piece of
chamois-leather. The first involves the loss  of some of
the alloy, which is carried away with the  surplus of
mercury, and neither is to be  relied upon as a means
of excluding an excess of mercury.
  There  are also several methods employed in mixing 
AMALGAMS.
55
amalgams.  Probably the most common one consists
in simply rubbing the alloy and the mercury together
in the palm of the hand.  This is certainly the most
expeditious, though not a very neat way, and much has
been said about manifestations of the physiological
effects of mercury following a long continuance of the
practice.  I have made considerable effort to ascertain
the correctness of this theory, in view of the fact that
some have attributed certain phases of ill-health  to
absorption of mercury applied in this way, but I have
been unable to trace a single case of  ptyalism or any
other well-marked sign of mercurial poisoning to this
cause.   It would be well to remember, however, that
the active properties of mercury are developed by a
state of fine division, and there is nothing- unreason-
                                       ed
able in  the belief that mercury, highly comminuted
by rubbing in the palm of the hand, may find  its -way
into the system and produce constitutional disturb-
ance.  In view of these facts, it  Mould be a proper
precaution to prevent contact of the  mercury Avith
the skin.   This may be accomplished by covering the
hand with a piece of rubber dam, forming a sort  of
mitten, leaving the fingers free and having an opening
for  the thumb to pass through.
  Small porcelain and glass mortars are also employed
in promoting  amalgamation, but they do not effect
the desired purpose speedily, in consequence of the
granules of the alloy becoming  burnished  by the
attrition of the pestle.   Heating the  mortar will,
however, greatly facilitate union.
  Mr. Fletcher has recently called attention to a simple
and effective method of mixing amalgams.  The re-
quired weight of filings and mercury are put into a long, 
56
DENTAL  METALLURGY.
narrow test-tube or bottle, and well shaken for a few
seconds.  The percussive force brought to bear upon
the mass promotes prompt union.
  Some difficulty may be encountered in introducing
amalgam fillings when the mercury has been reduced
to the minimum.   The semi-coherent mass, almost in
the form  of a powder, is not easily conveyed to the
cavity, especially if it is in the superior arch.  Fletcher
has recently devised a sort of mold by which amal-
gams mixed so dry as to be unmanageable may be
rapidly shaped into  a  convenient  M'orkable  form.
It consists of a cylinder, into M'hich the semi-coherent
mass is poured.  By means of a piston the powder is
compressed into disks of the desired thickness, which
may be introduced  into the cavity and solidly com-
pressed with  slightly-warmed instruments.   It  is
claimed that this arrangement practically does away
with the chief objection to the use of very dry amal-
gams.   Should the amalgam  harden  and become
unmanageable before the completion of the filling, it
may be rendered plastic and cohesive without disturb-
ing the process of crystallization or the property of
setting, by the use of slightly-heated instruments.  A
further addition of mercury Mill be found to greatly
impair, if  not destroy, these properties.
  Amalgams may be regarded as chemical compounds
having definite proportions,  and  capable  of  being
dissolved in an excess of mercury, in which condition,
however, they will no longer be found to fulfill the re-
quirements of a filling-material.  Hence the operator
should in no case  attempt to restore the plasticity of
an amalgam- Miaich  has once hardened by a further
addition of mercury. 
AMALGAMS.
57
   Forming Alloys for Amalgams.—-The putting together
 of the constituents of an alloy composed of tin, silver,
 gold, and platinum, is a matter of no great difficulty,
 as it does not require an extraordinary degree of heat,
 and it may be  easily accomplished in a stove or fur-
 nace  such  as  is  usually  employed  for heating  or
 cooking purposes.  The small reverberatory furnaces
 recently devised 'by  Mr. Fletcher will be found  to
 answer the  purpose admirably.   I  have used one
 successfully in a large number of melting operations.
 Their cost is only about $3.50 each.
   The  only difficulty likely to be met in forming
 an alloy of this  description is  oxidation of the tin,
 and the  formation  of  certain  definite compounds
 having a tendency to separate from the mass, thus
 affording an ingot which is not homogeneous.  Oxida-
 tion of the tin  may take place at the instant of union
 with  the platinum, and it is  therefore preferable  to
 melt the platinum and silver together first, and then
 add the tin and gold.  A quantity of borax should be
 fused in the crucible before the metals are melted, the
 object being to prevent adhesion  of the alloy to the
 sides of the crucible, to  facilitate pouring, and  to
 dissolve and hold in  solution any oxide MThich may
 be present.  Lastly, a layer of broken charcoal should
 be  placed  over the mass  before  the heating.  This
 will perfectly protect it from  oxidation.
   The formation of definite alloys, it has been shown,
 takes place with  the gradual cooling  of  the mass;
 the fusing-point and  density of these being  greater
 than of that which  remains fluid, they manifest  a
tendency to settle to  the bottom  of the crucible in a
solid state, and  in some  cases do not leave the crucible 
58             DENTAL METALLURGY.

in pouring.   Thus  the ingot may not  possess the
desired composition.  Again, the alloy may assume a
semi-solid form, float ing in masses in the more fluid por-
tion, settling at the  moment of pouring  at the sides
or bottom  of the  mold, the  result yielding an ingot
which is not uniform in composition, in consequence
of which it  has  been  recommended  that different
parts of every ingot  should  he tested;  but  the
difficulty may be  entirely avoided by carrying the
heat to a point of  complete fusion and pouring while
still  very  hot, before  the  tendency to  separate  is
developed.
  Oxidation  of the surface from contact  Mith  the at-
mosphere will retard amalgamation.   It  is therefore
better not to reduce the entire ingot to a  state  of fine
division.  It Mill be  found  to unite more readily Mith
the mercury if freshly filed off  as required for use.
This can easily be effected  with one of the coarse files
sold  at the depots  as vulcanite tiles.
  Other metals, such as palladium, copper,  cadmium,
bismuth, antimony, and zinc, have been used as con-
stituents of amalgams.
  Copper is  said  to control  shrinkage,  while it in-
creases  the tendency to discoloration.  It is also be-
lieved to exert a preservative influence on the tooth-
structure.  The salts of copper formed around amal-
gam fillings  certainly  do permeate and  may protect
the tooth-structure from further  decay, but too much
reliance should not be placed in the therapeutic theory
in connection Mith this class of amalgams.  It is ex-
ceedingly  difficult to  determine  such   a  question.
Amalgam  is in many cases placed in  teeth of  such
good quality  that almost  any filling-material would 
AMALGAMS.
59
answer a  conservative purpose,  and  the examples
which are often  presented of the  long duration of
such  fillings may prove nothing beyond the density
and superior quality of the tooth-structure.  Careful
and intelligent observation and experiment alone can
satisfactorily solve a question of this kind.
  Brittleness may be increased or diminished accord-
ing to the quantity of platinum present, and the re-
sulting amalgam will exhibit this quality equally with
the alloy.  An amalgam filling should always be strong
enough to retain  its  integrity of edge under the force
of mastication.   A formula  from which I  have  ob-
tained very good results is as follows:

      Silver......40 grammes.
      Tin......00
      Gold......3   "
      Platinum  .....     3   "

   Larger percentages of gold and  platinum afford no
better  results;*  but,  on  the  contrary, the alio}' is
rendered more brittle thereby ; its affinity for mercury
is lessened, while its capacity for the latter is increased.
as shown under the  head of " Platinum."
   Palladium and  mercuiy are said to make a very
good filling.   According  to Mr.  Thomas  Fletcher,
however, all alloys  in Avhich palladium enters as  a
constituent are utterly worthless;  combined M'ith tin
and  silver, it  has been found to  be  unsatisfactory.
Mr. Fletcher gives the results of a  number of experi-
  * Under the assumption that amalgams are benefited in proportion
to the amount of gold contained, Dr. W. G. A. Bonwill recommends
that from 10 to 20  per cent, of gold be dissolved in the mercury used
with the alloy. 
60
DENTAL METALLURGY.
ments with tin, silver, and palladium.*  "The alloys
given below MTere made from chemically-pure metals.
They were melted first at a high temperature, under
a layer of charcoal, in a clay crucible, Mith constant
stirring.   They M'ere then poured quickly  into a
thick and cold iron  ingot mold;  broken  up  and
remelted three times, to  insure  uniformity as far as
possible."
      Pd. 1, Ag. 5.  Result powdery and unmanage-
         able.
      Pd. 1, Ag. 5, Sn. 1.  Eesult ditto.  Both readily
         combined with Hg.
      Pd. 1, Ag. 5, Sn. 2.  Eesult same as above.
      Pd. 1, Ag. 5, Sn.  3.  Result very dirty to mix;
         makes a leaky plug.
      Pd. 1, Ag. 5, Sn. 6.  Result similar to last.
      Pd. 1, Ag. 3, Sn. 5.  Result very dirty; does not
         combine properly with mercury.
      Pd. 1, Ag. 6, Sn. 5, Au. 1.  Result similar to last.
      Pd. 1, Sn. 4.  Result very dirty;  does not set at
         all.

  In  consequence of  the uniformly bad  results  of
these combinations, Mr. Fletcher states that  for the
present he has discontinued any further experimen-
tation in this direction.
  Qualitative and Quantitative Examinations of Amal-
gam Alloys.—It is frequently necessary for the dentist
employing filling-materials of this class  to  be well
informed as to their composition, and it is also often
desirable to  be able to determine the composition  of
old amalgam fillings, the constituents of which, besides
* British Journal of Dental Science. 
AMALGAMS.
61
tin and silver, are unknown.  With a compound belong-
ing to the latter class the first step, after weighing,
would be to free it from mercury by heating to red-
ness, the loss of weight at the  second weighing indi-
cating the amount of mercury  which was  present.
After this it is to be treated  as an alloy, one gramme
of which may be placed in a test-tube or other suita-
ble glass vessel and acted upon by a sufficient  quantity
of chemically-pure nitric acid.  The silver is ilissolved
and converted  into  argentic nitrate.  The tin is oxi-
dized and becomes metastannic acid (5Sn  02,10H2 O).
The latter, in the form of a M'hite powder, settles to
the bottom of the vessel.  If gold forms part of the
alloy,  it  will  be  recognized, even in the  smallest
quantity,  b}T the very decided  purple color which  it
imparts to the  precipitate, due  to the formation of
purple of Cassius. Platinum may be  readily  detected
by the presence in the test-tube of the finely-divided
metal, quite black in color.
  At  this point in the experiment, if neither  gold nor
platinum  is present, the quantitative  estimation of
the alio}- is not difficult,  and may be  accomplished as
follows: The solution should be  rendered neutral by
evaporation, and diluted with a large amount of dis-
tilled  water.  The oxidized  tin will be found at the
bottom of the vessel.  After pouring off the  solution,
this should be washed, dried, and rendered anhydrous
by heating to redness, when it is ready for weighing,
every 100  parts indicating  78-66 of  tin.  Eeturning
to the  solution, the silver  is  next  precipitated  by
sodium chloride or  hydrochloric acid, and may be
collected by filtering.
  If cadmium  is  present in the remaining  solution,
                         6 
62
I)ENTAL METALLURGY.
 sulphurcted hydrogen Mill throw it down in the form
 of a yellow powder (sulphide of cadmium), the color
 distinguishing it from zinc sulphide, which is wiiite.
 The alkalies, potassa, soda, and ammonia, throw down
 the oxide of cadmium as a white hydrate.  Amnionic
 carbonate also produces a white precipitate, which is
 insoluble in  excess  of the precipitant.  The latter
 quality also distinguishes it from zinc, which is solu-
 ble under similar conditions.
   Zinc may be precipitated from a solution by potas-
 sic carbonate, added in  sufficient quantity to decom-
 pose any ammoniacal salts, ifv present, as such would
 prevent  the  precipitation of  the  carbonate  of zinc.
 The whole is now to be evaporated to dryness, hot
 water added, the zinc salt boiled, collected by filter-
 ing, and lastly, after washing, ignited to drive off the
 carbonic acid, when  oxide of zinc remains.  In quan-
 titative  estimation,  zinc is always  weighed  in  this
 form, the oxide being calculated as containing 80-24
 per cent, of the metal.
   If copper be present, as it frequently is in amalgam
 alloys, it will  be instantly detected  by the greenish
 hue which it imparts to the solution, after the " break-
 in g-up"  by nitric acid.   Indeed, the  appearance of
 the contents of the test-tube will, after the  student
 has acquired  some  experience, serve  to  convey  a
 pretty clear  idea  of the composition  of the alloy.
 For instance,  take one gramme of Arlington's alloy,
 composed of pure tin and silver, and act upon it with
 nitric  acid ; the contents of the test-tube will be  a
colorless  liquid  and a perfectly white powder.  In
another test-tube dissolve some of Lawrence's alloy,
and the nitrate, instead  of being perfectly colorless, 
AMALGAMS.                 63
as in the preceding experiment, will show a decidedly
green tinge, and  the  presence  of copper  is verified
by the blue color developed by the addition of am-
monia.  Gold and platinum will be detected in alloys
containing these  metals  by the appearances already
described.
  The presence of copper having been verified, that
metal may be  precipitated as cupric sulphide,  by
sulphureted hydrogen.   It may then be collected by
filtering, and after washing and drying may be oxi-
dized by  nitric acid, and again  be precipitated  by
potassa,  and  may then be weighed  as  an  oxide.
Should  copper and cadmium both be present, the
precipitate obtained by  sulphureted  hydrogen will
consist of sulphides of cadmium and copper.   Boil-
ing in dilute sulphuric  acid, however, dissolves the
cadmium, so that the copper  may be collected  by
filtering, after which the  cadmium  may be again
thrown down by  sulphureted hydrogen.
  The merest trace of  copper in solution may also
be detected by-placing a drop of the latter on a strip
of clean platinum foil and  touching it Mith a point
of zinc.  A spot  of reduced  copper Avill instantly
appear.
  For the quantitative analysis  of an alloy contain-
ing tin, silver, gold, and platinum, the first  step should
be to remove the  tin by deflagration.  This is accom-
plished by placing the  alloy, after weighing, in a
small crucible Mith some borax, and heating to bright
redness.   While at that high temperature small por-
tions of potassium nitrate  are added.   This is  de-
composed ; its oxygen unites Mith the tin,  converting
it into stannic  oxide (Sn  02).  After cooling,  the 
64
DENTAL METALLURGY.
 crucible may be broken, and the remaining button,
 together with any small  globules which may adhere
 to the sides of the crucible,  collected and weighed,
 the loss indicating the  amount of tin which was
 present.  If the deflagration has been thoroughly per-
 formed, the button will be entirely freed of tin, and
 it then remains to separate the silver from  the gold
 and platinum.  This may be accomplished either by
 nitric or sulphuric acid.  But, as the former will dis-
 solve  a considerable portion  of the platinum along
 with the silver, sulphuric acid, which does not thus
 affect the  platinum, affords more  accurate results,
 and is the agent usually employed in parting opera-
 tions where the alloy consists largely of silver, with
 appreciable percentage of platinum.
   The  button, now consisting of  silver, gold, and
 platinum, should be rolled into a thin  ribbon,  and
 then placed in  a glass or platinum vessel  with at
 least two and a half times its weight of concentrated
 sulphuric acid.   This is boiled, during which strong
 action is evinced by copious  disengagement of sul-
 phurous anhydride, and the silver is converted into
 a  sulphate.   The boiling is continued until all the
 silver is dissolved, when the gold  and platinum will
 be found at the bottom of the digester.   The liquid
 is  now poured off, and the silver recovered from the
 sulphate solution by  precipitation with  plates of
 copper, which reduce it in a more or less crystalline
 state.   The remaining alloy, now consisting of gold
and platinum, should be thoroughly washed, dissolved
in nitro-hydrochloric acid, neutralized by evaporation,
then dissolved in a large quantity of distilled water.
It  is  then ready for precipitation with oxalic  acid, 
AMALGAMS.
65
by Avhich the gold is thrown doAvn, and the platinum
remains in solution for subsequent treatment.  The
gold, which is now easily collected, should be washed,
dried, and heated to redness, and is ready for weighing.
   Lastly, the platinum may be  recovered from the
solution  by  precipitation  Avith  amnionic chloride.
When Avashed  and dried it will  be ready for weigh-
ing, and  every 100 parts may be considered as con-
taining 44-28 of platinum.
   Composition of some of the well-known Dental Alloys.
—The following formula? are from quantitative analy-
ses made by Dr. E. S. Wood, Professor of Chemistry
in the Harvard Medical and Dental Schools :*

      Arrington's Amalgam.—Silver, 40 per cent.; Tin,
          60.
      Diamond Amalgam.—Silver, 31-76; Tin, 6674;
          Gold, 1-50.
      Hood's.—Silver,  34-64; Tin, 60-37; Gold, 2-70;
          Iron, 2-29.  #
      Johnson & Lund's.—Silver,  38-27; Tin, 59-58;
          Platinum, 1-34; Gold, 0-81.
      Lawrence's.—Silver, 47-87;  Tin, 33-68; Copper,
          14-91;  Gold, 354.
      Moffitt's.—Silver, 35-17;  Tin, 6201;  Gold, 2-82.
      Townsend's.—Silver, 40-21 ;  Tin, 47-54; Copper,
         10-65;  Gold, 1-6.
      ToAvnsend's Improved.—Silver, 39-00; Tin, 55-69;
         Gold, 5-31.
      Walker's.—Silver, 34-89; Tin, 60-01; Platinum,
         0-90; Gold, 414.

  The folloAving formula Avith directions for forming
the alloy, kindly furnished  by Dr.  Ambler Tees, is
* Hitchcoi-k on. Dental Amalgams.  Trans. N. Y. Odont. Society.
                        6* 
66             DENTAL METALLURGY.

highly recommended by that gentleman as affording
excellent results :
     Tin.......40dwts.
     Silver.......24  "
     Gold.......1 dwt.
     Platinum......1  "

  " The gold, silver, and platinum, to be melted first
with  borax and kept in a state of fusion  for five
minutes.  The  tin to be melted  in a separate cruci-
ble, and the molten silver, gold, and platinum to be
poured  into the fused tin, and  the whole  quickly
poured into a  suitable ingot  mold  and  reduced to
powder with a  large machinist's file." 
CHAPTER VI.
MODES  OF  MELTING  METALS.
"V7ARIOUS forms of heating apparatuses, furnaces,
      etc., are of great importance to those Avho con-
duct metallurgical operations on a large scale.  We
shall, howeArer, in these pages confine ourselves ex-
clusively to the  needs of the dental laboratory,* in-
cluding a consideration of the appliances for soldering.
  These operations are performed by the use of the
oil- or alcohol-lamp, or the gas-jet, or by means of a
suitable  stove or furnace.   When kerosene oil  or
alcohol is  employed, it is of the first importance to
select a lamp  designed not only to meet the practical
requirements, but also Avith  a view  to  safety.  The
essentials are, first, to have the wick large  enough to
afford a flame of sufficient magnitude to enable the
operator to solder an  entire artificial denture, or to
fuse from one to two ounces of gold.   This would re-
quire a Avick of one and a quarter inches in diameter,
and about three inches long.   Its connection Avith the
reservoir or body of the lamp in Avhich the combust-
ible fluid is contained should  not be direct nor in such
  * Full and detailed descriptions of the different heating apparatuses,
together with the most approved  processes of reducing ores and of
melting large quantities of metals, will be found in Percey's, Phillips's,
and Makins's works on Metallurgy.
                                         (67) 
68
DENTAL  METALLURGY.
close proximity that explosive gas would be likely to
form.   The Franklin Safety Lamp, a cut of which is
annexed  (Fig. 1), will be found to ansAver every re-
quirement.  It consists  of a reservoir five inches in
diameter by two and a half inches deep.  The wick-
holder, three inches long by  two and a half inches in
diameter, is connected with the reservoir by a curved
tube five inches long by  three-sixteenths of an inch in
diameter.  Thus a sufficient quantity of the burning-
fluid is supplied to the Avick to afford a constant flame,
                           w7hile there is no danger
                           of the  heat from  the
                           wick-holder being  con-
                           ducted to the reservoir
                           to cause an explosion.
                             In  cities  and  large
                           towns where gas is avail-
                           able, that agent is to be
                           preferred, on account of
                           its  greater safety and
                           convenience. A gas-bur-
                           ner which AAill be found
                           to answer every require-
                           ment of the laboratory
may be constructed by attaching to the  base  of an
ordinary Bunsen burner, such as is sold  at the dental
depots, a piece of brass tubing six inches in length by
one and a quarter inches in  diameter.   Over the top
of this, in order to properly spread the flame, a piece
of fine brass wire-gauze is  fastened by means  of  a
ring of sheet-brass one-quarter of an inch in width.
Connection may be obtained with the gas-bracket in
almost any  part  of the room by means of  flexible
 
MODES OF MELTING METALS.
69
rubber tubing.    This  will  be found  to answer all
purposes of  soldering  as well as  of  melting  small
quantities of gold and silver.
   The blast and the flame are produced  by  the  bloMr-
pipe,* an instrument Miiich  has  long been used by
workers in metals for the purpose of soldering together-
small pieces of metal, and for melting  and  reducing
purposes generally.  The ordinary form consists of  a
conical brass tube, from two hundred to two hundred
and thirty or forty millimetres  long, curved at the
narrower end to nearly a right angle, so that the  flame
may be conveniently directed upon the piece of  metal
to be soldered or melted, as the case may be, Avhich is
held upon some suitable support, such as a piece of
charcoal, coke, or pumice-stone.  When the  bloAV-pipe
is used in  its simplest  form, by the mouth,  the  large
end of the instrument  is held between  the lips, and
the small end toAvard the flame.  The blast should not
be sustained by the respiratory organs, but, in  order
that an unbroken current may be kept up, the mouth
should  be filled  Avith air, to  be  forced  through the
blow-pipe by the muscles  of the cheeks.   While  these
are forcing the air through the bloAV-pipe, the connec-
tion between the chest and the cavity of the mouth
should  he closed  by the palate, which thus performs
the part of a valve.  The beginner is liable to fall into
  * The use of the blow-pipe for analytical purposes is credited to Anton
von Swab, a Swedish Councillor of Mines, who made use of the instru-
ment in the discharge of his official duties as early as 1738. Since that
date its use has been widely extended, and the importance of reactions
in  the dry way produced under the flame of the blow-pipe  is fully
recognized and established.  For full information on the subject the
student is referred to Plattner's "Manual of Blow-pipe Analysis." 
70
DENTAL METALLURGY.
the error  of not closing  the  connection between the
chest and  the mouth at the proper instant, and of ob-
taining the force necessary to propel the air through
the blow-pipe  from the lungs.   That this manner of
using the instrument may injure the organs of respira-
tion cannot for a moment  be doubted, and the operator
should early acquire the proper method, above de-
scribed.  To avoid tiring the muscles of the lip by
continual  blowing, the trumpet mouth-piece  has  been
recommended, and is shown in the annexed cut, Fig. 2.
This is merely pressed against the open  mouth, and
                      Fig. 2.



                                       a
an uninterrupted blast may  be  kept  up for a  long
time without causing the least fatigue of the orbicu-
laris oris, since that muscle takes but a passive part in
the operation.  This trumpet-piece, hoAvever, should
be so curved as to correspond with the shape of the
mouth;  otherAvise  it will require to be pressed very
forcibly against the lips in order to prevent the escape
of air.
  The bloAV-pipe should be constructed of either brass
or German silver,  as these alloys are  but poor con-
ductors of heat,   Silver is not Avell  suited for the
purpose, because it transmits temperatures so readily
that it soon becomes too  hot for the fingers.
  A long-continued  and  steady flame maintained by
the mouth blow-pipe is apt to cause disturbances in
the flame from the collection of moisture in  the  tube, 
MODES OF  MELTING METALS.
71
which is liable to be expelled by the pressure of the
air.   To avoid this a holloAv chamber is constructed
about midway in the instrument.   The length of the
instrument should be adapted to the eye of the opera-
tor, so that the object upon Avhich the flame is direc-
ted may be distinctly seen.
  An improvement in these instruments has recently
been  made  by Mr. Thomas Fletcher, F.C.S., of War-
rington,  England (see Fig.  3), by which temper-

                       Fig. 3.


atures beyond those which can he produced by the
ordinary gas and air blow-pipes are attainable. It not
only gives temperatures never  approached Avith the
old blow-pipe, but it is also in  every respect  more con-
venient,  easier to use, and better adapted  for every
class of work.   With the same amount of blowing as
Avith the common form, this blow-pipe Avill  do nearly
double the  work; if high temperatures are not re-
quired, the labor of bloAving is reduced in proportion.
The improvement consists in coiling the air-tube into
a light spiral over the point of the jet.   This  coil takes
up  the heat which  would otherwise  be Avasted, and
utilizes it by heating the air in its passage.  I  have
found this form of mouth blow-pipe to be avcII adapted
for fine analytical operations by cupellation  as well as
for all uses of the dental laboratory.
  Fletcher's hot-blast bloMT-pipe is so constructed that
the air-pipe is  coiled around the gas-pipe in a spiral
form,  and both are heated by three small Bunsen
burners underneath, which  are  controlled by a sepa- 
72
DENTAL METALLURGY.
rate stop-cock  as shown in Fig. 4.  It is claimed
that the power of this arrangement is about double
that of an ordinary blow-pipe; that Avhen the  jet is
turned  down to  a small point it will readily fuse
                          a moderately thick  plati-
          FlG- 4            num wire, and  that its
                          power  is nearly equal to
                          the oxyhydrogen jet. This
                          form of bloAV-pipe is Avell
                          adapted  to  continuous-
                          gum work where the teeth
                          are soldered to the plate
                          with pure gold. The blast
                          is obtained by means of a
foot-bloAver  (Fig. 5), connected with the blow-pipe
(Fig. 4) by a flexible rubber tube.  The reservoir of
the upper portion which holds the air is, Avhen the

                      Fig. 5.
bellows  is not in operation, merely a disk of  thick
coffer-dam rubber, which expands under the pressure
of the air while the bellows  is in motion, and thus 
             MODES OF MELTING METALS.         73

affords a very compact, powerful, and effective arrange-
ment.   The step for the  foot is very low and the
blower may be used with ease, Avhether the operator
is standing or seated. The pressure is perfectly steady
and equal.  If the rubber-disk is distended until forced
against the net, the pressure can be increased to almost
any extent desired.   It will give, if required, a heavy
and continuous blast through a pipe of i-inch clear
bore.
  When a small  amount of gold  or silver is to be
melted by means  of the mouth bloAV-pipe, it is usually
performed upon a support formed of charcoal.  A good
solid cylindrical piece of thoroughly charred pine coal
should be selected, and divided into lavo equal halves
by a vertical cut  Avith a  saw.   Upon the end  of one
half a  depression should be cut for the reception of
the metal to be melted.   On the flat side of the other
half, extending to the end, the ingot mold should be
carved of size and shape  governed by the require-
ments of the case.  The  two  halves should then be
brought together and secured  by a  piece of iron or
copper wire, Avhen they will be found to  practically
combine the requirements of crucible and ingot mold.
The depression in Avhich the metal is to be  melted and
the mold or receptacle should  be connected by means
of a gutter or groove.   The  flame  is now directed
upon the metal, and Avhen thoroughly fluid the char-
coal is inverted so that the fused metal will run into
the mold prepared for it  in the opposite half of the
charcoal.   This  is probably  the  simplest  form of
apparatus by Avhich small quantities of metal  can be
melted, and is often  employed in the dental laboratory
and b\- jewelers.
                        7 
74
DENTAL METALLURGY.
  Fletcher has devised an apparatus embodying the
same general principles as the one just described, for
quickly obtaining ingots of gold and silver Avithout
the use of a furnace.  It is shoAvn in the accompany-
ing diagram, Fig. 6: A,  representing crucible of
                molded carbon,  supported in posi-
    Fig. 6.      tion  by an iron  side-plate;  C,  the
                ingot mold; D, clamp,  holding ingot
                mold and crucible  in  position;  B,
                cast-iron stand upon Avhich the latter
                SAvivels.  The metal to be melted is
                placed  in  the crucible, A, and  the
                flame of the bloAAT-pipe directed upon
it until it is perfectly fused.   The Avaste heat serves
to make the  ingot mold hot.  The Avhole is tilted
over by means of the upright handle at the back of
the mold.  A sound ingot may be obtained by the use
of this simple little apparatus  in a very feAv minutes.
Simple contrivances of this kind are,  hoAvever, not
applicable  to melting operations  involving quantities
exceeding  one ounce.  In such  cases it is better to
employ a crucible and any stove  or furnace in Avhich
the temperature can be raised sufficiently.  This may
be  accomplished  in  an  ordinary cooking-stOATe,  a
blacksmith's forge, or a small fire-clay furnace, by the
use of anthracite coal, coke, or charcoal.
  By far the most convenient, compact, and effective
furnace for melting from  one to ten ounces  of gold
which has eATer been used is the neAV crucible-furnace
invented  by  Mr. Fletcher, Avhich can be obtained
at  the dental  depots.   The furnace is perfectly
adapted  to the  wants of the  mechanical  dentist.
It is  composed  of a  substance resembling fire-clay,
 
MODES  OF  MELTING  METALS.           75
•  but is  much  lighter in Aveight, and is said to possess
  only one-tenth its conducting power for heat,
    The furnace consists of a  simple pot for holding
  the crucible,  with a lid and a blow-pipe, all mounted
  on a suitable cast-iron base.   As compared Avith the
  ordinary gas-furnace  it appears almost a toy, OAving
  to its great simplicity.  The casing holds the heat so
  perfectly that the most refractory  substances can be
  fused Mith ease, using a common foot-blower.   Half
  a pound of cast-iron requires from seven to twelve
  minutes for perfect fusion, the time depending on the

                         Fig. 7.
gas-supply and pressure of air from the blower. The
power Avhich can be  obtained is far  beyond what is
required for most purposes, and is limited only by the
fusibility of  the  crucible and casing.  The crucible
will hold about ten ounces of gold.  An ordinary gas
supply-pipe of f^-  or  finch diameter will work  it
efficiently.  It requires a much smaller supply of gas
than any other furnace known; about ten  cubic feet
per hour is sufficient for most  purposes.   Crucibles
must  not exceed  2} by 2 inches.  Any common bloA\'-
pipe bellows will work the furnace satisfactorily except 
76
DENTAL METALLURGY.
for very high temperatures (fusion of steel, etc.), for  *
which a very heaAy pressure of air is necessary.  In
size it is but four inches in diameter  by three in
height.  I have used  one in my laboratory for the
purpose  of melting gold  and silver  and for general
metallurgical  experiments for  four  years, with the
greatest  satisfaction; and I have  also found it to be
most admirably adapted  to class demonstration,  for
which purpose, as a means of illustrating my lectures
on metallurgy. I  have had frequent opportunities to
use it.
  A modification of the apparatus has recently been
made,  adapting it  to  the use  of  refined petroleum
instead of gas as a fuel, thus rendering it of general
utility (see Fig. 8).  Thus improved, it is said  to be
                      Fig. 8.
in no way inferior in efficiency to the gas-furnace.
The burner of this furnace is  constructed upon the
principle of an atomizer, which, of  course, dispenses
with a wick; it  is supplied with  a device for regu-
lating the  supply of oil, which is operated  by the
milled nut  (marked A) shoM'n on the top of the reser-
voir in the  cut, and the addition of an annular jet of
air, which is regulated by turning the sleeve (marked 
MODES  OF MELTING  METALS.
77
B).  This burner is so arranged that in case any ob-
struction should occur it can  be  taken apart and
cleaned by separating the burner from the reservoir,
Avhich is accomplished by loosening the small screAvs,
drawing out the oil-tube, taking off the sleeve, B, and
removing the inside tube.
  These furnaces are so constructed that they may be
used for either gas or petroleum, the lamp being fitted
for adjustment in place of the gas-burner, so that the
same apparatus may be used for either.   The blast is
obtained by means of the foot-blower shoAvn on page
72, Avhich is connected with the furnace by  means of
India-rubber tubing, as seen in Fig. 7.
  An injector gas-furnace has recently been perfected
by Mr. Fletcher Avhich  seems to be avcII  adapted  to
the Avants  of  the dentist, chemist, or metallurgist
(see  Fig. 9).
                      Fig. 9.
  The construction of this  apparatus is upon  the
principle of the injector-furnace, and it is claimed that
its power and speed of working are practically Mith- 
78
DENTAL METALLURGY.
out limit, depending only upon the gas- and air-supply.
With a half-inch gas-pipe and  the small foot-bloAver
(see page 72) this furnace AAill melt a crucible full of
cast-iron scraps in ten minutes.  The supply of gas
required is exceedingly small.   Allowing  five cubic
feet of gas for heating up, it consumes about four feet
of gas for every pound of cast-iron melted,  and for
laboratory purposes it is the cheapest and most conve-
nient furnace in use.  It is very simple in construction,
and consists of tAvo  parts—an  upper portion, Avhich
forms the coATer, and a loA\Ter part, Avhich holds the
crucible Avhile in operation.
  Crucibles.—The term "crucible" is applied  to  a
chemist's melting-pot, made of earthenware or other
material, and so called from  the superstitious habit
of the alchemists of marking such ATessels with the
sign of the cross. The term  is  noAV generally under-
stood as designating  vessels in which metals are
melted in furnaces at high temperatures.  A  crucible
should possess the power of resisting high tempera-
tures without fusing or softening.  It should also be
capable of retaining sufficient  strength, MThile hot,
to prevent its crumbling or  breaking when  grasped
by the tongs.   Lastly, it should not crack either in
heating or cooling.
  For the purpose of melting  metals crucibles are
made of clay with admixture of silica, burnt  clay,
graphite, or other infusible material.  For the fusing
of platinum, Avhich requires  the intense heat of the
oxyhydrogen flame, they are formed of lime.   For
use  in  the  dental  laboratory,  graphite  crucibles,
Avhich can be obtained at  the dental  depots, Mill be
found to answer every purpose, and  they are  thor- 
MODES  OF  MELTING METALS.
79
 oughly reliable  in  strength  and durability.  They
 range in size from  two to  four inches  high,  and
 are  specially designed for  use  in the Fletcher  gas-
 furnaces.  When the  amount of metal to be melted
 is very small, say a half-ounce of gold, the smallest-
 sized  Hessian crucible  may be used  in  the small
 Fletcher apparatus.
   Crucibles suitable for melting platinum* or iridium
 are formed of two  blocks of lime, each block having
 a concaAity  or excavation, so  that when  the  tAvo
 pieces are placed together the center is hollow;  it
 is thus designed to hold the scraps of platinum to be
 melted.  The Ioavci-  block  is also arranged Avith a
 groove and lip, so that Avhen the metal becomes fluid
 it may be poured  into a suitable ingot mold by in-
 verting the crucible.  The  compound flame is intro-
 duced by tubes  passing through the center of the
 upper block  of lime forming the cover.
   Before melting any considerable quantity of gold
■ the crucible should be tested, particularly if the melt-
 ing  operation is  to be performed in an ordinary  coal
 stove, where a defective crucible might be the means
 of a considerable  loss.   A small amount  of borax
 should be placed in the vessel. Avhich should then be
 exposed to a high temperature.  Should  it not be
 perfect, the borax  glass will run through and glaze
 the  surface on the outside.  If the  crucible is found
 to be impervious, it should be so inverted  Avhile yet
 hot that the borax glass may cover the surface of the
 lip or groove out of Avhich  the  melted metal is to be
 poured.   This facilitates the pouring and prevents
 any portion of the metal from adhering to the side of
 the  crucible. 
80
DENTAL  METALLURGY,
  Ingot molds are constructed of various substances.
For  the reception  of  platinum melted  Avith  the
                                 oxyhydrogen
                                 blow - pipe  they
                                 are  formed   of
                                 lime or coke; for.
                                 gold and silver,
                                 they are common-
                                 ly made  of cast-
                                 iron, about  two
                                 inches square and
                                 from an eighth to
                                 three - sixteenths
                                 of an inch thick,
                                 andareconstruct-
                                 ed with  slightly
concave inner surfaces, as the shrinkage of the ingot
is greatest at the center. Ingot molds formed of soap-
stone are also emploj^ed.  The ingot  mold  should be
heated before pouring.
         jiIG  j j            Boiling or laminating is
                        accomplished  by  repeat-
                        edly passing the  metallic
                        ingot betMreen cylindrical
                        steel  rollers  from  three
                        to  four inches  in width.
                        These  are  so  arranged
                        that, by means of screAvs,
                        they are capable of being
                        brought  closer  together
                        every time  the  gold is
                        passed through.  The prop-
er degree of attenuation is determined by the gauge-
 
            MODES  OF MELTING METALS.          81

plate (Fig. 12).  Gold or silver is made into wire by
means of the draw-plate—an oblong piece of steel pro-
vided with a number  of gradually diminishing holes,
enlarged on the side Avhere  the gold enters. The gold
to be draAvn through may be prepared in a cylindrical
shape by melting and pouring into an ingot mold
provided  with a chamber  for the purpose  (some
ingot molds are so constructed).  The end of the rod
                     Fig.  12.
should be filed so as to readily enter the draAv-plate,
Avhich must be firmly screwed in a vise.   The  gold
is  then, by means of a strong pair of pliers, draAvn
through the  different  holes of the draw-plate  con-
secutively  until  the desired size  is reached.   At the
beo-inning  of the operation it Avill require frequent
annealing.
  Soldering must also, to a  certain extent, be re-
garded as coming under the general head of melting 
82
DENTAL METALLURGY.
operations, since it refers to the union of tAvo or more
pieces  of  metal by means of a  more  fusible alloy.
The conditions of successful soldering  are:  1. Con-
tact of the tAvo pieces to be united.  2. A clean  me-
tallic surface OA'er Avhich the solder is to Aoav.   3.  A
freely-floAving solder.  4. Proper  amount and distri-
bution of  heat.
  Contact of the pieces to be united is of the greatest
importance, as solder cannot be made to Aoav over an
open space.   If, for example, the object  to be soldered
be an artificial denture, it is an indispensable require-
ment that the backings be quite or A-ery nearly  in
contact Avith  the plate,  and, if gum teeth  be used,
that each backing touch its neighbor.  This  is not
difficult to accomplish if the teeth have been carefully
and accurately fitted to the plate and  to each other.
If, however, any  defects of this character are found
to exist after the teeth have  been invested, they
should be remedied by filling such spaces or crevices
with small pieces of gold  or silver, as the case may
be,  thus rendering the continuity of the parts com-
plete.   By the obseiwance of this precaution much of
the Aexation  in soldering  experienced by beginners
may be avoided, and  Avhen the other  conditions
named  have  been observed the  operation  becomes
exceedingly simple.   Solder runs  freely by the force
of  capillary  attraction  between  tMTo  closely-fitting
surfaces, just  as Avater will be drawn  against grav-
ity betAveen tAvo  panes of  glass in  close  contact.
In  soldering  artificial  dentures  which have been
carefully  arranged Avith reference to  contact of  all
the parts  to be united, I have on several  occasions
completed the operation  of soldering perfectly  by 
            MODES OF MELTING METALS.           83

merely heating the whole case in a charcoal furnace
Avith a good draft to the  fusing-points of the solder,
without using  the bloMT-pipe at all.   Thus it will be
seen that  the difficulties of soldering are mainly due
to a violation of one or more of the rules herein given.
   Cleanliness should ahvays be strictly observed in
soldering  operations.  The parts to be united should
present a bright  and clean  surface.  Darkening or
oxidation will  ahvays occur when gold or silver, the
purity of which  has been reduced  by  alloying, is
heated  to redness.  A  Aveak solution of sulphuric
acid and water, slightly heated, Avill quickly remove
discoloration resulting from this cause ; or, the borax
employed as a flux in soldering operations, will effect
the  same  result, Sy  dissolving*  the oxide Avhich
forms on  the surface, while it also protects from fur-
ther oxidation by excluding the oxygen of the at-
mosphere.  The  surfaces to be soldered should be
carefully  protected from any contact with plaster of
Paris, as  there is no substance used in the dental
laboratory more  likely to retard the union of the
[tarts and impair the final result  than this.  To this
end, all parts over which the solder is to Aoav should,
previous to their investment in sand and plaster, be
thoroughly covered  Avith the cement of resin and
beesAvax  commonly used  in the dentist's laboratory
as a temporary fastening for teeth, clasps, etc., Avhich
are to be  united  by soldering.  This will effectually
exclude plaster, and is easily removed after the invest-
ment has  sufficiently hardened.

