PRACTICAL DENTAL METALLURGY Copyright, 1911, 1918, 1924, By The C. V. Mosby Company 
(Printed in U. S. A.) 
Press of 
The C. V, Mosby Company 
St. Louis PRACTICAL 
Dental Metallurgy 
A Text and Reference Book for Students and 
Practitioners of Dentistry / 
Embodying the Principles of Metallurgy, and Their Application to 
Dentistry, Including Experiments 
VBY 
JOSEPH DITPUY HODGEN,1 D.D.S. 
IW—• 7 
Professor of Operative Dentistry (formerly Professor of Dental Chemistry 
and Metallurgy), College of Dentistry, University of California 
REVISED BY 
GUY S. MILLBERRY, D.D.S. 
Professor of Chemistry and Metallurgy and Dean of the College of 
Dentistry, University of California 
'SIXTH EDITION—COMPLETELY REVISED 
ST. LOUIS 
THE C. V. MOSBY 
1924, TO 
THE MEMORY OF 
OJlarkr IGa Wottr (kokkarfc, A. W., 0. 0. 
Late Professor of Orthodontia, 
Dental Department, University of California 
®l)ta Work to JttsrriM 
IN 
ADMIRATION OF HIS TALENTS, 
AND 
GRATITUDE FOR HIS TEACHINGS, CRITICISMS 
AND FRIENDSHIP PREFACE TO TITE SIXTH EDITION 
Twenty-seven years of continuous use of ITodgen’s 
Dental Metallurgy as a text in most of the dental col- 
leges of America is a compliment to the author both 
for his vision as to the need for such instruction in 
dentistry, and the form in which such instruction could 
be most satisfactorily given. 
There has been no desire on the part of the revisor 
to modify in this revision the pedagogical scheme 
primarily adopted by Dr. Hodgen, which has been 
sufficiently well thought of as to be imitated by other 
authors. 
However, recent dependable information accepted 
by chemists and metallurgists, and the essential 
changes resulting from research in these fields which 
relate to the subject matter in this book, must become 
a part of it. 
Many of the well established applied facts have been 
retained; other data rendered questionable by recent 
research have been deleted as has some of the material 
which has no particular bearing on the scientific phases 
of the study; as for instance, the history of amalgams. 
A study of the physical properties of amalgams by 
Arthur W. Gray, Ph.D., has given us such a clear 
understanding of the changes which amalgams under- 
go in solidifying, that through the kindness of Dr. 
Gray, hereby acknowledged, much of his published 
material with illustrations has been included in the 
chapter on amalgams. 
Another phase of research, commanding the atten- 
5 6 
PREFACE 
tion of metallurgists, is the metallographic study of 
metals and their alloys. Such a study has been and 
is being carried on in this college and the revisor is 
indebted to John S. Shell, B.S., for his contribution in 
this field as well as for his assistance in the revision. 
Some criticism of the text has been offered in that 
more of the fundamentals of the industrial aspects of 
mining and metallurgy should be given. It has never 
been the purpose of this text to fill such a place in 
metallurgical literature. It is intended to meet the 
requirements of the student who expects to engage 
in the practice of dentistry, and I hope it will continue 
to merit the approbation of teachers who appreciate 
that need. 
Guy S. Millberry. 
University of California 
September 15, 1924. 
FROM PREFACE TO FIRST EDITION 
In presenting this little volume to the practitioner and 
student of the dental profession, the author does not 
flatter himself that he is filling a void in such literature, 
or that a crying need has been felt in the profession for 
this particular production. It has, however, grown out of 
the exigencies of the writer’s own class-room and labora- 
tory after several years’ practical experience as an in- 
structor on its subject. 
The endeavor has not been to furnish a scientific and 
exhaustive treatise on metallurgy, but rather to present, 
in a clear and practical manner, the principles of that PREFACE 
7 
subject as the author sees them related and applicable to 
the everyday wants of the dentist. 
Keenly appreciating the reluctance with which this 
and the analogous study of chemistry have been pursued 
by the average student, the author has sought to awaken 
a deserving interest by doing away with the usual lectures 
and employing the work as a text book, subject to ex- 
planatory elaboration during the recitation; and to fur- 
ther make it so practical that it may be taken into the 
metallurgical laboratory and used as a manual for prac- 
tical and experimental work. It presupposes the student 
to possess a fair knowledge of the principles of inorganic 
chemistry, comprehending the reading and writing of 
formulae, atomic affinities, and the expression of equa- 
tions. 
Joseph D. Hodgen. CONTENTS 
CHAPTER I 
Chemistry, 17; Elements, 17;. Metallic Elements, 20; Metallurgy, 
20; Ore, 20; Gangue, 20; Slag, 20; Regulus, 21; Speiss, 21; 
Reduction, 21; Roasting, 22; Calcination, 22; Distillation, 22; 
Sublimation, 22; Scorification, 22; Occlusion, 22; Cementation, 
23; Dry Process, 23; Wet Process, 23; Noble Metals, 24; Base 
Metals, 24. 
INTRODUCTION 
CHAPTER II 
PROPERTIES OF METALS 
Metal, 27; Nontransparency, 28; Color, 28; Luster, 28; 
Metallography, 29; Odor and Taste, 29; Crystalline Form, 30; 
Malleability, Ductility and Tenacity, 30; Ductility, 31; Tenacity, 
31; Elasticity, 35; Sonorousness, 35; Fusibility and Volatility, 
36; Specific Heat, 38; Expansibility, 39; Conductivity, 41; Elec- 
tromotive Force, 42; Specific Gravity, 44. 
CHAPTER III 
Metallic Oxides, 46; Reduction of Metallic Oxides, 50; Metallic 
Sulphides, 53; Reduction of the Metallic Sulphides, 55; Metallic 
Chlorides, 58; Reduction of Metallic Chlorides, 59; Metallic Bro- 
mides, 60; Reduction of Metallic Bromides, 60; Metallic Iodides, 
61; Metallic Fluorides, 61; Metallic Cyanides, 61; Metallic Selen- 
ides, 62; Reduction by Electricity, 62. 
COMPOUNDS OF METALS AND NONMETALS 
MELTING METALS 
CHAPTER IV 
Refractory Materials, 64; Fluxes, 68; Fuel, 70; Reduction 
of Ores, 76; Furnaces, 77; Blowpipes, 85; Lamps, 93; Supports, 
9S; Ingot Molds, 100; Electric Furnaces, 102. 
9 10 
CONTENTS 
CHAPTER V 
Alloy, 117; Amalgam, 117; The Physical Properties of Alloys, 
123; Annealing and Tempering, 127; Influence of Certain Metals 
in Alloys, 129; A Solder, 129; Preparation of Alloys, 132; Eutec- 
tic Alloys, 134. 
ALLOYS 
CHAPTER VI 
Occurrence, 138; Reduction of Galenite, 138; Properties, 139; 
Dental Applications, 140; Compounds with Oxygen, 140; Actions 
of Acids on Lead, 141; Alloys, 142; Tests for Lead in Solution, 
145; Blowpipe Analysis, 146; Electrodeposition of Lead, 147. 
LEAD 
CHAPTER VII 
ANTIMONY 
Occurrence, 148; Reduction, 148; Properties, 149; Compounds 
with Oxygen, 149; Actions of Acids on Antimony, 150; Alloys, 
151; Tests for Antimony in Solution, 152. 
CHAPTER VIII 
TIN 
Occurrence, 153; Reduction, 153; Properties, 155; Dental Ap- 
plications, 155; Compounds with Oxygen, 156; Actions of Acids 
on Tin, 157; Alloys, 158; Tests for Tin Solution, 161; Elec- 
trodeposition of Tin, 162. 
CHAPTER IX 
BISMUTH 
Occurrence, 163; Reduction, 163; Properties, 164; Compounds 
with Oxygen, 164; Action of Acids on Bismuth, 165; Alloys, 165; 
Tests for Bismuth in Solution, 170. 
CHAPTER X 
ZINC 
Occurrence, 171; Reduction, 171; Properties, 172; In the Arts, 
174; Dental Applications, 175; Dies, 175; Zinc Oxide, 177; Zinc CONTENTS 
11 
Cements, 179; Orthophosphoric Acid, 181; Mixing Cements, 184; 
Action of Acids on Zinc, 187; In Alkalies, 188; Alloys, 188; Test 
for Zinc in Solution, 190. 
CHAPTER XI 
Occurrence, 192; Reduction, 192; Properties, 193; Compounds 
with Oxygen, 193; Actions of Acids on Cadmium, 194; Compounds 
of Cadmium, 194; Alloys, 194; Tests for Cadmium in Solution, 
196. 
CADMIUM 
CHAPTER XII 
COPPER 
Occurrence, 197; Reduction, 199; Properties, 202; Dental Ap- 
plications, 203; Compounds with Oxygen, 204; Action of Acids on 
Copper, 205; Alloys, 206; Dental-Amalgam Alloys, 212; Tests for 
Copper in Solution, 212; Electrodeposition of Copper, 213. 
CHAPTER XIII 
Occurrence, 214; Reduction, 216; Electric Furnace Reduction, 
220; Properties, 221; Modifications of Iron, 222; Cast Iron, 222; 
Wrought Iron, 223; Steel, 225; Carburized Iron, 230; Galvanized 
Iron, 231; Hardening and Tempering Steel, 232; Tempering, 234; 
Compounds with Oxygen, 236; Action of Acids on Iron, 236; 
Alloys, 237; Tests for Iron in Solution. 238. 
IRON 
CHAPTER XIV 
ALUMINUM 
Occurrence, 240; Reduction, 241; Properties, 242; In the Arts, 
242; In Dentistry, 243; The Compound with Oxygen, 244; Action 
of Acids and Alkalies on Aluminum, 245; Alloys, 246; Tests for 
Aluminum in Solution, 251. 
CHAPTER XV 
Occurrence, 253; Reduction, 253; Pure Mercury, 254; Proper- 
ties, 255; Uses, 256; Compounds with Oxygen, 256; Action of 
MERCURY 12 
CONTENTS 
Acids on Mercury, 257; Alloys, 258; Vermilion, 259; Tests for 
Mercury in Solution, 262. 
CHAPTER XVI 
Occurrence, 264; Reduction, 265; Chemically Pure Silver, 271; 
Properties, 274; Compounds with Oxygen, 274; Action of Acids 
on Silver, 275; Alloys, 275; Tests for Silver in Solution, 277; 
Eleetrodeposition of Silver, 278. 
SILVER 
CHAPTER XVII 
IRIDIUM 
Occurrence, 284; Reduction, 284; Properties, 285; Compounds 
with Oxygen, 285; Action of Acids on Iridium, 285; Alloys, 286. 
CHAPTER XVIII 
Occurrence, 287; Reduction, 287; Properties, 287; Dental Ap- 
plications, 289; Compounds with Oxygen, 289; Action of Acids on 
Palladium, 289; Alloys, 289; Tests for Palladium in Solution, 
291; Tungsten, 292. 
PALLADIUM—TUNGSTEN 
CHAPTER XIX 
PLATINUM 
Occurrence, 294; Reduction, 295; Fusing Platinum, 296; Prop- 
erties, 297; Dental Applications, 299; Compounds with Oxygen, 
300; Action of Acids on Platinum, 301; Alloys, 301; Tests for 
Platinum in Solution, 303. 
CHAPTER XX 
Occurrence, 304; Mining find Extraction, 309; Dredger Min- 
ing, 317; Flotation Process, 318; Cyanide Process, 318; Refining 
Gold, 320; The Roasting Process, 320; Parting Gold, 323; The 
Preparation of Chemically Pure Gold, 327; Properties, 332; Gold 
GOLD CONTENTS 
13 
Beating, 333; Annealing Gold, 338; Properties of Gold Foil, 339; 
Compounds of Gold with Oxygen, 342; Action of Acids on Gold, 
343; Alloys, 345; Gold Plate, 349; Clasp Gold, 351; Crown Gold, 
352; Inlay Gold, 352; Gold Solders, 357; Rules for Computing 
and Compounding Gold Alloys and Examples, 359; Tests for Gold 
in Solution, 364; Eleetrodeposition of Gold, 365. 
CHAPTER XXI 
AMALGAMS 
In the Arts, 370; Dental-Amalgam Alloys, 370; A Dental Amal- 
gam, 371; Formation of Dental-Amalgam Alloys, 371; Comminu- 
tion, 378; Ageing, 379; Mercury, 379; Amalgamation, 380; Ex- 
pansion and Contraction, 386; Flow, 393; Edge Strength, 396; 
Discoloration, 396; Conductivity, 397; Washing, 397. 
CHAPTER XXII 
A Binary Dental Amalgam, 398; Silver, 398; Tin, 399; Gold, 
400; Copper, 400; Platinum, 402; Zinc, 402; Palladium, 402; 
Cadmium, 403; Antimony and Bismuth, 404; Ternary Dental 
Amalgams, 404; Quarternary, Quinary, etc., Dental-Amalgams, 
405; Gold, 406; Copper, 406; Zinc, 406; Analysis of Dental 
Amalgams, 407; Mercury, 408; Tin, 409; Antimony, 409; Silver, 
409; Copper, 410; Cadmium, 410; Zinc, 410; Gold, 410; Platinum, 
411. 
CLASSIFIED AMALGAMS 
LABORATORY PROCEDURE FOR STUDENTS IN DENTAL 
METALLURGY 
Rules and Suggestions to Students, 421; Apparatus Required 
by Each Student, 426; Assignment of Lockers, 427; Compounds 
of Metals and Nonmetals, 428; Lining Fire Boxes: Handling 
Crucibles, 430; Electric Furnaces, 430; Metallurgy of Lead, 431; 
Metallurgy of Tin, 433; Metallurgy of Bismuth, 435; Metallurgy 
of Zinc, 436; Metallurgy of Copper, 439; Metallurgy of Iron, 
441; Metallurgy of Aluminum, 442; Metallurgy of Mercury, 443; 
Metallurgy of Silver, 444; Gold, 446; Amalgam Alloys, 450; Work 
to be Handed in, 451; Laboratory Reagents, 451. ILLUSTRATIONS 
FIG- PAGE 
1. Hydrogen generator 52 
2. Sectional view of blast furnace 78 
3. Beverberatory furnace 79 
4. Crucible furnace 80 
5. A small compact blast furnace 82 
6. A modified type of blast furnace 82 
7. Blast furnace for use with gasoline 83 
8. Iron melting pots » t 84 
9. Fletcher’s solid flame gauze-top stove 84 
10. Blowpipes 85 
11. Improved blowpipe 86 
12. Another form of blowpipe 87 
13. Candle flame 88 
14. Bunsen flame 89 
15. Blowpipe flame 91 
16. Soldering lamp 92 
17. Compound blowpipe 93 
18. Spirit lamp 95 
19. Self-acting lamp and blowpipe 95 
20. Apparatus for using gas 96 
21. Compound blowpipe 97 
22. Foot-bellows 98 
23. Asbestos soldering-block 99 
24. Carbon soldering block with a wooden handle . . . 100 
25. Circular asbestos soldering-block or tray, mounted on 
wooden handle 101 
26. A small hand furnace or soldering-pan 102 
27. Ingot molds for noble metals 103 
28. Apparatus suitable as a support for melting, and as an 
ingot mold 103 
29. An arrangement for melting and molding noble metals 
without a furnace 104 
30. Gronwall type of electric arc furnace 104 
14 ILLUSTRATIONS 
15 
FIG. PAGE 
31. Electric furnace 105 
32. Rheostat resistance coils; correct and defective wiring . 106 
33. Rheostat unassembled 107 
34. Rheostat; under surface of marble top 108 
35. Muffle cores . Ill 
36. Several types of muffles 113 
37. Standard type of muffle 114 
38. Complete furnace without the muffle in place . . . 115 
39. Temperature-composition diagram of gold and silver . 119 
40. Temperature-composition diagrams of alloys forming 
definite chemical compounds 121 
41. Temperature-composition diagram of copper and silver 122 
42. Temperature-composition diagram of gold and copper 122 
43. A furnace for purifying zinc 172 
44. Interior of bag house where oxides of metals are collected 
for commercial use 178 
45. Specimens of native copper from Lake Superior district 198 
46. A vertical section of a copper mine in the Lake Superior 
district 198 
47. Calumet and Heela mine 199 
48. A crude type of b ast furnace used by native Filipinos 
for the reduction of iron 217 
49. Sectional view of blast furnace 218 
50. A primitive Philippine Arastra 266 
51. A cupel 269 
52. James W. Marshall and John A. Sutter 307 
53. The “tail race” at Sutter’s Mill, California . . . 307 
54. A California prospector in early days 308 
55. Ancient gold mining in the Sudan 309 
56. Panning gold 310 
57. The “cradle” in use in the Alaskan gold fields . . 311 
58. Sluicing gold in Alaska 312 
59-60. Two views of hydraulic operations 315 
61. A primitive Philippine dredger operated by hand on the 
interior rivers 315 
62. A huge dredger operating in one of the rivers in the 
Alaskan fields 316 16 
ILLUSTRATIONS 
FIG. PAGE 
63. Photomicrographs showing a comparison between two 
•different castings 354 
64. A 9000-K. G. Olsen machine for testing materials . . 374 
65. Comparison of cylinders packed by testing machine . . 374 
66. Chart showing resistance to crushing strength offered by 
alloys of varying- ages . 379 
67. Mercury alloy ratio, packed under 141 kilos .... 381 
68. Mercury alloy ratio, under 400 kilos 382 
69. Mercury alloy ratio, under 1,131 kilos 383 
70. Results of varying titration time while a constant mer- 
cury ratio was used 384 
71. Results of varying titration time while a constant mer- 
cury ratio was used 384 
72. Doctor G. V. Black’s amalgam micrometer .... 385 
73. Gradual changes in expansion curve as alloy becomes 
progressively coarser 388 
74. Deviation of expansion under varying pressures . . . 390 
75. A dilatometer 391 
76. Views of amalgam cylinders used in measuring reaction 
expansions 392 
77. Observations made with dilatometer 393 
78. Graph showing results of crushing 63 cylinders of high- 
grade dental amalgam 395 
79. Test cylinders of amalgam 396 PRACTICAL DENTAL METALLURGY 
CHAPTER I 
INTRODUCTION 
CHEMISTRY is that branch of science which treats 
of the atomic conditions of matter, and especially of 
atomic changes. It comprehends the combination of 
diverse forms of matter producing new compounds, and 
the separating of already existing compounds into sim- 
pler ones, or resolving them into their ultimate princi- 
ples, which are called— 
ELEMENTS.—Substances whose molecules contain 
one kind of atoms only, and which all physical or chem- 
ical processes have as yet failed to break up or decom- 
pose into two or more dissimilar substances. It is not 
asserted that these substances are absolutely simple or 
elementary, or that they may not be found hereafter to 
yield more than one kind of matter, but merely so far 
as our knowledge extends it is so. 