  * Borax, when fused to a glass, has the quality of dissolving  metal-
lic oxides, and the different colors imparted to the "bead"  is one
means of discrimination in blow-pipe analysis. 
84             DENTAL  METALLURGY.
  A solder  to be employed  in  dental mechanism
should possess the quality of floAving freely, and be
as high in grade as the attainment of that property
will admit, so that it will sufiiciently resist the action
of the fluids of the mouth.   It should  also approxi-
mate  as  nearly as possible to the  color of the plate
upon  Mxhich it is used.  If the first condition, refer-
ring to the contact of  the  plates to  be united, be
observed, the amount  of solder required to effect con-
tinuity may be reduced to the minimum;  and thus Ave
shall have the smallest possible amount of the alloy ex-
posed to  the action of the fluids of the mouth, Avhile
Ave at the same time aA^oid the danger of fracture of
the teeth by the contraction in cooling of an inordi-
nate quantity of solder.   The latter, for all purposes
of the dental laboratory, should  be  in  the form of
plate of,  say, No.  27 in thickness, and this should be
cut into pieces of sizes corresponding to the extent of
the parts to be united.  Thus, upon each pin a small
piece of solder should  be placed, just large enough to
coArer it.   A piece of the same  size  should  also be
placed near  the top of each joint M-here the backings
come  together, Avhile  a larger piece should be placed
at the points of union betAveen backings and plate.
These  pieces of solder are made  to adhere to their
proper positions through the agency  of the borax,
Avhich is  used in the lump, and rubbed on a piece of
ground-glass with clean  Avater to a creamy consist-
ence, and then applied to the surface by means of a
camel's-hair pencil.
  The application and management of the heat in the
operation of soldering  is a matter requiring both  care
and judgment. The  temperature should at first be 
MODES  OF MELTING  METALS.
85
raised very gradually, in order that pieces of solder
may not be thrown off or displaced by the puffing-up
incident to the calcination of the borax, or, in the case
of an artificial denture, that the porcelain teeth may
not be  fractured by a too sudden elevation of tem-
perature.  Both parts to be united should be equally
heated;  therefore the heat  should  be  so  applied in
the case of  an artificial denture as to raise the teeth
and plate to an equal temperature; otherwise, should
the  plate  become  sufficiently  hot  while the teeth
remain  comparatively  cool (a condition likely  to
occur unless the fuel has been built up around the
outside  of the investment  covering the teeth), the
solder, Avhen the flame of the  blow-pipe is directed
upon it, Avill Aoav upon and  adhere to the plate.  In
other words,  it Mill manifest  a  preference for the
hottest  portion.  The failure  to  effect an equal dis-
tribution of heat preparatory to soldering is often the
cause of much A'exation and delay.  For example, in
the process  of uniting a rim to a  plate by soldering,
the rim, being so much smaller than the  plate, Avill
be more quickly heated,  in which  event  the  solder
will fuse and flow upon the rim,  and the attempt to
unite one to the other Avill not be  successful.   But to
avoid such a result  the flame of the blow-pipe should,
as a preliminary step, be directed exclusively upon
the plate until it has been heated to nearly the fusing-
point of  the solder,  when the pointed blue flame may
be directed upon the latter, and union of the rim and
plate can hardly fail to  take place.
  Supports.—In  melting small quantities of gold  or
silver, or in  soldering with  the blow-pipe flame, it is
necessary to perform these  operations  upon  a sup-
                         8 
86
DENTAL METALLURGY.
port made of some suitable body, such as charcoal,
coke, pumice-stone, or one composed of asbestos and
plaster, or charcoal and plaster, etc.
  Well-burned charcoal is especially suited  for both
purposes,  as it helps to increase the heat, and, in the
putting together of small quantities of gold or silver
solders, prevents oxidation of the base metals which
are added to reduce the fusing-point  of  the alloy
and cause it to flow freely.  Charcoal made from the
light woods,  such  as  pine, is best, because  it is not
so likely to throw sparks when the flame is directed
upon it as are the  harder  coals, such as that made
from oak, and, being softer, is much better adapted to
soldering  operations in which it is necessary to hold
together the pieces to be united by means of small
nails or tacks thrust into the support; as, for instance,
Avhere  a rim  is to be soldered to a plate, the  former
must be brought in contact Avith the latter upon the
charcoal, and so held during the preliminary soldering,
which  consists of uniting the rim to the plate with a
small piece of solder at some one point; after Avhich
the accurate  adjustment of the rim to the plate for
the final soldering is rendered much easier.
  A good solid piece of charcoal, sufficiently large,
should be  selected, and bound  with iron or  copper
wire, to  prevent breaking  into  pieces.  It  should
then receive a coating of plaster, half an  inch  in
thickness,  on all sides except  the one upon which
the object to be soldered is to rest.  This adds to  its
strength, and protects the fingers from being soiled
in handling.  Good charcoal, suitable for use in the
dental  laboratory,  cannot, hoAvever, always be found
when wanted, and it is therefore  often  necessary to 
MODES  OF  MELTING METALS.           87
use some other substance Avhich may be more easily
obtained.  Thus, those living in large  cities may be
compelled to employ pieces of coke as  supports in
soldering.  Next  to charcoal, coke is  most suitable
for that purpose.   It is more durable  than charcoal,
and when such a support, composed  of one large
piece, or even several smaller pieces, is bound together
Avith wire and coated with plaster, it Avill last  a long
time.   Large pieces  of  pumice-stone  also ansAver
well for  the  purpose of  holding small objects while
the flame of the blow-pipe is  directed  upon  them.
Neither  of  these, however, is so well  adapted as
charcoal for holders where small quantities of  inetals
are to be  melted, in  consequence of their greater
porosity  and  hardness, which  prevents  the cutting
of suitable pits for the reception of the metal to be
fused.
  A very good support for soldering purposes alone
may be formed by filling a cup made of sheet-iron
or  copper, five inches  in  diameter by five inches in
depth, Avith  a mixture of asbestos and plaster, or
plaster and finely-broken charcoal.  The vessel  should
be  supplied with a wooden handle, fastened  in the
bottom for convenience in handling.
  Plattner's  " Manual of Qualitative and  Quantita-
tive Analysis Avith the Blow-pipe," page 15, gives a
method of artificially preparing good solid supports
of charcoal which mighit be found of value in the den-
tal  laboratory.  It consists of mixing charcoal dust
(which must  not be too  finely ground)  with  starch
paste.   The latter is prepared by combining  one
part of starch with six parts of boiling Avater.  These
are stirred in an earthen pot until all the meal  is con- 
88
DENTAL  METALLURGY.
verted into paste.   This paste is rubbed in a porce-
lain mortar, with frequent additions of charcoal dust,
until the mass becomes too tough for further admix-
ture, when enough of the coal dust is kneaded in by
the hands to render the whole mass stiff and plastic.
From this the desired forms of blow-pipe coals can be
made, allowed to dry gradually and thoroughly,  and
then heated to redness in a  covered vessel  so as to
char the starch paste. The charring may be regarded
as complete Avhen the evolution of gases from  the
mass ceases, or when it has been heated to dull red-
ness.  Coals thus formed are  of the proper firmness,
and ring like ordinary good  charcoal when throAvn
on the table.
  Blocks formed of  graphite and  fire-clay have re-
cently been furnished as supports for holding objects
to be soldered, but they do not answer the purpose
well, in consequence  of  not  being sufficiently non-
conducting, and they  soon  become so hot in  the
operation of  soldering that it is impossible to hold
one in the hand for any length of time.
  Where  the object to be soldered is an artificial
denture containing a number  of teeth, a support that
will be found to answer all requirements is the hand-
furnace, such as is now furnished  by the dental de-
pots (see Fig. 13).  It consists of a funnel-shaped
receptacle of sheet-iron, with a  grate or perforated
plate near the bottom, and a* small door on one  side
underneath the grate for the  admission of air.  The
upper part of the holder is Surmounted by a cone-
shaped  top; to the bo^om is attached  an iron rod,
five or  six inches long, terminating in  a  wooden
handle.   This apparatus is designed  to serve both 
MODES OF  MELTING METALS.
89
    the purpose of heating the case and as a support or
    holder  during the soldering.   For the first it is not
,   well suited, being too small to contain fuel enough to
    admit of a thorough heating of the case;  but when
    the object to be soldered has been brought to  the
    proper temperature, it makes  a capital  holder for a
    set of teeth AAThile the flame of the blow-pipe is being
                         Fig.  13.
directed  upon it.  The best method of heating up a
case is to place it on a gas-oven, such as is employed
in the dental laboratory for  general  use,  and for
heating flasks in packing rubber work, etc.   A ring
of cast- or sheet-iron, six inches in diameter by tAvo
inches high, should then be placed around it for the
purpose of holding the charcoal, which, in pieces the
size  of a hen's egg, should be built around  the out-
                        8* 
90
DENTAL  METALLURGY.
side  of the case, so that it may be uniformly heated.
The  cone or top of the apparatus just described may
now  be placed over it.  The gas is then lighted, but
the full head should not be turned on until the moist-
ure of the  investment has  been driven off, when it
may be gradually increased until the case is  heated
to redness.  About thirty minutes will be required
to reach the proper temperature for soldering, when
the case may be lifted from the gas-oven with suita-
ble tongs and placed in the hand-furnace.  The live
coals used in heating up should also be placed around
the  outside of the  investment to prevent the too
rapid cooling  of the piece, should any delay in the
soldering occur.  When the latter operation has been
satisfactorily completed, the top may be placed tightly
on, and  all access  of air excluded in order that the
case  may cool slowly, and thus avoid the danger of
cracking the teeth. 
CHAPTEK VII.
  COMBINATIONS OF METALS  WITH
       NON-METALLIC ELEMENTS.


 rPHE  metals combine with  the  non-metallic  ele-
     ments, to form  a neAv class of bodies Avherein
 none  of the distinctive characteristics  of the con-
 stituents are discernible.  These are the
                      Chlorides,
                      Bromides,
                      Iodides,
                      Fluorides,
                      Cyanides,
                      Oxides,
                      Sulphides.
   Metals also  form definite compounds  with nitro-
 gen, phosphorus, silicon, boron, and carbon.
   Chlorides.—All metals combine Avith chlorine, and
 some of them in different proportions, as illustrated by
 the stannous and stannic chlorides, the first having a
 formula  of Sn Cl2, Avhile the composition of the lat-
 ter is Sn Cl4.  The capacity of the metals for combi-
nation Avith chlorine  is  not uniform.  The different
proportions are designated by the following terms:
             Monochlorides, such as K CI.
             Dichlorides,    "  " Ba Cl2.
             Trichlorides,    "  " Au Cl3.
             Tetrachlorides,  "  " Sn Cl4.
  The  chlorides may be prepared by acting upon the
                                        (91) 
92
DENTAL METALLURGY.
metals with chlorine gas,  or  with nascent chlorine
developed by hydrochloric  and nitric acids.*   Some
chlorides, on the other hand, are formed by bringing
a current of chlorine gas in contact with the  metal
in a nascent state.   In this way titanic chloride is
formed, the chlorine being passed over a heated mix-
ture of charcoal and titanic oxide.  Aluminium and
chromium chlorides may be similarly obtained.
  The rationale of the action of chlorine upon me-
tallic  oxides is that it drives out the  oxygen and
unites with the respective  metals to form chlorides.
The interchange may take place at ordinary tem-
peratures, as in the case of silver oxide, but in others
an elevation of temperature (sometimes to red heat)
is required.
  Many metallic chlorides are prepared by  acting
upon  the  metals with hydrochloric acid.  Zinc, cad-
mium, iron, nickel,  cobalt,  and tin  dissolve-readily
in hydrochloric acid, with liberation  of hydrogen.
Sometimes a chloride is obtained by substituting one
metal for another.  In this way stannous chloride is
frequently prepared by  distilling metallic  tin with
mercuric chloride—thus:
             Hg 012 + Sn = Sn Cl2 + Hg.
  Lastly, a chloride may be prepared by dissolving
a metallic oxide, hydroxide, or carbonate in hydro-
chloric acid.
  Bromides.—Bromine  unites directly with  most
metals, and  forms compounds analogous in compo-
sition and general properties to the chlorides.   Sea-

  * Aqua regia—i.e., two  volumes of hydrochloric  with one volume
of nitric acid. 
    COMBINATIONS WITH NON-METALLIC ELEMENTS. 93

water and many of the saline springs contain native
bromides, and  silver  bromide  occurs  as  a  natural
mineral.   The  affinity of bromine for the metals is
inferior to that of chlorine, and the  latter, Avith the
aid of heat, drives out the bromine and converts the
substance into  chlorides.
   Iodides are compounds possessing properties analo-
gous to those of the chlorides and bromides, and are
obtained by processes similar to those Avhich yield the
latter.   With the exception of those of gold, silver,
platinum, and palladium, they are not decomposable
by heat alone.
   Fluorides are compounds formed by heating hydro-
fluoric acid Avith certain metals, or by the action of
that acid  on metallic oxides.  They  may  also be
formed  by  heating  electro-negative metals—anti-
mony, for example—with fluoride of lead or  fluoride
of mercury. The fluorides are destitute of metallic
luster, and most of them are easily fusible, and  bear
a close resemblance to the chlorides.
   Metallic  oxides may be variously formed. Some
metals, by mere exposure to  air while  heated,  lose
their metallic  character,  and, by combination with
oxygen,  assume a totally different appearance.
   There  are several  methods of forming oxides  arti-
ficially, and some oxides are capable of being  con-
verted into  others of a higher degree.  Bed lead, for
instance, is  thus formed, the metal being first heated
without  alloAving it to fuse, when a protoxide  of a
yelloAv color is  formed; but on further exposure to a
temperature of 315-5°  C, Avith free access of air, ad-
ditional oxygen is taken up, and the mass assumes a
brilliant-red color. 
94
DENTAL  METALLURGY.
  Oxides of metals  are  also formed by heating a
nitrate or carbonate to redness, by Avhich means the
acid will be evolved while the oxide remains.  Thus,
a protoxide of lead may be formed  by heating the.
white carbonate of the metal, its color soon changing
to a lemon-yellow as  the acid present is driven off.
  Oxides of some of the metals—copper being an
example—are formed by first acting  upon the metal
Avith nitric  acid, and  in that way obtaining a nitrate,
Avhich is dried and heated  to dispel  the acid, when
the oxide will remain.
  Again, if Ave deflagrate some of the metals with a
body containing a large  amount of oxygen, we ob-
tain their oxides. Tin,  lead,  zinc, etc., are  in this
way removed  from  alloys in  Miiich they  enter as
prominent  constituents.   For  example, take,  say,
one gramme of an amalgam alloy, consisting of tin,
silver,  gold, and  platinum,  place in a crucible and
melt with  borax.  If crystals  of potassium  nitrate
are then dropped into the fluid mass the tin is con-
verted into an  oxide, and  is dissolved and held by
the borax glass.  If this part of the process is thor-
oughly  performed, the remaining button will  be
found to contain  only the noble metals, silver,  gold,
and platinum, which may be  easily separated  and
weighed, thus  affording a  very simple method of
quantitative analysis for ascertaining the proportions
of amalgam alloys.
  Metallic  oxides in the  form of hydrates are ob-
tained by treating an aqueous  solution of a metallic
salt Avith an alkali.  Thus, the  hydrated sesquioxide
of iron, commonly employed  as an antidote in  ar-
senical  poisoning, is produced by adding  ammonia 
   COMBINATIONS AVITH  NON-METALLIC ELEMENTS.  95

to ferrous  sulphate.  Zinc  sulphate  or  cupric  sul-
phate,  by the  addition  of caustic  potassa, yields
bulky hydrated oxides.  These in turn may be con-
verted into simple oxides by heat.
  Superficial oxidation may occur gradually by mere
exposure to  air at ordinary temperatures,  and the
action  will be accelerated  by the presence  of mois-
ture.   It frequently occurs, however, that  metallic
objects thus  superficially oxidized are so protected
by the neAvly-formed oxide from  further access of
air that  oxidation  can no longer go on;  but should
the rusted or tarnished surface of an iron or leaden
object  be removed, oxidation Avill again occur.
  Many metallic oxides are formed during fusion of
the metals.  Lead  and zinc are examples  of this.
The  former,  by continued  exposure to  a sufficient
degree of  heat, may be  entirely changed  into an
oxide,  and  the latter, when carried to a temperature
much  above  its fusing-point, burns Avith a  brilliant
light, during which the oxide is evolved  in the form
of white fumes, the incandescence accompanying the
combination being an evidence of the intense affinity
Avhich  the metal at an elevated temperature has for
oxygen.  Other of the metals are thus combustible.
The  familiar experiment  of converting iron  into
an oxide by throAving a jet of oxygen  gas upon a
red-hot bar of the metal is an illustration of the
fact, and many metallic oxides may be thus formed
by deflagration.
  There are,  hoAvever, a feAv noble metals possessing
so feeble an affinity for oxygen that they cannot be
made to combine directly with the latter; even when
the oxides of these are obtained by chemical means, 
96
DENTAL METALLURGY.
 the metals separate from the  oxygen  upon  being
 heated to redness.*  Gold and platinum are illustra-
 tions of this class of metals.  The  latter,  which is
 employed  as a base-plate in the " continuous-gum
 process" and for pins in artificial teeth, is subjected
 to the most intense furnace-heat Avithout the slightest
 oxidation of surface.
  Many of the metallic oxides occur in nature, a
 number  of the metals  being reduced from natural
 ores, which are oxides  of their respective metals,
 such as iron, tin, manganese, chromium, etc.
  Sulphides.—The  metals  unite  with  sulphur and
 form a class of compounds Avhich, in a chemical and
 economical point of view, are almost as important as
 the oxides.  These Avere formerly termed sulphurets.
 Many  of them are  found  as  natural  ores, and  are
 generally  brittle solids  possessing a  high metallic
 luster, the  latter quality being so marked in some
 that they  have been mistaken for gold.  Sulphur
 combines with  the  metals in varying proportions,
 and it may be observed that combination takes place
 in proportions similar to the oxides, the  only  excep-
 tions to this analogy being the alkalies and alkaline
 earths—there being but  two oxides of potassium,
 sodium, and  barium, Miiile there are no  less than
 five sulphides of these metals.
  All the  metallic sulphides  are solid at ordinary
temperatures, most  of them fuse at red heat, and
some sublime unchanged.  The admission of air to
the  heated sulphides is followed by their decompo-
sition and  conversion into sulphates, or, if they are
* See " Noble Metals." 
    COMBINATIONS  AVITH NON-METALLIC ELEMENTS.  97

exposed to higher and continued heat, into oxides.
The sulphides are all insoluble in water,  with the
exception  of  those  of potassium, iodine, strontium,
barium, and calcium. The metallic sulphides may be
artificially formed by the following processes :  by
heating the metals or their oxides with sulphur ;* and
from the sulphates by heating them with charcoal or
in a current of hydrogen, by passing a stream of sul-
phureted hydrogen  through  their solutions, or  by
adding to- them a  solution of an alkaline sulphide.

        Beduction of Metallic Compounds.
   The term " reduction," as used in metallurgy, refers
to the different methods of separating a metal from
its natural ores or  from combination with any non-
metallic element.   In some cases this is effected by
heat alone.  For example, the noble metals are sepa-
rated from oxygen  by  merely  heating  to 600° F.
(== 315-5° C)  Generally, however, the joint action of
heat and other agents for Avhich the non-metallic
constituents of the compound have greater affinity is
required.                           •
  This class of metallic compounds, whether natural
or artificial, is composed of bodies formed of dissimilar
elements  held together by  the  force of  chemical
affinity, and which are totally unlike either of their
constituents.  This  affinity ATaries  much in different
metals.   Thus, gold possesses very feeble affinities,
and Avhen combined Avith chlorine may be  partially
  * Silver is an example of this.  So great is its affinity for sulphur
that rubber, the indurating agent of which is sulphur, cannot be vul-
canized in contact with that metal.
                        9 
98
DENTAL METALLURGY.
precipitated by mere exposure to light or the atmos-
phere.  The facility with which it often passes from
one  element to another may be  observed in the
interesting  process  of manufacturing "shredded
gold,"* in Avhich an acid solution of the trichloride is
formed and slightly heated in a glass matrass; gum
Arabic or sugar dissolved in Avater is then added,
when beautiful web-like masses of pure gold are seen
to form  in the liquid, but unless these are quickly
removed by means of a glass spoon or dipper, they will
almost instantly dissolve and the gold again unite Avith
the  chlorine.   Lead, tin, zinc, iron,  and many other
metals evince stronger affinities;  hence they are not
so readily reduced, and require, in addition to heat,
the  presence of other substances, such as coal, coke,
charcoal, etc.  In other words, it is  necessary  to
expose them in contact with some  reagent betAveen
which and the non-metallic constituents of the com-
pound superior affinity exists, so that by union of
these the metal may be released.    Indeed, it may
be truly said that all analytical operations for  the
reduction of ores and the discrimination and estima-
tion of  unknown  bodies  are performed by  taking
advantage  of  the different  degrees  of chemical
affinity.   Thus, lead  which has  been OA^erheated or
subjected to frequent  or long-continued meltings
becomes partially oxidized  and  covered Avith  an
earthy-looking mass  consisting  of  semi-oxidized
metal, formerly called the " calx."  Further exposure
to heat  would simply have  the  effect of  converting
this into an oxide of a  higher degree, but if covered
* " Lamm's shredded gold."  See chapter on " Preparations of Gold." 
    COMBINATIONS  AVITH NON-METALLIC ELEMENTS.  99

Avith  finely-broken charcoal,  or  other carbonaceous
substance,* the  latter will  extract the oxygen, car-
bonic acid  will be  formed and  evolved,  while the
metal will be restored to a free state.
   Chlorides.—With the exception of the chlorides of
the metals of the alkalies and  earths, all  metallic
chlorides  are decomposed when  heated in a current
of hydrogen, hydrochloric acid and the pure metal
being the result.   The chlorides of gold and platinum
are decomposed by simple ignition.
  Argentic chloride, Avhen heated on charcoal, under
the flame of  the blow-pipe,  yields pure silver and
emits an odor of hydrochloric acid.  Placed in water
acidulated Avith sulphuric  or hydrochloric  acid,  ar-
gentic chlorides may be reduced by the addition of
pieces of  some easily-oxidized metal, such as zinc or
iron, the rationale of the  reaction being as  folloAvs:
the zinc displaces  the hydrogen of the H2 So4, zincic
sulphate  is formed, the liberated hydrogen  unites
with  the chlorine to form hydrochloric  acid, and
pure silver remains.
  Sulphuric acid decomposes  the chlorides and con-
verts  them into oxides, the oxygen being supplied
from  the water  present.   Some  chlorides  may  be
decomposed by heating them Avith a metal  which
has more  poAverful basic properties.   Thus, sodium,
when heated  Avith aluminium or magnesium chlo-
ride, Avill become  sodic chloride, with liberation of
the magnesium or aluminium.   Some chlorides are
  * In the dental laboratory beeswax is usually employed to deoxi-
dize lead or zinc which has become thick and earthy by frequent
meltings. 
100            DENTAL  METALLURGY.

reduced by  heating  with a mixture of sodic carbo-
nate and charcoal; other carbonaceous compounds,
such as sodic or calcic carbonate, are frequently used.
  Sulphides.—Beduction of the sulphides in some few
instances, such as those of gold, silver, and platinum,
is effected by heat alone.   The oxygen of the atmos-
phere unites with the sulphur,  Mrhich is evolved as
sulphurous acid.  In many cases, however, a portion
of the oxygen combines Avith the metal, and an oxide
instead of the free metal is obtained.   The reduction
of many of  this class of ores consists simply in such
interchanges.  The application  of heat and air in
some instances converts the sulphide into a sulphate,
which in turn may be decomposed at high tempera-
tures and separated  into  sulphurous acid and a me-
tallic oxide.  On the other hand, some of the sulphides
may, AAiien heated Avith access of air, be  converted
into permanent  sulphates capable of resisting high
degrees of heat.  The sulphides  of the noble metals,
when heated, part directly with the whole of their
sulphur,  leaving the metal in a pure  state.   Silver
sulphide thus reduced is also  partially oxidized, so
that a small portion  of argentic sulphate is formed,
which requires  for its reduction a still  greater eleva-
tion of temperature.
  Beducing agents, such as metallic  iron, hydrogen,
chlorine, etc., are frequently employed to combine
with sulphur.  If sulphides of lead  be heated Avith
iron, sulphide of iron and metallic lead result.  This
method is frequently practiced in the assay of galena,
clean iron nails being heated Avith the  ore.  The sul-
phides of antimony,  bismuth, copper, tin, and silver
are readily  reduced  by passing dry hydrogen over 
   COMBINATIONS WITH NON-METALLIC ELEMENTS.  101

them at red heat, the result of the reaction  being
the free metal and sulphureted hydrogen, the pro-
duct of  the union of the  hydrogen  and sulphur.
Dry chlorine will also decompose them, and combine
with both the metal  and the sulphur.  Nitro-hydro-
chloric  acid  converts the sulphides into chlorides,
and  hydrochloric acid in a  few instances acts simi-
larly ; its hydrogen,  combining with the sulphur, is
evolved  as  sulphureted  hydrogen.   Strong  nitric
acid also decomposes them, and  is often employed
in analyses of ores.  The  sulphur being thus oxi-
dized, the liberated metal combines with the acid to
form a nitrate, mercuric sulphide  or native cinnabar
being the only ore which cannot be thus reduced.
   Oxides.—The reduction of lead, zinc,  or  tin,  the
working qualities  of Avhich haAre been impaired by
frequent meltings with exposure to  air, may be
effected in the laboratory by placing the metal to be
treated  either in  a  large  clay crucible  or in  the
ordinary iron melting-pot employed by dentists. The
semi-oxidized metal  is then covered with powdered
charcoal,  when the  reaction described above takes
place, and the original properties of the metal are
restored.
  There arc  some oxides  to  which  the foregoing
treatment is not applicable, but these may be reduced
by passing  a current  of dry  hydrogen  over them
when heated to redness.  Makins gives the folloAving
very clear description of this  method of reducing
oxides:
  " A large two-necked bottle is fitted up in the usual
way for the evolution of hydrogen.   This has its
delivery-tube passed into a tube filled Avith fragments
                       9* 
102
DENTAL  METALLURGY.
of calcic chloride, for the purpose of absorbing the
moisture AA'hich may be carried  over with the gas;
to the other end of this drying-tube is connected the
tube Avhich is to hold the metallic oxide (generally
in a bulb blown upon this).  The gas bottle  should
contain about a couple of quarts, so  as to afford  a
steady supply, and the calcic chloride tube should be
long and well filled.  In operating, after the gas has
completely driven out the air in  the apparatus, heat
is applied to the bulb containing the oxide,  and its
reduction will be brought about.  The gas must be
kept up in a good stream,  so  as to drive out the
watery A^or formed by the decomposition.   Here
the hydrogen takes  the oxygen  of  the  oxide,  and
water is formed, Avhile the metal is set free."
  There are  metals Avhose affinity for oxygen  is so
strong that their union Avith  that element  cannot
be broken up by such means as  we have  described.
Deoxidation  of  these  metals must  be  performed
through the  agency of some other metal possessing
greater affinity for oxygen.   For  example, if oxide
of iron be  heated with potassium, the iron  will be
deoxidized, while the potassium will be  converted
into potash (K2 0).
  Some metallic oxides may be  reduced  by heating
with  sulphur,  part  of the latter abstracting the
oxygen, with Avhich it unites to form sulphurous acid.
A portion of the sulphur, however, unites with the
metal,  Avhich is converted into a sulphide, or a sul-
phate,  or  a mixture of both.  These must then be
treated according to  the directions already given for
the reduction of metals when combined with sulphur.
  There are also a few metallic oxides which chlorine 
   COMBINATIONS WITH NON-METALLIC  ELEMENTS. 103

gas will reduce.  Thus, platinum is  liberated from
combination Avith oxygen when exposed to a current
of dry chlorine.
  Probably the most powerful  means of  reducing
metals from combination Avith non-metallic elements
is that knoAvn as electrolysis.   It consists in exposing
a solution of a metallic salt to the decomposing influ-
ence of the galvanic  current.   A demonstration of
this  force  may  be  made by taking  a  solution  of
nitrate  of  lead  (plumbic nitrate) and immersing in
it a piece of zinc.  The latter soon  becomes covered
with needle-like crystals of pure lead ; the zinc re-
places the lead,  Avhich is set free  and deposited at the
point of galvanic action.  Or the same phenomenon
may be Avitnessed by immersing a piece of clean iron
in a  solution of  copper, or  a piece of copper in  a
solution of a salt of mercury,* the action only ceasing
when all the metal in the solution is reduced.
  * Reinsch's test for the detection of the mineral poisons is based upon
this principle. 
CHAPTER VIII.
                 GOLD.
Atomic  Weight,  197.  Symbol, Au (Aurum).
(~^ OLD is one of the few metals \AThich is found in
     the metallic state, and was probably one of the
first  known to man.   Allusions to it are frequent in
the Old Testament, and jewelry and vessels found in
Egyptian  tombs afford evidence of the perfection
attained in Avorking  it at a period  earlier than the
government of Joseph.  There are many  evidences
that  processes of alloying, refining,  and separating
gold  were practiced  at a very early period  of the
world's history.- According to Pliny, the metallurgy
of gold was known in his day.  Vitruvius  also gives
a detailed account of the method of recovering gold
by amalgamation  from cloth into which it had been
woven.  It was employed in Borne for the purpose
of fixing artificial  teeth  more than  three  hundred
years before the  Christian era, and a law  of the
" TAvelve Tables" makes exception with regard to
such gold, permitting it to be buried with the dead.*
The  great beauty of  color and luster, and the poAver
of resisting oxidation which gold  possesses, have
caused it to be valued from the earliest  ages  for the