Ninety-two elements are known to exist at the pres- 
ent time. Of these hydrogen is the lightest. Dr. Geo. 
E. Hale* says, “The heaviest of them are breaking up 
into lighter ones. A few stable elements can be broken 
up by artificial means in the laboratory but no known 
method of combining their constituents has yet been 
found. In the field of astro-physics there is some 
reason to believe that the heavier elements are built 
up from the lighter ones under conditions involving 
the phenomena of radiation and absorption of energy.” 
’Science, 1923, p. 1422. 
17 18 
PRACTICAL DENTAL METALLURGY 
The principal elements are arranged in alphabetical 
order in the following table: 
Table of Elements 
NAME 
SYMBOL VALENCE 
ATOMIC 
WEIGHT 
Aluminum 
... Al. 
Ill 
27.0 
Antimony (Stibium) .... 
... Sb. 
Ill, V 
. . 121.77 
Arsenic 
Ill, V 
74.96 
Barium 
II 
.. 137.37 
Beryllium (Glucinum) .. . 
... Be. 
II 
9.1 
Bismuth 
... Bi 
HI, V 
.. 209 0 
Boron 
... B. 
in' 
10.807 
Bromine 
Br 
i 
79 916 
Cadmium 
... Cd! 
n 
, . 112.40 
Calcium 
... Ca. 
n 
. . 40.07 
Carbon 
C 
IV 
19. non 
Celtium 
ct 
Cerium 
... Ce 
III IV . 
140 9,5 
Cesium 
Cs 
i 
1Z9 81 
Chlorine 
Cl 
i 
36 46 
Chromium 
... Cr. 
IT, III, VI 
52.0 
Cobalt 
• • • Co. 
II, III 
58.94 
Columbium (Niobium) .. 
... Cb. 
Ill, V 
93.1 
Copper (Cuprum) 
.. • Cu. 
I, II 
63.57 
Dysprosium 
... Dy. 
ITT 
.. 162.5 
Erbium 
Ill 
Europium 
Ill 
. • 152.0 
Fluorine 
. . . F. 
I 
Gadolinium 
.. . Gd. 
I 
. 157.3 
Gallium 
.. Ga. 
Ill 
Germanium 
IV 
72.42 
Gold (Auruin) 
... Au. 
I, III 
. 197.2 
Hafnium 
... Hf. 
Helium 
... He. 
4 0 
Holmium 
. .. Ho. 
. . 163 5 
Hydrogen 
... H. 
I 
Indium 
.. . In. 
ni 
Iodine 
.. . I. 
i 
. 126.92 
Iridium 
. . . Ir. 
TIT. TV 
. 1931 
Iron (Ferrum) 
TT. TTT 
55.84 
Krypton 
. . . Kr. 
82.92 
Lanthanum 
TTI 
. 139.0 
Lead (Plumbum) 
. . . Pb. 
TT, TV 
. 207.20 
Lithium 
. . . Li. 
T 
6.94 INTRODUCTION 
19 
Table of Elements—Cont’d 
NAME 
SYMBOL 
VALENCE 
ATOMIC 
WEIGHT 
III 
175.0 
Magnesium 
• • Mg. 
II 
24.32 
Manganese 
.. Mn. 
II, IV, VI, 
VII . 
54.93 
Mercury (Hydrargyrum) . 
.. Hg. 
I, II 
200.6 
Molybdenum 
.. Mo. 
Ill, IV, VI 
96.0 
. . Nd. 
III 
144.3 
Neon 
.. Ne. 
20.2 
Nickel 
. . Ni. 
II, III 
58.68 
Niton 
.. Nt. 
222.4 
Nitrogen 
.. N. 
III, V 
14.008 
Osmium 
.. Os. 
II, III, IV, 
VIII 
190.9 
Oxygen 
.. 0. 
II 
16.00 
Palladium 
.. Pd. 
II, IV .... 
106.7 
Phosphorus 
. • P. 
Ill, V 
31.04 
Platinum 
Pt 
II, IV 
195.2 
Potassium (Kalium) 
.. K. 
I ' 
39.10 
Praesodymium 
• • Pr. 
Ill 
140.9 
Radium 
II 
226.0 
Rhodium 
• • Rh. 
Ill 
102.9 
Rubidium 
• • Rb. 
I 
85.45 
Ruthenium 
Ill, IV, VI, 
, VIII 
101.7 
Samarium 
• • Sa. 
III 
150.4 
Scandium 
• • Sc. 
Ill 
45.1 
Selenium 
• • Se. 
II. IV, VI 
79.2 
Silicon 
• • Si. 
IV 
28.1 
Silver (Argentum) 
.. Ag. 
I 
107.88 
Sodium (Natrium) 
• • Na. 
I 
23.00 
Strontium 
. • Sr. 
IT 
87.63 
Sulphur 
. . S. 
II, IV, VI 
32.06 
Tantalum 
V 
181.5 
Tellurium 
IV, VI ... 
127.5 
Terbium 
. • Tb. 
Ill 
159.2 
Thallium 
• . Tl. 
I. Ill 
204.0 
Thorium 
. . Th 
TV 
232 15 
Thulium 
169.9 
Tin (Stannum) 
. . Sn. 
TT IV 
118.7 
Titanium 
• • Ti. 
ITT, IV ... 
48.1 
Tungsten (Wolfram) 
.. W. 
VI 
184.0 
Uranium 
.. U. 
TV. VI ... 
238.2 
Vanadium 
.. V. 
III. V 
51.0 
Xenon 
130 2 
Ytterbium 
.. Yb. 
in 
173.5 
Y ttrium 
Yt 
in 
RQ 33 
Zinc 
Tl 
65.37 
Zirconium 
IV 
90.6 20 
PRACTICAL DENTAL METALLURGY 
These ninety-two elements are classed under two 
great divisions; viz., metallic and nonmetallic. 
METALLIC ELEMENTS, the metals, or as they are 
frequently termed, the positive elements usually having 
the ending “um” or “ium,” which signifies possessing 
metallic properties, are about sixty-five in number, and 
the study of these constitutes— 
METALLURGY.—The science of economically ex- 
tracting metals from their ores, and applying them to 
useful purposes. 
AN ORE is a mineral containing one or more metals 
in a free or combined state. The chief ores from which 
metals are obtained are sulphides, oxides, or carbon- 
ates. In some instances metals are obtained in pay- 
ing quantities from such ores as chlorides, arsenides, 
sulphates, phosphates, or silicates. Gold and platinum 
are usually found in a free metallic state, then they 
are termed “native.” Tin, silver, copper, and some 
other metals are occasionally found native. 
j GANGUE.—The foreign material or impurity in 
which minerals are found embedded is variously known 
as “gangue,” “veinstone,” or “matrix.”’ This may 
consist of such carbonates as calc-spar, limestone; 
such silicates as feldspar, hornblende, and mica; such 
sulphates as heavy-spar; and such fluorides as fluor- 
spar. This is separated from the mineral by the miner 
in crushing, sorting, and washing operations known 
as “dressing,” after which the ore is sent to the 
metallurgist. Practically all this is now done at one 
plant known as the furnace or mill. 
SLAG is the fused metallic dross separated from 
the metal bearing compounds when the minerals of 
iron, copper, silver, nickel, and cobalt are fused with INTRODUCTION 
21 
arsenic, sulphur, or silica. Oxides unite with the silica 
and form a part of the slag. 
REGULUS.—When the minerals of iron, copper and 
silver are smelted or fused with substances containing 
sulphur, the resulting sulphide is known as “regulus” 
or “matte.” 
SPEISS.—When the minerals of nickel and cobalt 
are similarly fused and converted into arsenides, the 
combination is termed “speiss.” 
REDUCTION is the process of freeing a metal from 
its combinations. There are three methods employed, 
viz.: fusion, when the ore is subjected to heat and the 
metal separated from the ore and collected in a molten 
mass, usually at the base of the furnace; leaching or 
dissolving, when a solvent is applied to the ore or alloy 
and the metal subsequently precipitated from its solu- 
tion by chemicals; and gaseous, when heat is applied 
and the metal is volatilized and collected as a liquid 
or solid in separate Any substance em- 
ployed in effecting this result is called a “reducing 
agent.” Where heat is used the chief reducing agents 
are carbon, hydrocarbons, carbon monoxide,-.aud hy- 
drogen and the process is called smelting. In this 
process metallic compounds are usually converted into 
oxides, if they do not already exist as such, which is 
generally accomplished by heating them in contact 
with atmospheric air. For example, when zinc car- 
bonate is thus treated, the reaction or reduction is as 
follows: 
ZnC03 (+ heat) = ZnO + C02 
Then by addition of the reagent carbon the metallic 
zinc is obtained thus: 22 
PRACTICAL DENTAL METALLURGY 
2ZnO + C = 2Zn + C02 
Sulphides are reduced by partially converting the 
metallic sulphide into an oxide, with the aid of heat, 
when the remaining metallic sulphide reacts with the 
oxide produced, freeing the metal, as for example: 
PbS + 2PbO = S02 + 3Pb 
ROASTING: When metalliferous substances are re- 
duced to oxides by heating, in contact with atmospheric 
air, the process is called “roasting.” When they are 
similarly heated in contact with chlorine gas or with 
common salt, the operation is known as “ chlorinizing 
roasting. ’ ’ 
CALCINATION is the process of heating a substance 
at a temperature below its melting point. The object 
is to expel all volatile and organic matter, and, in the 
case of an ore, to render it more porous preparatory 
to roasting or smelting. 
DISTILLATION.—The act of separating in the form 
of vapor the more volatile portions of a substance by 
heat, and subsequently condensing them to a liquid 
state in some cooling receiver or worm. Mercury and 
zinc are extracted from their ores by this process, 
and the former metal is purified by redistillation. 
SUBLIMATION is an analogous process, except that 
the substance separated as a vapor is condensed as a 
solid. For example, arsenic is sublimed from ores 
containing it. 
SCORIFICATION is the process of converting the 
foreign substance present in a metallic compound into 
slag by oxidation and union with silica. The vessel in 
which the operation is effected is termed a “scorifier.” 
OCCLUSION is the property possessed by some metals 
of absorbing and retaining certain gases, thus—iron 23 
INTRODUCTION 
absorbs carbonic oxide readily, silver occludes oxygen, 
platinum will absorb considerable quantities of oxygen 
and hydrogen, and it has been demonstrated that pal- 
ladium foil under certain circumstances will absorb 
982 volumes of hydrogen. 
CEMENTATION is the reaction which takes place 
under heat between two substances without fusion.— 
Thus, when iron is heated with charcoal (carbon) a 
reaction takes place and the iron is said to become 
carburized. Such a reaction is known as “carburizing 
cementation.” When iron is heated with red hematite, 
Fe2 03, as an oxidizing agent, the impurities contained 
in it are modified or removed by the cement powder. 
Such a process is known as an “ oxidizing cementation. ’ ’ 
DRY PROCESS.—The operation of separating metals 
from metallic combinations or metalliferous matter by 
the agency of heat. 
WET PROCESS.—The operation of separating metals 
from metallic combinations or metalliferous matter by 
suitable solvents, such as the ordinary acids, etc., and 
then precipitating those metals desired with proper 
reagents or by an electrochemical process. 
Of the elementary metals mentioned, only fourteen 
are ordinarily employed in their true metallic condition. 
These are: 
Iron 
Copper 
Lead 
Zinc 
Tin 
Aluminum 
Nickel 
Antimony 
Magnesium 
Bismuth 
Gold 
Silver 
Mercury 
Platinum 
About twelve are more or less useful in the prepara- 
tion of medicines, in the arts for coloring pigments, 
and for alloying purposes. These are: 24 
PRACTICAL DENTAL METALLURGY 
Potassium 
Sodium 
Calcium 
Lithium 
Barium 
Manganese 
Arsenic 
Chromium 
Cobalt 
Cadmium 
Titanium 
Uranium 
The remaining metals are more or less rare, and 
many of them are of little or no practical value in the 
metallic state. However, the steel industry has been 
revolutionized by the use of some of these rare metals, 
such as vanadium, molybdenum, and tantalum in mak- 
ing alloys, and the use of tungsten in incandescent 
lamps and radium in medicine is indicative of the bene- 
fits which may be derived from further researches in 
metallurgic procedure. 
The metallurgist groups the metals into two classes, 
which are known as noble and base: 
NOBLE METALS are those whose compounds with 
oxygen are decomposable by heat alone, at a tempera- 
ture not exceeding redness. These are: 
Mercury 
Silver 
Gold 
Platinum 
Palladium 
Rhodium 
Ruthenium 
Osmium 
Iridium 
BASE METALS are those whose compounds with 
oxygen are not decomposable by heat alone, retaining 
oxygen at high temperatures. 
The base metals are further subdivided with refer- 
ence to their affinity for oyxgen and other chemical 
properties. 
The First Division contains five metals. They are 
very readily oxidized, and their oxides are all soluble 
in water, giving it a strongly alkaline reaction; so also 
are their phosphates and carbonates, with the excep- INTRODUCTION 
25 
tion of lithium phosphate, which is quite insoluble, and 
the carbonate, which is only sparingly soluble. They 
all energetically decomnose water at ordinary tempera- 
tures, liberating hydrogen, and forming hydroxides in 
solution. They are soft, of low specific gravity, and 
fusible at low temperatures. These are: 
Potassium 
Sodium 
Lithium 
Rubidium 
Caesium 
The Second Division contains six metals, all of 
which decompose water at ordinary temperatures with 
the exception of magnesium, combining with the oxy- 
gen. Their oxides of the common metals are more or 
less soluble in water, rendering it alkaline; but their 
neutral carbonates and phosphates are insoluble. 
These are: 
Barium 
Strontium 
Glucinum (Beryllium) 
Calcium 
Magnesium 
Badvum 
The Third Division contains twelve metals, of which 
but three are of much importance. Those which have 
been isolated do not decompose water at ordinary tem- 
peratures without the addition of a weak acid or a slight 
rise of temperature. Their oxides and carbonates are 
insoluble in water. These are: 
Aluminum 
Chromium 
Titanium 
Thorium 
Yttrium 
Zirconium 
Erbium 
Cerium 
Lanthanum 
Didymium 
Tantalum 
Columbium 26 
PRACTICAL DENTAL METALLURGY 
The Fourth Division contains nine metals, the chief 
of which decompose water at a red heat. These are: 
Iron 
Nickel 
Cobalt 
Manganesium 
Zinc 
Uranium 
Vanadium 
Thallium 
• 
Indium 
The Fifth Division contains four metals, which do 
not decompose water at any temperature. These are: 
Cadmi/um 
Lead 
Bismuth 
Copper 
The Sixth Division contains six metals. All the 
higher oxides of these metals have acid properties. 
These are: 
Tin 
Antimony 
Arsenic 
Molybdenum 
Tungsten 
Tellurium 
The principal nonmetallic elements may be divided 
according to their physical states at ordinary tempera- 
tures, thus: 
Gases 
Oxygen 
Hydrogen 
Nitrogen 
Chlorine 
Fluorine 
Helium 
Liquid 
Bromine 
Solids 
Carbon 
Boron 
Silicon 
Sulphur 
Selenium 
Phosphorus 
Iodine CHAPTER II 
PROPERTIES OF METALS 
A METAL is an elementary substance, solid at ordi- 
nary temperatures, with the single exception of mercury 
(a liquid solidifying at—39° C.), having a peculiar lus- 
ter, called metallic “luster,” insoluble in water, a con- 
ductor of heat and electricity, possessing the quality of 
uniting with oxygen to form a basic oxide, and having 
the property of replacing hydrogen in chemical reac- 
tions, as, for example: 
Zn + H2S04=ZnS04 + H2 
No line can be sharply drawn between metals and 
nonmetals; just as no line can be drawn between 
soluble and insoluble, poisonous and nonpoisonous, 
substances. The two elements, arsenic and tellurium 
may well be considered the intermediate links between 
the two classes. 
All metals, when exposed in an inert atmosphere to 
a sufficient temperature, assume the form of liquids 
and present the following characteristic properties: 
They are practically nontransparent and reflect light 
in a peculiar manner, producing what is called metal- 
lic luster. When melted in nonmetallic vessels, they 
take the shape of a convex meniscus. When exposed 
to greater temperatures, some sooner, others later, pass 
into vapors. What these vapors are like is not known 
in many cases, since, as a rule, they can be produced 
only at very high temperatures precluding the use of 
27 28 
PRACTICAL DENTAL METALLURGY 
transparent vessels. Silver vapor is blue, that of potas- 
sium green, and many others—mercury, for example— 
colorless. The liquid metals, when cooled down suf- 
ficiently, some at lower, others at higher temperatures, 
congeal into compact solids, endowed with relative 
nontransparency and the luster of their liquids. 
NONTRANSPARENCY.—Metals as a rule are non- 
transparent, or opaque, yet some have proved to possess 
the property of transparency in a low degree at least. 
In the case of gold, through the leaf, or thin films pro- 
duced chemically on glass plate, a light green color is 
transmitted. This is ascribed to the gold aggregating 
and allowing white light to pass through the inter- 
stices. Also very thin films of mercury are said to 
transmit light with a violet-blue color, and copper, it 
is claimed, is somewhat translucent; while silver in thin 
films .000083 of an inch thick is opaque in an atmos- 
phere of hydrogen or coal-gas, but in the air trans- 
parency begins at 240° C. and is quite complete at 
390° C. 
COLOR.—Most metals range from the pure white of 
silver and tin to the bluish hue of lead. Bismuth is a 
light gray, with a delicate tinge of red. Copper is 
called the “red metal.’’ Gold is a rich yellow; barium 
and strontium a straw color, while calcium exhibits a 
little deeper shade of that color. 
LUSTER.—Polished metallic surfaces, like those of 
other solids, divide any incident ray into two parts, 
of which one is refracted, while the other is reflected, 
with this difference, however, that the former is com- 
pletely absorbed, while the latter, in regard to polari- 
zation, is quite differently affected, which fact, in all PROPERTIES OF METALS 
29 
probability, accounts for the peculiar property of 
metallic luster. 
METALLOGRAPHY.—Broadly considered, metal- 
lography includes all those methods of investigation 
which throw light on the internal structure of metals 
and alloys. The most useful branch of this science is 
microscopic metallography or a study of prepared sur- 
faces of metals by means of the microscope. Their 
structure as revealed by the metallurgical microscope 
has revolutionized the metal industries, more particu- 
larly in connection with the steels, brasses and bronzes, 
but it is rapidly being applied to all of the metal in- 
dustries. The polished surface of a metal when etched 
with a suitable reagent, and examined under the mi- 
croscope shows the crystals which, due to interference 
during their formation, are irregularly shaped. The 
effect of forging, tempering and annealing is shown 
and in connection with the temperature composition 
diagram, the physical properties of the alloys can often 
be partially determined. The presence of imperfec- 
tions in cast metals can often be determined indicating 
the causes of failure of the metal under stress. 
ODOR AND TASTE.—Most metals are destitute of 
odor and taste. Peculiar odors are, however, evolved 
from some of them when heated; in fact, one of the 
means of determining arsenic consists in the recog- 
nition of its characteristic smell of garlic when heated. 
Iron, copper, or zinc when heated also evolve peculiar 
odors. The taste which is perceived in some is no 
doubt due to their peculiar character, although in 
some cases it may depend upon voltaic action set up 
by the chemical agency of the saliva, the metal not 
being perfectly pure. If a piece of zinc be placed 30 
PRACTICAL DENTAL METALLURGY 
upon the tongue, and a piece of silver under it, and 
the edges joined, a metallic taste will be perceived de- 
pendent upon slow solution of the zinc under galvanic 
action. 
CRYSTALLINE FORM.—Most metals are capable of 
crystallization, and their crystals belong to the fol- 
lowing systems: Regular—Silver, gold, palladium, mer- 
cury, copper, iron, lead; quadratic—tin, potassium; 
rhombic—antimony bismuth, tellurium, zinc, mag- 
nesium. 
Perhaps all metals assume a crystalline structure on 
congealing, differing only in degree of visibility. Anti- 
mony, bismuth, and zinc exhibit a very distinct crystal- 
line structure plainly visible in broken ingots. Tin is 
also crystalline, which fact is evinced by the “tin cry” 
when a bar of the metal is bent, the crystal faces 
sliding over one another; but the bar is not easily 
broken, and exhibits an apparently noncrystalline 
fracture. Gold, silver, copper, aluminum, cadmium, 
iron, lead, cobalt, and nickel are practically amor- 
phous, the crystals being so closely packed as to vir- 
tually produce a homogeneous mass. 
MALLEABILITY, DUCTILITY, AND TENACITY 
are properties possessed by some metals by virtue of 
the cohesive power of their molecules, and are to that 
extent kindred. 
Malleability is that quality possessed by a metal 
which permits it to be hammered or rolled into thin 
sheets without breach of continuity. Many metals 
possess this property relatively, it being the most won- 
derfully exemplified in gold. Leaves of this metal have 
been produced .000027 of an inch in thickness, each 
grain of which will cover an area of 75 square inches. PROPERTIES OP METALS 
31 
DUCTILITY.—Ductility is that property possessed 
by some metals by virtue of which they may be drawn 
into wire. The operation consists in forcibly drawing 
the metal through a series of holes, which gradually 
decrease in size, in a hard-steel draw-plate. Gold is 
also the most ductile of all metals, a single grain of it 
having been drawn into a wire 550 feet in length. 
This was accomplished by covering the gold wire with 
silver, which is also remarkably ductile, thus making 
a composite wire of greater thickness. After drawing 
this down to the greatest possible degree of tenuity, 
the silver was dissolved off by nitric acid, leaving a 
gold wire .0002 of an inch in diameter. 
TENACITY.—Tenacity is that property possessed 
by metals in consequence of which they resist rupture 
when exposed to tension. Their relative tenacity may 
be ascertained by preparing wires of exactly equal 
diameters and comparing the number of pounds weight 
each will sustain before rupture. 
These properties are shown relatively for some of 
the more important metals in the following table: 
Malleability 
Ductility 
Tenacity 
1. Gold 
1. Gold 
1. Iron 
2. Silver 
2. Silver 
2. Copper 
3. Copper 
3. Platinum* 
3. Platinum 
4. Aluminum 
4. Aluminum 
4. Silver 
5. Tin 
5. Iron 
5. Gold 
6. Platinum 
6. Nickel 
6. Zinc 
7. Lead 
7. Copper 
7. Tin 
8. Zinc 
8. Palladium 
8. Lead 
9. Iron 
9. Cadmium 
10. Nickel 
10. Zinc 
11. Palladium 
11. Tin 
12. Lead 
*Spme authorities give platinum first rank in ductility; though the 
majority are in accord with the above order. 32 
PRACTICAL DENTAL METALLURGY 
The two properties of malleability and ductility are 
closely related to each other, yet, as may be seen from 
the preceding table, they do not always parallel each 
other, for the reason that ductility in a higher degree 
than malleability is determined by the tenacity of the 
metal; for example, tin, though quite malleable, is very 
slightly ductile, and iron, while ninth in point of mal- 
leability, is fifth in ductility. In the operation of ham- 
mering out a metal which the quality of malleability 
permits, the granular particles are flattened and spread 
in all directions, while in those allowed by its ductility 
each granular particle is elongated into a fiber. 
There are several conditions which materially modify 
the properties of malleability, ductility, and tenacity, 
the most important of which are— 
Purity.—Gold is the most malleable of all metals, 
yet if the merest trace of lead, itself a soft and mal- 
leable metal, be contained in it, the gold becomes too 
brittle to be worked, and especially is this the case if 
the gold has any silver also with it, as most gold has. 
This destruction of malleability and tenacity is still 
more pronounced when antimony or similar metals are 
mixed with gold, even in minute quantities.* 
Temperature also exercises a very great modifying 
influence over these properties; for example, a bar of 
zinc obtained by casting is exceedingly brittle, but 
when heated to 100° or 150° C. it may be rolled into 
thin sheets or drawn into wire. Such sheet or wire 
then remains malleable and ductile after cooling. The 
explanation of this remarkable fact is, that the loosely 
cohering crystals have become intertwisted and forced 
into absolute contact with each other, and this is sup- 
*See chapter on Gold. PROPERTIES OF METALS 
33 
ported by the fact that the rolled zinc has a somewhat 
higher specific gravity than the original ingot. If the 
temperature be carried to 205° C. it again becomes so 
brittle that it may be poAvdered in a mortar. Extreme 
care, therefore, must be exercised in the handling of 
hot zinc dies, for if by accident one be dropped upon 
a hard surface it is likely to be spoiled. Aluminum, 
magnesium, and some other metals, which at ordinary 
temperatures possess little or no ductility, may be 
drawn into wire when heated. 
These qualities are greatly diminished in alloys by 
heating. Some forms of brass, for example, which are 
soft, tenacious, and ductile at ordinary temperatures, 
are made quite brittle by heating to dull redness. 
Again it is quite certain that 18-carat gold solder is 
brittle at red heat. 
The tenacity of metals in general is greatly dimin- 
ished by heating. The exceptions to this are in the 
cases of iron, steel, and gold. 
The table on page 34 shows the results obtained by 
Wertheim* in his experiments on a number of the 
metals at temperatures from 15° to 20° C. 
Annealing.—Pure iron, copper, silver, and other met- 
als are easily drawn into wire, rolled into sheets, or 
flattened under the hammer. But all these operations 
render the metals harder, and detract from their plas- 
ticity. Their original softness can be restored to them 
by annealing, i. e., by heating them more or less and 
then plunging them into cool water, oil, etc. In the 
case of iron, however, this applies only if the metal is 
perfectly pure. If it contains a few parts carbon per 
thousand, the annealing process, instead of softening 
*Annales de Chimie et de Physique (III.), xii. 34 
PRACTICAL DENTAL METALLURGY 
Name 
For Wire 1 Squa 
Weight (in Ki 
Permanent Elon- 
gation of l^oooo 
re Mm. Section, 
os) Causing 
Breakage 
Iron, drawn 
32.00 
61.00 
11 annealed 
Under 5.00 
47.00 
Copper, drawn 
12.00 
40.00 
‘ ‘ annealed 
Under 3.00 
30.00 
Platinum, drawn 
34.00 
11 annealed 
23.00 
Silver, drawn 
11.30 
29.00 
1 ‘ annealed 
2.60 
16.00 
Gold, drawn 
13.50 
27.00 
* ‘ annealed 
3.00 
10.00 
Zinc, drawn 
.75 
13.00 
‘ ‘ annealed 
1.00 
Tin, drawn 
.45 
2.45 
‘1 annealed 
.20 
Lead, drawn 
.25 
2.10 
‘1 annealed 
.20 
1.80 
the metal, gives it a “temper,” meaning a higher de- 
gree of hardness and elasticity.* 
Welding.—The process of joining two clean surfaces 
of a metal together by pressure is called welding. This 
property is possessed by iron at white heat, but lead 
and gold will cohere at ordinary temperatures in pro- 
portion to their purity. Two pieces of iron may be 
welded by a current of electricity sent through the 
junction, when the metal is heated by the resistance 
offered to the passage of the current. 
Thermite Welding.—Based upon the discovery that 
finely divided oxides mixed in volumetric proportions 
with finely divided aluminum will, when ignited in one 
spot, produce a temperature of about 3000° C. within 
one-half minute, without any supply of heat or energy 
from the outside. The affinity of aluminum for oxygen 
is such that it draws the latter out of the metallic 
*See chapter on Iron. PROPERTIES OF METALS 
35 
oxide, and combines with it, thus setting the metal 
free. For welding purposes, Fe203 is used. 
Forging.—The process of hammering metals out into 
various shapes. Some metals may be forged while 
cold, while others must be hot. This process demon- 
strates a property of metals known as “solid flow.” 
ELASTICITY.—All metals are elastic to this extent, 
that a change in form brought about by stresses not 
exceeding certain limit values, will disappear when 
the stress is removed. Strains exceeding the “limit of 
elasticity” result in permanent deformation, or, if suf- 
ficiently great, in rupture. This property may be in- 
creased in some metals by compounding and alloying. 
Thus, iron compounded with the proper amount of car- 
bon, has its elasticity increased to the very highest de- 
gree, while the metal itself is almost devoid of the 
quality. The same is true of copper and zinc, in some 
forms of brass, also of gold and platinum, when al- 
loyed with copper; both are soft and possessed of lit- 
tle elasticity, yet when combined in proper propor- 
tions with copper, an alloy is produced which is quite 
elastic and may be used for clasps for artificial den- 
tures. 
SONOROUSNESS.—This is a property possessed by 
the harder metals, and is quite marked in certain alloys, 
such as those of copper and tin, known as bell-metal, 
and in steel wires which produce the sound in pianos. 
Lead, which is but feebly, if at all, sonorous, may be- 
come so, it is claimed, if cast in the shape of a mush- 
room. Aluminum emits a characteristic sound when 
struck. The first article known to have been made of 
aluminum was a baby rattle for the infant Prince Im- 
perial of France, for which purpose it was well fitted on 36 
PRACTICAL DENTAL METALLURGY 
account of its sonorousness. Impurities sometimes in- 
crease the sonorousness of a metal, as in the case of 
antimony in lead. 
FUSIBILITY AND VOLATILITY.—All may be 
fused, and most of them are capable of being volatilized, 
but the temperature at which they become fluid differs 
greatly in different metals, as the following table shows: 
It will be remembered that mercury is in a fused state 
PROPERTIES OF METALS* 
Name of Metal 
Fusing Point, C. 
Boiling Point, C. 
Crystalline Form 
Aluminum 
658.7 
x2200. 
octahedral 
Antimony 
630. 
1330. 
hexag. rhomb. 
Bismuth 
271. 
1490. 
rhomb. 
Cadmium 
320.9 
785. 
crystalline 
Copper 
1083. P. 
2310. in H 
crystalline 
Gold 
1063. 
2610.-2000. 
regular 
Iridium, sp. g. 15.86 
2350. 
white spongy 
‘ ‘ sp. g. 22.42 
1950. 
reg. or hexag. 
Iron, pure 
1530. 
2450. 
cub. or reg. 
‘ ‘ wrought .... 
1600. 
octahedral 
‘ ‘ white pig. .. 
1075. 
‘ ‘ gray “ ... 
1275. 
‘ ‘ steel 
1375. 
Lead 
327.4 
1555. 
reg. or monocl. 
Magnesium 
651. 
1120. 
Manganese 
1230. 
1900. 
monoclinic 
Mercury 
—38.87 
357.33 
octahedral 
Nickel 
1452. 
Osmium 
2700. 
amorphous 
Palladium 
1550. 
reg. hexasr. 
Platinum 
1755. 
Potassium 
62.3 
757.5 
Silver 
960.5 Ps 
1950. 
Sodium 
97.5 
877.5 
Tin 
231.9 P3 
1450.-1600. 
Zinc 
419.4 
930. 
x greater than; P melts at 1065 in air; P2 melts at 955 in air; 
P3 varies with specific gravity. 
*\’an Nostrand’s Chem. Ann., 1922. PROPERTIES OP METALS 
37 
and volatilizes to a limited extent at ordinary tempera- 
tures. Osmium readily volatilizes before fusion. 
POUILLET »S SCALE OP TEMPERATURE* 
Incipient redness 525° C. 
Dull red 700 
Cherry red 900 
Deep orange 1100 
White 1300 
Dazzling white 1500 
Metals may be characterized as fixed and volatile. 
Of their volatility we have little precise knowledge. 
The boiling points of a few are given in the following 
table: 
Name of Metal 
Boiling Point 
Authority 
Mercury 
357.3° C. 
Olsen 
Cadmium .. 
785. ° O. 
C ( 
Zinc 
918. ° C. 
c c 
Potassium 
757.5° C. 
(( 
Sodium 
877.5° C. 
(( 
For practical purposes the volatility of metals may 
be classed as follows: 
1. Distillable below redness: Mercury. 
2. Those distillable at red heats: 
Cadmium 
Zinc 
Magnesium 
Potassium 
Sodium 
3. Those which are volatilized more or less readily 
ivhen heated beyond their fusing points in open crucibles: 
*Sexton. 38 
PRACTICAL DENTAL METALLURGY 
Antimony (very readily) 
Lead 
Bismuth 
Tin 
Silver 
4. Those which are with very great difficulty volatil- 
ized, if at all: 
Gold 
Copper (?) 
5. Those which are practically fixed, or nonvolatile: 
Copper (?) 
Iron 
Nickel 
Cobalt 
Calcium 
Aluminum 
Lithium 
Strontium 
Barium 
“In the oxyhydrogen flame silver boils, forming a 
blue vapor, while platinum volatilizes slowly, and 
osmium, though infusible, very readily.”* 
“It is doubtful,” says Makins, “if gold is volatile 
per se. But if gold be alloyed with copper, it has been 
shown by Napier to be considerably volatilized, so that 
quantities, amounting to 4T/2 grains, could be collected 
during the pouring out of 30 pounds weight from a 
crucible. * * * That mixtures of gold, silver, and 
lead, when cupellated together, volatilize considerably.” 
SPECIFIC HEAT.—Equal weights of different met- 
als have been found to absorb different amounts of 
heat when subjected to the same temperature. They, 
indeed, possess different capacities for heat. Thus, the 
amount of heat necessary to raise a given weight of 
water has been found to be 31 times as great as that 
required to raise an equal weight of platinum through 
the same interval of temperature; or, in other words, 
the amount of heat required to raise a given weight 
'William Dittmar. 39 
PROPERTIES OF METALS 
of water through 100° C. will raise 31 times the same 
weight of platinum through 100° C. of temperature. 
Thus, water being taken as the standard or unit, the 
specific heat of platinum is or 0.032 that of water. 
TABLE OF SPECIFIC HEATS AT 0° C. 