                * .Phillips's Metallurgy.
      (104) 
GOLD.
105
purpose of adornment, and as a circulating medium.
  Occurrence, Distribution, and Properties.—Gold is of
nearly universal  distribution, and is found in nature
chiefly in the metallic state as native gold.  It occa-
sionally occurs in combination  with tellurium, lead,
and silver, forming a peculiar group of minerals con-
fined to a feAV localities in Europe and America, these
being the only certain examples of natural combina-
tions  of the metal.  The  most important minerals
containing gold  are  sylvanite or graphic tellurium
(Ag Au Te2), containing about tAventy-four per cent,
of gold; calaverite (Au Te2), containing about forty
per cent, of gold, and nagyagite or foliate tellurium,
the composition  of Avhich is not definitely knoAvn.
It contains from  five to nine per cent, of gold.  The
metallic  sulphides, such as galena and iron pyrites,
usually contain sensible quantities of gold, the lead
ore being  almost invariably gold-bearing.   Native
arsenic and antimony also occasionally contain gold,
and a native  gold amalgam has been found in Cali-
fornia.
  Gold occurs in nature very nearly though never
quite  pure, being  generally associated Avith  silver.
Other metals  are occasionally found combined with
it, but in very small quantities; and  these  foreign
metals are peculiar to localities.   Thus. California
gold,  in addition to silver, Avhich is ahvays present,
may contain iridium;  Bussian gold often contains
platinum, and specimens of the native metal from
Brazil Avill not  infrequently  be found to contain
palladium. 
106
DENTAL METALLURGY.
Analyses of Native	3old from Various		Localities	
	Gold.	Silver.	Iron.	Copper.
United States:*				
California ....	9012	9-01	615	
Europe:				
Vigra & Clogan . .	9016	9-26	trace.	trace.
Wicklow (river) .	92-32	6-17	•78	
Transylvania . . .	60-49	38-74		0-77
Asia:				
Russian Empire—				
Brezovsk ....	91-81	8-03	trace.	•09
Ekaterinburg . . .	98-96	016	■05	■35
Africa:				
Ashantee ....	9005	9-94		
South America:				
Brazil ....	940	5-85		
Central America .	88-5	11-96		
Titiribi ....	76-41	2312		0-87
Cariboo ....	84-25	14-90		•03
Australia:				
South Australia . .	87-78	607	6-15	
Ballarat.....	99-25	0-65		
  Pure gold is of a rich yellow color, and  is nearly
as soft as lead.  It is, with one exception (platinum),
the heaviest substance in nature, being about nineteen
and a half times as heaAy as water.   These proper-
ties are all  sensibly modified  by admixture of other
metals.  Thus, the tint is lowered by small quantities
  * The yield of gold in the United States in 1876 was greatly in excess
of that of any other country on the globe, Russia being next in amount
produced. 
GOLD.
107
of silver, and heightened by copper.  Owing  to  its
exceeding softness, gold is commonly used alloyed, in
order to render it capable of resisting the attrition
to Avhich coins  and articles of jeAvelry are exposed.
  It is the most malleable of all the metals.  One grain
may be beaten into leaves Avhich Avould cover a sur-
face of fifty-six  square inches, and only 3 0 ^ 0 0 of an
inch thick.*
  Very thin gold  leaf  appears yelloAv  by reflected
and green by transmitted light.  Highly attenuated
films of  gold, Avhen heated, transmit rays of light
of a ruby-red color.  The pressure of  a  hard sub-
stance on the film will, hoAvever, so change its state
of aggregation that the green color Avill again appear.
  Gold is exceedingly ductile, but does not possess a
very  considerable  degree of tenacity.  A  grain of
gold, hoAvever, if covered by a more tenacious metal,
such  as  silver, may be  draAvn  into a wire  five hun-
dred feet in length.  It also possesses the remarkable
property of welding cold.  Thus, the metal, in the
state in Avhich it is obtained by precipitation by oxalic
acid, may be formed into disks or medals by compres-
sion between dies.
  The specific gravity  of gold varies according to
condition.   In the finely-divided state in Avhich it is
obtained by precipitation by oxalic acid it is 19-49.
The specific gravity of cast-gold is someAvhat less,
but Avhen compressed between dies, or by the rolling-
mill, it may be raised from 19-37 to 1941. Annealing,
  * The late Dr. S. S. White presented the author with a specimen,
securely mounted between plates of glass, which is but .^ 1    of an
inch in thickness. It is transparent and transmits green rays of light. 
 108           DENTAL METALLURGY.

 however, will restore  its previous density to nearly
 that of the cast metal.
   The atomic  Aveight of  gold  has been variously
 stated.   Berzelius gave  it as 196-67; Levol, 196-3;
 Wurtz, 196-5; Watts, I960; Bloxam, 196-6 ; Fownes,
 197.  There  seems also  to be a similar diversity of
 opinion regarding the temperature at Avhich it fuses.
 Thus, Daniell fixed  the melting-point at 1425° C.;
 Pouillet, 1200°  C.;  Guyton  de Morveau,  1380° C.
 The figures, 1102° C, given in Fownes's "Elementary
 Chemistry," are probably as nearly correct as any, and
 for all practical purposes will answer very well.
   The electric  conductivity of gold  is given by
 Mathiessen as  73-96 at  151° C, pure silver being
 100. The conducting power, hoAvever, depends much
 upon the degree of  purity, as the smallest addition
 of  another metal will A^ery considerably lower its
 conductivity.*
   The conductivity of gold for heat is stated as  53-2,
 as compared  Avith pure silver, 100.  Its specific  heat
 is -0324.
   Volatility.—The absence of uniformity in results of
 experiments Avith regard to this property, given by
 different investigators, Avould seem to leave the  mat-
 ter still in doubt.  Thus, Gasto Claveus and  Kunkel
 describe  similar experiments, Avherein  an ounce of
pure gold Avas placed "in  an earthen vessel in that
part of a glass-house Avhere the glass is kept  con-
stantly melted,  and retained in  a state of fusion for
two months, Avithout the  loss of the smallest portion
of its Aveight,"   On the other hand, Homburg, Lav-

          *See "Power of Conducting Electricity." 
GOLD.
109
oisier, and Maquer stated that Avhen a small portion
of gold is kept at a violent heat part of it is volatil-
ized,  and that a piece of silver held  in  the  rising
fumes Avill have its surface gilded.  It is quite prob-
able that, when a small amount of gold is mixed Avith
a large amount of zinc and heated in air, the  Avhole
of the gold will be dissipated Avith the fumes of oxide
of zinc.   Mr. Makins also  demonstrated  that gold,
silver, and lead, Avhen cupelled together, volatilize;
and he collected quantities of each metal from the
chimney  of  an assay furnace  which had  been in
use but a few Aveeks.  Gold may also be volatilized,
when in the  form of  leaf or highly-attenuated wire,
by passing a powerful charge of electricity through it,
  Forms of Native  Gold.—-The native metal is some-
times found in the  form  of  cubic crystals, in octahe-
dra, and in irregular and more complex shapes called
nuggets and  dust.    Crystals of  gold may also be
obtained artificially from  an amalgam  of gold one
part,  mercury tAventy parts.  The mixture  is  main-
tained at a  temperature of 80° C. for eight days.
The mercury is then removed by strong nitric acid,
leaving crystals of  gold, which  require to be heated
to redness to develop brilliancy  of surface.
  Gold is found in  quartz veins or reefs traversing
slaty  or crystalline rocks, alone or associated Avith
iron, copper,  magnetic and  arsenical pyrites, galena,
specular iron ore, and silver ores, and  more  rarely
Avith sulphide of molybdenum, tungstate of  calcium,
bismuth,  and tellurium  minerals.  It is also  found
among  the  detritus  of  disintegrated rock,* associ-
* In the form of small lumps called " dust."
               10 
110
DENTAL  METALLURGY.
ated with the metals of the platinum group.  In the
superficial alluvial or "placer" deposits it  has  been
remarked that the minerals Avith which it is found
intermixed are of great density and hardness, and
are the most durable  constituents  of disintegrated
rock.
  The yield of gold in easily-worked alluvial deposits
is often exceedingly  small.   It is stated that in the
Siberian gold-washings the proportion of gold ranges
from 12 grains to 1 dwt. to the ton of sand, while in
the lodes which require more labor to work the pro-
portion is but 8 dwts. per  ton, and in the "placer"
washings of California it is but 12 grains to the ton
of gravel.   In Australia the alluvial washings of
Victoria yielded 25 grains to the ton.  Vein  mining
being more difficult  and costly, necessitates a larger;
yield of the precious metal,  and 5 dwts., or about
five  dollars' worth of the precious  metal, is in moelt
gold-bearing localities regarded as a paying quan-
tity.
  The method of obtaining gold from alluvial de-
posts is exceedingly  simple, and consists in washing
away the lighter portions, leaving the heavy metallic
particles.   In the early days of gold mining  in Cali-
fornia this was accomplished  by means of a pan of
sheet-iron,  thirteen  or fourteen inches  in  diameter,
held in the hand and its contents exposed to a stream
of water; and on the large scale consists in washing
the alluvial deposits  into sluices or troughs by means
of continuous streams of water,—mercury or  amal-
gamated copper plates being sometimes employed to
collect the finer particles of gold.
  In vein mining the separation of the gold from the 
GOLD.
Ill
rock with Avhich it is mechanically mixed consists
in reducing the latter  to a fine powder in grinding- or
stamping-mills, and the gold is recovered by amalga-
mation, or by washing the pulverulent mass through
troughs lined Avith coarse woollen cloths, by which
means the lighter deposits are carried away with the
current, while the heavier metallic particles become
entangled in the fibers of the blanket until the sur-
face of the  latter  is completely covered, when it is
remoA-ed and its contents are washed off in  a suitable
vessel and reserved for amalgamation.
  In  the treatment  of gold by amalgamation the
process is frequently  retarded by a difficulty known
as the "sickening" or "flowering" of the mercury.
The latter,  losing its  bright metallic surface, is no
longer capable  of coalescing with other metals.  The
discoA^ery was made by Wurtz, in  1864, that by the
addition of a  small quantity of sodium to the mei^
cury the operation is  greatly facilitated, the addition
of the sodium  preventing both the " sickening" and
the " floAvering" of the mercury, Avhich is produced
by  certain associated minerals.  Some metallurgists
recommend the addition of 20 per cent, of zinc and
10 per cent, of tin.  It has been estimated that mer-
cury will dissolve from 0-05 to 0-08 per cent, of native
gold of standard 650  to 850 without loss of fluidity.
The solubility of the gold increases with its fineness.
When the  point  of  saturation has been  reached,
lumps of the  solid amalgam are introduced into an
iron vessel lined with a mixture of fire-clay and wood-
ashes, and  provided with an iron tube, by which the
fumes of mercury are passed through water and con-
densed.  The distillation being effected at a tempera- 
112
DENTAL METALLURGY.
ture below redness, the gold left in the retort is then
melted in a suitable crucible.
  Gold  is sometimes reduced from  the mineral by
exposing the ore, Avhich has been previously roasted)
to a current of chlorine gas.  By this means the gold
is converted into a soluble chloride, Avhich is removed
by washing with water.  The precious metal is then
recovered in the metallic form by precipitation with
ferrous  sulphate.   This  process is, when  carefully
performed, a very  accurate  one, and yields 97 per
cent, of the gold present in the ore.
  Refining Gold.—Methods   of  refining  gold  were
knoAvn and practiced in very ancient times, and  many
of them, though empirically employed, did not ma-
terially differ in principle from those in use at the
present day,   Thus, in Strabo's time the gold Avas
placed on the fire Avith three times its weight of salt
and  a quantity of  argillaceous  rock, Avhich in the
presence of moisture effected the deconrposition of
the salt,  Hydrochloric acid is  thus formed, Avhich.
at the high temperature employed, furnishes chlorine
to the  silver associated with the gold, Avhich is con-
verted into a  chloride.  A similar  process is still
practiced  in South America,
  Among other methods for the separation of gold
from silver or other contaminating metals, Avhich
ha\-e been in use from a remote  period, may be men-
tioned prolonged oxidation by  exposure to air, and
melting with sulphur, sulphide of antimony, and cor-
rosive sublimate.
  The old "quartation" process of refining, so-called
from the  fact that  an alloy is formed, four parts of
which contains three parts of silver and one of gold, 
GOLD.                  113
consists  in  first  forming an  alloy of the gold with
silver in the proportions given.  These  are melted
to insure homogeneity, and granulated* by pouring
into water contained in a Avooden vessel.  The pieces
are then collected and placed in a glass or platinum
vessel, and  acted upon by either nitric or sulphuric
acid.  When the presence of lead or tin is suspected,
these should be got rid of before subjecting the alloy
to the acid; otherwise the  platinum digester  would
be injured.  The removal of lead is accomplished by
cupelling the  alloy, while tin  may be effectually
removed by fusing the alloy with potassium nitrate.
On  account of greater  economy and the  closeness
with which it will  act upon  silver containing very
small quantities of gold, sulphuric  acid is  at the
present  day the  agent  most commonly  employed,
particularly where large quantities  of the  alloy are
to be treated.
  The nitric acid plan does not, as a rule, yield gold
of as high a degree  of fineness as the sulphuric acid
treatment, but the oxidizing  property of the nitric
acid is of great advantage in  refining gold contami-
nated with antimony and  other equally  injurious
metals.
  When  nitric acid  is employed, each ounce of the
granulated  alloy  is treated  Avith an  ounce and a
quarter of nitric acid of  specific gravity 1-32.
  The sulphuric acid process is based upon the facts
that the  concentrated hot acid converts silver and
copper into soluble sulphates  without attacking the
gold, the metallic silver  being  recovered from the
* Granulation is usually repeated twice or thrice.
                10* 
114            DENTAL METALLURGY.
sulphate in the form of needle-like crystals by thrust-
ing copper plates* into  it.   The sulphate of copper
resulting from the reaction is crystallized and becomes
an article of commerce.   The sulphuric acid should be
of specific gravity 1-84, and the alloy is boiled for three
or four hours in a platinum vessel Avith 2-5 times  its
Aveight of acid. The sulphurous acid fumes Avhich arise
are partially condensed before being allowed to pass into
the air.  When the acid has ceased  to act upon the
metal, a small quantity  of sulphuric acid of specific
gravity 1-53  is added, and after a  second  boiling the
contents of the vessel are allowed to settle; the liquid
is withdrawn from the gold, Avhich rests at the bottom
of the vessel, and is diluted until its density is 1-21 or
1-26.   The gold is then carefully washed  and melted
into ingots, which generally contain  from 997 to 998
parts of gold in the 1000.
  In  the nitric acid  process the supernatant liquid
consists mainly of  argentic nitrate.  The silver may
be  recovered  by  precipitation  with  chloride  of
sodium, argentic chloride resulting, which in turn is
exposed to a current of  hydrogen, liberating metallic
silver.^
  The dry method of refining gold before alluded to
consists in placing the granulated alloy and a mixture
of one part of chloride of sodium  and two parts of
brick-dust in alternate layers in a crucible until the
latter is full, when it is covered and placed in a Avood
fire and kept at dull redness for twenty-four hours.
By the united action of the moisture  furnished by the
Avood and the  silica of the brick-dust the sodic chlo-
* Iron plates are sometimes used.     j- See chapter on " Silver." 
GOLD.
115
ride is decomposed ; its sodium combines with oxygen
from the decomposition of the Avater, forming soda.
Avhich in turn  unites  Avith  silica  to  form sodic  sili-
cate.  The hydrogen of the Avater and the  liberated
chlorine form hydrochloric  acid;  these, at the tem-
perature  at  Avhich  the operation  must  be carried
on, furnish  chlorine to the  silver, converting it into
argentic chloride.   The latter, being fusible,  is ab-
sorbed by  the  brick-dust,  permitting the alloy to
be further acted upon, until nearly all the silver is
converted into chloride, the gold remaining compara-
tively free.
  There is also  another cementation  process given,*
for the purpose of acting upon the surface of gold
containing  a large  percentage of  silver, by Avhich
means it is  made to resemble fine gold.   It  consists
in subjecting the alloy, previously rolled thin and
covered  by  the cement-powder, to  a temperature
slightly  below its melting-point.  In this operation
the  mixture is  composed  of one part of  sodic chlo-
ride, one part of alum, one part of ferrous sulphate,
and  three of brick-dust.  At the high temperature
necessary the sulphates are decomposed, with libera-
tion of free  sulphuric  acid, Avhile chlorine is evolved
from the sodic chloride.   These act upon the silver,
which is subsequently found in the cement-poAvder in
the form of argentic chloride.
  Refining by chlorine gas, deAised  by Miller in 1867,
is a  valuable dry method  for separating silver from
gold.  The  process  is the one noAV practiced in  the
  *This process is attributed to Kerl,  and is described in Makins's
Metallurgy, p. 244. 
116            DENTAL METALLURGY.
Australian mints,  and has  been quite extensively
employed,  1,100,000  ounces of gold  having  been
refined by it in Sydney during the years  1871  and
1872,  the percentage of loss  during the  operation
being only 14 parts in the  100,000.  It consists in
converting the silver into chloride by the passage of
a stream of chlorine gas through the molten alloy.
By means of a clay pipe passing through the cover to
the bottom of the  crucible, and connected with the
chlorine-generator by means of a flexible tube, the
gas is passed rapidly through the melted  metal, and is
apparently absorbed by it.  The refining  is considered
as complete when orange-colored fumes begin to arise.
As soon as this evolution of gas is -noticed the crucible
should be removed from the  fire, to prevent the gold
itself  from combining Avith the chlorine.  The  chlo-
ride of silver, which is fusible, should be poured off
from the surface of the molten metal, and, if it retains
a small amount of the gold, this may be recovered by
fusing with a little carbonate of soda, which causes
the gold to separate and settle to the bottom of the
crucible.   This method is  capable of producing gold
of from 944 to 1000 fine.
  The gold is next melted into bars, and the argen-
tic  chloride is reduced to  metallic silver by placing
it between two  wrought-iron plates, and then im-
mersing  the  whole in a vessel of water  acidulated
with  sulphuric acid,  when, after  a few hours, the
silver will all be reduced.  It generally, however,
contains a small amount of  gold, Avhich  may be
recovered either by again dissolving the silver with
nitric acid, when the gold will be found at the bottom
of the vessel; or it may be  separated by fusing the 
GOLD.
117
argentic chloride, to which is added a small amount
of potassic carbonate  for the purpose of reducing a
little metallic silver. The latter, in subsiding through
the argentic chloride, reduces the  gold, which was
probably combined Avith the chlorine. While yet hot
and in  a fluid  state, the argentic chloride is  poured
off and reduced as before, when it will be found free
of gold.  The  little button Avhich  subsides to the
bottom of the vessel will be found to consist of gold,
the reduced sih'er, and some adherent argentic chlo-
ride.  The latter must be again decomposed by fusing
with  potassic  carbonate.   Theoretically, one  cubic
foot  of  chlorine  will conArert  eight and a quarter
ounces of silver into argentic chloride,  but in  prac-
tice about tAvice that quantity is required.  Thus far
the use  of chlorine for refining  upon a large scale
has proved to  be much more  economical and  expe-
ditious  than the  humid process, the time required
to part  three hundred ounces  in  one furnace being
about tAvo hours, and the average cost four cents per
ounce.
   Treatment  of Brittle Gold.—The slightest  admix-
ture  of such metals as arsenic, antimony, tin, lead,
etc., is sufficient to seriously impair the ductility of
gold.   In 1856 the coining  operations of the mint of
England were much embarrassed  by the importation
of brittle gold, in which the contaminating metal did
not exceed the tt^ part 0I> tne  mass-  To purify
the gold it was  exposed Avhile  in a state of fusion to
a stream of chlorine gas.* Avhich  removed the dele-
  * Mr. F. B. Miller, of Sydney, devised the method of treating the
molten metal with chlorine passed through it by means of clay tubes. 
118
DENTAL  METALLURGY.
tereous  substances  by converting  them into volatile
chlorides.   The toughness  of gold may also be  re-
stored  by  throAving a small quantity of corrosive
sublimate on the surface of the molten metal, the
vapor  of  which  converts  the  metallic  impurities
into chlorides, which are volatilized.   In the dental
laboratory gold is  liable to become  contaminated
with small particles of lead  or  zinc.   This may be
effectually removed by melting it with a mixture of
potassium nitrate and borax, when the foreign metals
will be oxidized and dissolved in the slag.  Another
process  consists in adding to the melted mass about
ten per cent, of  black oxide of copper.  But this
plan is objectionable, because the crucible is liable to
become much corroded, and even perforated, and the
standard fineness of the gold lowered, by  a portion
of the copper being reduced to the metallic state.
  The gold of this country is often found to contain
iridium, the presence of which  greatly impairs the
metal for coinage and other purposes. The little hard
grains occasionally met with in gold, upon which the
file makes no impression,  consist of iridium,  or a
native alloy of osmium and iridium, and are not com-
bined with the gold, but merely disseminated through
it.  The only dry method of separating iridium from
gold consists  in alloying the  latter with three times
its  weight of silver, by which means  the specific
gravity of the metal is so much loAvered that  the
iridium,  which is very  infusible  and of  a specific
gravity of 21-1, may subside to the bottom of  the
crucible, Avhen the  gold and  silver alloy may be
poured or ladled off.  As some gold will remain with
the residue, more silver must be melted with it, and 
                       GOLD.                    119

the operation repeated several times, until nearly all
the gold is removed.  What is left is then acted upon
by  sulphuric acid to dissolve the silver, when  the
iridium and some finely-divided gold will be left.
These may be separated by Avashing.
  Iridium  may also be separated from  gold  by the
wet process.  The gold is melted Avith three times
its Aveight of silver, and granulated to insure  admix-
ture.  The alloy  is then treated Avith  nitric acid,
Avhich dissolves  the  silver,  leaving the gold and
iridium at the  bottom of the vessel.  The gold may
now be acted upon by nitro-hydrochloric acid.  The
iridium may then be collected and washed to free it
from any  portion of the gold.   The latter may  be
recoArered  from its solution  by precipitation, oxalic
acid or sulphurous acid being usually employed.
  Preparation of Chemically-Pure Gold.—None of the
methods Avhich have  been described can ahvays  be
relied upon to afford  absolutely pure  gold.  When
nitric acid is employed  in the  quartation process,
gold  may be obtained from  993  to  997  parts in the
1000, Avhile sulphuric acid will frequently yield gold
up to 998 thousandths.
  There are several methods by which  chemically-
pure gold may be obtained.  Usually ordinary refined
gold, obtained by one of the methods above described,
is dissolved in  nitro-hydrochloric acid.   The excess
of acid  is  driven off, and alcohol and chloride of po-
tassium are added for the  purpose of precipitating
platinum, if any is present.  The chloride of gold
is then dissolved in pure distilled Avater, until each
gallon does not contain more than half an ounce of the
chloride.   Any silver present Avill be converted into 
 120            DENTAL METALLURGY.
           *
 argentic chloride, Avhich will settle to the bottom of
 the vessel, after Avhich the supernatant liquid should
 be carefully removed  by means of a syphon.  The
 gold may  be precipitated  by a stream of carefully-
 Avashed sulphurous anhydride, or by the addition of
 oxalic acid.  The precipitated metal is washed with
 dilute  hydrochloric  acid,  distilled  water, ammonia
 water, and again Avith distilled  Avater, and is then
 ready for melting.  This is done in a clay crucible,
 with a  small  portion of bisulphate of potash and
 borax.  The  melted  metal  should be poured into
 a stone ingot mold.  By this method gold, of Avhich
 the purity was 999-96, has been prepared, the precipi-
 tant being oxalic acid; but gold precipitated by that
 agent  from an  acid  solution  containing copper is
 always  contaminated with cupric  oxalate, to avoid
 Avliich the solution should be heated, with the addition
 of potash,  when  a soluble double oxalate of copper
 and potash is formed, leaving the gold in the pure
 state.
  The aqua regia used in  the preparation of chemi-
 cally-pure gold should consist of tAvo parts of hydro-
 chloric  and one  part of nitric  acid.  The  specific
gravity of the former should be about  1-16, and of
the latter  1-45.   Each ounce of gold will require for
its solution about three and one-half ounces of the
mixed acids.   The action of this upon the metal will
in the beginning be quite energetic, but as the solution
approaches saturation the application of moderate heat
is required to dissolve the last portion of the gold.
The greatest care must be exercised in the separation
of the gold solution from the argentic chloride, which
subsides to the bottom of* the vessel, and also to rid 
                       GOLD.                   121

the liquid of the small portion of silver held in solu-
tion by the acid.   The  solution is cautiously trans-
ferred to an evaporating-dish by means of a syphon,
and heat  is applied, and as  the bulk  is gradually
reduced by evaporation more argentic chloride will be
separated and deposited at  the bottom.  The  super-
natant liquid should  again be  carefully poured or
syphoned off, and this should be repeated as often as
the residue appears in the dish.  When the solution
has become viscid and of a deep ruby color, the  heat is
discontinued, and the auric  chloride soon crystallizes
in a mass of prismatic forms.  It should then  be dis-
soh^ed and largely diluted with distilled Avater acidu-
lated by a feAv drops of hydrochloric acid, and, after
standing for a few days to permit a further subsidence
of argentic chloride, it should be filtered, and is then
ready for precipitation.  This may be accomplished by
quite a number of different reagents, but the form of
the precipitated metal depends much upon the nature
of the precipitant, and it may be throAvn down in a
spongy condition, in sheets  resembling foil, as a poAv-
der, in a more or less crystalline state,  and in  scales.
The affinity of gold for other bodies is so Aveak that
care must be observed lest partial reduction be effected
by  merely adventitious conditions.  The highly-di-
luted neutral solution of the trichloride just described
is quite liable to such accidents;  indeed, it may occur
from exposure to  air, atmospheric nitrogen probably
being the active agent.  The addition of pure Avater
to such a solution may also cause slight precipitation,
but  the dilute solution  may be  protected from pre-
mature precipitation  by acidulation Avith  a  small
quantity of hydrochloric acid.
                        11 
122
DENTAL  METALLURGY.
   The best agents for the precipitation of gold are
oxalic acid, sulphurous  acid, and ferrous sulphate.
Oxalic acid will precipitate several  forms of gold,
from sponge-like masses to the different  crystalline
or powdery forms.  Its action is,  however, sloAver
than the others, and it requires to be slightly heated.
The reaction is shown in the following equation:
      2Au CI, + 3H2 C2 Oi = 6H CI + 6C 02 + 2Au.
  The chlorine of the auric chloride unites Avith the
hydrogen of the oxalic acid to  form hydrochloric
acid, the copious evolution of gas noticed during the
precipitation being the escape of the carbonic  acid
formed by the remaining elements of the oxalic acid.
The gold is thus set free.
  The so-called "shredded  gold" somewhat exten-
sively used by dentists  in filling teeth a  feAv years
since was produced by the addition of sugar or gum
Arabic to an acid solution of gold.  The exact modus
operandi  is as  follows: The pure gold is dissolved in
nitro-hydrochloric acid, and, without evaporating the
solution, it is  diluted by the addition of about two-
thirds its bulk of pure water.  Clean gum Arabic,
dissolved in boiling water to the amount of one-third
the bulk of the gold solution, is added to the latter,
and  the Avhole placed in a glass  matrass or evapo-
rating-dish and placed over a steam bath.  When the
proper temperature is attained, gold in the form of
leaves, shreds, or fibers  will be observed  floating in
the liquid.  When these become sufficiently coherent
to admit of removal they are lifted out by a vulcan-
ized rubber spoon attached to a glass rod, and placed
in a filter.  This operation is continued until the gum 
GOLD.
123
  Arabic or sugar, assisted by heat, has caused precip-
  itation of the entire amount of gold held in solution.
  The web-like  masses are then thoroughly washed,
  dried, and heated  to  dull redness.  As the elements
  entering into the  composition  of sugar  and gum
  Arabic  are  identical  with those of oxalic  acid, the
  reaction is probably the same as that which  occurs
  when the latter is employed as the precipitant.  With
  care in the application of the proper amount of heat,
  the action of precipitants of  this class is capable of
  regulation, thus affording uniform results.
    When the precipitated gold is intended for plate
  or  bars, it should  be well  Avashed, and fused in a
  perfectly new crucible.
    Sulphurous acid precipitates gold generally in the
  form  of a scaly metallic poAvder; hence it does not
  afford masses sufficiently coherent or sponge-like for
  use as a filling-material for the dentist.   The reaction
  which takes place is thus explained :
    2Au Cl3 4- 3H2 O + 3H2 S 03 = 6H CI 4- 3H2 S 04 4- 2Au.
    The Avater present  is decomposed, its  hydrogen
  uniting  with the chlorine of  the auric chloride to
  form  hydrochloric acid.  The oxygen of the water,
  attracted to  the sulphurous acid,  converts it into
  sulphuric acid, and the gold  is thus  liberated.
    Ferrous sulphate precipitates gold in the form of
  a light-brown powder.  Of the sulphate  crystals,
  about four times the weight of the  gold is dissolved
  in water.  This is added to the auric solution.  After
  the finely-divided gold has entirely subsided, it should
*. be boiled several times in dilute hydrochloric acid, in
  order to free it from all traces of the iron Avith which 
124
DENTAL METALLURGY.
it is liable to be contaminated.   The interchange,
which in this reaction results in the liberation of the
gold, is expressed by the folloAving equation:
    2Au Cl3 4- 6Fe S04 = Fe2 Cl6 4- 2(Fe2 3S 04) 4- 2Au.
  The ferrous salt parts with a portion of the iron
to the chlorine of the  gold salt,  thus forming fer-
ric  chloride and  ferric  sulphate, Avhile the  gold  is
liberated.
  As stated before, the  reduction of the metal from
the trichloride may be  effected (in, however, a less
satisfactory manner) by many different reagents, some
of* which are purely elementary.  Thus, sulphur, sele-
nium, carbon (charcoal), and phosphorus, each, when
introduced into a heated  solution, becomes  coated
with a film of metallic gold.  Reduction may also be
accomplished by some of the gaseous  bodies contain-
ing hydrogen.  Thus, gold may be precipitated by
arseniureted  and antimoniureted  hydrogen.  Many
of the  base metals, such as bismuth, zinc, etc., also
reduce gold from solution in the form of a  brown
poAvder.   It is also reduced on a platinum pole by
the electrical current.   In this  way the beautiful
form of gold made by A. J. Watts, of New York, is
produced.  In a solution of auric chloride plates  of
pure gold are suspended.  These are connected with
a battery, so that as the  solution loses its gold by
deposition of the metal it is re-supplied by the sus-
pended plates.  By this means large masses  of per-
fectly pure crystal gold may be obtained.
  Gold may also be precipitated  by  some  of the
metallic  salts, of which  nitrate of mercury and  chlo-«
ride of antimony may be named as examples.  Quite 
GOLD.
125
a number of organic substances will also precipitate
it, a prominent example of which is gallic acid.  The
tartrate, citrate, and acetate of potassium will also
reduce it. Some of the members of this class, however,
require the addition of heat, and to obtain  prompt
action with these agents the solution should be quite
neutral.
   Alloys of Gold.—The most  important alloys are
those with silver and  copper.  The coinage of the
present day, from which the dentist usually obtains
his plate, is mainly of  an  alloy of gold  and  copper,
in the proportion of 900 parts of gold in 1000.  Gold
coins were first introduced in England by Henry
III., in 1257.  They were of pure gold. Edward III.,
in 1345, established a standard of 994-8, and in  1526
Henry VIII. issued crowns of the double-rose, of the
standard  916-6.  In 1544  the standard of all  gold
coins was reduced  to  916-6, and again  in 1548 to
833-4.  Mary restored  the  old standard, 9948.   In
Elizabeth's reign coins  of both standards (916-6 and
994-8) Ave re  issued.  In America the  standard of
gold coin is 900.
  Alloys  of  gold for  bases for artificial dentures
should be of such fineness as Avill enable them to resist
chemical  action  of the fluids  of the mouth, while
at the same time they should possess the requisite
hardness, strength, and elasticity.  These properties
are usually conferred by the addition of copper and
silver, or either of these inetals singly; or by  copper,
silver, and platinum.  The quality of gold which is
to be introduced into  the  mouth should, as a rule,
not be of a less standard of fineness than eighteen
carats.  Care, hoAvever, should be obseiwed in remelt-
                       11* 
126
DENTAL  METALLURGY.
ing the scraps and filings of the draAver, that the
grade of the gold be not lowered by admixture  of
old plates, backings, etc., containing portions of sol-
der.   Indeed, much the safer rule is to remelt only
new scraps, on Avhich no solder has been used.  The
scraps and filings of doubtful  quality may  be sent
to the mint for coinage,  the charge for which, on
the one hundred dollars (the minimum amount re-
ceived by the United States  mint), is less than one
per cent.
  Gold  exceeding nineteen  carats in fineness  will
generally be found too soft and yielding for use  in
the mouth.  The amount of force which the plate
must sustain in mastication is much greater than
might be supposed; hence, if  the degree of purity
of the alloy be too high, the requisite  amount  of
rigidity and strength will be wanting, and the plate
will soon bend to  such an  extent that  it  Avill no
longer fit the mouth.   This difficult}7 may, however,
be avoided in the higher grades of gold plate intended
for dental  purposes by a slight admixture of plati-
num, by Avhich much greater  tenacity is obtained;
otherwise  the  plate Avill  require  strengthening by
doubling at such points as are most  liable to bend.
Plates for partial cases necessarily require  a great
amount of strengthening.  This adds greatly to the
expenditure of time and labor  in the construction of
the  plate.   It increases  its weight and does not
ahvays render the plate  sufficiently rigid to Avith-
stand the force of mastication.
   Gold plate suitable for dental purposes  may  be
prepared according to the following formulae, from
Richardson's " Mechanical Dentistry " : 
GOLD.
127
                 Gold Plate 18 Carats Fine.
          No.  1.                         No. 2.
  18  dwts. pure gold,        j    20 dwts.  gold coin,
   4  dwts. pure copper,           2 dwts.  pure copper,
   2  dwts. pure silver.            2 dwts.  pure silver.

                 Gold Plate 19 Carats Fine.
          No.  3.            1             No. 4.
  19  dwts. pure gold,        j    20 dwts.  gold coin,
   3  dwts. pure copper,          25 grains pure  copper,
   2  dwts. pure silver.       |    40 4- grains  pure  silver.

                 Gold Plate 20 Carats Fine.
          No.  5.            ]             No. 6.
  20  dwts. pure gold,            20 dwts.  gold coin,
   2  dAvts. copper,           1    18 grains copper,
   2  dwts. silver.                20 -f- grains  silver.

                 Gold Plate 21 Carats Fine.
          No.  7.                         No. 8.
  21  dwts. pure gold,            20 dwts.  gold coin,
   2  dwts. pure copper,          13 4- grains  pure  silver.
   1  dwt. pure silver.

                          No. <).
                   20 dwts. gold coin,
                    6 grains  copper,
                    74 grains  platinum.

                  Gold Plate 22 Carats Fine.
                         No. 10.
                   22 dwts. pure gold,
                    1 dwt. fine  copper,
                   18 grains  silver,
                    6 grains  platinum.

   On  account of its greater strength and  power of
resisting chemical action of the fluids of the mouth, 
128            DENTAL METALLURGY.
many  dentists prefer  to  use  gold  plate  twenty  or
twenty-one  carats fine, in which the reducing  con-
stituents  are  copper  and platinum, the  following
formula being an example :
                 20 dwts.  gold coin,
                 10 grains platinum.