1. Iron . 0.1162 
2. Nickel 0.934 
3. Cobalt 0.1030 
4. Zinc 0.0935 
5. Copper 0.0936 
6. Palladium 0.0592 
7. Silver 0.0559 
9. Tin 0.0559 
8. Cadmium 0.0548 
10. Antimony 0.0495 
11. Mercury 0.0334 
12. Gold 0.0316 
13. Platinum 0.0323 
14. Lead 0.0310 
15. Bismuth 0.0301 
16. Aluminum 0.2220 
EXPERIMENT: Prepare bullets of exactly equal weights 
of several of the above metals, such as zinc, silver, tin, cadmium, 
and lead; expose them to the same temperature, for the 
same length of time, and then drop them simultaneously upon a 
sheet of wax placed across an open side of a pasteboard box. They 
will be observed to melt their way through or into the wax in the 
order named. 
EXPANSIBILITY.—The expansion, of metals by 
heat varies greatly. The coefficient of expansion is 
constant only in metals that crystallize in the regular 
system. The others expand differently in the direction 
of the different axes, and to eliminate this source of 
uncertainty in making estimates of their expansibil- 
ity, these metals are employed as compressed powders. 40 
PRACTICAL DENTAL METALLURGY 
Name of Metal 
Expansion 
0° to 100° C 
Platinum, cast 
0.000907 
Gold, cast 
0.001451 
Silver, cast 
0.001936 
Copper, native 
0.001708 
Copper, artificial 
0.001869 
Iron, soft 
0.001228 
Steel, cast 
0.001110 
Bismuth, mean expansion 
0.001374 
Tin, compressed powder 
0.002269 
Lead, cast 
0.002948 
Zinc 
0.002905 
Cadmium, compressed powder 
0.003102 
Aluminum, cast 
0.002336 
Mercury 
0.018153 
The preceding table gives the linear expansion from 
0° to 100° C., according to Fizeau, the length at 0° 
being taken as unity:* 
“The high rate of expansibility of zinc renders if 
particularly valuable as a metal for dies upon which 
to form plates for the mouth in many cases. The metal 
is cast while fluid and at its extreme limit of expan- 
sion, which upon cooling returns to its minimum dimen- 
sions, and thus furnishes a cast a little smaller than 
the plaster model which it represents. It has been 
found that this contraction of the zinc die a trifle more 
than compensates for the expansion which takes place 
in the plaster model in setting, and in the majority of 
cases a plate made thereon adapts itself more accu- 
rately to the mouth than one made upon a die of less 
expansible metal. Even if the contraction undergone 
by the zinc is so great as to produce a die somewhat 
smaller than the mouth, so far from being a detriment, 
it is a positive advantage in most cases of full upper 
•William Dittmar. 41 
PROPERTIES OP METALS 
replacement, as under such conditions the pressure of 
the finished plate is greater upon the alveolar ridge 
than upon the central portions of the hard palate—a 
state of affairs the advantages of which are sufficiently 
obvious without explanation.”* 
CONDUCTIVITY.—Metals are good conductors of 
heat and electricity, but these qualities are very dif- 
ferently exhibited in different metals. All conductors 
tend to obey Ohm’s law; viz., the current is directly 
proportional to the electro motive force and inversely 
proportional to the resistance. Metals are generally 
believed to convey electric current around the con- 
ductor and heat within the conductor, but neither have 
been definitely proved. The ratio of heat and electric- 
ity in good conductors is very nearly constant and is 
proportional to absolute temperature. 
The following table gives the thermic and electric 
conductivities of some of the more important metals 
and alloys: 
t Name of Metal 
Electrical con- 
ductivity at 0° C. 
Thermal conduc- 
tivity at 0° C. 
Ag 1.00 
Silver 
681200 
1.000 
Copper 
640600 
.7198 
Gold 
468000 
.7003 
Aluminum 
324000 
.3435 
Zinc 
186000 
.2653 
Cadmium 
146000 
.2213 
Nickel 
144200 
.1420 
Iron 
131000 
.1665 
Platinum 
91200 
.1664 
Tin 
76600 
.1528 
Lead 
50400 
.0836 
Antimony 
27100 
.0442 
Mercury 
10630 
.0148 
Bismuth 
9260 
.0177 
*Dr. 1$. C. Kirk: Am. System of Dentistry, III, p. 793. 
fFrom Van Nostrand’s Chem. Ann., 1922. 42 
PRACTICAL DENTAL METALLURGY 
Makins states that among the results of Dr. Mat- 
thiessen’s experiments upon the electric conductivity 
of metals “are the facts that impurity of a metal or 
alloying it greatly diminishes its conducting power. 
Rise of temperature again has the same effect. Thus 
between 0° C. and 100° C. great diminution takes place, 
and that not uniformly, as some lose it much more in 
proportion than others, by thus raising the tempera- 
ture. Many lose as much as twenty-five per cent of 
their conducting power. ’ ’ 
An illustration of the comparative conductivity of 
the metals is illustrated in the electric furnaces with 
platinum coils. The electricity is readily transmitted 
from its source by the copper efferent wire, but when 
it meets the platinum that metal offers so much re- 
sistance to the passage of the current, on account of its 
low conducting power, that it becomes white-heated— 
incandescent. 
ELECTROMOTIVE FORCE.—It is well known that 
elements, particularly the metals, possess a property 
spoken of as electromotive force or potential difference, 
and elements have been classed in accordance therewith 
as the Electro-Chemical Series. Berzelius claimed that 
every atom is charged with both kinds of electricity, 
the electrical nature depending on the kind of elec- 
tricity present in excess, thus oxygen being strongly 
charged negatively held place at the negative end of 
the series, while the alkalies were placed at the positive 
end. 
The fundamental theory of Berzelius has been sup- PROPERTIES OP METALS 
43 
ported by J. J. Thomson who proved that the same 
element may be charged positively or negatively de- 
pending on conditions, and that the atoms may consist 
of both positive and negative ions or a nucleus and 
ions. 
The more common metals have been grouped in a 
series (see table, page 44) based on certain properties 
they exhibit, viz.: (1) Any metal will replace any 
other metal in solution below it in this series. (2) 
The oxides of the metals at the positive end down to 
and including manganese cannot be reduced to a pure 
metal even with the aid of a reducing agent; while the 
noble metals, beginning with mercury can be deox- 
idized by heat alone. The intermediate group are quite 
easily deoxidized by the aid of reducing agents. (3) 
All metals down to copper oxidize very readily, the 
alkalies combining so rapidly that heat is evolved and 
they must be kept in a liquid free from oxygen to 
remain permanent. The metals below copper do not 
oxidize to an appreciable extent. (4) Combinations in 
nature again prove this tendency since those metals 
above hydrogen are invariably found in a combined 
state, while those below it are most frequently found 
in a free state. In choosing metals to make a voltaic 
cell one should select those farthest apart in the series 
which are stable and durable enough to serve the 
purpose practically. Likewise, the dentist should give 
some thought to the selection of metals to be placed in 
the mouth in restorative work since the presence of un- 
noticeable stray electric currents may be detrimental 
to the permanence of tooth structure immediately ad- 
jacent to metal fillings or appliances. 44 
PRACTICAL DENTAL METALLURGY 
METALS IN ELECTROMOTIVE FORCE SERIES 
Positive End 
Cesium 
Cobalt 
Rubidium 
Nickel 
Potassium 
Tin 
Sodium 
Lead 
Lithium 
Hydrogen 0.000 
Barium 
Copper 
Strontium 
Arsenic 
Calcium 
Bismuth 
Magnesium 
Antimony 
Aluminum 
Mercury 
Manganese 
Silver 
Zinc 
Palladium 
Chromium 
Platinum 
Cadmium 
Gold 
Iron 
Negative End 
SPECIFIC GRAVITY.—This property varies in dif- 
ferent metals from 0.534 (lithium) to 22.477 (osmium), 
as shown below, and varies also with temperature and 
atmospheric pressure. 
Name of Metal 
Specific Gravity 
Authority 
Lithium 
0.534 
Olsen 
Potassium 
0.862 
Sodium 
0.9712 
Rubidium 
1.532 
ii 
Calcium 
1.5446 
Magnesium 
1.69-1.75 
ii 
Caesium 
1.87 
Glucinum 
1.85 
it 
Strontium 
2.54 
ii 
Aluminum . 
2.703 
Barium 
3.75 
it 
Zirconium 
4.15 
ii 
Vanadium 
6.025 
Gallium 
5.907 
ii 
Lanthanum 
6.154 
Lecoq de Boisbaudran 
Didymium 
6.544 
Hillebrandt and Norton 
Cerium . ... 
6.92 
Olsen 
Antimony 
6.69 
Chromium 
6.92 
Wohler 
Zinc 
7.142 
Karsten 
Manganesium 
7.42 
Brunner 
Tin 
7.294 PROPERTIES OF METALS 
45 
Name of Metal 
Specific Gravity 
Authority 
Indium 
7.12 
Richter 
Iron 
7.844 
Berzelius 
Nickel 
8.28-8.96 
Olsen 
Cadmium 
8.642 
Schroder 
Cobalt 
8.71 
Molybdenum 
10.281 
Olsen 
Copper 
8.89 
W 
Bismuth 
9.747 
Holzmann 
Silver 
10.S3 
Holzmann 
Lead 
11.34 
Deville 
Palladium 
11.4 
Deville and Debray 
Thallium 
11.85 
Crookes 
Rhodium 
12.1 
Bunsen 
Ruthenium 
8.6 
Deville and Debray 
Mercury 
13.595 
II. Kopp 
Tungsten 
19.6 
Olsen 
Uranium 
18.68 
Peligot 
Gold 
19.32 
Matthiessen 
Platinum 
21.16 
Olsen 
Iridium 
15.86 
Osmium 
22.477 
Deville and Debray CHAPTER III 
COMPOUNDS OF METALS AND NONMETALS 
Metals unite with each other indefinitely to form al- 
loys, preserving the metallic appearance and properties. 
They combine with nonmetals in definite chemical pro- 
portions to form compounds of a more precise nature, 
in which case the metallic characters are almost in- 
variably lost. These definite compounds include the 
Oxides 
Sulphides 
Chlorides 
Bromides 
Fluorides 
Cyanides 
Selenides 
Tellurides 
They also combine with 
Nitrogen 
Phosphorus 
Boron 
Silicon 
Carbon 
forming nitrates, phosphates, and phosphides, borates, 
etc. 
METALLIC OXIDES.—All metals combine with oxy- 
gen to form oxides, and most of them in several pro- 
portions. As a class they exhibit a greater disposition 
to unite directly with oxygen than the nonmetals, 
though few of them will do so in their ordinary con- 
dition and at ordinary temperatures. Several metals, 
such as iron and lead, are superficially oxidized when 
exposed to the air under ordinary conditions, but this 
would not be the case unless the air contained water 
and carbon dioxide, which greatly favor oxidation. 
46 COMPOUNDS OF METALS AND NONMETALS 
47 
Among the more important metals, five only are oxi- 
dized in dry air at ordinary temperatures, viz., potas- 
sium, sodium, barium, strontium, and calcium. The 
affinity of these metals for oxygen is so great that 
they must be kept under naphtha (C10H16) or some 
substance containing no oxygen. 
EXPERIMENT: With, a knife cut off a small piece of 
metallic sodium; observe it exhibits a brilliant luster but speedily 
tarnishes by combining with the oxygen of the air, forming the 
oxide (NaO) of sodium. Plunge the sodium into a jar of oxygen; 
it takes fire and burns with a brilliant yellow flame. 
Zinc on the other hand exhibits no disposition to 
combine with oxygen at ordinary temperatures, but is 
induced to do so at a moderate heat (930° C.), when 
it burns with a beautiful greenish flame, produced by 
the union of its vapor with the oxygen of the air, 
forming zinc oxide—ZnO. 
EXPERIMENT: With a piece of zinc foil form a tas- 
sel, gently warm the end, dip into a little flowers of sulphur, kindle, 
and let down into a jar of oxygen, when the flame of the burning 
sulphur will ignite the zinc, which burns with great brilliancy, 
forming oxide of zinc. 
A large number of the metals are oxidized during 
fusion. Lead, for example, may be entirely trans- 
formed into its oxide by continued exposure to suffi- 
cient heat. The oxides of others may be formed by 
heating a carbonate or nitrate of the metal to redness. 
For example, if ZnC03 be heated to a red heat C02 is 
evolved, leaving the pure zinc oxide (ZnO). Again the 
oxide of copper may be obtained by digesting that 
metal in nitric acid,—3Cu + 8HN03 = 3Cu (N03)2 + 
4H20 + 2NO—forming the nitrate of copper, which then 48 
PRACTICAL DENTAL METALLURGY 
may be decomposed by heat into nitric and cupric oxides. 
They are also formed from some salts; for example, 
if to a solution of sulphate or chloride of iron am- 
monium hydroxide be added the hydrated sesquioxide 
of iron (Fe2(OIi)6), the antidote for arsenic is formed. 
And zinc oxide may be obtained by adding potassium 
hydroxide to a solution of zinc sulphate. 
Deflagrating some metals with an oxidizing agent 
produces an oxide of the metal. Advantage is taken of 
this in rendering brittle gold malleable by roasting it 
with nitrate of potassium.* The contaminating tin, 
lead, zinc, antimony, etc., combine with the oxygen of 
the nitrate to form oxides, and are dissolved in the 
molten flux. 
Other metals, such as gold, platinum, iridium, rho- 
dium, and ruthenium, do not combine directly with 
oxygen, their combination being effected only by in- 
direct means, and with difficulty. 
Oxidizing Agents are substances such as— 
Oxygen (0), Potassium chlorate (KC103) 
Air (OandN), Sodium chlorate (NaC103), 
Potassium nitrate (KN03) Iron tetroxide (Fe304), 
Sodium nitrate (NaN03) Iron trioxide (Fe203), 
Carbon dioxide (C02) (at high temperatures in the 
reduction of iron) 
which, imparting a part or the whole of their oxygen 
to another substance, cause it to become oxidized; 
conversely— 
Deoxidizing Agents are substances such as— 
Carbon (C), Compounds of hydrogen 
Carbon Monoxide (CO), and carbon—hydrocarbons 
Hydrogen (H), and sometimes metals, 
*See chapter on Gold. COMPOUNDS OP METALS AND NONMETALS 
49 
which reduce oxides by combining with the oxygen 
which they may contain. 
Examples of oxidation— 
Zn + 0 = ZnO 
3FeC03 + 0 = Fe304 + 3C02 
3FeO + C02 = Fe304 + CO 
Examples of deoxidation— 
2KC103 + 3C = 2KC1 + 3C02 
Fe203 + 3H2 == 2Fe + 3H20 
Fe203 + 3'CO = 2Fe + 3C02 
Substitution or Replacement.—Just as chlorides are 
derived by substitution from hydrochloric acid, HC1, 
so may oxides be represented as being derived from one 
or more molecules of water, H20, by the substitution of 
a metal for hydrogen; with this difference, however, 
that water contains two atoms of hydrogen; therefore, 
the replacement may be only partial, producing the 
hydrated oxide, or complete, forming the oxide. Thus 
the monoxides may be formed by the replacement of 
both atoms of hydrogen by a monad, as Na20, Ag20, or 
a dyad, CuO, ZnO; while the higher oxides may be re- 
garded as two or more molecules of water, in which the 
hydrogen in a similar manner is replaced by its equiva- 
lent of metal, as Mn02, A1203. 
The oxides may be classed as Basic Oxides and Acid- 
forming Oxides. 
Basic Oxides.—When the replacement of the hydro- 
gen is complete, the resulting compound is a basic 
oxide—2K + HoO = K,0 + H„ 50 
PRACTICAL DENTAL METALLURGY 
Hydroxides.—When the replacement of the hydro- 
gen is incomplete, the resulting compound is a hydrox- 
ide—K + H20 = KOH + H, or with the dyad calcium, 
Ca + 2H20 = Ca(OH)2 + H2. 
Bases neutralize acids either partially or entirely, 
replacing either a part or all of their hydrogen, thus 
we have KHS04 and K2S04, which are salts. 
An alkali is only a class of base, and might be de- 
fined as a base which is very soluble in water, as K20 
and Na20. 
It will be observed that metals are capable of form- 
ing bases by combining with oxygen, or salts by com- 
bining with negative radicals. Many metals,* however, 
form acid-forming oxides or anhydrides; thus tin 
forms stannic anhydride (Sn02), and antimony forms 
antimonic anhydride (Sb205), and it is always found 
that the acid-forming oxide of a metal contains a 
larger proportion of oxygen than any of the other 
oxides which the metal may happen to form, thus: 
The Acid-forming Oxides are those metallic oxides, 
or anhydrides which form acids with water, as in the 
case of nonmetallic oxides. 
A number of metallic oxides are found in nature as 
ores from which the metals are reduced. Tin occurs 
as tinstone, Sn02, iron as Fe203, and Fe304, etc. 
REDUCTION OF METALLIC OXIDES.—The vari- 
able affinities exhibited by the metals for oxygen 
groups them into two classes already known as noble 
and base metals. 
Reduction of the Oxides of the Noble Metals.—So 
feeble is the affinity of the noble metals for oxygen 
*See Sixth Division, Chapter I. COMPOUNDS OF METALS AND NONMETALS 
51 
that their oxides are easily decomposed and the metals 
reduced without the aid of any other agency than that 
of simply heating to redness—about 700° C. 
Reduction of the Oxides of the Base Metals.—On the 
other hand the base metals exhibit a very strong af- 
finity for oxygen and the mere application of heat will 
not reduce them. Indeed, in many instances a decided 
increase of temperature serves only to strengthen their 
affinity and hence increases the proportion of oxygen 
in the compounds previously formed. Therefore, in 
addition to heat the assistance of some substance is re- 
quired whose affinity for oxygen is stronger than that 
of the metal and will, when favored by heat, abstract 
the oxygen from the oxide. Thus, the oxide of lead 
may be formed by heating the carbonate: 
PbC03( + heat) = PbO + C02, 
and driving off the carbon dioxide (C02). The lead 
oxide (PbO), however, cannot be further reduced to 
metallic lead by heat; on the contrary, if the heating be 
continued, the production of a higher oxide only will 
be effected. But if, in addition to heating, the oxidized 
lead be covered with a layer of pulverized charcoal, 
which will abstract the oxygen for its own use, uniting 
with it to form carbon dioxide, the lead will be re- 
duced or liberated. Such a reduction is accomplished 
by the reducing or deoxidizing agent, carbon, the ac- 
tion being favored by heat: 
2PbO + C ( + heat) = 2Pb + C02. 
When the lead and zinc used for counter-dies and dies 
in the laboratory are overheated or subjected to fre- 
quent or long continued meltings, they become par- 52 
PRACTICAL DENTAL METALLURGY 
tially oxidized and covered with an earthy looking mass 
consisting of partially oxidized metal. A continued ex- 
posure to heat would, as we have observed, have the 
effect of converting this into an oxide of a higher de- 
gree, but if the molten metal be covered with pulver- 
ized charcoal or carbonaceous substance, such as oil- 
fat, suet, or scraps of beeswax (hydrocarbons), the oxy- 
gen of the oxide will be abstracted, carbon dioxide 
formed and evolved, while the metal wTill be reduced 
to a free state. 
Reduction with Hydrogen.—Other oxides which can- 
not be reduced by deoxidizing agents favored by the 
conditions as stated above may, by the assistance of 
proper apparatus and heat, be reduced by a current 
of dry hydrogen. 
Fig. l. 
EXPERIMENT: Pass the delivery tube of an ordinary 
hydrogen generator (A, Fig. 1) into one end of a drying tube 
(B), well filled with fragments of calcium chloride, for the pur- COMPOUNDS OF METALS AND NONMETALS 
53 
pose of absorbing the moisture which may be carried over with 
the gas; connect the other end of the drying tube with a tube (C) 
upon which a bulb (D) has been blown for the reception of the 
metallic oxide. After the gas has completely driven the air out of 
the apparatus, heat is applied to the bulb containing the oxide. 
As the dry hydrogen flows over the heated oxide in a strong stream 
it combines with the oxygen—favored by heat—and passes out of 
the tube (E) as aqueous vapor, while the metal is left free. 
Reduction with Sulphur.—Some oxides may be best 
reduced by heating with sulphur, in which case sul- 
phur exhibits a greater affinity for the oxygen than 
the metal does, and abstracting it, forms sulphur diox- 
ide (S02). A portion of the sulphur, however, com- 
bines with the metal, converting it into a sulphide or 
sulphate, or a mixture of both. The reduction of such 
compounds is treated under metallic combinations 
with sulphur. 
Reduction with Chlorine.—There are a few oxides 
which may be reduced by chlorine gas. Thus platinum 
oxide is reduced in a current of dry chlorine. 
EXPERIMENT: Repeat preceding experiment, using cal- 
cium oxide in the drying tube, and dry chlorine gas. 
METALLIC SULPHIDES.—Metals combine directly 
with sulphur to form a class of compounds which, from 
a chemical and economical point of view, are almost 
as important as the oxides, since the ores of many of 
the most important metals are found as sulphides, as 
for example, galena (PbS); stibnite (Sb2S3); zinc- 
blende (ZnS) ; greenockite (CdS) ; copper-glance 
(CuS) ; iron pyrites (FeS2) ; cinnabar (HgS) ; silver 
glance (Ag2S), etc. These are generally brittle solids 
possessing so high a degree of luster that some of them 
have been mistaken for gold, hence iron pyrites has 54 
PRACTICAL DENTAL METALLURGY 
been called “fool’s gold.” In composition they re- 
semble the oxides and hydroxides, with many of which 
they are analogous. The exceptions to this analogy 
are the alkalies and alkaline earths, there being but 
two oxides of potassium, sodium, and barium, while 
there are no less than four sulphides of these metals. 
All the metallic sulphides are solid at ordinary tem- 
peratures; most of them fuse at red heat, and some 
sublime unchanged. When roasted in air at high tem- 
peratures, they are converted into sulphates; (ZnS + 202 
favored by high heat = ZnSOJ, or, if they are ex- 
posed to higher and continued heat, into oxides. 
They may be prepared by heating the metals or their 
oxides with sulphur, from the sulphates by heating 
them with charcoal, deoxidizing them, and from their 
soluble salt solutions by adding sulphuretted hydrogen. 
EXPERIMENT: To the following salt solutions in several 
test tubes add a few drops of hydrogen sulphide: 
Pb(C2H302)2 + H,S = PbS + 2HC2H302 
Lead acetate Lead sulphide 
(Black) 
2AsC13 + 3H2S = As2S3 + 6HC1 
Arsenious Arsenious 
Chloride Sulphide 
(Lemon Yellow) 
Cd(N03)2+ H2S— CdS + 2HN03 
Cadmium Cadmium 
Nitrate _ Sulphide 
(Yellow) 
2SbCl5+ 5H2S=3 Sb2S6+ 10HC1 
Antimonic Antimonie 
Chloride Sulphide 
(Orange Yellow) COMPOUNDS OF METALS AND NONMETALS 
55 
Zn(C2HjOa)2+ H„S = ZnS + 2HC2H302 
Zinc acetate Zinc sulphide 
(White) 
HgCl2 + H2S= HgS + 2HC1 
Mercuric chloride Mercuric sulphide 
(1st White) 
(2d Yellow Orange) 
(3d Brown) 
(4th Black) 
REDUCTION OF THE METALLIC SULPHIDES.— 
Since the ores of many of the most important metals 
are sulphides, and it is from such compounds that we 
derive our chief supply of copper, lead, mercury, sil- 
ver, antimony, and several other metals, the subject of 
their reduction is of great importance. 
Flotation Process.—Within the last decade metal- 
lurgists have devised such ingenious methods of re- 
covering metals from their ores on a higher percen- 
tage basis that many of the old ore dumps and slime 
beds are being worked over at a profit. The flotation 
process which is merely a preparatory stage in reduc- 
tion has developed since 1912 to the stage of handling 
20,000,000 tons of ore annually. It is essentially a 
slimes process, that is the ore bearing mineral is re- 
duced to a very fine powder by passing through jaw 
and gyratory crushers, rolling and ball mills, and 
various screens until finally it is reduced to a fine 
powder. To this is added an oil, usually a pine oil 
or creasol or creasote compound. This mixture or slime 
of sulphides, silicious or earthy gangue, oil and water 
is brought gently onto the surface of still water in a 
direction forming an acute angle with the surface of 
the water. The gangue, which has a greater adhesive 56 
PRACTICAL DENTAL METALLURGY 
preference for the water than the oil, sinks while the 
sulphides have a greater adhesive preference for the 
oil and the larger portion of it floats. This is known 
as fllm flotation. If to these slimes a small quantity 
of acid, or alkali, or oil with an acid or alkali, is 
added and gas bubbles are introduced from below the 
sulphide particles are brought to the surface and col- 
lect as a froth. This is known as froth flotation. These 
bubbles survive long enough to perform the metallurgic. 
duty of carrying these particles of rich ore to the sur- 
face where they are collected and dewatered by various 
filtering, decanting, and evaporating processes until 
the cake has reached a minimum content of moisture 
of about 14 per cent, when it is ready for further de- 
hydrating treatment preparatory to roasting. The 
various physical phenomena involved are surface ten- 
sion, adsorption, adhesion and viscosity though col- 
loidal conditions and electrostatic forces may play an 
important part, the latter being suggested by the fact 
that the sulphides most amenable to flotation are good 
conductors of electricity. Originally about three tons 
of oil were added to one ton of ore. Now from 0.5 to 
0.75 of a pound of oil is added to each ton of ore with 
greater success in handling. Copper, lead, and zinc 
are now obtained in large quantities by means of this 
process and where these ores carry any precious metals 
as in argentiferous galena their recovery adds to the 
total values. 
Reduction by Heat.—The reduction of some of the 
metallic sulphides, such as gold, platinum, silver, and 
mercury, is effected by heat alone. The oxygen of the 
air unites with the sulphur, which is evolved as sul- 
phur dioxide, SO?. In some instances, however, a por- COMPOUNDS OP METALS AND NONMETALS 
57 
tion of the oxygen combines with the metal, and an 
oxide instead of the free metal is obtained. In some 
cases the sulphide is oxidized and converted into a sul- 
phate, which in turn may be decomposed at high tem- 
peratures, separating into sulphur dioxide and free 
metal, or, at times, a metallic oxide. Then, again, some 
of the sulphides may, when roasted in air, be converted 
into permanent sulphates capable of resisting high de- 
grees of heat. 
Reduction with Iron.—Iron exhibits a strong affinity 
for sulphur and when favored by heat will abstract it 
from several metals, such as silver, lead, etc. Thus, if 
the sulphide of lead (galena) be heated with scraps of 
iron, metallic lead is freed: 
PbS + Fe = FeS + Pb 
or in the case of silver 
Ag2S + Fe = FeS + 2Ag. 
Reduction with Hydrogen.—The sulphides of such 
metals as antimony, bismuth, copper, tin, and silver are 
decomposed by passing a current of dry hydrogen over 
them at a red heat, the metal being reduced, while the 
hydrogen combines with the sulphur, forming sulphu- 
retted hydrogen: 
CuS + 2H = H2S + Cu. 
Reduction with Chlorine.—Dry chlorine gas also de- 
composes some metallic sulphides, combining with both 
metal and sulphur.* 
Reduction with Acids.—Nitrohydrochloric acid con- 
•Three chlorides of sulphur are known, even though both elements are 
negative. They are C12S2, CLS, and CI4S, the last in combination as SnCl4 
(C1(S),. 58 
PRACTICAL DENTAL METALLURGY 
verts the sulphides into chlorides, and hydrochloric acid 
in a few instances, acts similarly; its hydrogen com- 
bining with the sulphur is evolved as hydrogen 
sulphide. Strong nitric acid also decomposes them, the 
sulphur being oxidized and the liberated metal com- 
bines with the acid to form a nitrate. Mercuric sul- 
phide is the only one that cannot be thus reduced. 
METALLIC CHLORIDES.—All metals combine with 
chlorine, and some of them in several proportions; 
thus we have stannous (SnCl2) and stannic chlorides 
(SnClJ. 
Some of the chlorides occur in nature, those of sil- 
ver (AgCl) and mercury (Hg2Cl2) as minerals, and 
those of sodium and potassium in enormous quantities 
in the solid state and dissolved in waters. 
They may be regarded as derived, like the oxides, 
from a type—HC1—substituting for the hydrogen of 
one or more molecules of hydrochloric acid an equiva- 
lent in metal, thus: 
From 1HC1, are derived monochlorides like KC1. 
“ 2HC1 “ “ dichlorides, “ SnCl2. 
“ 3HC1 “ “ trichlorides, “ AuC13. 
“ 4HC1 “ “ tetrachlorides, “ SnCl4. 
Preparation.—They may be prepared by the action of 
hydrochloric acid upon the metals. Zinc, tin, cadmium, 
iron, nickel, and cobalt may be readily dissolved by 
hydrochloric acid, forming chlorides respectively and 
liberating hydrogen: 
Zn + 2HC1 = ZnCl2 + H2 
They are also prepared by the action of chlorine 
developed by the mixture of nitric with an excess COMPOUNDS OF METALS AND NON METALS 
59 
of hydrochloric acid. Gold and platinum are dissolved 
in this mixture (aqua regia) and stannic chloride is 
formed by its action on tin. 
Some are also prepared by subjecting the metal or 
its oxide to a current of dry chlorine gas. In this man- 
ner the chlorides of titanium, aluminum, and chromium 
may be formed. 
Sometimes a chloride is prepared by the substitution 
of one metal for another, thus stannous chloride may be 
made by distilling metallic tin with mercuric chloride: 
HgCl2 + Sn = SnCl2 + Hg. 
Other chlorides may be prepared by dissolving the 
oxides, hydroxides, or carbonates of the metals in hy- 
drochloric acid. 
REDUCTION OF METALLIC CHLORIDES.—The 
chlorides of gold and platinum may be decomposed by 
heat alone. Gold possesses so feeble an affinity for 
chlorine that solutions of the cloride of gold may be 
decomposed by mere exposure to light or atmospheric 
air. Solutions of sugar, gum arabic, oxalic acid, etc., 
readily decompose it.* 
Silver chloride yields pure silver and emits an odor 
of hydrochloric acid when heated strongly on char- 
coal. When placed in water acidulated with hydro- 
chloric or sulphuric acid, silver chloride may be re- 
duced by stirring with small pieces of iron or zinc; 
the reaction is as follows: 
Fe + H2S04 + 2AgCl — FeCl2 + 2Ag + H2S04.f 
*See chapter on Gold. 
tSee chapter on Silver. 60 
PRACTICAL DENTAL METALLURGY 
With the exception of the chlorides of the alkalies 
and alkaline earths all other chlorides may be decom- 
posed by heating them in a current of hydrogen, hydro- 
chloric acid and the pure metal being the result; but 
the evolution of the hydrogen must be well maintained, 
in order to drive off the hydrochloric acid formed, or 
it will react with the pure metal, forming fresh 
chloride. 
Some chlorides may be decomposed by heating them 
with a metal which has a more powerful affinity for 
chlorine; thus, aluminum chloride may be reduced by 
heating it with sodium. 
Sulphuric acid decomposes some chlorides and con- 
verts them into oxides, the oxygen being supplied by 
the water present. 
METALLIC BROMIDES.—Bromine, though less ac- 
tive than chlorine, unites directly with most of the met- 
als forming compounds analogous to the chlorides and 
resembling them closely in general properties. 
Silver bromide (AgBr) analogous to the chloride 
is found as a natural mineral. Nearly all bromides are 
soluble, and those of the alkali metals are found abun- 
dantly in sea water and in many saline springs. 
REDUCTION OF METALLIC BROMIDES.—The 
bromides are decomposed by oxidizing agents with lib- 
eration of bromine. The affinity of bromine for the 
metals being inferior to that of chlorine, the latter will, 
with the aid of heat, displace the bromine and form 
chlorides, but bromine cannot be displaced in a like 
manner by iodine: 
KBr + Cl — KC1 + Br. COMPOUNDS OF METALS AND NONMETALS 
61 
METALLIC IODIDES.—Many metals unite directly 
with iodine, forming compounds analogous to the chlo- 
rides and bromides. The iodides of potassium and so- 
dium exist abundantly in sea water and in some springs, 
and the iodide of silver occurs as a natural mineral. 
Most of them are soluble in water, lead iodide being 
only slightly so, while the iodides of mercury and silver 
are quite insoluble. 
A feAV of them, gold, silver, platinum, and palladium, 
are decomposed by heat alone, giving up their iodine. 
Ozone promptly decomposes all iodides, while atmos- 
pheric oxygen decomposes those of iron and calcium 
slowly. The relation of chlorine and bromine to the 
other halogens enables these elements to displace iodine 
and form analogous chlorides or bromides: 
KI + C1 = KC1 +1, or 
KI + Br = KBr +1. 
METALLIC FLUORIDES are formed by heating 
certain metals in the presence of hydrofluoric acid; by 
the action of that acid on metallic oxides; by heating 
electronegative metals, such as antimony, with the 
fluoride of lead or mercury. Volatile metallic fluorides 
may be prepared by heating fluor-spar with sulphuric 
acid and the oxide of the metal. With some metals 
fluorine occurs as a natural mineral, as with calcium 
(CaF2), and the double fluoride of aluminum and so- 
dium (A12F6, 6NaF). 
The fluorides are devoid of metallic luster; most of 
them are easily fusible and for the most part resemble 
chlorides. 
METALLIC CYANIDES are formed by the union 
of metals with the compound radical cyanogen, CN. 62 
PRACTICAL DENTAL METALLURGY 
Potassium and some other metals are converted into 
cyanides by heating them in cyanogen gas or the vapor 
of hydrocyanic acid. 
Cyanides very closely resemble the chlorides, bro- 
mides, iodides, and fluorides. 
METALLIC SELENIDES.—The element selenium 
very closely resembles sulphur in its chemical proper- 
ties; hence, it combines with metals in much the same 
manner. Native selenides are rarely found. 
REDUCTION BY ELECTRICITY.—Probably the 
most powerful means of reducing metals from their 
combinations with nonmetallic elements is obtained 
through the agency of electricity. To accomplish this, 
a solution of the metallic salt is subjected to the action 
of the galvanic current, and decomposed thereby.* 
This is simply and beautifully demonstrated by hang- 
ing a strip or coil of zinc in a solution of lead nitrate. 
After a few hours the zinc passes into solution, and 
exquisite crystals of lead have taken its place. 
The electric furnace of Eugene II. and Alfred H. 