  The union of platinum with gold yields an alloy
possessing great strength and considerable elasticity.
Such an admixture, however, has its disadvantages.
Owing to  its increased strength and stiffness, a much
thinner and lighter plate may be employed, without
the additional labor and cost of doubling the plate  at
what, in partial cases composed of ordinary 18-, 19-,
or 20-carat gold, would be weak points.  It may also
be justly claimed for gold alloyed with platinum that
it will perfectly resist  the action of the fluids of the
mouth. On the other hand, the richness of color  of
gold is always more or less impaired by the admixture
of platinum.   But perhaps the greatest objection  to
be urged against the employment of platinum-gold is
the increased difficulty of swaging a plate  composed
of it so that it shall perfectly conform to all  the de-
pressions  and irregularities of the model.  Having
invariably found, when the alloy contained any  con-
siderable  quantity of  platinum,  that the ordinary
method of swaging between zinc and lead was not
effective, I have for more than ten years  employed
zinc for counter-dies as well as for dies,—a procedure
which entirely overcomes any difficulty in swaging.*
  Gold for use in the formation of clasps should always
* See chapter on " Zinc." 
GOLD.
129
contain sutficient platinum to render it  much more
elastic than the alloys usually employed  in the plate
or base, so that on the  application of force upon the
denture in the  act of mastication the clasp, though
it  may yield slightly,  will  always  spring together
again  and accurately  embrace  the  tooth Avhich it
surrounds.   In  the perfect  adjustment of clasps to
remaining teeth the following points  are of impor-
tance: First, the model must be as  accurate  as a
plaster impression will afford;  second, the clasp
should be  thrown  around  the  thickest  or most
prominent part of the tooth ;  third,  the clasp should
be so arranged  as to fit accurately the convexity of
the tooth.  To successfully accomplish this the gold,
of about  No. 26 of the standard gauge, should be
cut by pattern, and  before any attempt is  made to
fit. it  to the  tooth it should be  bent Avith the clasp-
benders to correspond Avith the rounded surfaces of
the natural tooth.  Lastly, the contact of the clasps
Avith  the  tooth  should be uniform.   The ends of the
clasp  should be free, and it should be  attached to
the plate at one point, so that but little of its cir-
cumference shall be included in the union; othei-Avise,
if a large proportion of the clasp be soldered fast to
the plate, much of the quality of elasticity will be lost.
   The folloAving formula1 Avill  afford alloys of twenty
carats' fineness, suitable for clasps, backing, etc., Avher-
ever elasticity and additional strength are required:

       Formula No. i.                Formula No. 2.
    20 dwts. pure gold,           20 dwts. coin  gold,
     2 dwts. fine copper,           8 grains fine copper,
     1 dwt. fine silver,           10 grains fine silver,
     1 dwt. platinum.       I     20 grains platinum. 
130
DENTAL METALLURGY.
  Alloys of Gold employed  in Dentistry as Solders.—
These are a class of alloys  formed of the same metal
to be united, the fusing-point of which is reduced by
the addition of silver, copper, and brass.*   The  fol-
lowing formula, given  by Harris and Richardson,
produces solder of sixteen  carats fine, and is suitable
for use in connection with  eighteen- or twenty-carat
plate:
                   Formula No. t.
                 6 dwts. pure gold,
                 2 dwts. roset copper,
                 1 dwt.  pure silver.

  Formulae Nos.  2 and  3, from  Richardson's  "Me-
chanical  Dentistry,"  are  respectively  fifteen  and
eighteen carats fine, and, if carefully prepared, will
be found to ansAver fully all the requirements:
No. 2.—15 Carats Fine.
 6 dwts. gold coin,
30 grains silver,
20 grains copper,
10 grains brass.
No. 3.—18 Carats Fine.
30 parts gold coin,
 4 parts silver,
 1 part copper,
 1 part brass.
  Zinc is sometimes employed as a constituent in the
preparation of gold solder for the purpose of reducing
the fusing-point.  Thus, some dentists  use an alloy
composed of

      18-carat gold.....6 dwts ;
      Granulated spelter solder  .   .    .6 grains.
  An alloy of this composition is exceedingly brittle,
and hence difficult  to roll into plate Avithout break-
See page 34. 
GOLD.
131
ing into many pieces.  Its color is good, but I have
noticed that the surface of such solders, after flow-
ing, is apt to be pitted with small holes, and has not
the solid and uniform appearance that is desirable.
This may be due to the oxidation and escape of some
of the zinc.
  Method of Reducing  Gold to a  Lower or Higher
Standard of Fineness, and of  determining the  Carat
of any given Alloy.—The gold alloys used in  the labo-
ratory are generally made from pure  gold or gold
coin,  the standards of  which are  definitely  fixed.
A feAV simple rules  are here given,* by Avhich the
operator may readily determine the amount of alloy
necessary to reduce  either coin or pure gold to any
desired standard.
  To ascertain the carat of any giA^en alloy, multiply
24 by the  weight of gold  in the alloyed mass and
divide the product by the weight of the mass.   The
quotient is the carat sought.  For example, take the
following:
      Pure gold......18 parts.
      Copper.    .        .   .     .    .   4  "
      Silver.......2  "

                                      24  "
  The result may be thus expressed :
               24X18 --24 -=18 carats.

  To reduce gold to a required carat, multiply the
weight of gold used  by 24 and divide the product by
the required carat.   The quotient is the Aveight of
* Richardson's Mechanical Dentistry. 
132
DENTAL  METALLURGY.
the mass when reduced, from which subtract the
weight of the gold used, and the remainder is the
weight of the alloy to be added.
  To reduce gold from  a lower  to a higher carat,
multiply the weight of the alloyed  gold used by the
number representing  the proportion  of alloy in the
given carat;  divide the product by the figures repre-
senting the amount of alloy in the required carat.
The quotient is the weight of the mass when reduced
to the required carat  by  adding fine gold.  Thus, to
reduce one pennyweight of 16-carat gold to 18 carats,
the numbers representing the proportions of alloy are
obtained by subtracting 18 and 16 from 24.  The state-
ment is
                   6 : 8 : : 1 : 11;
from Avhich it will be seen that, to reduce one penny-
weight of 16-carat gold to 18 carats, one-third of a
pennyweight of pure  gold must be added to it.
  Again, if instead of using pure gold Ave desire to
raise the fineness of one pennyweight of 16-carat gold
to that of 18, by the addition of, say, 22-carat gold, the
numbers representing the proportions of the alloy
would be found by subtracting, in the example given,
16 and 18 from 22, the result being
                   4:6::1:1J.
Hence each pennyweight of 16-carat  gold Avould re-
quire a half-pennyaveight of 22-carat gold to reduce
it to 18 carats.
  The fineness of gold may be expressed in decimals
or in parts called carats.   The former is the system
employed  at  the United  States Mint and by metal-
lurgists and chemists, Avhile the latter is the usual
method of expressing the grade of  alloys  of gold 
GOLD.
133
among dentists and jewelers.  The following table
will show the relation of one to the other:
			Carats.	Decimals.
Pure gold......			24	1000
English coin			22	916-6
American coin			21-6	900
Dentists' gold			20	833-3
k <<			19-2	800
Jewelers' gold, best			18	760
" " good .			15	625
" " low grade			12	500
Common jewelers' solder			8	333-3
  There are many different  alloys used in the arts.
The greenish alloy used by jewelers contains 70 per
cent, of silver and 30 per cent, of gold.   " Blue gold "
is stated to contain 75 per cent, of iron.  The Jap-
anese employ a compound of gold and silver, the stand-
ard of which varies from 350 to 500.   This alloy is
exposed  to  the action of a  mixture of plum-juice,
vinegar, and sulphate of copper.  They also possess
a number of bronzes, in which  tin and  zinc are re-
placed by gold and silver.   The alloy known as shi-
ya-ku-do, extensively used by the Japanese for sword
ornaments, contains 70 per cent, of copper and 30 per
cent, of gold.
  Alloys  of  Gold  and Silver.—The density of those
natural alloys, the composition of which varies from
Au Ag6 to Au6 Ag, is greater than that calculated from
the densities of the constituent metals. Gold and silver
unite in all proportions, affording alloys of several tints,
ranging from th e color of silver to that of gold.  By the
                        12 
134
DENTAL METALLURGY.
addition of silver the hardness of gold is increased, and
it is rendered more fusible, while its malleability is not
materially diminished. Gold as found in nature always
contains silver, and all specimens of native silver will
likewise be found to contain gold.
  Gold and  Platinum.—Equal weights of the  two
metals yield an alloy of good malleability, with, how-
ever, some dullness of color.  An excess of platinum
renders the  alloy infusible  in an  ordinary blast-fur-
nace.   One part of platinum to 9-5 of gold will afford
an alloy of the same density as platinum.
  Gold and  Tin.—Alloys of tin and gold  are  hard
and brittle,  and the combination is attended  with
contraction.  Thus,  the alloy Sn Au has a density
14-243, instead of 14-828, as indicated by  calculation.
  Gold and Mercury.—These combine at all tempera-
tures, but the union may  be greatly facilitated by
heating, and a state of fine division still further assists
the process.   It is stated that an amalgam composed
of six parts of mercury to one of gold crystallizes in
four-sided prisms, and that, if the mercury is then dis-
tilled off, the gold is left in  an arborescent state.  The
operation of coating the surface of brass  or copper
objects with gold, extensively practiced some years
ago, and known as "fire-gilding," was based upon the
amalgamation of gold and mercury.  The process is
as follows:  The article to be gilded is given a uniform
coating of an amalgam made by heating six parts of
mercury with one part of gold, with  the surplus
mercury removed  by squeezing.   The  operation is
greatly facilitated  by first rubbing  the surface  with
mercurius nitrate.  It is thus given a superficial layer
of mercury.  It is now gently heated over some burn- 
GOLD.
135
ing charcoal, the amalgam in the meantime being
kept uniformly distributed over the surface by means
of a soft brush.  As the heat is continued and the
mercury is gradually driven  off, the surface assumes
a dull yellow color.   It is then ready for polishing,
which is accomplished by means of a wheel-brush
moistened Avith vinegar.  Yerdigris mixed with bees-
wax is applied, for the purpose of removing any re-
maining mercury by means of the affinity Avhich the
latter has for the acetate of copper.  This operation,
sometimes  called " water-gilding," is so dangerous to
health, in consequence of the liability of the operator
to inhale the volatilized  mercury, that it has been
almost entirely superseded by electro-gilding.
   Gold and Copper #ield a class of alloys of a reddish
color (between  gold and copper),  which are much
harder than  either of their constituents.   The  mal-
leability of the gold is not, however, much affected
by admixture of copper, provided the latter is pure.
It is stated that seven parts of gold with one of cop-
per exhibits  the  greatest amount of hardness which
it is possible  to obtain by union of these tAvo metals.
In the American coinage  the alloy is chiefly copper;
hence the coins are red in color and very hard.
   Gold and Palladium.—These metals  are stated to
alloy in all  proportions.  Chenevix states that  an
alloy composed  of equal parts of the two metals is
gray in color, less ductile  than its constituents, and
has the specific gravity of 11-08.  .W. Chandler Rob-
erts, assayer of the Royal Mint, London, states that
an alloy of four parts of gold and one of palladium
is Avhite, hard,  and ductile.   According to Makins,
the merest trace of palladium with gold will render 
136
DENTAL  METALLURGY.
the latter ATcry brittle.  Graham has  shoAvn  that  a
wire of palladium alloyed with from twenty-four to
twenty-five  parts  of gold does not exhibit the re-
markable retraction which, in pure palladium, attends
its loss of occluded hydrogen.
  Gold  and Zinc.—It appears that the latter metal
may be added to gold without destroying its ductility.
It is certain, however, that small quantities of it render
gold brittle.  Care should, therefore, be  observed in
the dental laboratory, where so much zinc is employed,
that small particles of it do not  find their Avay into
the gold filings.
  There are certain other metals which, when mixed
with gold in quantities as small  as the y^-o part of
the mass, render  it quite brittle  and unworkable.
These are bismuth, lead, antimony,  and arsenic.
  Compounds of Gold.—Two compounds of gold with
oxygen have been obtained,—Au2 O  and Au2 03,—but
neither of them is of any great practical  importance.
The chlorides of gold correspond in composition to
the oxides.
  Auric chloride, or trichloride, as  it  is more com-
monly called, is prepared by dissolving gold  in nitro-
hydrochloric acid.  The  excess of acid is driven off
by evaporation at a temperature not greater than
280° F.  (=138° C.); otherwise a part of it at least
will be converted into aurous chloride. The crystals
obtained by this process are ruby-red in color, and
very deliquescentt  The composition of  auric chlo-
ride is Au Cl3; atomic weight, 303-1.
  Aurous chloride is  obtained by heating the crys-
tallized  auric  chloride in a  porcelain evaporating-
dish  to  about  347° F. (=175° C).  If the tempera- 
GOLD.
137
ture is carried much beyond this point, say, to 392°
F. (=200° C), the compound will be decomposed
into metallic gold and chlorine gas.  Aurous chloride
is  yellowish  in  color and nearly insoluble  in cold
water.  Boiling  Avater,  however,  converts  it into
auric chloride and metallic gold.   Its composition is
Au CI;  atomic weight, 232-1.
  Auric chloride is the most  important of the com-
pounds of gold, and is the source from which most
of the preparations of gold  used in the arts  are  ob-
tained.  There are iodides of gold resembling the chlo-
rides in many respects.  Berzelius also described an
aurous sulphide.  These  are, however, not important.
  Purple of Cassius, which is  employed by manufac-
turers of porcelain teeth in obtaining the gum color,
and  in the industrial arts for imparting a red  color
to glass and porcelain, is a compound of gold, tin,
and  oxygen,  which are believed  to be grouped  ac-
cording to the formula
           Au2 O Sn 02, Sn O Sn 02 4H2 O.*
It may be prepared  in  the humid  way by adding
protochloride of  tin to  a mixture of bichloride  of
tin and terchloride of gold.  Seven parts of gold are
dissolved in aqua regia and  mixed with two parts of
tin,  also dissolved  in aqua  regia.  This solution is
largely diluted with water, and a weak solution  of
one  part of tin in hydrochloric acid is added, drop
by drop, until a fine purple  color is produced.  The
purple of  Cassius, in a state of fine division, remains
for a time suspended in the  water, but finally sub-
sides as a  purple powder.  The fresh precipitate dis-
* Bloxam's Chemistry, Organic and Inorganic
               12* 
138
DENTAL METALLURGY.
solves in ammonia, and exposure to light decomposes
the purple solution, during  Avhich process its  hue
changes to blue, and it finally becomes colorless,  and
metallic gold  is  precipitated, the  binoxide of tin
being left in solution.
  The  dry method* is the  one now employed by
manufacturers of porcelain teeth in the  preparation
of gum-enamel.  Two  hundred  and forty grains of
pure  silver,  twenty-four grains of pure gold,, and
seventeen  and a half grains of pure tin  are placed
in a crucible, with sufficient borax to cover the mass,
and melted.   In order to insure a thorough mixture
of the different  metals, the melted mass should be
poured from  a height  into  a vessel of  cold water,
and this process of granulation should be  repeated
at least three times, but at every melting the alloy
should. be  well covered with  borax to prevent loss
of the tin  by oxidation.  The vessel into which  the
melted mass is poured should not be a metallic one.
  The component parts of the alloy having now been
thoroughly incorporated, the next  step is to collect
the granulated mass and separate from it any adherent
particles of glass of borax.  The metal is then put
into a glass or porcelain evaporating-dish (the Berlin
porcelain is best), and sufficient chemically-pure nitric
acid is added  to  cover the metal.   The dish is now
placed over a sand-bath, and gentle heat applied and
continued  until chemical action ceases. •  If at this
  *The dry method of preparing purple of Cassius and the process of
manufacturing the gum-enamel were imparted to the author by the
late Professor Wildman, to whom is due the credit of having brought
the preparation of bodies and enamels to their present high state of
excellence. 
                       GOLD.                   139

point it is found  that all the metallic particles are
dissolved, the dish may be removed from the bath.
Should  any solid particles be found in the solution, a
little more nitric acid must be added, and the opera-
tion continued  until all  are dissolved.  The  silver
having  been  entirely dissolved  by the nitric  acid,
the solution should be poured off, and the remaining
oxide carefully washed until the  last trace of silver
is removed.   After several washings  with a large
amount  of pure  warm  water,   the  latter should
finally  be  tested  with a clear solution of common
salt, and if it  remains clear, Avithout show of milki-
ness, the silver is  all removed.   When the oxide is
sufficiently Avashed, the purple of Cassius should  be
dried by gently  heating, after which it is ready to be
incorporated Avith the silicious materials.
  The process of making gum-enamel is divided into
three stages : first, the preparation of the oxide; sec-
ond,-fritting, or  by the aid of heat  uniting the me-
tallic oxide with a silicious base;  and, third, diluting
the frit  so as to form the desired shade.  The first we
have already described. The frit is formed by mixing
eight grains of the metallic oxide (purple of Cassius)
Avith seAren hundred grains of feldspar, and  one  hun-
dred and seventy-five grains of a flux composed of

     Pure quartz     .   .     .        .4 ounces;
     Glass of borax  .        .   .     .1 ounce;
     Sal tartar ......  1 ounce;

fused  into  a glass and ground fine.  The oxide is
placed  in a smooth WedgAvood mortar and ground
separately as fine as it is possible  to get it.   The flux
is then added  in small quantities, and  the levigation 
 140            DENTAL METALLURGY.

 continued, after which the feldspar may be added and
 treated similarly.   It is of the highest  importance
 that the mass be reduced to the utmost degree of
 fineness, and an expert workman will  spend six  or
 eight hours  at least in levigating the quantity given
 in the formula.  While the mass is being ground  in
 the mortar foreign substances, such as small particles
 of wood, etc., must be carefully excluded; otherwise,
 during the vitrifying process, these will be converted
 into carbon, which will be sure to reduce a portion of
 the gold in fine metallic globules distributed through-
 out the mass.
  The vitrifying or fritting process consists  in pack-
 ing the mass, after the most thorough levigation,  in
the whitest sand crucible that can be obtained. (Dark-
colored  crucibles are liable to injure the frit by con-
tamination with iron.)  This must be provided with
an accurately-fitting cover made of the same material,
 or a suitable top may be formed of  a piece  of slide
 such as is used in  burning  continuous-gum work.
 Before placing the frit in the crucible, the interior sur-
 face of the latter should receive a thin coating of very
 fine quartz,  made into a paste with water, to prevent
 the frit  from adhering to it during fusion.  The frit
in a dry state is then packed in, and the cover tightly
luted to its place with kaolin.   The  crucible is then
to be buried in a strong anthracite-coal fire, and  to
remain there until the contents are fused.   The time
required to do this will depend upon the  size of the
crucible and the intensity of the heat.  Any ordinary
coal-stove provided with a good draught will answer;
but the fuel must be packed around and over the
crucible, and the heat carried to the highest attainable 
GOLD.                   141
point.   Usually about two hours will be required to
thoroughly fuse the mass, after which it is removed
from the fire and permitted to cool.
  The vitrified mass is removed from the crucible by
breaking  the latter.   Every particle  of adhering
quartz or portions of the crucible should be cleared
from the surface.  It  is then pulverized to a fineness
which Avill allow it to pass through a No. 10 bolting-
cloth  sieATe, and is ready for the third stage in the
preparation  of gum-enamel, Avhich consists of dilut-
ing the  frit with the proper amount of feldspar.   As
the strength of the coloring-pigment  varies accord-
ing to the degree  of fineness attained during  the
levigation, it is usually necessary to  make several
tests in order to arrive at the desired shade.  This
is accomplished  by mixing separately several differ-
ent lots in the folloAving proportions :
Gum frit ....	. 1 part;
Feldspar ....	. 2 parts
Gum frit ....	1 part;
Feldspar ....	. 3 parts
Gum frit ....	1 part;
Feldspar ....	. 4 parts
These  are applied to marked  pieces of  porcelain
body and  fused  in the usual way,  the result deter-
mining  the proportions necessary to produce the
desired shade.
  There is a compound known as " silicate of gold,"
used in ceramic  dentistry to impart a life-like yellow
tint to porcelain teeth.   This is  prepared  by grind-
ing together in  a WedgAArood mortar one hundred
and twenty grains of coarse feldspar, ten  grains  of 
142
DENTAL METALLURGY.
gold  foil,  and eight  grains of flux.*   These  aro
ground until the gold is  entirely cut  up, when the
mass is made into a ball  and placed on a slide and
fused, after which it is again ground fine and is then
ready for use.
  Hyposulphite of gold and soda, the sel d'or of the
photographers, is a double salt formed by adding a
solution of one part of terchloride of gold to a solu-
tion of three parts of hyposulphite of soda.  Alcohol,
in which  the  double salt  is soluble, is then  added.
The formation of this compound may be explained
by the equation, 8(N 02 S2 03) + 2Au CI, = Au2 S2 03,
3(Na2 S2 O,) + 6Na CI  + 2(Na2 S4 06).
  Fulminating  Gold.—When ammonia is added to
terchloride of gold, a buff-colored precipitate results,
which explodes violently  when gently heated.  Its
exact composition is not well established.
  Discrimination of Gold.—Protochloride  of tin is a
characteristic test for gold, affording a purple-brown
precipitate.   The smallest amount of gold dissolved
in a large quantity of  water may be detected  by the
addition of a few drops  of this reagent.  Thus, a
pale brown precipitate may be obtained in a pint of
water containing but the one-fiftieth of a grain of gold.

  * White bottle-glass, which does not contain lead or iron, may be
used to reduce the fusing-point of enamels, but, owing to the uncer-
tainty  of the composition of glass, most of the manufacturers of
porcelain  teeth make a fine glass, for this purpose, of the following
proportions:  Pure quartz, four ounces;  glass of borax, one ounce;
Bal tartar, one ounce.  These are  first ground separately, then thor-
oughly mixed, and placed in a white crucible provided with a cover
which  must be tightly luted, and then thoroughly fused in the fire.
If perfectly pure materials are used the result will be an exceedingly
brilliant, colorless, and transparent glass. 
                       GOLD.                   143
   Ferrous sulphate is  also a  delicate test  for the
presence  of gold, and  will  detect  a very  minute
amount.  By this reagent the  gold is thrown down
in the form of a brown powder, which, after washing,
drying, and heating to  redness, affords the metal in   t
a finely-divided state.
   Sulphureted hydrogen (H2 S) added to a solution of
terchloride of gold  affords a  brown  precipitate of
auric sulphide.  Nitrate of mercury also precipitates
from solution  a brown powder, which after heating
yields finely-divided gold.  Finely-divided gold,  sus-
pended in water,  imparts a violet or  red color to it.
Colored fluids, containing minute particles  of gold
in a  state of  suspension,  may be obtained  by the
action of phosphorus dissolved  in ether upon a very
weak solution of gold in aqua regia.   After standing
for a long time the fine particles of gold are deposited,
haAing the same tint as that which they previously
exhibited when suspended in the liquid.  The blue
particles, being less minute, are soonest deposited, but
the red particles require many months to settle down.
The  one-hundredth of a grain of gold is capable of
imparting a deep  rose color to  a cubic inch of fluid,
and  the different colors thus produced  are taken
advantage of in painting upon porcelain, a beautiful
ruby-red color being the result  of the pigment thus
obtained.
  Assays of Gold  Ores,  Quartz, etc.—The  specimens
of ores should  first  be heated  to redness, and then
thrown into cold water to facilitate powdering, which
may be accomplished  in  an  ordinary Wedgwood
mortar.  Several  lots of three  hundred grains each
should be weighed and examined separately, and the 
144
DENTAL  METALLURGY.
assays made from these averaged for the result.  To
the separate portions of powdered ore equal weights
of litharge, half their weights of sodic carbonate, and
about half of powdered charcoal, are added and thor-
oughly mixed with the ore.   Each portion is  then
placed in a crucible, a little borax sprinkled over the
top, and it is ready for heating in a  suitable blast- or
wind-furnace.  The heat at first should be gradual, so
that the active effervescence caused  by the escape of
carbonic acid from the soda salt may not force portions
of the mixture from the crucible.  After a short time,
however, the danger  from this cause having passed,
the heat may be carried to bright  redness, or  until
the whole has fused.   An  ingot mold with two aper-
tures has been recommended for the reception of the
fused  mixture, which at this point is ready for pour-
ing, the slag being turned  into one concavity and the
reduced metal into the other."  The button will be
found to consist of lead and gold, the former reduced
from the  litharge and the latter from the auriferous
ore.   These are to be separated by cupellation.
  If the  ore contains much iron pyrites, or is of the
nature of " sweep " (the name given to residues which
accumulate in the dental laboratory and other places
where gold is worked), it  will be necessary to roast
it in a shallow fire-clay dish  placed in a  muffle;  and,
in the case of pyrites containing about seven penny-
weights to the ton, the operation should be conducted
with one  thousand grains.  The roasted ore is then
fused with a mixture consisting of red lead, one thou-
sand grains; sodic  carbonate, six hundred grains ;
powdered charcoal, forty grains, and borax, five hun-
dred grains.  The mixture is introduced into a clay 
GOLD.
145
crucible, which it should half fill, and is fused in an
air-furnace.  The button  of reduced lead may be
removed either  by pouring the contents of the cru-
cible into a mold, or by breaking the crucible when
cold.
  Assay by  Scorification. — Scorification  resembles
cupellation,* but the oxide of lead produced in the
operation,  instead of sinking into a porous  cup, is
held in a  flat saucer of fire-clay, and dissolves the
earthy constituents of the ore, leaving the precious
metal to pass into another portion of lead, Avhich re-
mains  in the metallic  state.  About two hundred
grains of the roasted ore are placed in the scorifier,
and intimately mixed Avith five  hundred grains  of
granulated and fifty grains of borax lead.   The con-
tents of the  scorifier are  fused in a muffle.  Air is
admitted to oxidize  the  greater  portion of the lead.
At the conclusion of the operation the litharge should
be perfectly fluid and coArer  the molten lead.  The
slag may be freed  from particles of  precious  metal
by the addition,  at the conclusion of the operation,
of a small quantity of powdered anthracite, Avhich
reduces a portion of the litharge to metallic globules,
which fall  through the  slag  and unite Avith the lead
button.   The gold  is then separated  by cupellation,
and the silver, Avith Avhich it is almost always asso-
ciated, by parting with nitric acid.
  Assaying.—This term refers  to the quantitative
estimation of one constituent of an alloy or mineral,
and is accomplished by cupellation when the alloying
metal is copper,  and " parting "  Avhen the  debasing
* See page 146.
    13 
146
DENTAL METALLURGY.
metal consists of silver.  Usually both operations are
necessary.  From five to  sixteen grains of the gold
are wrapped in sheet-lead, with pure silver equal  to
two and a half times the amount of  gold supposed
to be present.  The weight of lead  employed Avhere
the assay is standard  gold* is 8 to 1, and the  ratio of
the weight of lead to the weight of copper assumed
to be  present is  100-1.   The assay  is now to  be
treated by cupellation, a process which is thus briefly
and clearly described  by Mr. AV.  Crookes:
  " The gold alloy is fused with a  quantity  of  lead
and a little silver, if silver is already present.   The
resulting alloy, Avhich is called the ' lead  button,' is
then submitted to fusion on a very porous support
made of bone-ash and called a '  cupel.'  The fusion
is effected in a current  of air,  Avhich oxidizes the
lead.   The  heat is  sufficient to  keep the oxide  of
lead fused.   The porous cupel has the property of
absorbing melted oxide  of lead  without  taking up
any of the metallic  globules, exactly in the same
way that blotting-paper will absorb Avater Avhile it
will not touch a globule of mercury. The heat being
continued, and  the current  of airf- ahvays  passing
over the surface of the melted lead button, and the
oxide of  lead or litharge being  sucked  up  by the
cupel as fast as it is formed, the metallic globule rap-
  * 22-carat, or coin.
  f The process  of cupellation is generally performed in a furnace
provided with a muffle for the reception of the cupels, and arranged
so as to admit of a current of air over the fused button.  The lead
used in cupellation should be of absolute purity, otherwise, as lead
is always liable to contain silver, the latter would necessarily combine
with the assay and vitiate the accuracy of the result. 
GOLD.                    147
idly diminishes in size until at last  all the lead has
been got rid of.  Now, if this were  the only action,
little  good  would haAre been gained, for we should
have  put lead into the gold alloy and taken it out
again.  But another action goes on Avhile the lead is
oxidizing in the current of air.  Other metals, except
the silver and gold,  also oxidize, and are carried by
the melted litharge into the cupel.  If the lead is,
therefore,  rightly proportioned to  the standard  of
alloy, the resulting button will consist of only gold
and silver, and these  are separated by the operation
of parting, Avhich consists in boiling the alloy (after
rolling  it  into  a thin plate) in  strong nitric acid,
which dissolves the silver and leaves the gold  as a
coherent sponge."*
  As the accuracy of the result of an assay is liable
to be influenced, either by retention of silver or copper,
or  by loss  of gold  by volatilization in  the muffle,
solution in the acid,  or retention in the cupel, it is
necessary  to employ " check assays," made on pure
gold,  with AAiiich the  alloy assay is Aveighed in com-
parison ;  and, as will be seen, the  weight of gold
indicated by the balance is liable to be either greater
or  less  than  the amount originally present in the
alloy.   The  following formulaf will serve  to shoAV
the correction to be applied:
  Let 1000 be the weight of alloy originally taken.
  p, the weight of the piece of gold finally obtained.
  x, the  actual amount of gold in the alloy expressed in thou-
sandths.
  a, the weight of gold (supposed to be absolutely pure) taken
as a check, which approximately equals x.

   * See " Quartation."     f Annual Report, Mint of England. 
148
DENTAL METALLURGY.
  b, the loss or gain  of weight experienced by a during the
process of assay, expressed in thousandths.
  k, the variation of "check  gold"  from absolute purity,
expressed in thousandths.
  Then the actual amount of fine gold in the check-piece
= a(l—j-uTro)> an(l x-> the corrected weight of the assay, will
~P—1 o 6 0~t~^ > ^ Deing added or subtracted according as it is
a loss or gain.
  If a be assumed to be equal to x, this equation becomes
                            p+b
                     X =---~ lc
                         * 4" 1000
  Example.—Let p = 901-1 thousandths.
                a = 920-0      "
                & =  0-3      "      gain in weight.
                k=  0-1      "
  Then by the first formula
                x = 901-1—^4-^-1—0-3.
  For, as & is a gain in weight, it must be deducted.   Hence,
                a; = 901-1—0092—03
                 = 900-708.
  And by the second  formula
                       901 1—0-3
                   x=  1_1_  01
                        1 i T¥inr
                     = 900-708.

  Gold-Beating.—In all  probability the art of gold-
beating  originated  among  Oriental  communities,
with whom the love of gold  ornaments  has ahvays
been  a  distinguishing characteristic.  The art is of
great antiquity, and is  referred to  by Homer and
Pliny.  On  the coffins  of Theban  mummies speci-
mens of leaf-gilding were  met with,  where the  gold
in a very thin  state resembled  modern  gilding.  It
is stated that the Incas of Peru did not understand
the art  of  gold-beating beyond the  preparation of 
GOLD.
149
sheets or plates, which they nailed on the walls of
their temples.
  Gold  designed for manufacture  into leaf is vari-
ously alloyed, according to the color required.  The
following is a list showing the proportions of alloy
per ounce required to produce certain tints:
Color of Leaf.	Proportions of Gold.	Proportions of Silver.	Proportions of Copper.
	Grains.	Grains.	Grains.
Red .	456 460	—	20-24
Pale Red .	464	—	16
Extra Deep Red	456	12	12
Deep Red.	444	24	12
Citron	440	30	10
Yellow .	408	72	—
Pale Yellow .	384	96	—
Lemon	360	120	—
Circen or Pale .	312	168	—
White .	240	240	—
  For filling operations quite pure gold is used.  It
also is generally prepared by beating, but some of the
heavier numbers of foil are produced by rolling. There
are two varieties,  cohesive and  non-cohesive, exten-
sively used in the  United States at the present time,
the methods of manipulating Avhich, are widely dif-
ferent.  In  the former  the  characteristic quality of
cohesiveness, Avhich is  greatly  diminished by  com-
pression of the fibers in  beating, is restored by heat-
ing to redness, and this is best effected by placing the
foil upon a sheet of mica, which is held over  a spirit-
lamp.  The habit common among dentists, of taking
                        13* 
150
DENTAL METALLURGY.
up the foil on the point of the plugger and passing
it through the flame of a spirit-lamp, is not productive
of the best results, the gold being made harsh  by
contact with the flame, whereas it should, in addition
to cohesiveness, possess at least some of the kid-like
softness of the non-cohesive variety.   Some of the
manufacturers of gold foil for dental purposes pro-
duce a " soft" variety, in which cohesiveness cannot
be developed  by heating.  This quality may be at-
tained by alloying, or by depositing carbon upon the
surface, as the latter cannot be driven off by heating.
  The corrugated gold introduced within a few years
belongs to this class of foils.  It is prepared by plac-
ing the sheets of gold between leaves of a particular
kind of unsized paper, and tightly packing it in iron
boxes, which are exposed to a temperature sufficiently
high to carbonize the paper.  These are then allowed
to cool, and on opening them the gold is found to be
exceedingly soft and non-cohesive, and  to present a
peculiar corrugated condition of surface, Avhile it is
incapable of being rendered  cohesive by annealing.
  Non-cohesive foil is used in the form  of cylinders,
made by rolling a ribbon or strip of foil, or as pellets,
mats, or ropes.  These are introduced into the cavity
by means of plugging instruments  with or without
serrations, the force  employed being for the most
part hand-pressure, though  the hand-mallet is much
used by  many operators as a means of impacting
non-cohesive  foil.  The advantages claimed for non-
cohesive  foil  are that less  time is consumed in its
introduction,  and that in consequence of the greater
softness which it possesses it is capable of being more
thoroughly burnished to the edges of the cavity. 
GOLD.
151
  When non-cohesive foil is used union does not take
place between  the particles of gold introduced into
the cavity. They are simply made to adhere mechani-
cally by Avedging the mats, cylinders, or  pellets, as
the case may be,  one against the other, into a cavity
properly prepared  to retain  them.   On  the  other
hand, between  particles of gold wherein the charac-
teristic quality of cohesiveness  remains unimpaired,
that property manifests itself Avhenever  two pieces
arc brought in  contact, and if cohesion be  facilitated
by the application of sufficient force, homogeneity
results.  Hence, the methods of operating with the
two  kinds of foil must necessarily differ.   Non-cohe-
si\7c foil is introduced in pieces of more or less bulk;
the cohesive variety is  introduced  in  much smaller
pieces, each piece being carefully Avoided to the others
by means of the electro-magnetic  mallet,  the  hand-
mallet, the " automatic" plugger, or by hand-pressure.
  The method of preparing cohesive foil is thus de-
scribed by  Dr. M. H. Webb,  of Lancaster, Pa.: "A
half-leaf of No. 4 gold foil for  small, a whole sheet
for medium, and tAvo leaves for large  fillings, should
be taken from  the book by means of  the foil-carrier
or spatula, and placed upon a piece of  spunk covered
with whito kid.   The  foil should  bo folded Avith an
ivory spatula into a tape-like form, eight or ten lines
in Avidth respectively, Avhich are then cut across into
small pieces about one-twelfth  of an inch in Avidth.
Heavy foils, ranging  from No. 30 to No.  60, may be
advantageously employed in extensive contour opera-
tions.   The ordinary light  numbers, however, Avhen
prepared  in the  manner described, can more  easily
be impacted into small cavities, fissures, and grooves." 
152            DENTAL  METALLURGY.
  For cohesive gold the cavity is carefully prepared,
the edges of enamel smoothly and  evenly  finished.
A  groove or undercut is then made toward the cut-
tino;-edo;e and toward the cervical wall, and a start-
ing-point drilled  in the dentine  toward the palatal
edge for the purpose  of anchorage.   Into  this the
gold is carried by means of hand-pressure, and by the
same means worked into  the grooves or undercuts.
The point in which to  start the filling should not be
deep, yet sufficiently so to retain the small pieces of
gold first introduced while  others  are  being  built
upon them.  When the first pieces are firmly fixed,
the electro-magnetic mallet may be employed to the
end.  If the cavity be  small, the gold should be pre-
pared from a half-leaf of No.  4 foil, so folded as  to be
equivalent  to No. 12 or 16, and then cut into strips
about one-twenty-fourth of an inch in width.
  Although much diversity of opinion exists among
dentists regarding the  relative value of cohesive and
non-cohesive foil, it may Avith safety be stated that,
skillfully directed, either is capable of affording good
results.   But, like all other filling-materials, each has
its proper place.  Thus, in a  majority of crown-cavi-
ties, it would be  a  sheer Avaste of time to fill exclu-
sively Avith cohesive foil;  Avhile, on the other hand,
there are many  approximal cavities  in  which the
walls have been  rendered so thin by the process of
decay  that probably  the electro-magnetic mallet
alone could be relied  on  to  thoroughly impact the
gold to walls  and periphery.  In such cases the co-
hesive foil should be  folded  of No. 4, and  cut into
narrow strips as above  described, the main object
being to avoid the application of much force, such as 
GOLD.
153
would be required in the consolidation of large mats
or cylinders of non-cohesiAre gold.  Indeed, it may be
stated that one of the greatest adA'antagcs in filling
with  cohesive foil  by the electro-magnetic mallet is
the thoroughness and safety Avith Avhich the gold may
be packed against Aery frail walls.  The merits of the
two are by their respective adArocates often unfairly
presented,  and the value of each may be stated as fol-
lows : CohesiATc foil in very small pieces is, Avith the
electric plugger, capable of being brought into perfect
apposition  Avith the most delicate  walls  of  enamel
with  comparatively little danger of fracture;  non-
cohesive foil, in much  larger masses, may Avith less
expenditure of time be introduced into cavities where
the Avails arc sufiiciently strong to withstand the force
required to consolidate the  mats or cylinders, and,
so far as the  preservation of the tooth is  concerned,
affords perfectly good results.
  Gold Leaf and Foil.—The  process of beating gold
is conducted in the  following manner:  The  metal is
first alloyed according to the  color desired, and, in
order to improve its malleability, it is  melted  at a
higher temperature than is necessary for mere fusion.
It is then cast into an ingot and rolled into  a ribbon of
a half-inch  in Avidth and ten feet in length to the ounce.
After this it is annealed and cut into pieces of about
six and a half grains  each, and placed between the
leaves of a " cutch," Avhich is about half an inch thick
and three and a half inches square,  containing about
one hundred and eighty leaves of a tough paper manu-
factured in France.  Fine vellum Avas formerly much
used for this purpose, and it is yet often interleaved in
the proportion of about one of vellum to six of paper- 
154
DENTAL  METALLURGY.
The hammer employed by gold-beaters weighs about
seventeen pounds, and  rebounds, by the elasticity of
the skin, to such an extent that each stroke involves
but little labor.  It requires about  twenty minutes'
beating to spread the  gold to the size of the cutch,
and if it is intended for filling teeth it is  carried no
further than the cutch  stage.  If, howeArer, it is to be
still further  attenuated, each leaf is taken from the
cutch and cut into four pieces, when it is put betAveen
the skins of a " shoder," four and a half inches square
and three-quarters of an inch thick,  containing about
seven hundred and twenty skins.  The shoder requires
about two hours' beating with a nine-pound hammer.
As the gold will spread unequally, the shoder is beaten
upon after the larger leaves have reached the edges,
the effect of which is  that the  margins of larger
leaves come  out of the  edges in a state of dust.  This
allows time  for the smaller leaves to reach  the full
size of the shoder,  by  Avhich a general evenness in
the size of the leaves is obtained.  Each leaf is again
cut into  four pieces and placed between the leaves of
a  "mold,"—an  appliance composed  of  about nine
hundred and fifty of the finest gold-beaters'  skins.
Its dimensions are five  inches square by three-fourths
of an inch thick.  The management  of the gold in
the " mold" is the last and most difficult stage in the
process of gold-beating, and the fineness of the skin
and judgment of the Avorkman will  greatly influence
the final result.
   The process of lamination may be thus described:
During the first  hour the blows of  the  hammer are
directed principally upon the center of the mold, by
which means  the  edges of the  leaves are made to 
GOLD.
155
crack, but they soon coalesce and unite; so that, after
beating, no trace of the rupture is left.  After having
been beaten for an hour  in a  mold, until the  leaves
have attained a thinness of 15 fo 0 0 part of an inch
in thickness, green rays of light begin to be transmit-
ted, if the gold be pure; but, if largely alloyed with sil-
ver,  rays of a pale-violet hue pass through the gold.
  The membrane called " gold-beaters' skin," used in
the make-up of the  shoder and mold,  is the outer
coat of  the  caocum  or blind  gut  of the ox.  It is
immersed in a potash solution, and scraped with a
blunt knife to free it from fat.  It is then stretched
on  a frame, two membranes arc glued  togeflner,
treated Avith camphor in isinglass, and  subsequently
coated Avith albumen, and cut into squares of five or
fiAre  and a  half inches,  and  is ready for use.  It is
stated that the caeca  of three hundred and eighty
oxen are required to yield enough of the membrane
to make up one mold of nine hundred and fifty pieces,
only two and one-half skins being obtained from each
animal.   Dryness is a matter of great importance,
and, as the  leaves are  liable to absorb moisture from
the atmosphere, they require hot-pressing every time
they are used, and if this precaution is  neglected the
leaf will be pierced with innumerable holes or reduced
to a pulverulent state. 
CHAPTER IX.
                  SILVER
Atomic Weight, 108.  Symbol, Ag (Argentum).
 QLLVEB  may be classed as next to gold in  its
     manifold uses and great malleability and duc-
 tility.   It has been known from the earliest ages,
 and" alloyed with certain proportions  of copper, it
 has been adopted by all civilized nations for purposes
 of coinage, and for articles of plate and ornamenta-
 tion.
  Properties of Silver.—It is  distinguished  from  all
 other metals by its brilliant Avhiteness.   Its  specific
 gravity is  10-53.   In hardness  it  is between gold
 and copper.  It is one of the most ductile and mal-
 leable  of  the metals,—indeed,  Avhen calculated   by
 weight, it is not  even surpassed by gold.  For  ex-
 ample, one  grain of gold may be beaten out to  the
 extent of 75 square inches, and the same weight of
 silver to  98 square inches.  Taking a cubic inch of
 gold at 4900 grains, this gold leaf is 369165o part of
 an inch in  thickness, or about 1200 times thinner
 than  ordinary  printing-paper.*   But  the   silver,
 though spread over a larger surface, will be thicker,
 owing  to  the difference of specific gravity betAveen