Cowles, of Cleveland, Ohio, has greatly advanced the 
production of such metals as aluminum from corundum, 
boron from boracic acid, and silicon fi’om quartz. The 
furnace is constructed in the form of a rectangular box 
of fire-resisting material, lined with a mixture of fine 
charcoal and lime. It has a removable cover, which is 
perforated with openings to allow the escape of gases 
evolved. In the sides of this furnace the electrodes, 
two plates of gas carbon, are let in by means of which 
a powerful electric current is introduced. The charge 
*The reduction of iron in the electric furnace is not carried on in this 
manner, as we ordinarily conceive of the term solution, though the ore is 
reduced after being liquefied by the intense heat produced by the carbon arc. COMPOUNDS OF METALS AND NONMETALS 
63 
consists of the coarsely crushed ore and coke frag- 
ments. The essential feature of the process consists, 
therefore, in employing in the furnace a substance like 
carbon, whose high resistance to the passage of the 
current causes the production of a prodigiously high 
temperature, and which at the same time, is capable 
of exercising a powerful reducing action on the ore. 
Dr. Heroult, inventor of the “Ileroult electric fur- 
nace/’ states that analyses prove that electrolytic steel 
shows 20 per cent higher tensile strength and elonga- 
tion than ordinary steel. 
In very recent years the reduction of ores by elec- 
trolysis has given indications of superseding the older 
blast and reverberatory furnace methods. The prin- 
cipal reasons for this are (1) the production of elec- 
trical energy by water power, generally within the 
immediate vicinity, and without the aid of fuel, and 
(2) a purer quality of product. The purest and best 
grades of copper for electrical purposes are reduced 
from the ore by electrolysis. CHAPTER IV 
MELTING METALS 
REFRACTORY MATERIALS.—Dentists frequently 
have occasion to use refractory materials, indeed they 
are using refractories of some sort in every day prac- 
tice, but probably have never considered them as such. 
A refractory substance is one which is capable of with- 
standing high temperatures without marked changes 
in form or composition, and its value in the industrial 
world is in direct proportion to this, the predominating 
property. 
In the natural state they are found as asbestos, talc, 
mica, slate, clays including kaolin, feldspar, quartz and 
magnesite and may have been derived from any one 
of the three primal types of rock; i. e., igneous, sedi- 
mentary, and metamorphie. They are divided into three 
classes with reference to their reaction; viz., acid, such 
as ganister and Dinas clay; neutral, such as fire clay, 
chrome, ironstone, and graphite; and basic, such as 
dolomite bauxite and alumina. It will be noted that 
where silicon dioxide (Si02) predominates, the refrac- 
tory material is acid in character and where the con- 
tent is low, the refractory is basic. 
Artificial refractories manufactured from natural 
products with suitable bonding material are found to 
be particularly valuable in dentistry. Of these Alun- 
dum made by melting' and purifying a high grade 
bauxite and then crushing to grains of suitable sizes 
and adding a ceramic or other bond is used extensively 
G4 MELTING METALS 
65 
in porcelain shell crown work and in the constructing 
of electric muffles. The purest form contains more than 
99 per cent aluminum oxide while the impurer grades 
contain some oxides of iron, titanium and silicon. 
Pure Alundum melts at 2050° C., the bonding mate- 
rials lowering the fusing point somewhat. Certain 
grades retain their form without appreciable shrinkage 
or expansion, possess high heat conductivity for a re- 
fractory material and great mechanical strength. 
The purposes for which refractories are intended to 
be used determines their selection. Some are intended 
to withstand high and prolonged temperatures, some to 
withstand the scorifying action of the substances fused 
in contact with them, and in particular this determines 
their selection for crucibles, while others such as quartz 
are designed to withstand sudden and extreme changes 
in temperature. The fusing points of some of the more 
common refractories used as furnace linings are as 
follows: 
Common fire brick 1555° C. to 1725° C. 
Bauxite “ “ 1620° C. to 1800° C. 
Silica “ “ 1700° C. to 1722° C. 
Chromite “ “ 2050° C. 
Magnesia “ “ 2720° C. 
Ganister is composed of Si0289.5, AI2O34.8, Fe02.8, CaO.l, IC20.1, 
Ho02.2. 
Dinas Clay = Si0298.3, Al203.7, FeO.2, CaO.2 K20.1, H2O.S. 
Kaolin, which is the purest form of fire-clay, contains Si02 45-60, A1203 
33-40, HoO 11-14. 
Dolomite = CaC0354.34 and MgC0345.66. In this case the carbon di- 
oxide is removed by heat, leaving the oxides of calcium and magnesium, 
which are entirely basic. 
Bauxite = variations: A1203 30.3-76.9; HsO 8.6-31.1; Fe203, 0.1-48.8; 
Si02 1.1-41.5; Ti02, 1.6-4.0. 
Fire-clays are essentially hydrated silicates of alumina, which resist 
exposure to high temperatures without melting or softening. They con- 
tain small amounts of lime, magnesium, oxide of iron, potash, etc., and 
some mechanically mixed silica, and should not fuse lower than 1500° C. 
Graphite (Cumberland) = C91.55, volatile matter 1.1, ash 7.35. 
Hiorns. 66 
PRACTICAL DENTAL METALLURGY 
Crucibles.—These are vessels designed for calcining 
or fusing substances which require high temperatures. 
A good crucible should be tough, infusible, capable 
of withstanding sudden changes of temperature with- 
out fracture, and should not be readily corroded by 
metallic oxides. The most infusible crucibles are those 
made with clays containing the largest amount of silica, 
and the smallest quantity of calcium and iron oxides. 
A good crucible may be made with two-thirds fire-clay 
and one-third burned fire-clay and coke dust, which pre- 
vents it being distorted when burnt. The power of re- 
sisting corrosion may be tested by melting copper in the 
crucible and adding a little borax. The latter unites 
with any copper oxides that may be formed, and will 
corrode the crucible rapidly unless it is of good quality. 
Graphite, black lead, or plumbago crucibles are made 
of fire-clay mixed with varying proportions (25 to 50 
per cent) of plumbago or coke dust. The best ones are 
made with purified plumbago, as the natural material 
often contains impurities in the ash which would act 
injuriously in the clay. Instead of using black-lead 
crucibles, clay ones lined, or “brasqued” with char- 
coal paste are often employed. The graphite crucible 
is the most enduring of all crucibles, but it should never 
be used in melting or alloying noble metals without first 
being tested by subjecting it to a red heat, as a crack 
or other imperfection may exist that escapes the notice 
while the vessel is cold. Again, bubbles of air or par- 
ticles of organic substances occasionally become mixed 
with the material, which upon being heated, cause 
the crucible to be broken, thereby risking the loss of 
the metal. 
There are a variety of clay crucibles, the most im- MELTING METALS 
67 
portant of which are: (1) French—Of excellent quality, 
smooth, carefully made, but somewhat brittle; (2) 
London—Close-grained reddish brown, refractory, and 
resist well the corrosive action of metallic oxides; (3) 
Cornish—Quite refractory, but are of a more acid char- 
acter than the preceding, and hence are more readily 
attacked by metallic oxides; (4) Hessian—These are 
exceedingly useful refractory, not readily corroded. 
They are composed of Si02, 54 parts; A1203, 41 parts; 
CaO, 2 parts; Fe203, 1 part; and they have been made 
in Grossalmerode since the fifteenth century. They 
may be used for rough fusions, but when precious 
metals or their alloys are to be fused in them, they 
should be first thoroughly lined with a surface of 
borax, or the rough, porous sides will absorb a con- 
siderable portion of the molten metal. Being of acid 
character, they are also subject to corrosion by basic 
fluxes, with which they form fusible compounds. They 
are well adapted to the fusion of noble metals where 
no fluxes are introduced for chemical action. Though 
they do not show a great resistance to extreme heat, 
they are very slightly affected by sudden alterations 
in temperature, as they may be plunged cold into a 
strongly heated furnace, or white-hot into cold water 
without cracking. The Cornish crucible, though very 
similar to the Hessian variety, is not quite so rapidly 
perforated by corrosive fluxes. 
Crucibles are also made of porcelain, gold, silver, plat- 
inum, iron, etc., but their use is confined almost entirely 
to the cheftiical laboratory. 
Platinum is fused either in a crucible of gas carbon or 
in a concavity carved in a block of quicklime, the 68 
PRACTICAL DENTAL METALLURGY 
latter of which forms part of the furnace described in 
the chapter on platinum. 
FLUXES are certain fusible substances which, when 
heated with metalliferous matter, assist in the fusion 
and aggregation of the metallic globules by cleansing 
and protecting them from foreign matters, such as 
gangue, oxides, sulphides, chlorides, etc. 
With these foreign substances the flux forms a fusible 
slag from which the metals held as oxides, sulphides, 
chlorides, etc., may be subsequently reduced. 
Like the refractory materials, fluxes may be classified 
as acid, neutral, and basic in their reaction. Thus, 
when gold quartz is fused with sodium carbonate, the 
quartz, a siliceous or acid gangue, reacts with the 
carbonate forming sodium silicate, liberating carbon 
dioxide, and separating the gold which is held me- 
chanically. 
A number of fluxes are used for the specific purpose 
of removing certain impurities or debasing elements 
from molten metals. This they accomplish in two 
ways—first, by acting as simple solvents for the im- 
purity, as mentioned previously, and forming a slag; 
second, by forming compounds, such as oxides, sul- 
phides, chlorides, etc., with the debasing elements, 
which are either volatile or soluble in the molten flux. 
Others act in a reverse manner; these are reducing 
agents, the function of which is to reduce to a metallic 
state such metallic oxides as are dissolved in the mol- 
ten metal, and which confer friability or brittleness 
upon the metal when cast. 
The following may be enumerated as the fluxes of 
most common application, with their uses defined: MELTING METALS 
69 
Borax, sodium tetraborate, Na2B407, 10H2O. This 
salt is of almost universal use, but should be first fused 
to drive off its ten parts water of crystallization, and 
the glassy mass thus obtained is to be powdered. When 
highly heated it is of acid reaction, combining with 
metallic oxides to form borates; at lower temperatures 
it takes up foreign matters generally, setting the metal 
free and so cleansing its surface as to allow of com- 
plete aggregation of the particles into a button form. 
It is found native in abundance in California, Europe, 
Peru, and other localities. It is also artificially pre- 
pared by neutralizing boric acid with soda ash. 
Sodium Carbonate, Na2C03,10H2O. This salt may be 
preferred to potassium carbonate from the fact that 
the latter is quite deliquescent. It decomposes silicates, 
as already instanced, and much easier when charcoal 
is present. It forms fusible compounds with metallic 
oxides and decomposes some chlorides, for example, 
silver chloride. 
Potassium Carbonate, K2C03, is quite similar to the 
sodium salt; it dissolves the earthy impurities, with 
which it forms an exceedingly liquid flux, thus en- 
abling the heavier particles of metal to sink through 
the fluid mass and collect in a button at the bottom of 
the crucible. 
Potassium Nitrate, saltpetre, nitre, KN03, is an ex- 
ceedingly useful flux in the purification of noble metals. 
When used as a flux, and heated, it energetically gives 
up a portion of its oxygen to base metals which are thus 
oxidized, and the alkaline nitrate becomes a nitrite. 
Sodium Chloride, NaCl, powdered and heated, to pre- 
vent its decrepitation, is sometimes added to molten 
substances which induce much ebullition in order to 70 
PRACTICAL DENTAL METALLURGY 
check the latter and protect the substance operated 
upon from the action of atmospheric oxygen. Like 
amnionic and mercuric chloride, it forms chlorides with 
some metals. It is the most reliable flux in fusing 
brass and should be put in the crucible at the beginning 
of the heat. 
Black Flux, a mixture of potassium carbonate and 
pulverized charcoal, is an excellent reducing agent and 
assists in the fusion of substances. 
Lime, Silica, and Alumina, or lime with the silicate 
of aluminum, are employed together; the silica to ab- 
stract certain bases by forming with them fusible sili- 
cates, while the two bases, lime and alumina assist in 
the fusion of the silicates thus formed. A single sili- 
cate with one base is generally less fusible than a double 
or multiple silicate with two or more bases—hence the 
two bases, lime and alumina, are used with the silica. 
Plumbic, Cupric and Ferric Oxides are used as fluxes 
in some metallurgic operations; the first forming an 
alloy of lead and silver; the copper oxide for purifying 
gold and the ferric oxide as a flux for silica. 
Many prepared fluxes have been introduced from 
time to time for dental soldering operations, but none 
possess any great advantage over pulverized dehy- 
drated borax. 
A liquid flux used by jewelers and found useful in 
dental solderings is made by dissolving equal parts of 
borax and boric acid in about sixteen parts of water. 
FUEL.—Combustible substances that may be quickly 
burned in air, producing heat capable of being applied 
to economic purposes. 
Fuels are chiefly compounds of carbon and hydro- 
gen, some are hydrocarbons. They contain other MELTING METALS 
71 
elements, but are essentially carbon and hydrogen. If 
oxygen is contained, the proportion of hydrogen may 
be equal to, or greater than, but never less than that 
required to form water with oxygen. 
Calorific Energy.—The amount of heat a unit weight 
of a body is capable of yielding when completely 
burned. It is usually measured by the number of the 
units of weight of water it will raise one degree of tem- 
perature Centigrade. 
Thus in the subjoined table the calorific energy of 
wood charcoal, for example, is given as 8080, that is to 
say, one gram of wood charcoal when completely oxi- 
dized to carbon dioxide will yield sufficient heat to raise 
8080 grams of water through one degree Centigrade; 
so with the other substances composing the table. 
The calorific energy of a fuel containing carton, hydro- 
gen, and oxygen is approximately the sum of the calorific 
energies of the carton and that of the disposable hy- 
drogen* 
The experimental and calculated calorific energies of 
substances do not agree. This is due to the heat ab- 
sorbed in their decomposition. 
EXAMPLE No. 1.—Determine the calorific energy of marsh gas (CH4). 
C = 1 X 12 = 12 (The atomic weight of carbon is 12.) 
H4 = 4 X 1 = 4 (The atomic weight of hydrogen is 1.) 
CH4 == 16 (The molecular weight of marsh gas.) 
In one pound of CH4 there is then or % 
lb. of carbon, the calorific energy of 
carbon is 8080 (see table) hence: % X 8080 =: 6060.0 
In one pound of CH4 there is Yie or 1/4 lb. of 
hydrogen, the calorific energy of hydrogen 
being 34462 1/4 X 34462 = 8615.5 
Therefore the calculated calorific energy of marsh gas is ....14675.5 
*Disposable Hydrogen.—The amount of hydrogen which may be com- 
bined with oxygen is not available as a source of heat, and is called “non- 
disposable” hydrogen; the excess of hydrogen over the amount which may 
be combined with oxygen being available is called “disposable” hydrogen. 72 
PRACTICAL DENTAL METALLURGY 
EXAMPLE No. 2.—Determine the calorific energy of olefiant gas 
(C2HO. 
EXAMPLE No. 3.—Determine the calorific energy of ethine (C2H2). 
EXAMPLE No. 4.—Determine the calorific energy of alcohol (C2 
H6OH). 
EXAMPLE No. 5.—Determine the calorific energy of bisulphide of 
carbon (CS2). 
The calorific energies of different substances ob- 
tained experimentally, by the method mentioned pre- 
viously, is given in the following table: 
TABLE OF CALORIFIC ENERGIES 
Hydrogen (H) burned to water (H20) 34500 
Carbon (C) “ ‘‘ carbon dioxide (C02) 7854 
Carbon (C) “ “ carbon monoxide (CO) 2405 
Carbon Monoxide 
(CO) “ “ carbon dioxide (CO.,) 5640 
Silicon (Si) “ “ silicon dioxide (Si02) 7407 
Sulphur (S) “ “ sulphur dioxide (S02) 2168 
Methane (CH4) “ “ carbon dioxide and water 
(C02 + HoO) 13287 
Ethane (C2H4) “ “ carbon dioxide and water 
(COo + HoO) 12214 
Ethyl Alcohol “ “ carbon dioxide and water 7108 
(C2H5OH) (C02 + H20) 
Illuminating gas burned 4440 to 7370 
Petroleum “ 9600 to 11000 
Tallow “ 9500 
Calorific Intensity is the pyrometric degree of heat 
obtained when a substance is completely burned. 
Pyrometry is the measurement of high temperatures, 
and is accomplished by means of an instrument called 
a pyrometer. There are several types as (1) Com- 
pounds which fuse at graded known temperatures; (2) 
Resistance, which depend on variations in the resis- 
tance of a thermo-electric couple; (3) Expansion, which 
is based on the difference in expansion between a 
steel tube and a graphite rod. They are seldom ac- 
curate and rarely used above 540° C.; (4) Optical, 
which utilize the changes in brightness of a heated object; 
and (5) Radiation pyrometers, MELTING METALS 
73 
The first type is used chiefly in the ceramic in- 
dustry and has little value in crucible or muffle work. 
Seger cones graded to fuse at differences of 20° in tem- 
perature are the common types. The second type de- 
pends on three factors, first, the amount of current; 
second, the constancy of the current; and, third, the 
ability to withstand the conditions under which it is 
used. Each instrument consists of three parts, the 
thermo junction, the leads, and the galvanometer. The 
thermo junction may consist of one platinum wire, and 
one platinum 90%, Rhodium 10%, wire, joined at one 
end, or it may consist of an alloy of iron, nickel and 
aluminum coupled with an alloy of nickel chromium 
and copper. The Platinum Rhodium couple known as 
the Le Chatelier can be used to 1600° C. (2900° F.) 
and will withstand constant heating to 1480° C. (2700° 
F.), while the base metal couples will stand a constant 
use of 1090° C. (2000° F.). The leads are usually of 
copper of the same resistance for which the galvanom- 
eter is calibrated and the latter instrument is con- 
nected in series in the circuit and calibrated to read in 
degrees of temperature. This type is extensively used 
in the fusing of dental porcelain with considerable sat- 
isfaction especially where an automatic circuit breaker 
is included. The optical pyrometers are extensively 
used in foundries where large amounts of metal are 
fused. 
FUEL.—The fuels used in dental laboratories are pe- 
troleum, gasoline, alcohol, acetylene, and coal gas. 
Petroleum.—Kerosene or coal oil is one of the prod- 
ucts in distilling crude petroleum, and is much used 
where gas is not available. Since most dental lamps and 
stoves are of metallic construction, due precaution must 74 
PRACTICAL DENTAL METALLURGY 
be exercised to use only good “high test” oil, i. e., that 
which has been properly freed from the volatile prod- 
ucts of petroleum and is capable of withstanding the 
maximum temperature' developed by the lamp-flame 
without evolving dangerously combustible gases. It 
has been found that 5 per cent of crude naphtha reduces 
the flashing point from 118° to 70° F.* 
Gasoline.—A colorless, volatile, inflammable liquid; 
one of the products of the distillation of crude petro- 
leum, having a specific gravity of .629 to .667 at 60° F. 
It is so volatile that if a current of air be passed through 
it at ordinary temperatures a highly dangerous com- 
bustible gas is formed by the mixture of gasoline vapor 
(5 to 8 per cent) and atmospheric air. Most of the 
disastrous explosions and fires caused by gasoline are 
not due to the liquid which can be burned with im- 
punity under proper precautions, but to this very ex- 
plosive mixture which is easily ignited by the glow 
of a lighted cigarette or a carelessly handled match. 
Such explosions are as likely to occur in the open air 
as in a closed room. It is much used as a fuel in vapor 
stoves and for carburizing air-gases, etc., see Fig. 7. 
Alcohol.—A colorless, volatile, inflammable liquid, 
chiefly obtained from the fermentation and distillation 
of saccharine fluids, as grape sugar, or the distillation 
of wood. The former is known as ethyl alcohol, the 
latter as methyl alcohol, and a combination of the two 
with some strongly odorous or bitter tasting combus- 
tible substance is known as denatured alcohol. Alco- 
hol is miscible in all proportions with water, hence the 
*A quick method of determining a low flashing point is to pour about 
two c.c. of the oil to be used on the surface of a glass of water, and then 
pass a lighted match over the surface. If the vapor is lighted, the oil is 
too low grade for furnace work. MELTING METALS 
75 
possibilities of dilution are great. Those using the 
liquid fuel will find it to their advantage to use a 
U. S. Custom House hydrometer with Trade’s and 
Proof Mark scales to determine the alcoholic content 
of their purchases. 
90% alcohol has a specific gravity of 0.826 
80% “ “ “ “ 0.856 
70% “ “ “ “ 0.882 
The heat of combustion of ethyl alcohol is nearly 
twice that of methyl alcohol and it is intensified by 
injecting a blast of air into the burner. Denatured 
alcohol is usually sold at about two-fifths the price of 
ethyl alcohol. 
Acetylene.—Formula C2H2, obtained by the action 
of water on calcium carbide, is a volatile gas, easily 
compressed into liquid form and thus stored for con- 
venient use. When a jet of oxygen or air is injected 
into a blast lamp connected with an acetylene container 
and the mixed gases are ignited, a very intense heat is 
produced. This constitutes the oxy-acetylene welding 
flame, and the temperatures obtained are so high that 
the product is at present unsuited for dental labora- 
tories. A modified type of burner and blowpipe will 
add a very useful fuel to the dental laboratory, since 
the condensed gas is easily obtained in convenient sized 
storage tanks notv. 
Coal Gas.—Illuminating gas as it is frequently called 
is a distillation product of the varieties of coal known 
as bituminous and cannel. 
EXPERIMENT: Fill the bowl of an ordinary clay pipe 
with small fragments of bituminous coal, lute over with clay 
and place in a bright fire; immediately smoke is seen to issue 76 
PRACTICAL DENTAL METALLURGY 
from the stem which projects beyond the fire. The smoke soon 
ceases, and if a lighted taper is then applied to the orifice of the 
stem, the issuing gas burns with a bright steady flame, while a 
proportion of a black, thin, tarry liquid oozes out from the stem. 
After the combustion ceases, there is left in the bowl of the pipe 
a quantity of char or coke. 
This simple experiment is, on a small scale, an exact 
counterpart of the process by which the destructive 
distillation of coal is accomplished in the manufacture 
of gas. The products of this distillation process are 
classed in the gas works as gas, tar, ammoniacal liquor 
and coke. The gas is purified by removing the tar and 
ammoniacal liquor, and then passed into the pipes for 
consumption. It is composed of a variety of substances 
divided into two classes; viz., (1) Nonluminous dilu- 
ents, embracing hydrogen (H), marsh gas (CH4), and 
carbon monoxide (CO) ; (2) luminous constituents, 
which include the hydrocarbon gases acetylene (C2H2), 
olefiant gas (C2H4), propylene (C3H6), butylene (C4H8), 
and most important of all the vapors of the benzol 
(C6H6), and the naphthalin (C10Hg) series. 
REDUCTION OF ORES.—Occasionally metallic 
ores are obtained in compact masses of comparatively 
pure metal, from which the accompanying matrix or 
gangue can be detached by the hand or hammer, but 
such instances are rare. In most cases the ore com- 
prises but a small percentage of the gangue. Hence 
it is expedient to purify it as much as possible before 
attempting to liberate the metal. This is accomplished 
generally by crushing and washing out the earthy 
matter as far as practicable. The ore is then subjected 
to roasting, amalgamating, or dissolving operations for 
the reduction or liberation of the metal. MELTING METALS 
77 
The great majority of metals are reduced by heat. 
,In this process the ore, along with some kind of flux, 
is exposed to the direct action of a powerful fire, which 
in most cases has a chemical as well as a physical func- 
tion. It is intended, with the assistance of the flux, 
to break up or burn away some chemical compound or 
component, or it is meant to deoxidize the ore. 
For these fiery operations immense furnaces are con- 
structed of brick, granite, or other building stone, and 
lined with refractory or fire-resisting clay, brick, etc. 
FURNACES are best classified, by the method 
adopted for supplying air, into two classes; viz., (1) 
blast furnaces, (2) chimney draught furnaces. 
Blast Furnaces are supplied with air from a source 
under pressure (B' Fig. 2) sufficient to overcome the 
resistance to its free passage presented by the packed 
columns of fuel, flux and ore. These are the oldest 
and simplest forms of metallurgic contrivance. The 
open hearth blacksmith’s forge is a simple type of the 
same principles involved in the completely closed-in 
blast-furnaces of gigantic dimensions* in use for work- 
ing and reducing the various compounds of iron. Fig. 
2 is a vertical section of a blast-furnace. The upper 
cone DC is known as the stack proper, the lower one 
from the broadest part C to the tuyeres B, as the boshes, 
and the lower cylindrical part A, B, as the hearth. 
A Chimney Draught, Air, or Wind Furnace is sup- 
plied with air drawn through it by a partial vacuum in 
the chimney formed by the heated gases on their way 
to the atmosphere. The reverberatory furnace is a type 
*In the Middlesborough district, England, is a furnace 103J4 feet in 
height, and of 33,000 cubic feet capacity. 78 
PRACTICAL DENTAL METALLURGY 
of this class. Fig. 3 represents a vertical section of the 
reverberatory furnace. 
Fig. 2.—Sectional view of blast furnace. 
The characteristic point in this furnace is, that the 
fire-chamber A is separate from the one in which the 
material to be operated upon is placed—the heat and MELTING METALS 
79 
flame passing over the charge as from A, D, E. B is a 
low wall dividing the fireplace from the working bed C, 
and is known as the fire-bridge. At the opposite end 
there is sometimes a second bridge of less height called 
the flue-bridge, E. The ore is introduced from hoppers 
at H, the slag is withdrawn at K, and the metal run out 
by a tap hole at L. 
For melting gold and silver, as for all ordinary melt- 
ing operations, Mr. Makins recommends one after the 
Fig. 3.—Reverberatory furnace. 
style of Fig. 4, which is known as a crucible furnace. 
This may be built in an ordinary house-flue with a chim- 
ney whose height is about thirty times the diameter of 
the furnace—or thirty feet in height, for a furnace of 
one foot in diameter. 
A third class of furnaces is known as Muffle Furnaces, 
and under this head are to be found the assayer’s furnace 
and the continuous-gum furnace. The principle of these 
is the avoidance of contact of the substance heated 80 
PRACTICAL DENTAL METALLURGY 
with either fuel or flame. This is accomplished by the 
use of a muffle which is a chamber communicating with 
the external air and into which the article to be heated 
is introduced. This chamber or muffle is placed in the 
combustion chamber, and is surrounded by the burn- 
ing fuel but does not communicate with the combus- 
tion chamber. The electric dental porcelain furnace is 
of the muffle type modified, however, in that the heat is 
Fig. 4.—Crucible furnace. 
produced by the resistance of a given conductor to the 
passage of the electric current rather than by the com- 
bustion of fuel. 
Dental Laboratory Furnaces.—For melting metals in 
the dental laboratory, the small, compact blast-furnace 
devised by Mr. Fletcher, and shown in Fig. 5, is the 
simplest and most convenient. 
It consists of a cylindrical casing and perforated 
cover made of fire-clay which has been mixed with 
three or four parts by bulk of sawdust and burned. MELTING METALS 
81 
Through a hole near the bottom of the casing the mixed 
air and gas is injected, the latter being regulated by a 
check near the mixing chamber. The gas is received 
from as large a supply-pipe as convenient, and the air 
driven in by means of the foot-bellows. The crucibles 
used should not exceed 2 by inches. According to 
Mr. Fletcher, “With half-inch gas-pipe and the smallest 
foot-bellows the smallest sized furnace will melt a 
crucible of cast iron in seven minutes, tool steel in 
twelve minutes, and nickel in twenty-two minutes, 
starting with all cold.” Gold, silver, or copper may be 
readily fused in one of these furnaces where gas is ac- 
cessible. Where gas is not convenient, the metals or 
dental amalgam alloys may be melted very satisfac- 
torily in a near-by blacksmith’s forge, or in a coke or 
coal fire in an ordinary stove or open fireplace if the 
draught is sufficiently strong. If the draught is weak, 
the combustion of the fuel may be better accomplished 
by improvising a blast by passing a small piece of gas- 
pipe between the grate-bars of the fireplace or stove 
and attaching to this the hose from the foot-bellows. 
In this manner a considerable quantity of gold, silver, 
copper or alloy may be melted with little trouble. 
A modified type of Fig. 5 has been devised (Fig. 6) 
retaining all its peculiar advantages, but burning petro- 
leum, instead of gas, as fuel. The burner dispenses with 
a wick, by being constructed on the principle of an 
atomizer. It is supplied with a device for regulating 
the supply of oil, which is operated by the milled nut at 
A, and for the supply of an annular jet of air which is 
regulated by turning the sleeve B. 
The construction is such that it may be taken apart 82 
PRACTICAL DENTAL METALLURGY 
and cleaned, in case of any obstruction. The furnace 
stands are interchangeable for either gas or petroleum. 
Where illuminating gas is not attainable, a much more 
convenient form of furnace than that shown in Fig. 6 
Fig. 5. 
may be had as illustrated in Fig. 7. The gasoline gen- 
erator placed beneath the bench is attached to foot- 
bellows and furnace. 
Fig. 6. 
For those metals which fuse much before redness, 
such as zinc, lead, tin, and their alloys, iron ladles are 
usually employed. In the dental laboratory for melt- 
ing zinc, lead, or alloys, for making dies and counter- MELTING METALS 
83 
dies, iron melting pots (Fig. 8), capable of holding 
from 6 to 10 pounds of metal, are used. The metal may 
Fig. 7. 
be most conveniently melted over one of Fletcher’s 
solid flame gauze-top stoves, shown in Fig. 9. The 84 
PRACTICAL DENTAL METALLURGY 
stove is so constructed that the gas mixed with the proper 
proportion of air from below is burned above the gauze 
top, yielding a blue flame, intensely hot and perfectly 
solid and uniform. The consumption of gas is about two 
cubic feet per hour for each square inch of gauze sur- 
Fig. 8. 
face. It will melt an ordinary pot of lead in 12 min- 
utes, depending on the gas supply. An apparatus in 
which gasoline may be used, when gas is not available 
(much used by plumbers for melting solder), is recom- 
Fig. 9 
mended by Dr. Kirk* for melting zinc and lead in the 
dental laboratory. In the absence of gas supply it is 
probably more convenient to melt these metals in the 
open fireplace or in the stove. 
•American System of Dentistry, iii, p. 816, Melting metals 
85 
BLOWPIPES.—For minor melting 
operations, such as melting small quan-' 
tities of gold, silver, or copper, or in 
soldering, the blowpipe in some of its 
variously modified forms is usually em- 
ployed. These instruments are classi- 
fied as simple and compound. 
A simple blowpipe of plainest pattern 
is shown in Fig. 10, A. It consists of a 
tube of brass or other metal tapering 
gradually from the larger end, which is 
inserted in the mouth, to the other ex- 
tremity, which is curved and mounted 
with a cone-shaped tip to protect it from 
the action of the flame; the caliber of 
the instrument terminates here in a 
very small orifice. The point of the in- 
strument is frequently tipped with a 
more refractory metal, such as platinum, 
and the end to be received in the mouth 
is frequently tipped with a nonoxidiz- 
able metal such as silver. The whole 
is usually from twelve to fourteen inches 
in length, and the large extremity from 
one-half to three-fourths of an inch in 
diameter. 
As more or less moisture accumulates 
in the tube from the mouth, a second 
form has been devised (Fig. 10 B), to 
the stem of which, nearer its smaller ex- 
tremity, is adjusted either a spherical 
or cylindrical chamber, which collects 
and retains the moisture as it forms 
Fig. 10. 86 
PRACTICAL DENTAL METALLURGY 
within the pipe. The moisture is prevented from flow- 
ing into the smaller end of the tube beyond by the 
projection of that portion of the stem a slight distance 
into the chamber. 
Fletcher has much improved this simple form of 
blowpipe by coiling the smaller extremity of the stem 
into a light spiral over the point of the jet (Fig. 11). 
The air as it traverses the coil is heated, producing a 
hot blast instead of a cold one, as in the old form. Such 
an instrument enables the operator to produce a higher 
temperature than that produced with the ordinary pipe 
with the same amount of energy. The same pipe may 
be fitted with a hard rubber mouthpiece, which is less 
tiresome to grip in the mouth. 
Fig. 11. 
Another form by the same inventor is illustrated in 
Fig. 12. This is wholly unlike any mouth blowpipe 
yet devised, and admits of considerable latitude of 
movements in the application of heat by the rubber 
tubing connected with it. The mouthpiece is so con- 
structed that a shield protects the lips in such a manner 
that long-continued blowing may be practiced without 
undue strain on the lips, while the opening is well un- 
der the control of the tongue. It is also provided with 
a condensing chamber and interchangeable tip, either 
plain or coiled. 
Heat.—In the dental laboratory heat is obtained 
either from the combustion of fuel or from electric 
energy, the former being its commoner source. Solid MELTING METALS 
87 
fuel, as coal or coke, is no longer in use, having been 
succeeded almost entirely by either liquid or gaseous 
fuel. Alcohol, gasoline, and kerosene are the liquids 
used for this purpose, the gas is commonly either 
ordinary illuminating gas or natural gas in those re- 
gions in which it is available. These all owe their 
inflammability to the fact that they are hydrocarbons, 
combustion of which takes place when they are heated 
in air. One of the phenomena of combustion is the 
production of flame, which is simply burning gas. 
Flame.—The simplest flames with which we are ac- 
Fig. 12 
quainted are those of hydrogen or carbon monoxide 
burning in air or oxygen. In such as these the burn- 
ing gas undergoes no decomposition. The combustion 
consists of the simple union of an inflammable gas with 
oxygen: 
H2 + 0 = H20. 2CO + 02 = 2C02. 
The flame of either of these gases burning from the 
end of a tube appears as a burning cone, which upon 
investigation is found to be hollow, the combustion only 
taking place on the surface of the cone where the in- 
flammable gas is mixed by diffusion with the air. 88 
PRACTICAL DENTAL METALLURGY 
Substances which undergo decomposition and yield 
more than one product of combustion present a more 
complex flame structure. The flames of hydrocarbons 
commonly employed for illuminating purposes, such as 
the candle, illuminating gas, and oil, are practically 
identical in points of construction and a description of 
one will suffice for all. 
The Candle Flame.—On approaching the wick with 
the flame of a match, the wax (or other hydrocarbon of 
which the candle may be made) melts, is drawn up in 
Fig. 13.—Candle flame. 
the fibers of the wick hy capillary attraction and there 
converted by the heat into gaseous hydrocarbons, which 
ignite, and in their chemical union with the oxygen of 
the air produce the flame. In such flames, as in the 
simpler ones already referred to, there is first, about 
the wick or burner, the dark cone, A, of heated un- 
burned gases. Above and about the apex of this cone is 
a second cone, B, which in comparison with the rest of 
the flame, seems nearly opaque, and which emits a bright 
yellow light. At the base of the flame there is a small 
calyx-like region, C, which appears bright blue in color MELTING METALS 
89 
and is nonluminous. Then enveloping the entire flame 
there is a faintly luminous, hardly perceptible, bluish- 
purple mantle, D (Fig. 13). 
The dark cone, A, as has been explained, consists of 
unburned gases and in reality is not a part of the 
flame. However, chemical changes are taking place 
Fig. 14.—Bunsen flame. 
therein, owing to the heat from the sheath of combus- 
tion surrounding it. 
Cone B is ordinarily spoken of as the luminous cone. 