  * Gold has, for the sake of experiment, been beaten out to the extent
given above, but the 3 0 *Q Q Q of an inch, as given on page 107,  is as
thin as is ever required for practical purposes.
      (156) 
SILVER.
157
gold and  silver.  The extent of the malleability of
gold and  silver has not  yet been definitely deter-
mined, as the means employed to test it have failed
before there was any appearance of the malleability
of either of them being exhausted*
  In tenacity silver surpasses gold.  It fuses at about
1873° F., and during fusion absorbs oxygen to  the
amount of about twenty-two times its own volume;
but at the instant of solidification it undergoes con-
siderable  expansion, while at the same time it parts
with the  oxygen, which  makes  its escape through
the thin crust  formed over the fluid metal, carrying
with  it fine  globules of  the metal, which may  be
observed  adhering  to  the sides of the crucible.   It
is the best conductor of heat and electricity known.
It possesses no  direct  attraction for oxygen ; hence
it is not  oxidized by  dry or moist air  at  any tem-
perature.   It is, howeA^er,  oxidized by ozone, and
tarnished by air containing sulphureted hydrogen,
which blackens the surface Avith a superficial layer
of sulphide of silver, which is removed by a solution
of cyanide of potassium.
  With the exception  of  nitric, silver is not affected
by dilute acids ; but hot concentrated sulphuric acid
converts it into sulphate of silver, and  Avhen boiled
with strong hydrochloric  acid it dissolves to a slight
extent in the form  of chloride  of silver,  which is
precipitated by  the addition of Avater.
  Occurrence and Distribution.—In the  middle ages
Austria was  the chief source from which silver was
obtained, as an  associate metal Avith lead.  At  the
* W. Chandler Roberts, Assayer Royal Mint.
               14 
158           DENTAL METALLURGY.
present day the United States,  Peru,  and Mexico
supply large quantities.
  Silver is found, first, as native silver,  occurring in
flat masses, occasionally, and sometimes crystalline
in form.   In this country it occurs with native cop-
per, masses frequently being met with in which the
two metals are diffused, the silver showing in specks
upon the copper.
  Native silver is usually free from any considerable
admixture with other metals, although  it invariably
contains - traces of  gold, antimony, etc.  It is also
found as  chloride, iodide, and bromide.
  The most common ores from which silver is derived
are those resulting from combination with sulphur as
sulphides.  These  may be divided into  three kinds :
First  may be mentioned the common  sulphide, of
Mexico, called vitreous sulphide.   It is a protosul-
phide, is  very fusible, and readily yields silver when
made  to  give up  its  sulphur.  Another  sulphide
closely resembling the first, called brittle silver ore, is
found in South America and in some parts of Europe.
It is  readily decomposed by heat, and,  during expo-
sure to high temperatures, evolves fumes of arsenic
and antimony.  A third sulphide, found in nearly
all silver mines in the form of ruby-colored, trans-
parent crystals, is called red silver ore, and is asso-
ciated, to some extent, with oxides.  The compo-
sition of  this  ore has  been given as follows: Silver,
56 to  62; antimony, 16 to 23;  sulphur, 11 to  14;
oxygen, 8 to  10.
  The chloride or native  horn-silver  is  quite  an
abundant ore of  South America  (Chili).   It is a
true chloride, and, like precipitated chloride of siU 
SILVER.
159
ver, darkens Avhen exposed to sunlight.   Its compo-
sition is given as,  silver, 75-3; chlorine, 24-7.
   Methods of Separating Silver from  its Ores.—As
much of the silver of commerce is extracted from
ores too poor to admit of its economical separation
by any process of melting or fusing, even in regions
where fuel is plenty, recourse to the method known
as  "amalgamation" is necessary.    This  depends
simply  upon the easy solubility of silver and asso-
ciated metals in  mercury.  The ore  is  crushed  to
powder, mixed with a sufficient  quantity of common
salt, and roasted at a dull red heat in  a suitable fur-
nace.   By this treatment any sulphide of silver
contained is converted  into chloride.   The  mixture,
which  consists  of  much  earthy matter,  metallic
oxides,  soluble salts, silver chloride, and  metallic sil-
ver, is sifted and placed in barrels arranged to revolve
on  axes.  Scraps  of iron and water are  added, and
the whole agitated together for the purpose of reduc-
ing the silver chloride to the metallic state.   A suffi-
cient quantity of mercury is then  added, and the
agitation  continued until the metallic particles are
dissolved, forming a fluid  amalgam which is readily
separated from  the  mud or earthy matter by subsi-
dence and washing.  It is then strained through a
strong linen cloth  or other suitable fabric to separate
the fluid mercury from the more solid  portions  of
amalgam.  These  latter are subsequently exposed to
heat in  a retort, by Avhich the remaining  mercury is
distilled off.  The silver, more or less impure from
admixture with  other metals contained in the ore, is
thus obtained.
  In order to prevent loss during the  amalgamation 
160
DENTAL METALLURGY.
process, in consequence of a tendency on the part of
the mercury to combine with sulphur, oxygen, etc.,
technically knoAvn as "flowering," in which condition
it may be washed away  together with  the silver it
has taken up, from one to two per cent,  of sodium is
added to the mercury.  The great affinity of sodium
for sulphur and oxygen prevents " floAvering" of the
mercury.
   Considerable quantities of silver are obtained from
argentiferous galena,* and,  indeed, it may be stated
that nearly every specimen of native lead sulphide
will be found to contain traces of this metal.   When
the proportion of the precious metal present is suf-
ficiently large to insure its profitable separation, the
ore is  reduced as usual,"!" the silver remaining with
the lead,  and is then treated according to a  process
discovered by Mr. Pattinson, by Avhom it  was found
that, when lead containing a considerable amount  of
silver is fused and carefully stirred while it is alloAved
to cool slowly, crystals much less rich in silver than
the mass  before melting  will form, and separate and
subside to the bottom.  These crystals of poorer lead
are removed  by means  of  perforated ladles.   The
silver  is  thus concentrated.  This  method of sepa-
rating silver from lead, as practiced on a large scale,
is thus described by Mr. Makins in his " Manual  of
Metallurgy:"
   " A series of iron pots, from nine to twelve in num-
ber, are employed.  These are hemispherical, of about
fiATe feet in diameter, and  calculated  to hold a charge

  * Silver is invariably present in this form of lead ore, but not always
in paying quantities.
  fSee chapter on "Lead." 
                      SILVER.                   161

of about nine tons of metal each.   They are set in
brick furnaces adjacent to each other, but with quite
distinct  flues, furnaces,  dampers,  etc.   The  lead,
assorted  according to its richness  in silver, is then
placed in the pots in the  following order: Some lead
containing ten ounces of silver per  ton having to be
worked, nine tons of it would  be placed in the fifth
pot and melted.   After complete fusion it is skimmed
with a perforated ladle, Avhich removes the dry oxides
for subsequent reduction, Avhile it permits the fluid
lead to run back into the pot.  The fire is then drawn,
and the  metal stirred while it slowly  cools until it
begins to thicken.  The  Avorkman  at  this stage of
the operation  employs  an  iron  ladle  of eighteen
inches in diameter by five  inches  deep, perforated
Avith half-inch holes, and furnished  with a A'ery long
handle.  This handle he raises above his head, sinking
the bowl into the lead until it reaches the bottom.
Then, by using the handle as a lever, and depressing
it as far as possible, the ladle full of crystals is brought
into view,  and, by means of a  hook  and chain fast-
ened to a crane, is suspended and left to thoroughly
drain, after Avhich the crystals are  turned into  the
fourth pot.  This operation is continued until tAvo-
thirds of the lead in the fifth pot  has been passed
over in crystals to the fourth pot, under which a fire
is made and the crystals again melted.  The remain-
ing three tons of molten lead in the fifth pot, which
by the separation of the crystals  contains  sih-er
equaling twenty ounces  per ton, is  now  ladled into
the sixth pot.  The results  of the preceding opera-
tions  may be  summed up as follows: In pot 5, nine
tons of ten-ounce lead equals ninety ounces of  silver,
                        14* 
162
DENTAL METALLURGY.
of which six tons of five ounces (thirty ounces silver)
works  into pot 4; or three tons of twenty ounces
(sixty ounces silver) is ladled into pot  6.  The work
now proceeds until  all the  pots are  in operation.
Three tons of five-ounce lead would be added to the
six  tons passed into  pot 4, while six tons of tAventy-
ounce lead would be carried into pot 6.  Six tons from
pot 6 would work  into number 5, and  three  tons  in
bottoms  will be put back into the same  pot  from
number 4, filling it again Avithout the addition of pig-
lead.  The bottoms or portions which remain after the
ladling become'by  that process so rich  in silver as  to
often contain six hundred  ounces to the ton.  This is
finally submitted to cupellation, by which means the
complete separation of the silver is effected."
  The cupel and its  application may be thus briefly
described :  Bone-ash is mixed with Avater, made into
a cup, with a suitable mold, and dried.  This is called
the cupel,* and has the property of absorbing oxides
when they are combined with  oxides of  lead in a
state of fusion.  Impure silver is mixed  with a certain
quantity of lead, determined by the amount of im-
purity supposed to exist in the alloy.  The mixture
is melted in the cupel  in  a current  of air until the
whole of the lead  is  converted into oxide,  which,  in
a fused state, sinks into the porous cupel, carrying
along with it the  other impurities, the silver being
left behind in a pure state.  The whole operation  is
based on the absence of attraction for oxygen evinced
by the noble metals even when exposed to high tem-
 * These may be obtained at the chemists' furnishing-shops ready for
use. 
SILVER.
163
peratures, and on the affinity possessed by the base
metals for oxygen under similar conditions.
  Cupellation may be accomplished either in a muffle
arranged Avith reference to the passage of a current
of air, so that oxygen may be freely supplied to the
melted metal, or  it may be performed  under the
oxidizing flame of the blow-pipe.  The latter opera-
tion is often  employed in  blow-pipe analysis.   A
certain amount of the alloy is mixed with about four
times its weight of pure lead,  and then placed on
the cupel and the oxidizing  flame of  the blow-pipe
directed on it.   The oxidizing process soon begins,
and in about thirty minutes  all  the lead Avill be con-
verted into litharge, which is fusible,  and is readily
absorbed  into the  porous substance  of  the  cupel,
carrying Avith it all the oxidizable metals that may be
present.  At this point, the button having parted Avith
every  trace  of  the latter, assumes an exceedingly
bright appearance, technically called the  "brighten-
ing of the  button," thus offering a certain means of
ascertaining when the process of cupellation is com-
plete.  Cupellation, under the oxidizing flame  of the
bloAv-pipe,  for quantitative  discrimination, requires
careful management, particularly Avhen the silver has
parted Avith the base metals  and approaches a state
of purity.   For it is  at this stage of  the  operation
that the Avell-known property  of melted silver,  of
absorbing  oxygen from the atmosphere,  and then
parting with it as it approaches the point of solidifi-
cation, may be observed.  The giving-off of the  ab-
sorbed oxygen is what causes "sputtering," by which
minute globules of the metal are thrown off and lost.
thus rendering the assay inaccurate. 
164
DENTAL METALLURGY.
  Besides the method of obtaining silver above de-
scribed, the metal may  be obtained by  converting
sulphides into chloride, the latter being easily reduced
to metallic silver by the  wet method.  The sulphide
is also sometimes converted into sulphate, when the
silver may be reduced from the solution by precipita-
tion.
  Another method of separating silver from its ores
consists in roasting the  latter with common salt to
convert the silver into chloride, which is dissolved
out of the mass by means of a strong  solution of
chloride of sodium; the silver is then recovered in
the  metallic  state  by  precipitating with  copper.
Hyposulphite of soda has also been employed to dis-
soWe out the chloride of  silver, the resulting solution
being precipitated  by sulphide of sodium, yielding
sulphide of silver, Avhich  requires roasting to drive off
the sulphur and liberate  the metallic silver.
  Compounds of Silver.—-There are three  compounds
of silver  Avith  oxygen :  the sub-oxide, Ag O ;  the
oxide, Ag2 O; and the peroxide, which is thought to
have the  formula  of Ag2 02.  The oxide is the only
one  having any practical importance.   Being the
base  contained  in the salts  of silver, it  is obtained
by adding caustic potassa or baryta-water to a solu-
tion of nitrate of silver.
  Silver nitrate (Ag N 03) is prepared by dissolving
silver in nitric  acid by  the  aid of gentle heat, after
which it is evaporated to dryness or until it crystal-
lizes.  These crystals are  colorless, transparent, and
soluble in an equal Aveight  of cold and  in half the
amount of boiling water.   They are also soluble in
alcohol.  Nitrate of silver is fusible, and when poured 
SILVER.
165
into cylindrical molds  forms the lunar caustic em-
ployed by surgeons.  At high temperatures (red heat)
it is decomposed, yielding pure metallic silver.
  Silver sulphate (Ag2 S 04) is prepared by boiling
metallic silver in sulphuric acid.
  Silver sulphide is remarkable for being so soft and
malleable that medals may be struck  from  it.   It
may be formed as a black precipitate by the action of
hydrogen sulphide (H2 S) upon a solution  of silver
nitrate, or it may be formed by heating silver Avith
sulphur in a covered crucible.  It is the affinity ex-
isting between these tAvo elements which renders the
combination  of silver and  vulcanizable rubbers  im-
practicable.  Silver sulphide  is  not soluble  in dilute
sulphuric or hydrochloric  acid, but  is readily dis-
solved  by nitric  acid.  Metallic silver also  dissolves
sulphide of silver Avhen melted Avith it.
  Silver  chloride (Ag CI)  is  the form  into  which
silver is  commonly converted in separating it from
other metals or from its ores.  It is  a white, curdy
precipitate, and may be obtained from a solution of
the nitrate by the addition of sodium  chloride or
hydrochloric acid.   When freshly prepared it is per-
fectly  Avhite,  but  soon darkens, and  eventually
becomes quite  black by exposure to solar light, part-
ing Avith a portion of its  chlorine, and  becoming a
a subchloride (Ag2 CI).
  Silver chloride may also  be formed by suspending
a silver leaf in a glass vessel containing chlorine gas.
and when thus prepared it is  not blackened  by ex-
posure  to light.  Argentic  chloride is fusible at 500°
F.   A much higher heat converts it into vapor, but
does not decompose it.  It  is soluble in ammonia. 
166
DENTAL METALLURGY.
  Discrimination.—The  chlorides and hydrochloric
acid precipitate Avhite argentic chloride, and so del-
icate is the test  that when one part of silver is dis-
solved in 200,000 times its weight of water it may
be  readily  detected  by the opalescence  Avhich  is
imparted to the  fluid  by the precipitant.   This pre-
cipitate is always changed  by exposure to  light to a
violet-black, but  the presence of mercury* will pre-
vent discoloration.  It is insoluble in nitric acid, but
is readily soluble in ammonia, and may be fused to a
horny mass without decomposition.
  Sulphureted hydrogen added to  a  solution con-
taining  silver throws  down a black  precipitate  of
silver sulphide, which is not soluble in dilute acids,
alkalies, or  potassic cyanide.   Sulphuric acid at a
temperature  of  212°  F. will, however,  dissolve it,
with separation of the sulphur.
  Ammonia or potassa, when employed as a precipi-
tant, throws  doAvn a brown oxide, insoluble in the
latter, but soluble  in  the former, and if freely ex-
posed to air this solution will  deposit  fulminating
silver.
  The blow-pipe is frequently  used  in  the discrim-
ination  of silver compounds, and when heated  on
charcoal with  sodic carbonate they yield a bright
bead of metallic silver, often accompanied  by a red-
colored  deposit on the  charcoal.
  Quantitatively the  estimation  of  silver  may  be
effected either by  the usual humid process or  by
assaying.   The first  consists in precipitating the
metal as  chloride, which is to  be  separated and
* Mercurous chloride. 
SILVER.
167
weighed.   The precipitation is effected as follows:
The silver solution is acidulated by nitric acid; hydro-
chloric  acid or sodic chloride,  slightly in  excess, is
then added.   But, as silver chloride is to  a  certain
extent soluble in  either of these,  an undue  excess
must  be avoided.   The chloride must noAv be  care-
fully and repeatedly Avashed  and filtered in  a  thor-
oughly  dry filter,  previously weighed.   After the
solution has passed through the filter, the latter with
its  contents is dried and Aveighed,  and the weight,
minus the weight of the filter, will be the amount
of silver chloride present.
  The dry method  or  assaying process consists in
forming an alloy of  the silver Avith lead, and  is  espe-
cially applicable to ores and the sweep of the dentist's
laboratory.  The  specimen to be  treated  is  heated
with from twelve  to thirty times its weight  of pure
granulated lead in a bone-ash cupel, which is placed
in a muffle so  arranged that a current of atmospheric
air may pass  freely over the  vessel and  oxidize the
lead.  This oxide  of lead, being quite fusible,  com-
bines Avith any base metal present and oxidizes it,
uniting subsequently with the oxide as a fusible slag,
Avhile the gold  or silver will be held  by the unoxi-
dized portion  of the lead.  In the treatment of speci-
mens of alloys, such as plate or coins, a quantity of
the specimen  is accurately Aveighed and mixed Avith
from four to five times its weight of pure granulated
lead.  It is then placed in the cupel and exposed to
heat, as above described, until all the lead is oxidized
or conArerted into  litharge, Avhen the remaining but-
ton assumes the brilliant appearance of surface be-
fore alluded to, which denotes that the base metals 
168
DENTAL METALLURGY.
or oxidizable  constituents have  been oxidized and
taken up by the lead oxide.  This button is then to
be weighed by  means of a delicate assay balance,
and the loss of weight denotes the amount of alloy
that was present.
  Pure Silver.—Pure silver, which is reckoned as 1000
fine, may be obtained from standard  or other grades
of silver by dissolving them in  nitric acid slightly
diluted with water, the solution being much facilitated
by  exposure to  gentle heat.  If gold be associated
with the alloy it will be found at the bottom of the
vessel, in which  case it  will be  necessary  to use  a
syphon to remove the argentic nitrate solution.  The
silver is now to  be  precipitated  in the form of chlo-
ride by the addition of  an excess of common, salt.
When all has subsided the liquid is carefully poured
off, and the chloride thoroughly washed to remove all
traces of acid.   The chloride is then placed in water
acidulated with  hydrochloric acid (an  ounce of chlo-
ride requiring six to  eight ounces  of Avater) and
pieces of clean wrought-iron put in it, when a copious
evolution  of hydrogen follows, Avhich, uniting with
the chlorine of  the argentic chloride, liberates me-
tallic silver. The latter should not be disturbed until
the last particle of it is thus reduced, Avhen it will be
found to be a spongy mass. The undissolved iron
should now be  carefully removed, the  ferrous and
ferric chloride  carefully decanted,  and the  silver
Avashed in hot water containing  about one-tenth  its
bulk of hydrochloric  acid.   This is repeated several
times,  and  finally  the silver is again thoroughly
Avashed with pure hot water. The silver, after dry-
ing, is  then ready for melting, and if care  has  been 
SILVER.
169
observed in the process it Avill be found  to  be of a
fineness of 999-7 parts in 1000, the 0-3 of impurity
present being due  to  traces of iron.  The chlorides
may be acidulated  Avith sulphuric acid, and reduced  .
with zinc instead of iron.
  Another method of  precipitating  silver  in the
metallic  form consists in placing a sheet of copper
in a  solution  of argentic nitrate.   The metal  is
thrown down in a  crystalline form.   Silver thus ob-
tained is never free from traces of copper.
  Pure silver can  only be obtained from samples of
a lower grade by fusing the pure  chloride Avith sodic
carbonate.  The reaction is shown in the following
equation :
     2Ay CI -f Na2 C ().,   Ag, -|_ 2Na CI 4- O 4- C 02.

Owing to the copious evolution of carbonic acid gas
which takes place during the decomposition, some of
the silver may be thrown from the crucible, and loss
may occur  by  the absorption ly the  crucible  of
some of the fusee I chloride.  To avoid this the sides
of the vessel  should  be coated with  a  hot saturate
solution of borax.
  A  composition of 100 parts  of argentic chloride,
704 of calcic  carbonate (chalk), and 4-2 of charcoal,
has been recommended as a means of  obtaining pure
silver.   This mixture  is heated to dull  redness for
thirty  minutes, and then raised to full redness;  car-
bonic acid and  carbonic oxide are  given off;  the
calcic chloride is converted into  calcic  oxychloride,
underneath  Avhich, in  the bottom of the crucible,
will be found the button of pure silver.
  Alloys of Silver.—In consequence  of its softness,
                         15 
170
DENTAL METALLURGY.
silver in the pure state is liable to considerable loss
by attrition.   For all useful purposes,  however, the
requisite amount of hardness may be conferred upon
it by the addition of a small proportion of copper.
Thus, silver for coinage and manufacturing purposes
usually contains  in 1000  parts  from 900  to  925  of
silver  and from  75 to 100 of copper.  The term
"standard sihTer" refers  to the metal  thus alloyed
with copper, that of the United  States coinage being
silver 900 parts, copper 100.
  Previous to the introduction of vulcanized  rubber
as a base for artificial dentures, standard silver was
much employed in the United States for temporary
dentures, when cheapness  was an  important  con-
sideration.  In England a much more durable alloy
is used, in Avhich the alloying metal is platinum in the
proportion of from three to ten grains of the latter to
each pennyweight of  silver.  The advantages  pos-
sessed  by this alloy over ordinary  standard silver
may be summed up as follows : It resists Avear  better,
and not  even  a suspicion can be reasonably enter-
tained  of any ill effects occurring, either locally  or
to the general system, from its presence in the mouth.
It permits of  the employment  of a higher grade of
solder, and it  is a much  more rigid alloy than ordi-
nary standard or coin silver.  Hence  it  makes  a
stronger artificial denture, which is less  likely  to
haAre its  adaptation  impaired  by  bending.    But,
Avhile the purity of silver is preserved when plati-
num is the sole alloying  component, it must not  be
supposed that its affinity for sulphur is thus materially
lessened, or that its tendency to blacken when brought
in contact with  that  element  or its compounds is 
SILVER.
171
 obviated.   Indeed,  it may be  stated that platinum
 added  to  silver in such  small quantities does  not
 decidedly  protect  the latter from  the  action  of its
 ordinary solvents.  Such an alloy of silver, for  in-
 stance, would  not only be readily dissolved by nitric
 acid, but the platinum  also,  though unaffected ordi-
 narily by that menstruum, Avould readily yield to it
 when combined with silver.
   It is a  somewhat common belief that the putting
 together of silver  and platinum in the formation.of
 an alloy of this kind, owing  to the infusibility of
 platinum and the wide difference in the fusing-points
 of the two, is a matter of great difficulty.  It should
 be borne in mind, hoAvever, that betAveen the metals
 more or less affinity exists, especially at high tem-
 peratures;  hence it is only  necessary  to introduce
 the  platinum, rolled into  thin ribbons, into the cru-
 cible containing the  silver in a state  of complete
 fusion,  and the platinum will be observed to quickly
 fuse  and mix  with the  latter.   It is  sometimes
 thought advisable  to add larger quantities of  plati-
 num than the amount here given.  This may be done
 by adding the platinum until the  alloy becomes
 infusible, and this result Avill be attained  as soon as
 the  amount of platinum added is sufficient to  raise
 the  fusing-point of the  alloy above the  capacity of
 the ordinary melting apparatus.
   Silver Solders.—When the plate to be  united con-
sists of pure silver alloyed Avith platinum, the solder
may be formed of the  standard metal (coin),  Avith
the addition of from one-tenth to one-sixth its weight
of zinc, according  to  the amount of platinum con-
tained in the  alloy.  Silver  solders  are,  hoAvever, 
172            DENTAL METALLURGY.
generally composed of  silver,  copper,  and zinc,  or
silver and brass in variable proportions, of Avhich the
following are examples:
                       No. i.*
     Silver.......66 parts.
     Copper
     Zinc  ....
Silver
Copper
Brass  .
Silver .
Brass wire
No. 2.1
No. 3.
30	[i
10	u
6 dwts	
2	"
1	ii
H	dwts
40	grs.
  In putting together the constituents of silver sol-
ders, the affinity for oxygen manifested by zinc, brass,
and  copper,  Avhen exposed  to  high  temperatures,
should be remembered, and in order to guard against
loss the  mode of procedure  should  be as  folloAvs:
The silver, placed in a clean crucible, Avith a sufficient
quantity of borax to cover it, should be thoroughly
fused, and, Avithout permitting it to cool in the least,
the zinc, brass, or copper, as  the case may be, should
be  quickly  added.   Before  pouring,  it should  be
shaken or agitated to insure  admixture.  When  cool,
it may be removed from the ingot mold and rolled
into plates of, say, 27 of the standard gauge.
  The surface of standard silver may be whitened  by
being heated and immersed in dilute  sulphuric  acid.
It is in this way that frosted silver is produced.  The
acid, dissolving the oxide  of silver from the surface,
leaves a quite pure superficial film.
       * Richardson's treatise on Mechanical Dentistry.
       fIbid. 
                      SILVER.                   173

  Silver may be deposited upon the surface of another
metal by connecting the article to  be silvered Avith
the negative (zinc) pole of the galvanic battery, and
then immersing it  in  a solution made by dissolving
cyanide of silver in a solution of cyanide of potas-
sium.  The current decomposes the argentic cyanide,
and the metal is deposited upon the  object connected
with the negative pole.   During this decomposition
the cyanogen, liberated  at the  positive  (copper or
platinum) pole, acts upon a silver plate Avith Avhich
this pole is connected, the quantity of silver dissolved
at this pole  being  precisely equal to  that deposited
at the opposite pole; the  silvering solution is ahvays
maintained  at the same strength.
15* 
CHAPTER X.
        PLATINUM.
Atomic Weight, 197-6.   Symbol, Pt.
TDLATINUM is found in nature in flattened grains
    of varying sizes, more or less  alloyed Avith  pal-
ladium, rhodium, ruthenium, and iridium.*   It occurs
in Brazil, Peru,  Australia,  and California.  Russia,
however, furnishes the largest  supply of platinum,
from  the Ural  Mountains.  It  Avas  discovered in
1736 by Anton Ulloa, at Choco, in South America;
but, inconsequence of its infusibility and unworkable
nature, no  use was  made of it, and its presence in
mining products Avas considered  a hindrance.  Dr.
Wollaston devised the first practical process of  work-
ing it, and  in 1859  Deville and  Debray published
improved methods of fusing large quantities of plati-
num.
  The method  of Wollaston,  which consists of a
series of chemical processes of  a rather complicated
nature, may be thus described :  The ore is first heated
Avith nitric  acid  to  dissolve any copper, lead, iron,
or silver.  It is then washed and heated Avith hydro-
chloric acid to remove  any magnetic iron  ore that
 * A group of rare metals only found in platinum ores, and known
as the platinum metals.
      (174) 
PLATINUM.
175
may be present;  after which the ore is to be treated
with nitro-hydrochloric acid, diluted with an  equal
bulk of Avater, to prevent  the iridium, Avhich is gen-
erally  present, from being  dissolved.   The  propor-
tions  of acids are one  hundred and  fifty parts  of
hydrochloric to forty parts of nitric.  Three or four
days' digestion, aided by gentle  heat, is necessary to
complete solution.  The suspended matter, generally
consisting of iridium, is  allowed  to subside, Avhen the
solution may be syphoned off.
  Amnionic chloride* is next added as a precipitant,
and  throws down  the yellow crystalline  ammonio-
platinic  chloride, which is readily decomposable by
heat, yielding platinum  in a finely-divided  state.
  The liquid  from which  the precipitate is obtained
will  still be found to contain about eleven  parts of
platinum, together Avith all  the associated  metals.
These are  all throAvn down  by means  of a  plate of
zinc,  and washed  carefully and again dissolved  in
nitro-hydrochloric  acid.   A small quantity of strong-
hydrochloric acid  is added to avoid precipitation of
lead or palladium. Avhen precipitation of the  remain-
ing platinum may be   again effected by amnionic
chloride.  This precipitate Avill require careful wash-
ing in cold Avater  to remove iridium, which during
the process forms  a  double salt with amnionic chlo-
ride.
  The next stage in  the operation consists in  sepa-
rating the metal from the ammonia salt by ignition,
and, as it is important  to the success of the subse-
quent working that the precipitate shall remain in a
About forty parts. 
176
DENTAL METALLURGY.
finely-divided  state, too  great an  amount of heat
must be avoided, otherwise cohesion of the particles
Avill  take  place.  Ignition is generally accomplished
by the folloAving means :  The precipitate is heated in
a graphite crucible until nothing  remains but the
finely-divided  platinum.   This is powdered, should
it be found someAvhat lumpy, in  a Avooden mortar
Avith  a  wooden pestle, sifted through a fine  lawn
sieve, and mixed with Avater to the consistence of a
stiff  paste.  This is placed in a brass mold Avith a
slightly tapering cylindrical cavity of about seven
inches in length, provided with a loosely-fitting steel
stopper, which enters to  the depth of a quarter  of
an inch.   The mold is first oiled and set  up in a ves-
sel of water.   The platinum mud is then introduced,
and  as it  settles into the water air is displaced, and
the platinum  is thus made to fill every part of the
mold.  The water is allowed to drain, and its remo-
val may be aided by pressure.  Ultimately, however,
the mold  is placed in a press worked by a powerful
lever, by which the mass sustains an enormous press-
ure, after  which the plug and the column of plati-
num are removed by gently tapping the mold.  It is
then heated in a charcoal fire, in order to thoroughly
dry it and to burn off any adherent oil.
  The next step, Avhich depends upon  the quality of
welding possessed by platinum, consists in heating
the porous cylinder in a  blast-furnace to white heat,
Avhen it is removed, set upright on  an anvil, and
hammered on  the ends in order to weld the particles;
after which it is coated Avith a mixture of borax and
carbonate  of potash, and again heated for the pur-
pose of removing traces of iron which  is dissolved 
PLATINUM.
177
 by the mixture, the latter being removed by immer-
 sion in dilute sulphuric acid.  The bar of platinum is
 iioav read}- for use, and may be rolled or hammered.
   It may readily  bo  surmised that so imperfect a
 means of obtaining a solid  bar of metal as the latter
 part of the operation just  described cannot always
 he relied upon for the production of a uniform and
 solid specimen;  and,  indeed, platinum prepared in
 this Avay, though of great purity, is liable to blister
 upon its surface, this being probably due to minute
 globules of air incased  in the body of the ingot dur-
 ing the forging, Avhich, during the conversion of the
 ingot into plate  by means  of rollers, are elongated
 and spread out in the form  of blisters.
   The dry metallurgies  operations of Deville and De-
 bray  consist in heating in a reverberatory furnace
 about tAvo hundred-Aveight  of platinum ore  with an
 equal Aveight of galena (sulphide of lead).  "When the
 ore is sufficiently heated (to  bright redness), portions
 of the galena are added and mixed  Avith the ore by
 constant stirring.  An equal amount of litharge is
 next added, in order to supply oxygen to the sulphur
 of the lead ore, Avhich passes'off as sulphurous anhy-
 dride, reducing all  of the lead Avhich combines Avith
 the platinum.   After remaining in a state of fusion for
 a short time the  upper portion is ladled off,  and will
 be found to consist of an alloy of lead, platinum,  and
 smaller portions  of palladium and  silver, the latter
 being introduced from the galena, Avhich ahvays con-
 tains more or  less silver.  The heavier metals of the
platinum  group, by their greater density, subside to
the bottom.
  Cupellation is now resorted to in order to separate 
178
DENTAL  METALLURGY.
the platinum from  the lead.  This consists of  tAvo
distinct operations.  The first is performed at the
ordinary furnace-temperature, and is continued until
by  loss of lead  the fusing-point of the remaining
alloy rises to  such an extent that a state  of fusion
can no longer be maintained.   The second and final
operation is performed in an apparatus Avhich serves
the purpose of both a furnace and cupel.  It is formed
of blocks of thoroughly burned lime.  In form it may
be described as a sort of basin or concavity Avith a
similar piece for a eoA^er. The lower part is intended
for  the reception of the metal; through the center
of the upper  portion  or cover pass  the tubes for
the oxyhydrogen jet, while the loAver portion is pro-
vided Avith a lip or spout for pouring the melted metal.
The tubes which pass through the top for the trans- .
mission of the two gases  are generally formed of
copper Avith platinum tips.   The outer and loAver
tube carries hydrogen, while the inner and upper
one carries  a jet  of oxygen, into the middle of the
flame.  The tubes are  furnished Avith stop-cocks, so
that the supply may be regulated.  When the object
is merely to fuse some scraps of platinum, the lime-
furnace is first  put together,  the hydrogen jet is
lighted, oxygen is then turned on, and  the interior
of the apparatus soon becomes heated.  The platinum
is then introduced in pieces through a small hole at
the side, and quickly fuses after entering the furnace.
  When used as a cupel the lime absorbs the impuri-
ties, and  the platinum is kept in a  state of fusion
until all the lead is oxidized, when the metal may be
poured from the lime-cupel into an ingot mold formed
of coke or plates of lime.   Some difficulty may be 
PLATINUM.
179
experienced at the moment of pouring, in consequence
of the dazzling white  surface  of the  molten metal.
From  seven to eight pounds may be melted in this
Avay in from forty to sixty minutes.
  Although such metals as palladium, osmium, gold,
silver, and lead are A^olatilizod at the  intense  heat
used, it  has been found that platinum  obtained by
the  Deville-Debray method is not  as  pure  as  that
obtained by Wollaston's plan.
  Properties.—Platinum  is  someAvhat   whiter  than
iron.  It is exceedingly infusible, requiring the flame
of the compound blow-pipe (oxyhydrogen) to render
it fluid.   In both the hot and cold state it is exceed-
ingly malleable and ductile.*  It is the  heaviest sub-
stance in nature, its specific gravity being 21-5, and
it is exceeded  in tenacity only ly iron and copper.
No single acid attacks  it, and it  is unaffected by air
or moisture at any temperature.  It is therefore of
great a alue in  the  construction of chemical vessels.
  At bright-red heat platinum Avelds quite  readily,
and  injured vessels may be repaired in this Avay.  In
the  finely-divided state, as  obtained by Wollaston's
process, it may be made into small vessels by pressing
the  pulverulent metal  into suitable molds,  heating
and  hammering to  complete the  Avelding of the par-
ticles.
  * Wollaston, in endeavoring to substitute platinum for the spider's
web usually employed in micrometers, made platinum wire finer than
had hitherto been obtained.  This  was  accomplished by  forming a
coating of silver  upon a platinum wire, and then passing it through
the draw-plate, after which he dissolved the silver, leaving the plati-
num  the 3 0qq 0 of an inch in diameter, a mile of which, notwith-
standing the high specific gravity of the metal, would only weigh a
single grain. 
180
DENTAL METALLURGY.
  Platinum possesses  the remarkable property  of
inducing chemical combination between oxygen and
other gases.  Even in the compact condition it pos-
sesses this quality, as demonstrated by the familiar
experiment of suspending a coil of platinum Avire  in
the flame of a spirit-lamp, and suddenly extinguishing
the flame  as soon as the metal  becomes  entirely
heated,  Avhen, by inducing the combination of the
vapor of the spirit Avith oxygen, the Avire Avill  con-
tinue to gloA\r. An instantaneous light apparatus has
been made in Avhich a jet of hydrogen is throAvn upon
a ball of spongy platinum; the latter induces combi-
nation between  the oxygen condensed between its
pores and  the spirit-vapor,  and ignition takes place.
  Platinum-black, in Avhich the metal exists in an
exceedingly  fine state  of division,  possesses  this
power  of  promoting combination of  oxygen with
other gases to the highest degree.  In  this form it is
capable of  absorbing eight hundred times  its volume
of oxygen.  No combination, however, takes place
between the two, the gas being merely  condensed
Avithin the pores of the metal ready for combination
with other bodies;  hence, if a jet of hydrogen be
throAvn upon a small lump of this powder, ignition
ensues.  During the operation of melting, platinum
absorbs oxygen and gives it off in cooling, " sputter-
ing," as silver does under like conditions.
  The  proper solvent for  platinum  is nitro-hydro-
chloric acid,  the  chlorine evolved being  the active
agent.  Alloyed  Avith silver, however,  platinum Avill
be  dissolved  in  nitric acid,  and when platinum  is
found in gold as an alloy it may be  separated by
quartation Avith silver. 
PLATINUM.
181
  Alloys.— Kqual weights of platinum and gold afford
a malleable alloy ; the brilliancy of appearance char-
act eristic of gold is, hoAvever, much lessened by the
admixture.  The tAvo metals, combined in the pro-
portions of*  1  part of platinum to 9-5 of gold, form
an alloy of the same density as platinum.  An excess
of platinum Avith gold yields an alloy which is infusi-
ble  at ordinary furnace-heat.
  The tenacity of gold is very greatly increased  by
admixture of  platinum, Avhile at the same time it is
rendered more elastic.
  Platinum and  silver  may be combined in all pro-
portions, constituting alloys of greater hardness than
either of their  constituents, while the color is  be-
tween the color of silver and  that of platinum.  Hot
sulphuric acid Avill dissolve the silver from an alloy of
this kind, and Avhen one part of platinum is  alloyed
Avith ten parts of silver both metals  may be dissolved
by  nitric acid.
  Platinum and mercury do not amalgamate readily,
and combination can only  be effected by  rubbing
finely-divided platinum, such as is reduced from the
amnionio-chloride, in a heated mortar with mercury
moistened Avith  Avater acidulated Avith acetic acid.
By this means  an unctuous  amalgam  is obtained,
which has been employed in  platinizing metallic  ob-
jects in a manner similar to that knoAvn as fire-gild-
ing.
  The value  of platinum as  a constituent in alloys
for  dental amalgams has of  late been greatly ques-
tioned.   The  author found, as  the  result  of  a  large
number  of experiments, that it rendered the  alloy
very brittle; and, Avhile its presence seemed to retard
                        16 
182
DENTAL METALLURGY.
 amalgamation, it increased the capacity of the alloy
 for mercury (see page 53).
   Iridium confers upon platinum great hardness and
 tenacity;  indeed, the alloy resulting from this com-
 bination is so rigid that it is with the greatest diffi-
 culty it can be  swaged into plates.  It is, neArerthe-
 less, an alloy of  great value to the mechanical dentist,
 as it affords a means of obtaining greater strength
 in artificial dentures of the "continuous-gum" class,
 and it has been  used in the author's laboratory since
 1870 in connection with vulcanized rubber, the plate
 being constructed of iridium-platinum, with the teeth,
 single or in sections, attached by means  of rubber.
 The swaging requires the  use  of the zinc counter-
 die, and when the ridge is very prominent it is best
 not  to  attempt  to carry the plate entirely over it,
 but to allow the rubber to  take its place.  An arti-
 ficial denture constructed in this Avay has no superior
 in point of strength and durability.
  Nothing but pure gold should be used as a solder
 in uniting two pieces of platinum or iridium-platinum.
 Indeed, so feeble is the union betAveen the  latter and
 an ordinary gold solder that two pieces united by its
 agency may be  readily torn apart with the pliers.
 The addition of iridium is also of value in the con-
 struction of platinum vessels  for experimental labo-
 ratory use,  as the  metal  is thereby rendered more
 resistant to high temperatures, and less susceptible
 to the  action of  chemicals.
  Platinum combines Avith tin in all proportions, and
the resulting alloy is hard, brittle, and more or less
fusible. Between the platinoid metals and tin, at the
moment of fusing together, phenomena very suggest- 
PLATINUM.
183
ive of true chemical union have been observed, and
if tin and platinum foils be rolled together and heated
before the blow-pipe, combination takes place explo-
sively.   It is in consequence of this affinity that two
such metals, one  of which is infusible at  ordinary
furnace-temperature, while the  other is readily fusi-
ble at a low degree of heat, may, with the greatest
facility, be melted together to form an  alloy*
   Oxides.—Platinum unites with oxygen to form tAvo
compounds—the monoxide or  platinous oxide (PtO),
and the dioxide or platinic oxide (Pt 02).   The first
is obtained as a black powder by digesting the dichlo-
ride  with  caustic potash.  The second (Pt 02) may
be prepared by adding barium nitrate to a solution of
platinic sulphate.  Barium  sulphate  and platinic
nitrate  are thus formed, and from the latter caustic
soda precipitates one-half of the platinum as platinic
hydrate, a bulky broAvn powder, which, when gently
heated,  becomes  black and anhydrous.  It is  also
formed Avhen platinic chloride  is boiled Avith an excess
of caustic soda, and acetic acid added.  It combines
Avith bases  and dissolves in  acids.   Platinic oxide
with ammonia forms  an explosive compound, which
detonates  violently at about 400° F.   Both oxides of
platinum are reduced to the metallic state by heating
to redness.
  Platinic chloride (Pt  Cl4) is  the most useful salt of
the metal, and is the one from  Avhich all the platinum
compounds  are obtained.  It  may be  prepared by
dissolving  scraps of platinum in a mixture of four
measures  of hydrochloric acid with one of nitric
* See chapter on " Alloys." 
184
DENTAL METALLURGY.
acid, one hundred grains of platinum requiring the
presence of two ounces of hydrochloric acid.  After
complete solution the liquid is evaporated at a gentle
heat to  a syrupy consistence, redissolved in hydro-
chloric acid,#and again evaporated to expel excess of
nitric acid.  The syrup-like fluid solidifies on cooling
to  a  red-brown  mass, which is deliquescent  and
readily dissolves  in Avater or alcohol.
  Spongy platinum is prepared by heating the yellow
crystalline precipitate  obtained by the  addition of
ammonic chloride.
  Platinous chloride (Pt Cl2) may be formed by heat-
ing platinic chloride to a point someAvhat  above 450°
F.  A very high temperature reduces it to the metal-
lic state.
  Sulphides.—The compounds Pt S and Pt S2 are
produced by the action of hydrogen sulphide, or the
hydrosulphide of an  alkali metal, on the dichloride
and tetrachloride of platinum  respecthrely.  They
are both  black, insoluble substances.
  Discrimination of Platinum Salts.—1st. A  blackish-
brown  precipitate, insoluble in nitric or hydrochloric
acid singly, Avill be throAvn down ly the  addition of
hydrogen sulphide (H2 S).
  2d. Ammonia  or potash  throws  down a yellow
crystalline precipitate.
  3d. A  brown hydrated  platinic oxide  is precipi-
tated from the salts of platinum  by the  addition of
soda, and it should be remembered that the  precipitate
is soluble in an excess of the soda,
  4th.  A deep broAvn color is imparted to solutions
of platinum salts by  the  addition of stannous chlo-
ride, but  no precipitate is obtained. 
Platinum.
185
  Quantitatively,  platinum may be  separated  from
other metals with Avhich it is likely to be associated
by  precipitating  with ammonia  chloride.  This is
added to the platinum solution, followed by  a  little
alcohol.  The precipitate is collected,  washed  with
alcohol, and dried, Avhen  it is ready for Aveighing.
Every 100 parts will contain 44-28 of platinum.
16* 
CHAPTER XI.
          IRIDIUM.
Atomic Weight, 198.  Symbol, Ir.
TRIDIUM, named from Iris, the rainbow, because
    of the varied colors of its compounds, has already
been mentioned as occurring  in the insoluble alloy
from the platinum ores, and  disseminated in  small
hard points throughout the substance of California
gold.   It is also obtained Avhen  crude platinum is
dissolved in nitro-muriatic acid.  A gray, scaly, me-
tallic substance is  found at the bottom of the vessel,
which  has  entirely resisted the action of the acid.
This is osmiridium, a native alloy of iridium and os-
mium.   The subsequent treatment for the separation
of the  two metals  consists in reducing them to pow-
der, combining them with an equal Aveight of dry so-
dium chloride, and heating to redness in a glass tube,
through which moist chlorine  gas is allowed to pass.
The tube is connected with a receiver containing a
solution of ammonia.  The gas is quickly absorbed,
and iridium chloride and osmium chloride are formed.
The first remains combined with the sodium chloride,
Avhile the osmium chloride, being a volatile substance,
passes  into the receiver.  The contents  of the tube,
consisting of iridium and sodium chlorides, when cold,
are dissolved with water, and mixed Avith an  excess
of  sodium  carbonate  and  evaporated  to  dryness.
       (186) 
iridium.
187
After ignition in a crucible, boiling in water and dry-
ing, the metal  may be reduced by hydrogen (at a
high temperature), and  heating  successively  Avith
water and strong  hydrochloric acid to free it of the
alkali  and iron.   What remains consists  of metallic
iridium in a finely-divided state.
   Pr<>j>erties.—Iridium is an  exceedingly hard  and
brittle metal, nearly Avhite in color, and fusible only
Ly the oxyhydrogen  bloAV-pipe. ly which  means it
has been converted into  a white mass having some-
what the appearance of polished steel.   It is hard*
and brittle while  cold, but  is rendered somewhat
malleable  at red  heat.   Its  density  is  about  the
same as that of platinum.   It has been  obtained
in  tolerably compact masses  ly  compressing some
of  the metal in a very fine  state and then heating
to the highest point  attainable in a forge-fire.  The
density of a sample of iridium prepared in this Avay
Avill not exceed 160.
   When reduced by hydrogen at low temperatures it
dissolves in nitro-hydrochloric  acid, but is  rendered
insoluble in all  acids by exposure to Avhite heat.  It
may again be dissolved by igniting it Avith a mixture
of the chloride of potassium and sodium in a current
of chloride.
  Alloys.—Platinum containing a  small quantity of
iridium is rendered more  rigid, and is of great value
as a means of strengthening continuous-gum work,
  s IU hardness is such that the hardest file will make no infpression
on it.  In working California gold, which often contains disseminated
through it small grains of a native alloy of osmium and iridium, the
file is sensibly injured by contact with it, while in coining operations
much inconvenience and injury are caused by its presence. 
188
DENTAL METALLURGY.
by forming the backing of it, especially in  partial
lower sets, where, in addition to the tAvo pieces of
pure platinum covering the gums back of the natural
(front) teeth, an extra piece of platinum alloyed Avith
iridium, No. 26, may be used. It also answers Avell
in combination with vulcanizable rubber,* for either
entire or partial cases, and though decidedly the most
refractory of the various alloys employed in the dental
laboratory, may be perfectly swaged by the use of a
zinc counter-die.  In the construction of partial cases
it may  be  employed for clasps,  but wherever it is
necessary to unite two pieces by soldering nothing
but pure gold should be employed as the solder. Ordi-
nary gold solders do not afford a strong union.
  Iridium  unites  Avith  oxygen,  sulphur,  chlorine,
and iodine, to  form oxides, sulphides, chlorides,  and
iodides.
  Discrimination.—With ammonium  or  potassium
chloride, iridium solutions afford a  dark reddish-
brown crystalline precipitate of ammonium or chlor-
iridium, the color of which, and* the fact that it is
reducible to soluble  chlor-iridium when treated Avith
hydrogen sulphide,  distinguishes it  from the corre-
sponding platinum precipitate.
* See chapter on " Platinum." 
CHAPTER XII.
                 PALLADIUM.
        Atomic Weight, 106-5.   Symbol,  Pd.

~DALLADIUM, rhodium, iridium,  ruthenium,  os-
      mium,  and  davyum*  constitute   a  group  of
metals Avhich  possess many properties in common.
They are also  closely*allied ly natural  association.
   (.'rude platinum is a native alloy of platinum with
these metals, and is the source whence  they  are usu-
ally obtained.f   Palladium  is,  hoAvever, occasionally
found  native  in  a  comparatively pure state  inter-
mixed Avith platinum,  from  which metal  it may
be readily distinguished by the fibrous appearance of
its grains.
   It  is obtained at the present time chiefly from the
  *This metal, named in honor of Sir Humphry Davy, was discovered
by Kt-rn in 1877, in platiniferous sand.  It was obtained from the
mother liquors after the separation of platinum, palladium,  osmium,
and iridium, by heating them with an excess of ammonium  chloride
and nitrate.  A deep red precipitate was obtained, which after calci-
nntion at a red heat left a grayish mass resembling platinum sponge.
This, when  fused by the oxyhydrogen blow-pipe, furnished  a silver-
white metal of great hardness, though malleable at a red heat, having
a density of 9-39;  soluble in aqua regia, but only slightly acted upon
by boiling sulphuric acid.
  f Palladium was, a few years since, obtained in considerable quanti-
ties from Brazilian gold, with which it was associated as an alloy, but,
this means of supply having failed, it has become too expensive for
employment in the industrial arts.
                                             (189) 
190
DENTAL METALLURGY.
solution of crude platinum, after that metal has been
separated by precipitation with ammonic  chloride.
The remaining liquid is neutralized by sodium car-
bonate, and mixed  with  a  solution  of  mercuric
cyanide; palladium cyanide separates  as a whitish
insoluble substance, which, on being washed,  dried,
and heated to redness, yields metallic palladium in a
spongy state, which admits of welding into a solid
mass in the same manner as platinum.
  In appearance palladium resembles an alloy of plat-
inum and gold, Avherein the proportion  of the former
greatly exceeds that of the latter.  It  possesses the
qualities of malleability and ductility,  but in  those
properties  it is  probably inferior to platinum.  Its
density differs very much from platinum, being only
11-8.  It is more oxidizable than platinum, and when
heated to redness  in the  air, especially Avhen in  a
finely-divided state, it acquires a superficial film of
oxide of a bluish color, Avhich may be again reduced
at a high temperature.  It does not, however, oxidize
in the air unless the temperature is raised to red heat.
It is the most fusible of the platinum metals, and
requires about the heat needed to fuse malleable iron
to reduce it to a state of fluidity, in which condition
it absorbs oxygen and parts Avith it again in cooling
in the same way that silver does.   It is dissolved by
nitric acid, but its best solvent is nitro-hydrochloric
acid.   It is attacked by iodine, and may. be distin-
guished from platinum by heating a drop of tincture
of iodine upon it, when it will show a stain, Avhile
platinum similarly treated is quite unaffected.
  Alloys.—In a  finely-divided  state it unites readily
with mercury, and there would appear to be some 
PALLADIUM.
191
chemical affinity between  the two, the  union being
accompanied by evolution of heat.  As the amalgam
cools  it sets and becomes tolerably  hard, and it  is
stated that it expands in hardening.*
  Mr. Colemanf  states that palladium amalgam sets
very rapidly, and Avhen mixed in large enough quan-
tities  to fill good-sized cavities  it evolves so much
heat as to explode Avith emission of  light.  He also
gives the  following description of the manner  of
mixing and applying the amalgam : " About as much
mercury as Avould fill the cavity to be  treated  is
placed in the palm of the hand, and the  palladium
poAvder  very gradually  added.   It   requires  some
careful  rubbing with  the  fore-finger before the two
become incorporated,  when it should be divided into
smallish pellets,  and these rapidly carried, one after
another, to the cavity, each  piece being  Avell  com-
pressed, and rubbed into the irregularities of its walls
by  a  burnisher  or compressing-instrument."   Mr.
Coleman further states that this is probably the most
durable of all the  amalgams, but  the most difficult
to manipulate.  Its surface changes to a black color,
but, as  a rule, it does not stain  the structure of the
tooth.
  Palladium has  been used as a constituent in dental
alloys (amalgams), and when  added to a gold, silver,
and tin alloy it probably has about the same effect
as does platinum.   It has been  observed, hoAveA-er,
that dental alloys in Avhich it is a constituent blacken
  * Hitchcock on Dental Amalgams, page 33, Transactions of the New
York Odontological Society, 1874.
  1 Manual of Dental Surgery and Pathology, page 129. 
192             DENTAL METALLURGY.

to a greater  extent than when it  is omitted.   Mr.
Fletcher,* after a series of experiments, finally aban-
doned its use in dental amalgams.
  Silver and palladium unite in all proportions, form-
ing alloys Avhich  retain an exceedingly brilliant sur-
face.
  Gold and palladium, in  equal proportions, form a
hard, gray alloy.   Indeed, all the  alloys formed of
these two metals  are exceedingly hard.
  Palladium and  platinum form a hard alloy, which
fuses below the melting-point of palladium.
  It is quite probable that palladium, either alone or
alloyed Avith  other metals, might be advantageously
employed in prosthetic dentistry, but its high price
(about fifty dollars per ounce) practically excludes
it from the dentist's laboratory.
  Palladium enters into  combination with chlorine
(Pd Cl2),  oxygen  (Pd O  and Pd 02),  and  sulphur
(Pd S).
  Discrimination.—Mercuric cyanide is the chief test
for palladium.y  It precipitates a  yelloAvish-white
cyanide, soluble in hydrochloric  acid, which  is easily
reduced  by heat  to metallic palladium,  Avhen it  is
ready  for Aveigbing.
  * See chapter on "Amalgams."
  f There are other reagents employed in the discrimination of pal-
ladium,—sulphureted hydrogen, potash, ammonia and its carbonates,
ferrous sulphate, and stannous chloride.  Mercuric cyanide, however,
is the one generally  employed  in the quantitative estimation of pal-
ladium. 
CHAPTER XIII.
                  IRON.
Atomic Weight, 56.  Symbol, Fe (Ferrum).
 T I JON  is present  in nearly all forms of rock, clay,
    sand, and  earth.   It  is the most Avidely diffused
of the natural coloring ingredients, and its presence
may be  readily distinguished by the  color Avhich it
imparts.   It is found  in varying proportions in plants
and the  bodies of animals, the blood of the latter con-
taining about 05 per cent, of iron associated Avith its
coloring matter.
  Iron seems to have been known very early in the
world's history, and at a remote period instruments of
agriculture and war  were manufactured of it.*  Its
chief ores are  oxides,  carbonates, and sulphides.
Metallic ironf is met  Avith in nature in the meteorites
or metallic masses of unknown origin which occa-
sionally  fall to the earth.J  The carbonates and oxides
are the  ores  from Avhich iron  is  chiefly obtained.
Their  reduction—the oxides especially—is  exceed-
  * Archaeologists distinguish a bronze age in prehistoric times inter-
mediate between those of stone and iron.
  t Metallic iron, though of exceedingly rare occurrence, has been
found at Canaan, in Connecticut, forming a vein about two  inches
thick, in mica slate.
  I Isolated masses of soft iron, sometimes of large dimensions, have
been found upon the surface of the earth in South America; they are
supposed to have had a similar origin.
                         17             (193) 
191            DENTAL  METALLURGY.
ingly simple,  and consists in merely  heating them
in contact Avith  carbonaceous compounds, by which
means the metal is liberated.
  Properties.—Pure iron is Avhite in uolor, extremely
soft  and tough, and has a specific gravity  of  7-8.
Iron may be regarded as possessing a greater number
of valuable qualities than any other metal;  hence
it occupies the highest  place in the useful arts.  Al-
though possessing nearly twice as much strength as
the strongest of  the  other metals,  it is yet one of the
lightest, and  is therefore  peculiarly fitted  for use in
the construction of bridges, ships, etc.  It is rendered
so ductile by heating that it may be rolled into very
thin sheets or drawn into the finest wire; and  yet
at ordinary temperatures it is the least yielding of
the metals in common use, and may always be relied
upon to afford a rigid  support.   An iron  Avire one-
tenth of an inch in diameter is capable of sustaining
seven hundred and five pounds.  It is very difficult of
fusion, and before becoming liquid passes through a
soft  or pasty condition.  Pieces of iron pressed or
hammered while in this state cohere or Aveld together.
   The fusing-point  of  iron has been  estimated at
2900°  F.  It is soluble in nitric, dilute sulphuric, and
hydrochloric acids, but is not much affected by strong
sulphuric.   Chlorine, iodine, and bromine attack  it
readily.  Under certain circumstances it is not acted
upon by strong  nitric acid.  If a piece of platinum
wire be kept in  contact Avith it it will remain in this
acid for many Aveeks Avithout  being acted upon.  Its
crystalline form is supposed to be the cube.   When
rolled into bars or dra\vn into wire it possesses a fibrous
texture, upon the perfection of which much of its 
IRON.
195
strength and value depend.  It is the most tenacious
of all the metals.  At red heat iron decomposes Avater,
evolving hydrogen, and is changed  into the  black
oxide.  It is a strongly magnetic metal, but loses this
quality Avhen  heated to redness.
   Iron  does not oxidize in dry air at ordinary tem-
peratures,  and it  may  be immersed in Avater  from
Avhich the air has been carefully excluded without
change.  Contact  Avith a more elect ro-posithe metal
will also prevent oxidation.  Thus, fine steel instru-
ments are sometimes packed for exportation by avrap-
ping in thin  sheet-zinc.   For a  description of the
compounds of iron and the reagents employed in its
discrimination, the student is referred to FoAvnes's
" Elementary  Chemistry."
   The A^alue of iron does not depend alone upon its
physical properties, for it enters into a large number
of compounds Avhich are of great use in the arts, and
its chemical relation to  carbon is such that the addi-
tion of a small quantity of that  element  comrerts it
into steel, harder and more elastic than  iron, Avhile
a larger quantity of carbon produces cast-iron, Avhich
is so fusible that many useful  articles may be  made
of it by casting.
   Steel. — Herodotus  states  that among  the  most
precious gifts presented  by  the Indian monarch
I'orus to Alexander the  (Jreat Avas a pound of steel.
the value of which at that time  has  been estimated
at about two hundred dollars.  At a later period the
manufacture of steel in its application  to warlike
instruments Avas carried to a great state of perfection
in India and in the south of Europe.
  Steel differs from iron in possessing  the property 
196
DENTAL METALLURGY.
of becoming very hard and brittle, if, when heated
to bright redness,  it  is suddenly  cooled by being
plunged into water.  Steel is simply iron chemically
combined Avith the  precise amount of carbon  Avhich
will produce the condition referred to, together with
additional toughness.   It does not, however, become
decidedly steel-like  until the carbon  amounts to 03
per cent.   The hardest steel contains about 12 per
cent, of carbon, and Avhen that  amount is exceeded
it begins to assume the properties of  cast-iron.
  There  are two processes by  which steel may be
produced.  Bars of iron imbedded in charcoal powder
in a suitable crucible or chest made of  some substance
capable of  resisting the fire are, after several  hours'
exposure to heat, converted into steel,  the iron taking
up the requisite  amount  of carbon.   The  product
of this operation is called  blistered steel, and is far
from uniform,  either  in composition or texture, as
portions  of the bars thus  produced will be  found to
contain more carbon than others, and the interior to
be more or less porous. For the purpose of improv-
ing its quality the bars are cut into short lengths,
made up into bundles, heated to the welding-point,
and placed under a powerful tilt-hammer, which con-
solidates  each bundle into  one mass.   This is called
shear steel.
  Fusing and casting steel is another process for the
treatment of the blistered form, by which is produced
the best and most homogeneous  variety.  It consists
in fusing about thirty pounds of broken fragments of
blistered steel  in a plumbago  crucible, the surface
being protected from oxidation by glass melted upon
it.  When perfectly fluid the steel is cast into ingots, 
IRON.
197
and when it is desirable to form a very large ingot,
several crucibles are simultaneously emptied into the
same mold.   Cast-steel is  superior  in density and
hardness to shear steel, and is the form best adapted
to the manufacture of fine cutting-instruments.  It
is, hoAvever, somewhat brittle at red heat, and much
care and skill are required in forging it. The addition
to it Avhile fused of one part of a mixture of charcoal
and oxide of manganese affords a fine-grained  steel,
which may  be cast into a bar  of Avrought-iron in the
ingot mold, in order that the tenacity of the iron may
be an offset to the brittleness of the steel Avhen forged
together, Avhile it affords an economical compound  in
the manufacture of cutting-implements, the iron form-
ing the back and the steel the edge of the instrument.
  Ressemer* steel is produced by forcing atmospheric
air  into melted cast-iron.   The carbon,  which  is
oxidized more  readily than the iron, escapes in the
form of carbon monoxide, combustion of which takes
place on coming in coidact with atmospheric air, and
sutficient heat is thus generated to keep the tempera-
ture above  the  melting-point  of  steel during the
operation.   The current of air  is stopped as  soon  as
the decarburation has progressed far enough, when
a quantity of Avhite pig-iron, containing manganese,
is added to the fluid metal for the purpose  of assist-
ing the separation of gas from the melted metal.  It
is then read}' for casting.
  Hardening and Tempering.—Hardening of  steel  is
effected by subjecting  the object to extremes  of tem-
  * For other methods of producing steel, see Percey's, Phillips's, or
Makins's works on Metallurgy.
                        17* 
198            DENTAL METALLURGY.
perature.  The common practice is to first coat the
surface  of the metal with some carbonaceous sub-
stance, such as soap, to prevent scaling and oxidation
of the surface.   Ferro-cyanide of potassium has also
been used for surface-hardening.  This salt contains
cyanogen (C21S"2), a gas consisting of twelve parts by
Aveight  of carbon, and fourteen  of  nitrogen.   This
is  decomposed at the high  temperature  which  is
employed, and supplies carbon to the surface of the
metal.  This salt is, however, better suited to the pro-
cess known as case-hardening, while in re-tempering
dental instruments soap answers every requirement.
  The metal is next heated to the  point of full red-
ness, and themsuddenly plunged into  cold Avater, oil,
tallow, or mercury, or, in the case of small objects,
is  merely placed  on  a large piece of cold  metal.   It
is thus rendered very hard, while at  the  same time
it increases slightly in volume.
  If hardened steel be heated to  redness, and alloAved
to cool  slowly, it  is  again converted into soft steel,
but it may be proportionally reduced by heating  to
a temperature short of redness, the  proper point of
Avhich may  be ascertained by noting certain colors
Avhich appear on  the  ground or brightened surface
of a steel instrument when held over a flame.  This
discoloration is due to the formation of a thin film
of oxide, and as the temperature  rises the film be-
comes thicker and darker, and the instrument softer.
It is  therefore necessary to  plunge  the instrument
into a cold menstruum  the instant,the  color indicating
the desired  degree of  hardness  is reached.  The fol-
lowing  table indicates the tempering heats of various
instruments: 
IRON.                    199
Temperature.	Color.	Use.	
430° to 450° F.	Light yellow.	Enamel chisels.	1
470° F.	Medium yellow.	Excavators.	
490° F.	Brown-yellow.	Pluggers.	
510° F.	Brown-purple.	Saws, etc.	
520° F.	Purple.	Wood-cutting tools	
530° to 570° F.	Blue.	"When elasticity is	desired.
  In " letting doAvn " or tempering dental instruments
the flame of a spirit-lamp  may be  employed, the
instrument being placed in it; the flame should strike,
however, some distance from the cutting end, and
Avhen the proper color  reaches the end it should be
thrust into water.  Another very convenient means
of effecting the same result consists in heating an
iron bar to redness at one end, and then fixing it in
a vise.  The object to be tempered is placed in con-
tact with this until the  desired tint appears.
  Steel when fractured shows a fine silky appearance
of  the broken surface.  Overheating, hoAvever, de-
prives it of carbon, when the fractured surface pre-
sents a coarse granular condition, shoAving that it is
unfit for use for fine cutting-instruments.
  Case-hardening consists in conferring the hardness
of steel  upon the  external surface  of iron objects
Avhich are to be subjected to considerable Avear, such
as gun-locks, etc.,  and is accomplished by  heating
them  in some  substance rich  in carbon (such as
bone-dust,  cyanide of  potassium,  etc.),  and  after- 
200
DENTAL METALLURGY.
ward chilling in Avater.  The body of the piece  so
treated retains the toughness of iron.
  Malleable iron is produced by a process the reverse
of that employed  in case-hardening.  It consists  in
heating the object, usually made of cast-iron (Avhen
great softness and tenacity are required), for some
hours in contact with  oxide  of iron or manganese,
by which its carbon and silicon are removed.
  A steel instrument may be readily distinguished
from iron by placing a drop of nitric acid upon it, a
dark stain being produced upon steel by the separa-
tion of the carbon. 
CHAPTEPv XIV.
                 MERCURY.
Atomic Weight,  200.  Symbol. Hg (Hydrargyrum).

A TERCURY (quicksilver) has been known from a
      very early  period.   It is the only metal Avhich
is liquid at the ordinary temperature, but it becomes
solid at 39°  F. below zero.  It is frequently found in
nature  in the metallic state, and it is probable that
the first supplies  of the metal  were from this  source.
The ancients distinguished between such mercury and
that obtained by reduction from the ores  by desig-
nating  the native metal  as argentum vivum and the
reduced as hydrargyrum,—a fact which has led some
to doubt Avhether they were believed to be  the same
metal.
  The sources of mercury are cinnabar or mercuric
sulphide (the ordinary ore from which the metal is
obtained); horn quicksilver, or native calomel; native
amalgam  of siher and  mercury, sometimes found
trickling from crcwices in the ores.  It is also occa-
sionally found in  globules disseminated through the
native sulphide.
  Occurrence.—It  is found inconsiderable quantities in
Almaden in  Spain. Idria in Austria, and has recently
been found  in  great abundance and of remarkable
purity in California and Australia.  The metal is ex-
tracted from the sulphide at Idria by roasting the ore
                                      (201) 
202            DENTAL METALLURGY.
in a kiln, which is connected with an extensive series
of condensing-chambers  built of brick-work.  The
sulphur is converted, by the air in the kiln, into sul-
phurous acid gas,  while the mercury passes off in
vapor, and is condensed in the chambers.  The greater
portion of the mercury  of commerce is produced at
the Austrian mine at Idria, whence it is exported in
bottles  of hammered iron,  containing seventy-five
pounds each, in a  state  often nearly, though never
quite, pure.   It is, hoAvever, frequently, Avhen pur-
chased  in small quantities, adulterated with  tin and
lead, Avhich metals  do not materially modify its state
of fluidity.   The presence of debasing metals such as
these may be detected by scattering  a little upon  a
clean glass  plate, Avhen it " tails " or leaves  a track
upon the glass.  Lead,  which is its most frequent
impurity, may be removed by exposing the mercury
in a thin layer (in a broad, shallow dish) to the action
of nitric acid diluted with tAvo parts of Avater, which
should cover its surface and be allowed to remain in
contact with it for several days, with occasional stir-
ring.  The lead is thus oxidized by the acid, and after
digestion may be washed aAATay.
  Distillation is the  means  most frequently recom-
mended for the purification of mercury, but it is now
regarded as an uncertain one, since, if zinc or bismuth
be  present, they will  be  sure to distil over into the
receiver Avith the mercury.
  In distilling or redistilling mercury a strong glass
retort should be used, in size corresponding Avith the
quantity of the metal  to  be operated upon,* and

  * In quantities exceeding two or three  pounds iron retorts are
employed. 
MERCURY.
203
filled  one-third with  mercury, upon the surface of
which is placed a layer of clean iron  filings.  The
retort  should  be  imbedded in a  sand-bath, Avith the
neck  made to incline so as to dip beloAv the surface
of the water, with Avhich the receher  is half filled;
and, in order to facilitate condensation of the metallic
vapor, the  receiver should  be  surrounded by cold
water.  Should  there be a film  of oxide  upon the
surface of the distilled mercury  a  small quantity of
hydrochloric acid will dissolve it, Avhen the mercury
may be Avashed and dried  at a moderate heat.   An-
other  and  better  method  is to  substitute coarsely-
powdered cinnabar for the iron filings.  The sulphur
liberated  from the  former converts foreign  metals
into sulphides, Avhile the mercury present is liberated.
  Probably the most certain means of obtaining mer-
cury free from admixture of other metals is to operate
upon one of the salts of mercury ; as, for instance, the
red oxide, the bichloride  (corrosive sublimate), or
pure  vermilion.  These  are readily decomposed by
heat,  and Avhen the red oxide is employed, simple dis-
tillation is sufficient.  Should the metal after distilla-
tion show  a film of oxide, the latter may be easily
removed Avith very dilute nitric acid slightly warmed.
Where vermilion or the chloride is to be reduced, the
distillation Avill be greatly  facilitated by the addition
of one part of lime.
  It is important that  the mercury employed for
dental purposes should be  quite pure, and doubtful
specimens  may be effectually freed of the presence
of the adulterating  metals named by  the  folloAving
very simple means:  A small amount  of mercurous
nitrate is dissolved in water, and into this the impure 
204            DENTAL METALLURGY.
mercury is placed.   The salt will be decomposed,
the adulterating metals oxidized,  and they will  be
replaced by  the  mercury  of the salt.  The same
result may also be attained by digesting in a solution
consisting of one part of nitric acid and eight parts
of water for several  hours at a temperature of 130°
or 140° F.  The mercury should be placed in a flask
or glass dish Avith a broad, shallow bottom, and Avill
require frequent shaking or stirring.  The dilute acid
has little or no effect upon the mercury, while it
readily dissolves and combines Avith the impurities.
  Another very simple means,  said  to  have  been
devised by Dr. Priestley, has frequently been em-
ployed in purifying mercury.  It consists in placing
the metal Avith some fine-ground loaf-sugar in a bot-
tle, Avhich, after being securely corked, is vigorously
shaken for a short time; it is then opened and air
blown in by means of a bellows; again stopped and
shaken as before, and, after repeating this treatment
three or four times, the mercury is filtered through
a cone made of smooth paper, A\ith a fine pin-hole at
its apex.  The sugar, to Avhich the oxides of  foreign
metals adhere, remains behind.
  The method of  filtering mercury through chamois-
leather is to most dentists a familiar means of exclud-
ing a superabundance  of mercury from amalgams,
but is not to be relied on as  a means of affording pure
mercury.
  Properties.—As before stated, mercury is fluid above
a temperature of —39° F.   Below that  point, how-
ever,  it solidifies, and may be hammered or welded
like other metals.  During solidification it contracts
and exhibits  octahedral crystals.  When pure, the 
MERCURY.
205
 fluid metal is exceedingly lustrous.  It boils at about
 660° F.   It  is volatile even at the  ordinary tem-
 perature, and  this property is greatly increased by
 heat.  There  have been  curious illustrations of the
 disposition to assume a state of A^apor  which  this
 metal  evinces.*  It is readily soluble in strong nitric
 acid, but is dissolved in sulphuric acid only by the
 assistance of  heat.  Hydrochloric acid has no effect
 upon it.
   When shaken in air, or rubbed with grease, turpen-
 tine, or other substances, such as sugar,  chalk, etc.,
 mercury  loses  its  metallic  appearance, and  is con-
 verted into a gray mass, as in mercurial ointment,
 etc.  This was formerly regarded as an oxidation of
 the  metal, and the belief was probably  favored by
 the  fact that  mercury, in  a  state of fine division,
 becomes active for therapeutic purposes.  The micro-
 scope,  however, has revealed that such preparations
 are  composed of metallic  globules of about 7-^5- of a
 line  in diameter.
   Mercury amalgamates more or less readily with
 gold, silver, tin, zinc,  lead, bismuth,  cadmium, potas-
 sium, etc., and with a greater degree of difficulty with
 platinum, palladium, and copper.  In some instances
 combination between mercury and other metals takes
 place  with considerable  violence, as in the case of
 potassium,  in which  light  and heat are  developed.
 Many  of the amalgams become solid and  crystalline,
 as illustrated  in dental amalgams, and for the most

  * Burnet relates an instance in which some mercury in leather bags,
forming  part of the cargo of  a ship, escaped into the bilge of the ves-
sel.  An elastic fluid was soon evolved, which covered  every metallic
article on board, while the crew, to a man, were salivated.
                        18 
206
DENTAL  METALLURGY.
part they may be looked upon as definite compounds.
Indeed, a native compound of mercury and silver has
been  found crystallized in octahedrons and  other
forms of the regular system.  The liquid amalgams
are probably in many instances  solutions of definite
compounds  in an excess  of mercury; if these are
pressed through ehamois-leather the mercury is ex-
cluded, carrying with it but a small portion of the
other metals, while a solid  amalgam, frequently  of
definite atomic constitution,  remains behind.
  Compounds.—Mercury unites with oxygen to form
mercuric and mercurous oxides,  both of which are
highly poisonous.  With chlorine it forms two com-
pounds, mercuric chloride (Hg Cl2), commonly called
corrosive sublimate, and mercurous chloride (Hg2 Cl2),
familiarly known as calomel.  With sulphur, however,
mercury combines to form sulphates and sulphides.
Of the latter we have  mercuric  sulphide (Hg S), a
compound of far greater interest  to dentists than any
other of the salts of mercury,  in consequence  of its
extensive use as a coloring  pigment in vulcanizable
rubbers and celluloid.   It is  the most common ore  of
mercury, and, as  such, is termed cinnabar;  Avhen
produced artificially it is known as vermilion.   The
best quality of the latter is produced by the Chinese.
Their process  of manufacturing, for a long time a
secret, consists  in  stirring a mixture of one part of
sulphur and seven parts of mercury in an iron pot;
chemical union takes place,  the result of the combi-
nation being a black powder.  This is divided into
small lots, which are emptied separately into suitable
subliming pots, heated to redness. When a sufficient
quantity has been placed in the pots they are covered 
MERCURY.
207
up, and the  heat  is continued for thirty-six hours,
with occasional stirring by means of an iron rod passed
through the lid.  Lastly, the pots are broken, and the
vermilion adhering  to the upper portions  levigated
and dried.   It may also be formed by rubbing three
hundred parts of mercury with one hundred and four-
teen parts of flowers of sulphur,  moistened with a
solution  of  caustic  potash.  The resulting product,
which is  black, is then  digested at about 120°  F.,
with seventy-five parts of hydrate of potash and four
hundred of  water, until it acquires a fine red color.
   Vermilion may be adulterated  Avith red lead,  di-
sulphide of  arsenic  (As2 S2), ferric oxide, brick-dust,
or any cheaper substance of a similar color; and the
discomfort sometimes caused by wearing vulcanized-
rubber artificial dentures may be in part due to the
presence of such deleterious substances as the arsenic
and lead salts referred to.
   Vermilion is an inert  mercurial  compound,* and
is quite insoluble in  either nitric, sulphuric, or hydro-
chloric  acid.  It is  unaffected by  water, alcohol, or
the alkalies.  Nitro-hydrochloric acid (aqua regia),
hoAvever, dissolves and converts it into corrosive sub-
limate (Hg CI,), and by exposure to a temperature
of 600° F. vermilion is decomposed, and  the reduced
metal may be collected in glolmles by condensing the
vapor.
   Pure vermilion, in combination with rubber, is not
likely to produce deleterious effects when worn  in
the mouth, nor is it  probable that this compound can
  * In the less civilized countries the ancients used cinnabar to paint
their bodies, without any bad effects.  Makins, p. 128. 
208
DENTAL METALLURGY.
 be decomposed chemically and converted into a poi-
 sonous salt of  mercury  by mere  contact with the
 saliva.   The mechanical dentist will,  hoAveATer, do
 well to avoid  the use of nitro-hydrochloric acid in
 removing tin foil from the surface.
   Regarding the presence of free mercury in rubbers
 before or after vulcanizing, Prof. Austen stated that
 the researches of Prof. Johnston with the microscope,
 and Prof. Mayer by chemical analysis,  failed to dis-
 cover  the slightest  trace in samples  of that Avhich
 had been used by him for several years.   Prof. Wild-
 man observed  that  sulphur sublimed during vulca-
 nization, but did not find the smallest  trace of free
 mercury.*  Prof. Austen failed by any mechanical
 force to press  out any metallic globules, and during
 his entire experience with indurated rubber as a base
 for artificial dentures never, evTen with the microscope,
 detected the slightest particle  of metallic mercury
 upon the surface of  any finished piece.
   If it is true, as some assert, that free  mercury has
 occasionally been observed in rubber, then its presence
 must have been due to the use of an imperfect quality
 of vermilion;  but that the latter, when  pure, is ever
 reduced during the process of vulcanizing, or by wear-
 ing in the mouth, is  not at all probable.
   The modified condition of that portion of the sur-
face of the mouth in contact with the rubber plate,
often  accompanied  by a  sensation of heat, has  been
attributed to an electrical action, due to  the fact that
rubber, "like   sealing-wax,  is a powerful negative
electric."f
     * Harris's Principles and Practice of Dentistry, p. 682.
     f Ibid, p. 681. 
MERCURY.                  209
   The real solution  of the question, however, will
probably be found in the following conditions : 1st.
The non-conducting  quality of the  substance.  2d.
The rough condition  of the surface, due to careless-
ness or want of skill in construction.  3d.  Want of
care on  the part of  the wearer,  in  not  frequently
cleaning the piece of portions of food and the secre-
tions of  the  mouth, which are likely to  undergo
chemical change by long confinement in contact with
the tissues, and thus become irritants.
   The author  has  frequently noticed this  inflamed
condition Avhere  the  denture was of gold or silver,
but always in cases where the plate  Avas  seldom re-
moved  or cleansed.  It is  true, however,  that the
trouble referred to is  more common in rubber- or cel-
luloid-work ; but in  both of these there are  more
conditions favoring such a result than are found in a
metallic denture.   The  fact that the symptoms are
not constant, and that by far the greater number of
mouths in Avhich rubber  or  celluloid is worn are
not in the least affected by it, would seem to confirm
this view.
   Discrimination.—The  presence of the soluble salts
of mercury may be detected by Reinsch's test,* which
consists in placing a clean strip of copper in  the solu-
tion; metallic mercury will be immediately deposited
upon it, giving it a sihery-white  appearance.  The
strip of copper is then  heated in a glass tube, by which
the mercury is sublimed, and may  be  detected in the
form of minute globules adhering to the sides of the
tube after condensing.
'■• See works on Chemistry.
        18* 
210
DENTAL METALLURGY.
  Insoluble compounds of mercury may be detected
by placing a small portion in a glass tube and cover-
ing with a layer of dry sodium carbonate, and then
heating.   If mercury be present it will separate and
condense in  globules  in  the cool parts of the tube.
This test is based on the fact that all mercurial com-
pounds are decomposable by a temperature of ignition.
  Mercury is also precipitated from its soluble combi-
nations by a solution  of stannous chloride  used  in
excess.
  Hydrogen sulphide  and ammonium sulphide pro-
duce in solutions,  both of mercuric and mercurous
salts, black precipitates insoluble  in ammonium sul-
phide.   The quantity of the reagent should  be suffi-
cient to produce complete decomposition; otherAvise a
white precipitate will  be formed, consisting  of mer-
curic sulphide, with the original salt.   An excess of
hydrogen sulphide, however, instantly turns  the pre-
cipitate black.   This reaction is regarded as charac-
teristic of mercuric salts.
  Caustic potassa  or  soda, Avhen added to solutions
of mercuric salts, produces a yellow precipitate.
  Ammonia or ammonium carbonate produces a white
precipitate insoluble in excess.
  Potassium or sodium carbonate causes a red-brown
precipitate.
  Potassium iodide throws down a bright scarlet pre-
cipitate, soluble in excess either of the mercuric salt
or of the alkaline iodide. 
CHAPTER XV.
               COPPER.
Atomic Weight, 63-4.  Symbol, Cu (Cuprum).
/COPPER is a metal with which mankind has been
     acquainted from the  most remote periods, and
probably the first metallic compound employed Avas
copper  alloyed Avith  tin (bronze), of which many
relics in the form of  arms, ornaments, and  domestic
implements, evidently belonging to an early period
in prehistoric times,  are still  to be found.*  It is
probable, however, that the production  of  the pure
metal is an operation  of a more recent date.
  Copper ores are  found in many parts of America
and Europe.  In some parts of the United States the
nati\re metal is found  in immense masses many hun-
dred  pounds in  weight, sometimes  slightly inter-
mixed Avith silver.  Nothing is certainly known of the
origin of these, but they are supposed to have been
formed  from the cupric sulphide,  Avhich, by  exposure
to air and moisture, Avas converted into sulphate, and
then, by electro-chemical agency, reduced to the me-
tallic state.
  There are several ores which yield copper.  The
one most commonly  employed, however, is  copper
  *The epoch marked by the use of bronze is known in archaeological
chronology as the Bronze Age.
                                      (211) 
212
DENTAL  METALLURGY.
pyrites, a combination of sulphide of copper and iron.
  The blue and green carbonates, known respectively
as azurite and malachite, are beautiful minerals, exten-
sively used in Russia and Bohemia in the manufac-
ture of  ornamental objects.  They contain upwards
of fifty  per cent, of copper.
  The process of obtaining copper from an ore. such
as copper pyrites, may be thus briefly described: The
ore is heated in a reverberatory furnace for the pur-
pose of converting the iron sulphides into oxide.  The
copper,  which remains unaltered, is then heated Avith
a silicious sand, which combines with the iron oxide
to form a slag, and separates from the heaAier (copper)
compound.  By repeating  this  process the  iron  is
finally got rid of, when the copper sulphide begins  to
decompose in  the  flame-furnace,  parting Avith  its
sulphur and absorbing oxygen.  The resulting oxide
is. hoAAever, reduced by the aid of carbonaceous mat-
ter and  a high degree of heat.
  Properties.—Pure copper maybe obtained by decom-
posing a solution of pure sulphate of copper  in the
galvanic current.  If the negative wire be attached
to a copper plate immersed in the  solution, the pure
metal will  be deposited on it, and may  be  readily
stripped off.
  The chief A'alue of copper in the useful  arts is due
to its great malleability, in which quality it  is onfy
exceeded by gold and silver.  It  fuses at about 2000z
F.  It expands in solidifying, and absorbs oxygen very
much in the same manner as silver does under similar
conditions.  In tenacity copper ranks next to iron, and
a copper wire  of one-tenth of an inch in diameter
Avill support  about  385  pounds.   Its poAver of con- 
COPPER.                  213
 ducting electricity is nearly equal to  that  of silver,
 while in the transmission of heat it is  surpassed only
 by silver and gold.   It is readily soluble in nitric
 acid, but in sulphuric acid only Avith the assistance of
 heat.  Hydrochloric acid  attacks it slowly, and in
 vacuo is inactive.  The specific gravity of  copper is
 8-93.  For  the compounds  of copper  Avith  the  non-
 metallic elements the student is directed to FoAvnes's,
 Bloxam's, and other works  on chemistry.
   Alloys.—Copper  does not readily unite with  mer-
 cury Avithout the assistance of heat.   There is, hoAv-
 ever, an amalgam of pure  copper and mercury ex-
 tensively used in Europe under the name of Sullivan's
 amalgam.   Its preparation is as folloAvs: Pure copper
 in a finely-divided state is obtained by boiling a con-
 centrated solution  of cupric  sulphate with  distilled
 zinc until the blue  color of  the salt disappears, when
 the zinc should be removed.  The copper, which will
 be found in a pulverulent mass at the bottom of the
 vessel, should be washed with dilute  sulphuric acid,
 subsequently in  hot distilled Avater, and dried.  It is
 then moistened Avith a solution of nitrate of mercury,
 by  Avhich  means  the  copper becomes completely
 coated with mercury.  The mercury  is then added
 to it to  the extent of twice  the weight  of copper
 (3 of copper to 6 of mercury).  It is then rolled into
 small,  lozenge-shaped pieces, which  become quite
 hard, and are supplied to  the profession in bottles
 containing an ounce  or more.  This amalgam pos-
 sesses the property of softening with heat and again
 hardening, and when employed as a filling-material
one of the lozenge-shaped pieces  is placed in a small
iron spoon made and sold for the purpose, and heated 
214
DENTAL METALLURGY.
over the flame of a spirit-lamp until small globules of
mercury are  driven to the surface, when it is placed
in a small glass or porcelain mortar and rubbed into
a smooth  paste.  Some recommend washing Avith a
Aveak solution of sulphuric acid, or soap and water,
and lastly with clean water alone, to remove the last
traces  of either acid or soap, and finally squeezing
through chamois-leather to exclude  surplus of mer-
cury, when  it  is ready to be introduced into the
cavity.  It requires several hours to  harden.
  Mr. Fletcher says of this amalgam  that " it is an
absolutely permanent filling, as the copper salts per-
meate  and perfectly preser\Te  the tooth."   It is said
to be quite  insoluble in the mouth.   It,  however,
becomes intensely black, and  imparts  a most  objec-
tionable stain to the teeth.
  Copper  unites readily with all other metals, and
many of the resulting alloys are of great value in the
industrial  arts—of  even more value than  the pure
metal.   It is  added to silver for the purpose of con-
ferring sufficient hardness upon the latter to enable
it, in the  form  of coin or plate, to withstand the
attrition to  Avhich such articles are exposed.   The
formation of a perfectly uniform alloy of siher and
copper is a process  attended with some uncertainty,
owing  to  a  tendency on the  part of the copper to
separate and pass off toward the edges as the ingot
solidifies.  Thus, in  silver coins one portion  of the
piece will frequently be found to contain more copper
than another.
  The  decimal proportions of copper  and silver in
standard silver (coin) of several different nationalities
are as  follows: 
COPPER.
215
Of the United States	silver 900,	copper 100.
" France ....	" 900,	" 100.
" England ....	" 925,	" 75.
" Indian rupees	" 947,	" 53.
" Germany—Prussian thalers	" 811,	" 189.
" Prussian silver groschen	" 283,	" 717.
  The properties conferred upon gold by the addition
of copper are similar to those produced upon silver.
These have already been  alluded to  on page  170.
The decimal proportions  in  the  gold coins  of the
United States, France, and Holland are:  gold, 900;
copper, 100; Avhile  English coins are composed of
916-6 of gold and 83-3  of copper.  In coin-gold mal-
leability is not greatly interfered Avith.  Gold may,
hoAvever,  be rendered brittle by  large amounts of
copper, or Avhen the latter is impure.
  Copper and platinum form an alloy, Avhen the pro-
portions are equal, of nearly the same specific gravity
and color as gold.  Copper also unites with palladium
to form a light, brassy alloy. By admixture Avith lead
or bismuth copper  is  rendered quite brittle.  The
principal alloys in which it forms a leading ingredient
are brass, bronze, and German siher.
  Aluminium bronze is formed of pure copper Avith
from Iavo  and a half to ten per cent, of aluminium.
It is quite  malleable,  and  has  a  fine,  rich,  golden
color.   Phosphor-bronze  is copper  combined Avith
from three to fifteen per cent, of tin and from one-
quarter to two and  a  half per cent, of phosphorus.
Other metals, such as silver, nickel, cobalt, antimony,
and  bismuth, frequently enter into the composition
of bronzes.
  Copper  in small  quantities (from five to seven per 
216
DENTAL  METALLURGY.
 cent.) is said by Mr. Fletcher to confer upon amalgams
 the quick-setting property obtained  by the  addition
 of platinum.  It is, hoAvever, considered inferior to
 platinum  as  a constituent in dental alloys; but in
 the absence of platinum, amalgams are improved by
 the addition of a small proportion of copper.
  It is stated* that an  alloy of tin 10, silver 8, gold
 1, copper  1, has been extensively used  (in England
 probably)  under the  names of gold amalgam  and
 platinum amalgam.
  Hydrogen sulphide (H2 S) and ammonium sulphide,
 when added to a copper solution, afford a brownish-
 black cupric sulphide.
  Caustic potash throws down a pale-blue precipitate
of cupric hydrate, which changes to blackish-brown
anhydrous oxide on boiling.   Ammonia also gives
a blue precipitate, soluble in excess, affording a  deep
purplish-blue solution.
  Potassium ferrocyanide gives a red-broAvn precipi-
 tate of cupric ferrocyanide. It may also be detected
in very weak  solutions  by placing a  drop on a slip
of clean platinum foil.  A point of zinc is then placed
in so  as  to touch the foil, and instantly a spot of
reduced copper appears.
  A green  line is imparted  to the oxidizing flame of
the blow-pipe when a copper salt is heated in it.  It
also communicates a green tint to borax when heated
Avith it.
  There are several methods which may be advan-
tageously  employed for  the estimation of copper.
The operations of the dentist,  however, are chiefly
*' Fletcher. 
COPPER.
217
confined to  the examination of  amalgam  alloys.
The alloy should first be acted upon by nitric acid;
silver, if  present, may  then be  recovered  in  the
form  of chloride; after which  the copper may be
precipitated  from the remaining  solution either as
oxide, sulphide,  or  in the  metallic state.   Before
attempting the estimation of an alloy,  a  qualitative
examination should  first  be made (page  61), and
if the solution to be examined is found to contain no
other metal  whose oxide is thrown down by  caustic
potassa, an excess of that agent is to be added.  In
the resulting precipitate, Avhen boiled, Avashed, dried,
and Aveighed,  every  one   hundred  parts  may  be
estimated as containing 7985 per cent, of metallic
copper.
   When hydrogen sulphide or  ammonium  sulphide
is employed as  the reagent, the resulting  cupric
sulphide is usually oxidized by nitric acid, and again
precipitated  ly potassa, so as to estimate as oxide.
   The estimation as metallic copper is accomplished
as follows : Place in the solution contained in  a plati-
num  dish a piece of zinc, adding also a little hydro-
chloric acid.  The  electrolyzing action instantly
commences, and continues  until the solution is color-
less and the zinc completely dissolved.  The finely-
divided metallic copper will be  found at the bottom
of the vessel.  This is to be Avell Avashed, dried, and
Aveighed.
19 
CHAPTER XVI.
             ZINC.
Atomic Weight, 65-2.   Symbol, Zn.
H^HE  ancients Avere undoubtedly acquainted with
    an ore (probably cadmia*) which they employed
with copper to form brass.  Many objects  of ancient
manufacture, analyzed at different times, have been
found to contain zinc.f   The extraction of the metal
itself, however, is probably a modern discovery.
  Metallic  zinc is never met with in nature.  The
principal ores  are  the red oxide—the sulphide of
zinc (blende) and the native carbonate (calamine).
The latter is the most valuable of the zinc ores, and
is preferred for the extraction of the  metal.  It is
first roasted to expel water and carbonic acid; then
mixed with fragments of coke or charcoal, and  dis-
tilled at a full red heat in an earthen retort.  Carbon
monoxide escapes, while the reduced metal volatilizes
and is condensed by suitable means.
  Properties.—Zinc is a brittle, crystalline metal, with
a density varying from 6*8 to 7-2.  Until  about  the
commencement of the present century the valuable
property possessed  by this metal, of becoming quite
  * An ore used by the ancients, containing cadmium and zinc.
  f Phillips made a number of analyses of such objects, all of which
contained zinc.
      (218) 
zinc
219
malleable betAveen 248° and 302° F.,* Avas not known;
hence, prior to that discovery it was but little used
in the industrial arts.   Zinc fuses at 773° F. (below
red heat).  At a bright red heat it boils and vola-
tilizes, and if heated in air combustion takes place,
during which it unites with the atmospheric oxygen,
Avith  brilliant incandescence.   At 410° F. zinc is so
brittle that it may be powdered in a mortar.
   Alloys.—With mercury zinc forms an exceedingly
brittle amalgam.  The tAvo combine in the cold state,
but union is greatly facilitated by heating.  Zinc is
occasionally employed  as a constituent  in  dental
alloys.  An amalgam has been suggested, the propor-
tions of Avhich are  "approximately"  given as,  tin,
50 odd;  silver, 30;  gold, 5 to 7;  zinc, 2 to 4; but as
to Avhat  property  is conferred by the zinc  in  the
formula Ave are, unfortunately,  not informed.
   Added to silver, in the proportion of 2 of zinc to 1
of silver, a nearly white malleable a^loy results.
   The color of gold is heightened by the addition
of zinc, Avhile its  malleability is greatly impaired.
Makins  states that gold  rendered standard by zinc
is a  greenish-yelloAV,  brittle alloy, with a specific
gravity above the mean.
   Combination between zinc  and platinum or  pal-
ladium may be effected at a comparatively Ioav tem-
perature, and is accompanied  by evolution of light
and heat.  It is stated that an  alloy of 16 parts of
copper, 7 of platinum, and 1 of zinc closely resembles

   * Between 120° and 150° C. (248° and 302° F.) zinc may be rolled
or hammered without the least  danger of fracture.  Sheet-zinc of
commerce is manufactured by this means. After being treated in this
way, it retains its malleability when cold. 
220
DENTAL METALLURGY.
16-carat gold,  is quite malleable, does not tarnish in
air, and is capable of resisting cold nitric acid.
  Zinc and  lead  mix Avith each other to a very lim-
ited extent.   If equal parts of the two metals are
melted together  and allowed to  cool, they will be
found to have separated into tAvo layers, the upper,
and consequently the lighter one, zinc, retaining 1-2
per cent, of the lead, while the lower layer consists
of lead alloyed Avith 1-6 of zinc.  The necessity of
carefully keeping these tAvo metals separate in all
molding operations  in  the dental  laboratory  will
readily be  appreciated, as a failure  to  observe pre-
caution in  this direction  will be followed by vex-
atious consequences.  If by accident lead becomes
mixed with zinc, the  lead, by  its  greater specific
gravity, will  settle to  the bottom  and  fill  up the
deepest portions of  the sand matrix,  representing
the alveolar ridge,  the  most prominent  portion  of
the  die.   This  may  not be  discovered until an
attempt to swage is made,  when the  die will be
found  to be totally unfit for the purpose.  In such
cases the mixed metal should be discarded and new
zinc substituted.
   Zinc and tin unite in all proportions Avithout diffi-
culty.   Alloys of zinc  and tin are  frequently em-
ployed in casting dies for  swaging plates. Richard-
son* gives a formula for an alloy consisting of zinc,
4  parts;  tin,  1 part;  which, he states,  fuses  at  a
lower temperature, contracts less in  cooling, and has
less surface-hardness than zinc.   Fletcher, however,
states  that  all alloys of zinc and tin are  superior to
* Mechanical Dentistry, p. 142. 
ZINC.
221
zinc alone for dies.  The impression from the sand
he believes  to be much finer, and the shrinkage in
cooling greatly reduced.  Zinc 2, tin 1, is given as the
best proportion.*  Makins states that zinc and tin,
when combined in equal proportions, form a white,
hard  alloy,  not very malleable or ductile, which  is
capable of being worked as readily as brass.
  Zinc and copper unite in various proportions to
form  many different grades of brass, known respect-
ively  as  pinchbeck,  Manheim  gold, similor, Bath
metal, Prince  Rupert's metal, Muntz's sterro, Gedge's
and Aich's metals.  German silver and the Chinese
alloys known as pacfong and tutenag are also alloys
of zinc and copper, Avith the addition of nickel.
  Dies  and Counter-Dies.—Zinc  is  the metal  most
commonly employed in  the formation  of  dies for
SAvaging plates, and is superior  to any of its alToys.f
Another  important  application  of  zinc is  in the
formation of counter-dies.  The die is placed  in the
iron ring when  a Bailey flask is employed,  or  in-
vested in the  molding-sand and then  surrounded by
a suitable iron ring in  the old-fashioned way.  The
zinc is then heated and poured in upon the zinc die
just at  the  moment of complete  fusion.   Should
the metal be accidentally allowed to  remain in the
fire too  long, and thus  reach a higher temperature
than  is necessary, it should not  be poured until  it
begins to solidify at the edges.  The belief seems to
be pretty general that melted zinc cannot be poured
  * Practical Dental Metallurgy, p. 69.
  f The author has not found the alloys of zinc and tin to be, in any
respect, superior to zinc alone for dies.
                        19* 
222
DENTAL METALLURGY.
upon a zinc die Avithout causing cohesion,* but if the
necessary precaution regarding the proper tempera-
ture at which the, metal  is poured is observed  it is
impossible for union to take place,  and Avhen  cool
the die and counter-die will separate quite as readily
as though the latter was of lead.   It seems strange
that this valuable expedient for the dental laboratory
has not found a place in the text-books on mechanical
dentistry.  It frequently occurs that the zinc die and
lead counter-die are totally inadequate to bring a plate
(particularly if the latter is of platinum-gold or irid-
ium-platinum) into perfect adaptation to all parts of
a model,  especially where the  palatal arch  is  very
deep and the rugse prominent.
  The zinc counter-die  is also of  especial service in
partial cases where a number of teeth remain.  These
are cut off from  the  plaster model previous to mold-
ing within one-sixteenth of an inch of the margin of
the  gum, so that a sufficiently distinct impress  may
be made in the plate to serve as a guide in filing the
latter to fit around the natural teeth.
  Where the  swaging is likely to be attended  with
difficulty, at least three sets of dies and  counter-dies
should be made.   The most imperfect of these should
be furnished with a  lead  counter-die, and used  as a
preliminary die upon Avhich to start the plate.   The
next in quality may be used with the zinc counter-die,
and the nearest perfect of the three, Avith a lead coun-

  * If the melted metal be  poured, at a temperature of 800° F., upon
a die having a temperature of 70° F., the fused zinc, by contact with
the iron ring and  by radiation, will lose heat enough to cause its tem-
perature to fall far below the fusing-point, and it will probably not
impart to the die more than 400° F. 
ZINC.
223
ter, reserved as a finishing-die.  When the plate, by
means of the horn or wooden mallet and some prelimi-
nary SAvaging with a light hammer, has been made to
assume  somewhat the form of the die, and has been
carefully carried past  the  stage Avhen pleating or
wrinkling of the plate is likely to occur, it should be
trimmed to the proper dimensions, annealed, and
placed betAveen  the  die  and zinc counter-die, and at
first gently tapped with a hammer until the die passes
Avell into the counter-die,  when one  or  two sharp
blows Avith a heaAy hammer, either upon the die or its
counter, will carry the plate into perfect  adaptation
to all parts  of the former.   Some slight compression,
however, of the prominent points of the die is likely
to occur in the use of the zinc counter, so  that it will
be necessary to anneal and gh^e the plate tAvo or three
sharp blows between the finishing-die  and its  lead
counter-die; after Avhich it  will be found to perfectly
tit the  mouth, Avithout  any attempt to compensate
for contraction of the zinc.*  It Avill be seen that the
zinc counter-die is not intended  to supersede, but is
merely  used as  an adjunct to, the lead counter, and
there is probably no  better means  of  carrying  the
plate to the deep parts  of the model, and of obtain-
ing a sharp, Avell-defined impress of the  rugae and
prominent parts of the model.
  Zinc  will, under favorable conditions,  unite Avith
iron, and it frequently attacks the cast-iron ladle in
Avhich it is  melted, and  may  penetrate the side and
escape  into the fire.  Accidents of this kind,  Iioav-
  *The subject of shrinkage of zinc when used for dies in forming
metallic plates has been fully referred to on page 21. 
224
DENTAL METALLURGY.
ever, may be avoided by coating the inside of the
ladle with Avhiting.
   Compounds of Zinc.—The oxide and the chloride are
the compounds of this metal most frequently employed
by dentists.  The first forms the chief ingredient in
the  plastic filling-materials  known  as oxychlorides
and oxyphosphates.  Zinc oxide is  a Avhite  poAvder,
the product of the combustion of the metal.   It turns
yellow on  heating, but resumes its pure white color
on cooling.  Chloride of zinc, prepared by acting
upon the metal with hydrochloric acid, or by heating
metallic  zinc in chlorine, is a  fusible, deliquescent
substance, quite soluble in water and alcohol.
   Oxycbloride of zinc, the Avell-known filling-mate-
rial, consists of a poAvder and a fluid.  The first is
prepared by various formulae.   One  in common  use
is  as folloAvs : Grind together in a mortar, borax, two
grains;  fine  silex, one grain;  oxide ,of zinc, thirty
grains.  When thoroughly mixed these are placed in
a small crucible and heated to bright redness.  This
is  called the frit, and  when cool requires grinding
to again reduce it to a pulverulent state.  It is then
thoroughly mixed  with  three times  its weight of
calcined oxide  of zinc.  The fluid usually employed
Avith the powder consists of  chloride of zinc diluted
Avith Avater in the following proportions : Deliquesced
chloride of zinc, one ounce;  water, five or six drams.
The oxyphosphate poAvders are similar  mixtures.*

 * Oxide of zinc, two hundred parts; silex, eight; borax, four; ground-
glass, five, levigated under water to insure complete admixture, then
dried by evaporation, calcined at a white heat, and pulverized, has
been found to be equal in durability and working qualities to any of
the numerous oxyphosphates now in the market. 
ZINC.
225
The fluid, however, is prepared by dissolving in pure
water some glacial phosphoric acid, and then evapo-
rating until the solution attains the consistence of
glycerin.
  The presence of zinc in  solution is distinguished
by  the folloAving reactions:  A  Avhite  precipitate
soluble  in  excess of the alkali is obtained by  the
addition of caustic  potash,  soda,  or  ammonia, and
zinc is distinguished from all other metals ly ammo-
nium sulphide, which precipitates Avhite  sulphide of
zinc, insoluble in caustic alkalies. 
CHAPTER XVII.
          CADMIUM.
Atomic Weight, 112.   Symbol, Cd.
 /CADMIUM, a metal closely allied to zinc, was dis-
      covered by Stromeyer and Hermann in 1817.
 It does not occur in the metallic  state, and there is
 only one  definite mineral known  Avhich  contains it
 in  quantity, namely, the  sulphide, or greenockite,
 which is found in Renfrewshire, England.  This con-
 tains 77-7 per cent, of cadmium and 22-3 per cent, of
 sulphur.
   The production of cadmium is confined to  a ATery
 few localities in Belgium and England.  It occurs in
 zinc blende to the extent of about 0-2 per cent.  In
 the calcination of the blende the cadmium, volatilizing
 at a loAver temperature than the zinc, passes off before
 the latter assumes the form of vapor.  The oxide of
'cadmium is collected in condensing-tubes, and is sub-
 sequently reduced  to the metallic state  by heating
 with carbon.
   Cadmium is a white  metal,  with a slight bluish
 tinge.  It is somewhat  lighter in  color than  zinc or
 lead.  It  is susceptible of a high polish.  It has the
 fibrous fracture characteristic of soft, tough  metals.
 It  differs  from  zinc in its  crystalline form,  that of
 cadmium being the octahedral, while that of zinc is
       (226) 
CADMIUM.
227
rhombohedral.   It  is  harder than tin, but  not so
hard as zinc, and is sufficiently malleable  to admit
of rolling into thin sheets.  Its specific gravity after
fusion  is  86.  Its  electric conductivity is 22-10,—
someAvhat loAver than that of  zinc.  It melts at a
temperature  beloAV redness (315° to 320° G).
  Cadmium has been used in the formation of dental
alloys, but its employment as a constituent in amal-
gams is iioav so generally condemned that it is seldom
used for that purpose.
  Probably the best test for cadmium is  the color
afforded  when  it  is volatilized and oxidized under
the bloAV-pipe  flame.  This is  of a reddish-brown,
/.inc under the same conditions  giving  a  deposit
which is a bright yellow Avhile  hot, becoming Avhite
on cooling.   It may also  be detected, by precipitation
from an acid solution, as a yellow sulphide, and may
in this Avay be  distinguished  from zinc, as zinc sul-
phide does not  separate  except  from neutral or alka-
line solutions.
  In quantitative analysis cadmium is ahvays esti-
mated as oxide, being separated  from solution as
carbonate by precipitation Avith carbonate of sodium,
Avhich is  converted into oxide by calcination.  It
may also  be separated from its solution in acids by
means of zinc, Avhich  precipitates it  in a dendritic
form, like the Avell-known lead tree. 
CHAPTER  XVIII.
       ALUMINIUM.
Atomic Weight, 27-4.   Symbol, Al.
 A LUMINIUM, though obtained in the metallic
      state  as  early as 1828 by Wohler, remained  a
mere laboratory  product until 1858,  when  Deville
improved the mode of production to such an extent
that its separation became an ordinary manufacturing
operation.
  A mixture of the double chloride of aluminium and
sodium, or the double fluoride of aluminium and so-
dium (cryolite), is heated to redness with the metal
sodium, when energetic  chemical action takes place,
during Avhich chloride of sodium is formed and the
metal aluminium  separated.
  Aluminium may be  separated by electrolysis.  The
electric current from a ten-cell battery, provided with
carbon poles, is passed through the fused salt.  The
metal appears at the negative  pole in large globules.
  Aluminium is nearly the  color of new zinc.  It is
very malleable and ductile, and admits of rolling into
thin sheets,  or it may be  drawn into fine wire.  It is
highly sonorous,  and  has the power  of conducting
heat and electricity  in  about the same degree as
silver.  It is only two and a half times heavier than
water  (four times lighter than silver).  Its  specific
gravity is 2-56,  and it  melts at a red heat.
      (228) 
ALUMINICM.
229
  Aluminium does  not oxidize in air,  and is  not
attacked by sulphur compounds.   It is not attacked
by strong nitric acid, and is insoluble in dilute  sul-
phuric acid, but it may be readily dissolved in either
dilute  or  strong hydrochloric  acid.  The  metal is
easily dissolved in solutions of caustic potash or soda.
  Alloys.—Aluminium forms alloys Avith nearly all
the metals.  That Avith copper* is the most important,
and presents  a closer resemblance to  gold than, per-
haps, any other alloy.   It is used  for  articles of
jewelry, for mountings of astronomical instruments,
and for making balance-beams.
  Aluminium with tin and zinc forms a brittle alloy,
and Avith silver it yields a hard, though Avorkable, com-
pound.  It does not  amalgamate with mercury.
  Aluminium is employed in  the manufacture of
very small weights,  such  as the milligramme of the
metric  system—a use  to  Avhich,  in  consequence of
its exceedingly Ioav specific gravity, it is particularly
well adapted.   Its  lightness,  strength, and resist-
ance to oxygen and the sulphur compounds,  are
properties Avhich Avould seem to point to this metal
as a suitable  substance as a base for artificial teeth.
The readiness, however, Avith Avhich it is attacked by
alkaline solutions renders it unfit for use  in the con-
struction of a permanent  artificial denture.
  Aluminium,  notwithstanding its  extreme light-
ness, may be  cast Avith great exactness.   Dr. J. B.
Bean, Avho patented  a process for casting aluminium,
succeeded in producing castings of exquisite fineness.
 * Aluminium bronze—alloy of copper with five per cent, of alumin-
ium.
                        20 
230
DENTAL  METALLURGY.
Indeed, it may be stated that Bean succeeded in over-
coming all the physical difficulties encountered in the
effort to render aluminium available in prosthetic
dentistry, but its susceptibility to the action of alka-
line solutions finally compelled him to abandon it.
  There are two methods which have been employed
in the construction of artificial dentures of this metal.
The one most  frequently  resorted  to  consists in
merely swaging a plate in the ordinary way, which
is perforated with  a number  of counter-sunk  holes
along the part covering the top of the alveolar ridge
as a means of fastening the teeth, which are attached
with rubber or celluloid.  Sets of teeth made in this
way have been known to do good service for eight or
nine years, but they showed unmistakable evidence of
the action of the oral fluids.   In the second method
the plate is cast, but disintegration in this case pro-
gresses with much greater rapidity.  As the plate is
cast separate from the teeth, and the latter are  after-
ward attached by means of tin or an alloy of tin and
aluminium, it is probable that the galvanic action inci-
dent to the presence of two metals greatly hastens
solution of the plate, as  some of the  dentures  made
by Bean failed after a few months' wear.
  For some time the difficulty of soldering aluminium
prevented the metal from being  applied to useful
purposes, and no solder for it fit  to be introduced
into the mouth is yet known.   The one recommended
for  general use  in the manufacture of  articles of
ornamentation  is composed of copper, four parts;
aluminium, six parts; zinc, ninety parts.   The use
of this  requires  some skill and experience.  At the
moment of fusion small aluminium tools are used, the 
ALUMINIUM.
231
friction of which is  necessary to  induce adhesion.
No flux can be employed, as it is liable to attack the
metal and prevent union.
  The only oxide of  this metal is  alumina (Al2 Os).
It is  prepared by mixing a solution  of alum with
excess of ammonia.   The resulting precipitate (alu-
minium hydrate) is of a bulky, gelatinous character,
and requires to be calcined at a high temperature;
after which it may be described as  a perfectly white
powrder, soluble  in caustic potassa, or soda, and not
readily acted upon by acids.   Corundum and emery
are nearly pure  alumina.  The ruby and  sapphire are
also transparent varieties of alumina in a crystalline
state, their brilliant colors being due to oxide of chro-
mium.
  Alumina forms the  base of all the silicates, Avhether
in a crystalline state,  as feldspar, or in a disintegrated
condition,  as clay (kaolin).
  For the  discrimination of the  salts  of aluminium,
see any of the recent works on chemistry. 
CHAPTER XIX.
                  LEAD.
Atomic Weight, 207.   Symbol, Pb (Plumbum).
HHHE reduction of lead is effected in a reverberatory
    furnace, in which the broken lead  ore (galena)
is  roasted at a  dull red  heat, by which means the
sulphide becomes  oxidized and converted into sul-
phate.   At this  stage of the  operation  the contents
of the  furnace  are thoroughly mixed and the tem-
perature raised, which causes the sulphide and sul-
phate to react upon each other, producing sulphur-
ous oxide and metallic lead.
  Lead is the softest metal in common use, and may
be said to be the least tenacious.  In fusibility it also
surpasses all other metals commonly employed in the
metallic state except tin, the fusing-point of lead being
617° F. = 325° C.  It is quite malleable and  ductile,
and will admit of being rolled into thin sheets or foil,
in which form it was at one time much used in filling
teeth.   Its chief use in the dental laboratory consists
in the formation of counter-dies.
  Alloys.—Lead  unites with  tin  in  all  proportions,
the resulting alloys being more tenacious and fusible
than either constituent.   By the addition of bismuth
the fusing-point is reduced below the  boiling-point
of water.
      (232) 
LEAD.
233
  Lead amalgamates readily with  mercury, conden-
sation accompanying  the  union.   The noble metals
are all rendered brittle and unworkable by the pres-
ence of lead.   There are some properties peculiar to
alloys of lead  and silver Avhich are turned to advan-
tage in  the separation  of silver from lead when it
occurs as a native alloy.   Lead containing a consid-
erable amount of silver will remain  fluid at a lower
temperature  than  other  specimens  containing  a
smaller  amount,  thus affording an opportunity for
the poorer lead to crystallize, when it is ladled out.*
  The smallest amount of lead in gold will greatly
impair the ductility of the latter.  Makins states that
" Hatchett found that  y^r  of lead  destroyed  the
coining qualities of gold."  Gold reduced to standard
fineness by lead is light-yellow in color, and quite
brittle.  The contents of the dentist's gold-drawer
are always liable to contamination by small pieces of
lead, the latter being  much used in the form of thin
sheets in  the  formation of patterns by which  the
gold or silver plate is  cut.  As the working qualities
of the precious metals are seriously impaired by its
presence, means should be instituted to insure its com-
plete removal.  This may be  accomplished by cupel-
lation, or by melting the gold or silver in a  crucible,
and adding nitrate of potassium when the  point of
complete fusion has been reached.
  Lead and platinum, like tin and platinum, appear
to possess considerable affinity for each other, and an
alloy of the two  can  be formed at a comparatively
low temperature.
* See chapter on " Silver."
        20* 
234           DENTAL METALLURGY.

  An alloy of lead and platinum is very hard  and
brittle.  With palladium lead also forms a very hard
and brittle alloy.
  The most valuable alloys of lead are those which
it forms with tin, antimony, and bismuth, constituting
solders, pewter, type-metal, etc.
  For the discrimination  of lead, the student is
referred to Fownes's or other  standard works on
chemistry. 
CHAPTER XX.
                   TIN.
Atomic Weight, 118.   Symbol, Sn (Stannum).
rpiIE metal tin has been known for probably three
     thousand years.   It is found in all parts of the
world, chiefly as oxide.  In reducing the ore it  is
first powdered  and roasted to free it of sulphur and
arsenic.  It is  then exposed to a high temperature
with charcoal, and the metal is thus liberated.
  Pure tin is white in color, and is perfectly soft and
malleable.  It has  a density of 7-3, and  its fusing-
point is 458-6° F. (237° C).   It is but  slightly acted
upon by air, but when heated much above its melt-
ing-point it oxidizes freely, and is converted into a
yellowish-white powder,—the well-known polishing
putty. The  action of nitric  acid upon tin is to con-
vert it into a white hydrated dioxide.   It is dissolved
by  hydrochloric  acid,  assisted by  heat,  and forms
stannous chloride. Nitro-hydrochloric acid acts upon
tin  Avith much  energy,  converting it  into  stannic
chloride.
  Alloys.—Tin  is readily dissolved in mercury  (see
page 205).   With silver it forms a malleable alloy,
which is considerably harder than tin.   The late Dr.
Bean used tin alloyed with a small percentage of sil-
ver for lower sets, which he cast directly upon the
teeth after the ordinary cheoplastic method.
                                      (235) 
236
dental metallurgy.
  Alloys of tin and  silver, in which  the former is
slightly in excess, are much used as amalgam alloys.
Tin  10, silver 8, gold  1, is also frequently employed
in filling teeth; and tin 10, silver 8, gold 1, copper 1,
has, according to Fletcher, been largely used as " gold
and platinum"  amalgam.  It is stated that from 5 to
7 per cent, of copper  has  the  property of replacing
platinum in  amalgams, conferring the quick-setting
quality claimed for platinum.*
  Dr. G. F. Reese has recently formed an alloy for a
base for artificial dentures composed of twenty parts
of tin, one of gold, and two of silver.f  This is cast
directly upon the teeth, the process being similar to
the cheoplastic method.
  The alloys which have been used in the cheoplastic
process are chiefly composed of tin, silver, bismuth,
and,  in some  instances, cadmium and antimony.
  According to Makins, gold and tin form a malleable
alloy,J and gold reduced to standard by pure tin re-
tains its malleability.
  Tin and platinum in equal proportions afford a hard
and quite brittle alloy, fusible at a comparatively low
temperature.  When it is remembered that the fusing-
points of these metals almost  represent  extremes of
temperature, it would seem that their union must be
attended  with difficulty,  but, as has  already been
stated,11 it is probable that some affinity exists between
  * T. Fletcher.
  f "Alloys and Amalgams Chemically Considered," J. Morgan Howe
M.D.
  % A precipitated alloy of gold and tin, having the form of a black
powder, may be formed by  acting upon a concentrated solution of
trichloride of gold with stannous chloride.
  || See chapter on " Alloys." 
TIN.
237
the two, as platinum is readily dissolved by and alloys
with the fused tin.
  With palladium tin is said to form a brittle alloy.
  With lead tin forms the  chief part in the  alloys
used for soft-soldering, and in the compounds known
as pewter and Britannia metal.   Tin solders are com-
posed of two parts of tin to one of  lead.  Pewter
consists of four parts of tin to one  of lead, while
Britannia metal is formed by the addition of small
quantities of antimony and copper.
  Alloys of tin and lead are  harder and tougher
than either  metal  singly, and they are  more fusible
than the mean of  their constituents.   The addition
of bismuth to such an alloy lowers the melting-point
to a remarkable degree, and the fusing-point is  still
further reduced by the addition of cadmium.   Thus,
an alloy composed of 15  parts of bismuth, 8 of lead,
4 of tin, and 3 of cadmium,  fuses at 145° F. = 63° C.
  The alloy known as " Wood's  metal," occasionally
employed by dentists in replacing teeth on vulcanite
plates, is composed of 7 parts of bismuth, 6 of lead,
and 1 of cadmium, and fuses at  180° F. = 82° C, a
point much  below the boiling-point  of water.  In
replacing a broken tooth ly means of Wood's metal
the usual dovetail is cut in the rubber plate Avith a
fine saAV,  the tooth is fitted to its place, and the
fusible alloy is packed in with a spatula heated in a
spirit-lamp.
  Lead 75, tin 5, and antimony 20 parts, is the com-
position of the best form of  type-metal.
  With copper tin affords a number of very  useful
alloys.  Bell-metal is formed of 78 parts of copper
to 2 of tin.  Gun-metal is formed of 90  per cent, of 
238
DENTAL METALLURGY.
copper to  10  per cent,  of  tin.  Speculum-metal is
formed of 6 parts of copper,  3 of tin, and 1 of arsenic.
  Babbitt-metal—tin  12  parts, antimony 3, copper 2
—is sometimes used in the dental laboratory for dies,
and is thought by many  to be superior to zinc.
  Bronze is an alloy of copper and  tin,  and some-
times zinc.  It is affected by changes of temperature
in a manner precisely the reverse  of that in which
steel is  affected, becoming soft and malleable Avhen
quickly cooled, and  hard  and brittle when alloAved to
cool  slowly.   The art of making bronze was prac-
ticed before any knowledge of the working of iron
existed, and it was used at a very early period in
the manufacture of weapons.
  Commercial  tin is liable to  contain minute quan-
tities of lead,   iron, copper, arsenic,  antimony,  bis-
muth, etc.  Pure tin may be precipitated in crystals
by the feeble galvanic current excited by immersing
a plate of tin  in a strong solution of stannous chlo-
ride.  Water is carefully poured on so as not to  dis-
turb the layer of tin solution.   The pure metal will
be deposited on the bar  of tin at the point of junc-
tion of the water and the metallic solution.
  Perfectly pure tin  may also  be  obtained by  dis-
solving commercial tin in hydrochloric acid, by which
it is converted  into stannous chloride.  After filtering:,
this solution is evaporated to a small bulk, and treated
with nitric acid, which instantly converts the stan-
nous chloride into stannic oxide.  This is thoroughly
washed  and dried, and exposed to red heat in a cruci-
ble  with  charcoal.   A button  of  pure tin will  be
found at the bottom of the crucible.
  Pure tin in  the form of foil  is frequently used in 
TIN.
239
filling  teeth, for Avhich  purpose it doubtless  ranks
next to gold.  Tin foil is also employed in connection
Avith non-cohesive gold in filling approximal surfaces
of cavities in bicuspids and molars.  Tavo  sheets of
foil,  one of gold  and the other of  tin, are placed
together and made  into mats or cylinders.   These
are carefully packed against the cervical margins of
the cavity.  The  frequent failure  of ordinary gold
fillings  at  this  point  has  led some practitioners to
entertain the theory that between the tooth-substance
and the gold there  is galvanic action, to which the
lime-salts  of the tooth yield,  and  that in  the com-
bination of tAvo metals, whether it  be tin and gold or
amalgam and gold, the galvanic action is confined to
the metals, the tooth-substance being thus protected.
  The appearance of a filling formed of tin and gold
would seem to confirm this theory, as it soon becomes
dark in color,  and  presents  a  surface  resembling
amalgam,  but effectually protects the margins from
decay.*
  Solvents.—Tin is readily dissolved by either  of the
three mineral acids.   Sulphuric acid  converts it into
stannic sulphate.  Tin dissolved in hydrochloric acid
forms  stannous chloride.  By the action  of  dilute
nitric acid tin is not dissolved, but  is converted into
stannic oxide, Avhich  settles to the  bottom of the
vessel  as  a Avhite poAvder.   This,  when  rendered
anhydrous by heating to  redness,  affords  the Avell-
known polishing powder called "polishing putty."
  Chlorides.—There  are two chlorides of tin,—stan-
  * Prof. James Truman, Report of Proceedings of Odontological
Society of Pennsylvania, November, 1881. 
240
DENTAL METALLURGY.
nous chloride or protochloride of tin (Sn  Cl2), and
stannic chloride or bichloride of tin (Sn Cl4).   Stan-
nous chloride is prepared by dissolving tin  in hydro-
chloric acid, the action being assisted by gentle heat.
Stannic chloride is obtained by dissolving tin in nitro-
hydrochloric acid  (aqua  regia).  These  two  com-
pounds of tin  are  employed in the preparation of
purple of Cassius, in which process stannous chloride
is added to a mixture of stannic chloride and trichlo-
ride of gold (see page 137).
  For other compounds of tin, see Avorks on chemistry.
  Discrimination.—Tin  is  detected before the bloAv-
pipe by fusing  the compound  under examination on
charcoal Avith sodium carbonate, Avhen a bead of the
metal  is obtained.   From a tin solution caustic pot-
ash and  soda precipitate a white hydrate, soluble in
excess.  Ammonia affords  a similar precipitate, not
soluble in excess.  Hydrogen sulphide and ammonium
sulphide throAV down a dark-broAvn precipitate of
monosulphide.  Trichloride of gold added to a dilute
solution of stannous chloride causes a purple precipi-
tate (purple of  Cassius). 
CHAPTER  XXI.
     ELECTRO-METALLURGY.

n^HE origin of electro-metallurgy was undoubtedly
     due to the early experiments of Wollaston and
Davy, Avhile the credit of its development belongs to
the late Professor Daniell, who devised the particu-
lar  form of battery which bears his name.  A  Dan-
iell cell  consists  of a  copper vessel containing  a
saturated solution of sulphate of copper.   In this is
placed a porous cylinder containing dilute  sulphuric
acid.  A rod of amalgamated zinc is immersed in the
acid, and on the tAvo metals being connected electrical
action  is  immediately set up, and the zinc, which
forms the positive element, is dissolved, with forma-
tion of sulphate of zinc;  the sulphate of  copper  is
reduced, and metallic copper is deposited upon the sur-
face of the copper vessel, which forms the negative
element of the combination.   It  was  observed that
the copper thus deposited took the  exact shape  of
surface on which it was thrown, presenting a faithful
counterpart of the slightest indentation or  irregular-
ity.  De la Rue called attention to this fact in a paper
published in 1836, but no practical  application was
made of it until  1839, when Professor Jacobi, of St.
Petersburg, published his discovery  of  a means  of
producing copies of engraved copper plates by the
agency of electricity,
                        21            (241) 
242
DENTAL METALLURGY.
  In 1840 Mr.  Murray announced  that an electro-
deposit  of metal could be formed upon almost  any
material, provided its surface was rendered a conduc-
tor of electricity by a thin coating of graphite (black-
lead).  Instead of  copying the object in a  metallic
medium, it is only necessary to take a cast in plaster
of Paris, Avax, gutta-percha,  or any  convenient mate-
rial, and then to coat the surface with finely-powdered
graphite applied with a camel's-hair pencil.
  The Gramme machine, a recent modification of the
magneto-electric apparatus, consists of a ring of soft
iron  carrying a number of  coils of insulated copper
Avire, caused  to rotate between  the poles of a fixed
horse-shoe  magnet.  The currents induced in the
coils are collected by two metallic disks, whence they
may be drawn off for use in electro-deposition.   The
core  being circular, the magnetization proceeds  con-
tinuously, affording a uniform current.  Both poles
of the magnet are used, producing simultaneously
two opposite continuous currents.  These and similar
sources  of electricity enable the electro-metallurgist
to deposit a metal upon a matrix or to coat one metal
Avith another.
  The  art of electro-metallurgy is  divided into two
branches, electrotypy  and  electro-plating.   In  the
former the reduced metal is separated from the mold
on which it is deposited, forming a  distinct work of
art, while in the latter the deposited metal forms an
inseparable part of the plated object.  Electrotypy
is employed  in producing copper duplicates of en-
gravings on wood and of any kind of type-matter for
printers' use.  A cast of the object is first taken in
wax or gutta-percha, and the surface of this mold is 
ELECTRO-METALLURGY.
243
 brushed over with black-lead, and it is then, by means
 of a wire, suspended in a bath of sulphate of copper
 connected with  a battery.  In a  few hours a suffi-
 ciently thick plate of copper is deposited to afford a
 perfect copy, which is  then strengthened by being
 backed Avith type-metal.
  Electro-plating, by which silver is deposited on
 the surfaces of objects of copper, brass, or German
 silver, was introduced soon after the discovery of the
 art of electro-metallurgy.  The article to  be plated
 must first be thoroughly cleansed by immersing it in a
 hot solution of causttc  potash, and also by means of
 the "scratch-brush," and sometimes by "pickling" it
 in a bath of nitric and other acids. The surface is then
 given a thin film of mercury, by washing the article
 with  a solution of mercuric nitrate.  This is called
 "quicking."  The article is then  rinsed with water
 and transferred to the silver bath, which consists  of
 a solution of cyanide of silver in cyanide of potassium
 —a very poisonous compound.  Plates of silver are
 suspended from a rectangular  frame connected with
 the positive pole, while the articles to be plated are
 suspended by Avires attached to the negative pole.
 The quantity of silver to be deposited depends upon
 the requirements of the case.   One ounce of silver
 per square foot  forms for ordinary purposes a suffi-
 ciently heavy coating.
  Electro-gilding is effected by means similar to those
employed in electro-silvering. The solution employed
is generally the double cyanide of gold and potassium,
and is used hot,  the  temperature ranging from 130°
F. to 212° F., according to the  ideas of the operator.
  Nickel-plating Avas first introduced in 1869, by Dr. 
244
DENTAL  METALLURGY.
Isaac Adams, of Boston, who patented a process for
depositing nickel  from solutions of double salts of
sulphate of nickel and ammonium.
  Iron may also be deposited from the double sul-
phate of iron and ammonium.  Practical application
is now made of this discovery, and engraved copper
plates are found to be much more durable when faced
with electro-deposited iron.  Plates for printing bank-
notes are sometimes treated in this way. 
INDEX.
Acid, nitric, action of, on silver.................................... 168
    nitric, in the quartation process of refining gold......... 113
    nitro-hydrochloric (aqua regia)................................ 120
    sulphuric, in the quartation process of refining gold... 118
Acids, action of, on alloys.............................................  44
Alloying, the purpose of..............................................  34
Alloys as definite compounds........................................  35
    color of................................................................  37
    composition of......................................................  40
    conductibility of....................................................  24
    decomposition  of...................................................  41
    density of.............................................................  36
    for solders............................................................  34
    fusibility of..........................................................  39
    influence of constituent metals in.............................  41
    Matthiesen's definition of.......................................  36
    of gold employed in dentistry as solders.................... 130
    of silver employed in dentistry as solders.................. 172
    oxidizability of.....................................................  44
    preparation of.......................................................  43
    properties of.........................................................  34
    specific gravity of.................................................  37
    table of...............................................................  40
    temper of.............................................................  43
    the study of.........................................................  33
Alumina.................................................................... 231
Aluminium................................................................ 228
    alloys of.............................................................. 229
    Bean's method of casting........................................ 229
    bronze............................................................ 40, 215
    solder for............................................................. 230
    solvents of............................................................ 229
    swaged plates of.................................................... 230
                                                245 
246
INDEX.
Amalgams.................................................................  45
    composition of some of the well-known.....................  66
    copper,  cadmium, bismuth, antimony, and  zinc as
      constituents of...................................................  58
    definition of.........................................................  45
    discoloration of.....................................................  47
    expansion of.........................................................  46
    experiments with..................................................  48
    for dental purposes................................................  45
    formation of.........................................................  45
    forming alloys for.................................................  57
    influence of different metals in........'........................  49
    introducing fillings of............................................  56
    methods of mixing................................................  55
    of Dr Ambler Tees............................................ 65  66
    qualitative and quantitative examinations of..............  60
    quantity of mercury to be used in............................  54
    shrinkage of........................................ ................  46
Ammonium................................................................  17
Argentiferous galena................................................... 160
Argentum (silver)...................................................... 156
Arsenic, odor of.........................................................  18
    Bloxam's classification of................................... 15  16
Assay of amalgam alloys.............................................  €1
Atomic weights of metallic elements......................... 12  13
Auric chloride............................................................ 136
    oxide.................................................................. 136
    iodide.................................................................. 137
Aurous chloride.......................................................... 136
    oxide.................................................................. 136
    sulphide............................................................... 137
Aurum (gold)............................................................ 104

Babbitt-metal............................................................ 238
Beating gold.............................................................. 153
Bellows for blow-pipe..................................................  72
Bessemer steel............................................................ 197
Black-lead crucibles....................................................  78 
INDEX.
247
Blast-furnaces.............................................................  75
Blistered steel............................................................. 196
Blow-pipes................................................................  69
    oxyhydrogen........................................................ 178
    supports for use with.............................................  85
Bone-ash cupels.......................................................... 162
Borax........................................................................  83
Brass.................................................................. 218, 221
Britannia metal........................................................... 237
Brittle gold, treatment of............................................. 117
Bromides, metallic......................................................  92
Bronze...................................................................... 238

Cadmium.................................................................. 226
Calamine..................................................................  28
Calomel..................................................................... 206
Carbon, amount of, in iron and steel.............................. 195
Case-hardening........................................................... 199
Cast-iron................................................................... 196
Cast-steel............................................................. 196 197
Charcoal as a reducing agent........................................ 101
Chlorides, metallic......................................................  91
    preparation of.................................................. 91  92
    reduction of.........................................................  99
Cinnabar.................................................................. 206
Coke for supports in soldering.......................................  87
Copper..................................................................... 211
    alloys  of.............................................................. 213
    amalgam....................................................... 213 214
    as a constituent in amalgams.................................. 215
    discrimination of.................................................. 217
    properties of........................................................ 212
    solvents of........................................................... 213
Corundum................................................................. 231
Crucibles...................................................................   78
Crystallization...........................................................   30
Cupellation................................................................ 163
Cupels....................................................................... 162
Cyanides, metallic......................................................   91 
248
INDEX.
Ductility.....................................................................   26

Electro-deposit of metals...............................................  243
Electrolysis................................................................  103
Electro-metallurgy......................................................  241
Electrotype, origin of..................................................  241
Elements, metallic.......................................................   12
Emery.......................................................................  231

Flame, blow-pipe........................................................   69
    management of.....................................................   85
Fluorides, metallic......................................................   93
Flux.........................................................................  139
Forging  platinum.......................................................  179
Fulminating gold.........................................................  142
    silver....................................................................  166
    mercury..............................................................  210
Furnace, lime, for melting platinum...............................  178
Fusible metal............................................................  237
Fusing-points of  metals.................................................   19

Galena, argentiferous..................................................  160
Gauge-plate...............................................................   81
Gold.........................................................................  104
    alloys of..............................................................  125
    chlorides of..........................................................  136
    clasps for partial artificial dentures..........................  128
    coin....................................................................  133
    compounds of.......................................................  136
    containing iridium................................................  118
    different forms of  precipitated................................  122
    discrimination of..................................................  122
    foil, cohesive........................................................  149
    foil, non-cohesive..................................................  150
    in combination with tin in filling teeth.....................  239
    Lamm's shredded..................................................  122
    oxides  of.............................................................  136
    precipitants for....................................................  122 
                          INDEX.                      249

Gold, precipitation of, by ferrous sulphate....................  123
    precipitation of, by oxalic  acid...............................  122
    precipitation of, by sulphurous acid........................  123
    properties, occurrence, and distribution of................  105
    pure, preparation of.............................................  119
    quartation process of refining.................................  112
    refining...............................................................  112
    swaging, when alloyed with  platinum.....................  128
    Watts's crystal.....................................................  124
Gum frit....................................................................  141
Gun-metal.................................................................  237

Hot-blast blow-pipes....................................................   72
Hydrogenium.............................................................   16

Ingot molds...............................................................   80
Iodides, metallic.........................................................   93
Iron..........................................................................  193
    fusing-point of.......................................................  194
    meteoric...............................................................  193
    native..................................................................  193
    properties of..........................................................  194
    solvents of............................................................  194

Kaolin.......................................................................  231

Lamps, soldering.........................................................   68
Lead.........................................................................  232
    alloys of...............................................................  232
    amalgamation of.................................................... 233
    desilvering of.......................................................  233
    discrimination of..................................................  234
    properties of.........................................................  232
    reduction of..........................................................  232
Magnetic iron............................................................. 195
Malleability of metals..................................................  25
Mercury....................................................................  201
    adulterations of..................................................... 202 
250
INDEX.
Mercury chlorides....................................................... 206
    compounds........................................................... 206
    discrimination of.................................................. 209
    filtration of.......................................................... 204
    native.................................................................. 201
    occurrence of....................................................... 201
    ores, reduction of.............................................201 202
    oxides of............................................................. 206
    Priestley's plan of purifying................................... 204
    properties of......................................................... 204
    pure, to obtain.......................................71............. 203
    purification of, by digestion.................................... 202
    quantity of,  to be used in amalgams........................  54
    redistillation of..................................................... 202
    sources of......................................................,...... 104
    sulphides of.......................................................... 206
Metallurgy,  definition of..............................................   7
Metallic bromides.......................................................  92
    chlorides...............................................................  91
    cyanides..............................................................  91
    fluorides...............................................................  93
    iodides..................................................................  93
    oxides..................................................................  93
    sulphides..............................................................  96
Metals, base................................................................  15
    capacity for  heat of...............................................  20
    color  of...............................................................  17
    conduction of electricity of....................................  23
    conduction of heat of.............................................  23
    effects of alloying in.............................................  34
    elasticity and sonorousness of.................................  30
    expansion of, by heat............................................  21
    fusibility of.........................................................  18
    fusing-points—table of...........................................  19
    malleability, ductility and tenacity of......................  25
    noble...................................................................  14
    odor and taste of....................................................  18
    properties  of.........................................................  14 
                          INDEX.                      251

Metals, table of............'..............................................  12
    volatility of..........................................................  31
    volatility of, agents which induce...........................  32

Nickel-plating........................................................... 243

Oxides, metallic.........................................................  93
Oxides, reduction of.................................................... 101

Palladium.................................................,............... 189
    alloys of.............................................................. 190
    amalgams............................................................ 191
    cost of................................................................. 192
    discrimination  of.................................................. 192
    properties  of................................................:....... 190
    sources of............................................................. 189
Pewter..................................................................... 237
Phosphor-bronze........................................................  42
Platinum.................................................................. 174
    alloys of.............................................................. 181
    amalgamation  of................................................... 181
    associate metals with............................................. 189
    chlorides of......................................................... 183
    Deville's furnace for melting.................................. 178
    properties of......................................................... 179
    pure................................................................... 179
    solvents of............................,.............................. 180
    welding.............................................................. 179
    Wollaston's method of preparing............................ 174
Polishing-putty.......................................................... 239
Purple of Cassius....................................................... 137

Quartation process  of refining  gold............................... 112

Reduction of metals...................................................  97
Refining gold............................................................ 112
Reinsch's test....................................................... 103, 209
Rolling mills.............................................................  80 
252                      INDEX.

Ruby........................................................................ 231

Sapphire................................................................... 231
Silicate of gold.......................................................... 141
Silver....................................................................... 156
    alloys of.............................................................. 169
    analysis of........................................................... 166
    chloride of........................................................... 165
    cupellation of...................................................... 167
    deposition of, by battery........................................ 173
    discrimination of.................................................. 166
    estimation of........................................................ 166
    native................................................................. 158
    nitrate  of............................................................. 164
    oxide of............................................................... 164
    precipitation of, by copper...................................... 169
    precipitation of, by iron.......................................... 169
    precipitation of, by sodium chloride......................... 168
    precipitation of, by zinc.......................................... 169
    properties of......................................................... 156
    pure...................................................................... 168
    separation of, from ores......................................... 159
    solders  for........................................................... 171
    solvents of........................................................... 168
    spitting of, during fusion....................................... 163
    sulphate of........................................................... 165
    sulphide of............................................................ 165
Solders for  aluminium................................................ 230
    gold..................................................................... 130
    silver................................................................... 172
    used in dentistry.............................................130, 172
Specific  gravity of alloys.............................................  37
Speculum-metal......................................................... 238
Stannic  chloride......................................................... 239
Stannum (tin)............................................................ 235
Steel......................................................................... 195
    blistered............................................................... 196
    cast.................................................................... 196 
                          INDEX.                      253

Steel, discrimination of................................................ 200
    hardening............................................................ 197
    tempering............................................................ 197
Sulphides, metallic............................ ........................  96
    reduction of......................................................... 100
Supports, for use in melting and soldering.......................  85

Tellurium........................................;.........................  15
Tenacity of metals......................................................  26
Tin, alloys of............................................................. 235
    amalgamation of.................................................. 235
    chlorides of.......................................................... 239
    discrimination of................................................... 240^
    estimation of........................................................  61
    foil..................................................................... 239
    in amalgams........................................................  49
    oxide of...............................................................  61
    pure, preparation  of.............................................. 238
    refining............................................................... 238
    solvents of........................................................... 239
Titanium..................................................................  17
Type-metal................................................................ 237

Vermilion................................................................. 207

Welding properties of platinum.................................... 179
W ire-drawing............................................................  81
Wood's metal............................................................. 237

Zinc........................................................................ 218
    alloys in dentistry................................................. 220
    alloys of.............................................................. 219
    counter-dies......................................................... 222
    dies for swaging plates.......................................... '^21
    discrimination of................................................. 225
    expansibility  of....................................................  21
    in amalgams........................................................ 219
    oxychloride of...................................................... 224
    properties of......................................................... 218 
 
 
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