It has probably been concluded that the luminosity in 
flame is due to: (1) the presence of solid matter, (2) 
the density of the flame gases and (3), the temperature 
of the flame. 90 
PRACTICAL DENTAL METALLURGY 
The blue region, C, may be regarded as being largely 
made up of the combustion of carbon monoxide. 
The faintly luminous mantle, D, is probably a zone 
of complete combustion, in which those substances 
which have been incompletely oxidized in the other 
portions of the flame, chiefly hydrogen and carbon 
monoxide, are finally converted into water and carbon 
dioxide. 
The Bunsen and Blowpipe Flame.—When a certain 
amount of air is mixed with coal gas or any other 
hydrocarbon gas before combustion, the gas burns with 
a pale blue, nonluminous, smokeless flame, which has a 
three-cone structure (Fig. 14). 
Cone A contains the mixture of combustible gases and 
air (oxygen). In the Bunsen burner the air is drawn in 
through the openings near the base of the metal tube. 
The mouth blowpipe conveys a blast of air into the 
center of the flame. In the compound blowpipe flame 
the blast of air (oxygen) is injected into the combustible 
gases from the lungs of the operator or by some me- 
chanical means, such as a bellows, through a concen- 
tered tube, while the gas is conveyed by the outer and 
larger tube (Fig. 15). 
The Reducing Flame, (or deoxidizing flame).—The 
inner cone, B, presents the gas burning with a pale-blue 
flame, rendered so by the presence of oxygen in the gas. 
If an oxidized piece of copper be placed in a Bunsen or 
blowpipe flame in the position of the line marked B' B', 
it will be noticed that the metallic sheet brightens in 
the area covered by the flame. This is accounted for 
by the fact that this region of the flame contains highly 
heated but unburned hydrogen or hydrocarbons, which MELTING METALS 
91 
have the power to abstract and then combine with the 
oxygen of the copper oxide, thus freeing or reducing 
the copper; hence, this region is known as the deoxidizing 
or reducing flame. 
This is the flame used for soldering, as it reduces any 
oxides that may be on the solder, or parts to be soldered, 
and, also cutting off the oxygen of the air from con- 
tact with the heated metals, it prevents any reoxidation 
of them. 
The Oxidizing Flame.—The outer cone, C, presents a 
pale-blue or purple color and is the zone of complete 
combustion. Gases which have escaped combustion in 
Fig. IS.-—Blowpipe flame. 
the inner cone are oxidized in the outer one by the 
ample supply of oxygen in the atmosphere surround- 
ing it. 
A bright piece of copper held in the position of the 
line C' C' will be quickly darkened by the formation of 
copper oxide upon its surface. This is accounted for by 
the fact that the copper becomes heated, and, being 
unprotected, is unable to resist the affinity of the oxy- 
gen in the air surrounding it, and is therefore oxidized. 
Hence, the term oxidizing flame. 
Any attempt at soldering with this flame results in 
oxidation of the base metals of the solder and parts to 
be soldered, so that additional fluxing will be necessary 92 
practical dental metallurgy 
before the solder can flow. Continued misuse of the 
flame may so greatly raise the carat of the solder, by 
oxidizing out the base metals, as to make its fusing 
point dangerously high, or the presence of the oxides 
mixed with the solder may make its flowing impossible. 
Because of the chemical nature of combustion, it is 
evident that the proportion between the air and the gas 
must be definite and fixed to obtain the highest heat, 
and this must be regulated when the blowpipe is in use. 
If too little air is supplied, imperfect combustion takes 
place and the full degree of heat is not developed. On 
Fig. 16. 
the other hand, the luminosity of the flame is increased, 
the heat being inversely related to this. If too much 
air is forced in,* the temperature of the flame must nec- 
essarily be reduced by the current of cool and uncom- 
bined air. 
Reduction on Charcoal.—Reduction is much more 
easily effected by the employment of a block of charcoal 
as a support. It not only assists in heating the bead of 
metal by becoming hot, but it also assists in the reduc- 
*The best mixture of coal-gas and air is 1 part gas to about 5 or 7 parts of 
air by volume. It is better to mix the air and gas before combustion.—Sci. 
Am., Feb. 6, 1909. MELTING METALS 
93 
ing action by combining with the oxygen of the oxide, 
forming carbon dioxide, and liberates the metal. 
Fig. 17. 
LAMPS.—Flames for soldering may be derived from 
oil, spirit, or gas lamps, 94 
PRACTICAL DENTAL METALLURGY 
Oil Lamps.—The fluid hydrocarbon, petroleum, or 
coal oil is very inexpensive, and where gas is not avail- 
able is much used. Fig. 16 represents a soldering lamp. 
An oil lamp to be satisfactory should hold about one 
to two pints and should have a tapering spout from 
three to five inches in length. The spout should be 
well filled with wick, but not too tightly, for fear of 
preventing free saturation with the oil. Proper care 
should be exercised to guard against all accidents oc- 
casioned by ill-fitting parts, filling and adjusting. With 
a good lamp, an entire artificial denture can be sol- 
dered, or one or two ounces of gold melted. Pure sweet 
oil or lard oil may also be used in these lamps for 
soldering. 
Fig. 17 illustrates a compound blowpipe (D) used 
with gasoline gas. It is provided with a generator (A) 
and bellows (B) with which it is connected (C) similarly 
to that in Fig. 7. 
Spirit Lamps.—Much the same lamps, as illustrated 
in Fig. 16 may be used for alcohol, which is much 
preferable to coal oil on account of its cleanliness and 
the less liability to accident. With a lamp similar to 
the one represented in Fig. 18, the spirit is entirely 
uninfluenced by the heat of the flame, and explosion 
is rendered almost impossible. 
In Fig. 19 is represented a self-acting lamp and blow- 
pipe. The lamp reservoir and the boiler will each hold 
about a half-pint of alcohol. Lighting the flame under 
the boiler vaporizes the alcohol in it rapidly, the pres- 
sure forcing the vapor through the pipe into the large 
flame at the side of the lamp, forming a very practicable 
and efficient blowpipe. The forc.e of the blast is regu- MELTING METALS 
95 
lated by raising or lowering the boiler; the spread of 
the flame by using the larger or smaller nozzle. The 
appliance is substantially made of spun brass, and the 
Fig. 18. 
boiler is provided with a safety-valve. A set screw on 
the upright permits the boiler to be raised or lowered 
or swung to one side. One of the nozzles is carried 
Fig. 19 
on the top of the safety-valve; the other in position on 
the pipe. 
Gas Lamps.—The gas may be most effectively used 96 
PRACTICAL DENTAL METALLURGY 
by an apparatus on the principle of the one illustrated 
in Fig. 20, which consists of a sort of Duplex Bunsen 
burner. 
Compound Blowpipes.—The difficulty in maintain- 
ing a flame of uniform size and intensity, owing to the 
Fig. 20. 
fact that the blowpipe and lamps are separate, the 
lack of latitude allowed the operator by the fixed posi- 
tion of the blowpipe, and the introduction of gas in 
the experimental laboratory led to a form known as 
the compound blowpipe, Fig. 17. This instrument is 
so constructed that it virtually consists of a lamp and MELTING METALS 
97 
blowpipe all in one. In general it consists of two 
metallic concentric tubes, one a smaller, terminating in 
a fine jet and placed within the first, so that the finer 
jet is accurately centered in the orifice of the larger 
tube, Fig. 21. Gas is supplied to the larger tube by an 
offset tube on the side of the nearer end, and flowing 
through the space in the large tube on all sides of the 
enclosed smaller tube to the opposite end, where it is 
Fig. 21. 
ignited. Air from the lungs or other source is trans- 
mitted through the inner tube to the center of the 
flame. The supply of both gas and air may be regu- 
lated in most of the latter patterns by checks within 
reach of the fingers of the same hand holding the in- 
strument. The blast from the mouth is most convenient 
for small heating, but when high temperatures are de- 
sired for some time, one of the various forms of me- 98 
PRACTICAL DENTAL METALLURGY 
chanical blowers is necessary. A far more satisfactory 
apparatus is found in the foot-bellows devised by Mr. 
Fletcher and shown in Fig. 22. 
SUPPORTS.—When soldering or melting gold or 
silver with the blowr-pipe flame, it is necessary to place 
the article to be soldered, or the metals to be melted, 
upon some sort of a support. Such supports may be 
improvised of blocks of charcoal, if the temperature 
is not to be too high, or large blocks of pumice stone 
encased in plaster, giving the whole a variety of forms. 
Fig. 22. 
One, designed by Professor C. L. Goddard which the 
author uses very comfortably, was made by making a 
mold of a hemisphere from a smooth croquet-ball, by 
pouring some plaster of Paris into a pasteboard box 
about five inches square, and then dipping the ball, 
and removing it when the plaster had hardened. The 
mold thus made was then varnished and filled with 
soft plaster, on the top of which was imbedded a 
large piece of pumice stone. When this hardened, the 
hemisphere was separated from the concavity, and the MELTING METALS 
99 
block containing the latter cut down until it covered 
but little over half of the hemisphere, when it was rein- 
serted. The whole was then varnished, and presented 
a very compact, convenient soldering block, fitted in a 
socket which permits it to be poised at almost any 
angle. 
Blocks of charcoal may also be covered on all sides 
but one with about one-half inch thickness of plaster. 
They then furnish clean and convenient supports for 
small solderings and meltings. 
Fig. 23. 
Fig. 23 forms a convenient asbestos soldering-block, 
and Fig. 24 represents another more easily handled. 
The block is of carbon and is furnished with a wooden 
handle. Fig. 25 represents a circular asbestos solder- 
ing-block or tray, with raised rim, set in a brass box, 
mounted on a wooden handle. The four holes are for 
the reception of brass pins, to hold the work in place. 
The investing material is made of a prepared asbestos 
fiber. This material is simply dampened. When the 
objects to be soldered consist in part of artificial teeth, 
such as a denture or bridge, a support of the style of 100 
PRACTICAL DENTAL METALLURGY 
Fig. 26, a small hand-furnace or soldering-pan is very 
satisfactory. It consists of a funnel-shaped receptacle 
made of sheet iron, with a light grate or perforated 
plate of the same material adjusted near the bottom, 
and an opening on one side, underneath the grate, for 
the admission of air. The upper part of the holder is 
surrounded by a cone-shaped top, which may be readily 
removed by a handle attached to it, while to the bot- 
tom of the furnace is attached an iron rod, 5 or 6 
inches in length, enclosed in a wooden handle at its 
unattached end; when the case is sufficiently heated, 
the top may be lifted off, and the case remaining in the 
Fig. 24. 
furnace soldered with the blowpipe in the usual man- 
ner, the furnace then serving the place of a support. 
INGOT MOLDS are usually made of iron in various 
forms to suit the requirements, those for the noble 
metals generally having the form shown in Fig. 27, 
which is so constructed that the side next to the handle, 
which also acts as a set-screw, can be moved laterally 
upon the opposite side, so that the intervening slot 
may be made narrow or wide. Ingots are also fre- 
quently east into molds of sandstone, charcoal, com- 
pressed carbon, pumice stone, or asbestos preparations. 
Fig. 28 represents such an apparatus suitable as a sup- 
port for melting, and as an ingot mold for the molten MELTING METALS 
101 
metal by merely tipping the slab and placing a cold, 
flat surface over the still heated metal in the mold. It 
is very important to have the mold free from moisture 
before pouring the molten metal in it, since the sudden 
Fig. 25. 
generation of steam may scatter the metal, causing a 
loss or perchance producing serious burns. 
Fig. 29 is an arrangement for melting and molding 
noble metals without the use of a furnace. Referring 
to the engraving: A is a crucible of molded carbon sup- 
ported in position by an iron side-plate. C the ingot 102 
PRACTICAL DENTAL METALLURGY 
mold. D a clamp holding the crucible and ingot mold in 
position, and swiveling on the cast iron stand B. The 
metal to be melted is placed in the crucible A, and the 
flame of a blowpipe is directed on it until it is per- 
fectly fused. The waste heat serves to make the ingot 
mold hot, and the whole is tilted over by means of the 
upright handle at the back of the mold. A sound ingot 
may be obtained at any time in about two minutes. 
Fig. 26. 
ELECTRIC FURNACES^—These are of two distinct 
types. (1) The arc furnace and (2) the muffle furnace. 
The arc furnace is employed principally for the reduction 
of metals from their ores and for the compounding of 
alloys requiring a high temperature. They are based 
on the principle of feeding the ore, flux and reducing 
agent around the electrodes to close a circuit. The MELTING METALS 
103 
heat generated by passing the current through this 
charge raises the temperature and fuses the mass, thus 
reducing the ore. (Fig. 30.) 
Where fuel is scarce and hydroelectric energy is 
available in the neighborhood of ore deposits, electric 
Fig. 27. 
reduction furnaces are very practicable. Only one-third 
as much carbon in the form of charcoal or coke is re- 
quired in electric furnaces since it is only required as 
Fig. 28. 
a reducing agent, the electric energy through the 
resistance of the mass producing the heat. They may 
be used for the smelting of certain alloys because they 
can be easily controlled and being of a smaller type 
than blast furnaces are suited for smaller charges. 104 
PRACTICAL DENTAL METALLURGY 
Nearly all the ferro alloys are now made in electric 
furnaces. 
Every dentist should be able to do porcelain work 
and since this requires a muffle type of furnace and 
Fig. 29. 
the electric dental furnace is the cleanest and most 
practicable, one ought to understand the simple un- 
derlying principles of its construction so that if neces- 
Fig. 30.—Gronwall type of electric arc furnace of two and one-half tons 
capacity. One carbon electrode is inserted in the base and the other in 
the top. When the steel is molten the furnace is tilted and the metal 
poured into ladles for casting. 
sary a furnace could be repaired or reconstructed in a 
short time to meet any emergency. 
The furnace consists of a rheostat and muffle con- 
nected in series. The rheostat is merely one or more MELTING METALS 
105 
resistance coils in series which will enable the operator 
to regulate the strength of the current passing through 
the furnace. Resistance is that property of a con- 
ductor which inhibits or modifies the current passing 
through it and is due to the composition, form, and 
molecular structure of the conductor. 
Fig. 31. 
Since resistance to the passage of the current pro- 
duces heat, it is necessary that the coils have a high 
fusing point. Resistance coils in rheostats are usually 
made of iron or some of its alloys, with copper, nickel, 
and chromium predominating. The construction of an 
electric furnace is a requirement in the College of 
Dentistry, University of California. The type used is 106 
PRACTICAL DENTAL METALLURGY 
described and illustrated in the following pages. The 
base is of cast iron in three parts, the bottom and sides 
being cast in one piece, the ends being separate and 
removable. Plenty of space for the circulation of air 
is provided so that the resistance coils will cool by radi- 
ation. (See Fig. 31.) The base carries five tin tubes 
Fig. 32. 
one inch in diameter which fit at either end over slightly 
tapering projecting rings on the inner side of the cast 
ends. Air passes freely through the hollow tubes to 
aid in cooling the rheostat. Each tube is covered with 
sheet asbestos fastened with shellac or fine iron wire 
and then the tube is wound with 20-gauge tinned iron 
wire, the ends being soldered to the last coil to pre- MELTING METALS 
107 
vent unwinding. (See Fig. 32.) In addition to this 
soldered joint a brass strap is formed tightly around 
the end of each resistance coil and fastened with a 
very small stove bolt Y'6xl/2 inch. Should the solder 
become fused by the heat generated in the coils, the 
clamp will prevent its unwinding. This clamp, by 
adding another washer and a lock nut, serves as a 
Fig. 33. 
convenient aid to connect the alternate ends of the 
coils with one another, or for attaching a conductor to 
the middle of a coil as in No. 5, and No. 7, Fig. 33. A 
marble slab, 8^x91/4x% inches drilled as represented 
in Fig. 34 together with the necessary binding posts, 
contact points, etc., completes the rheostat. The four 
holes at corners are for the long stove bolts used to 108 
PRACTICAL DENTAL METALLURGY 
clamp the slab to the base and the four screws with 
no conductors attached are to fasten the muffle base to 
the slab. 
A and B, Fig. 34, are the binding posts to which are 
connected the leads from the source of electrical en- 
ergy. (See also Fig. 38.) C and D are the connecting 
Fig. 34. 
posts for the muffle terminals while L is the base of 
the lever bar. The resistance coils are connected by 
means of asbestos insulated wire to the corresponding 
numbers of the contact buttons. (See Fig. 33.) No. 1 
button is always left with no conductors attached, thus 
serving as a dead button or a cut-out switch. In all MELTING METALS 
109 
rheostats it is the usual custom to cut out fifty per 
cent of the resistance with the first throw of the lever 
bar, and the next cut-out includes fifty per cent of the 
remainder of the resistance. This is approximated as 
follows: When the muffle and rheostat are connected 
and the current is on, with the lever bar on button No. 
1, no current is passing through the furnace, since this 
is a dead button. When the lever bar is moved to but- 
ton No. 2, the current flows from binding post A (Fig. 
33) to L (lever bar), to button No. 2, to wire No. 2 
to the first resistance coil, through all the resistance 
coils to wire No. 8, to button No. 8, to muffle terminal 
C, through the muffle to terminal D, to binding post B, 
and back to its source. 
When the lever bar is moved to button No. 3, two 
resistance coils or two-fifths of the resistance is cut 
out (see Fig. 31) and when the lever bar is moved to 
No. 4, another coil or three-fifths of the resistance is 
cut out. The remaining numbers 5, 6, 7, 8, cut out 
one-half a coil each. When the lever bar is on No. 8, 
the current is flowing only through the muffle, the rheo- 
stat being cut out entirely. It is well to state that in 
this or any other electro-heating device using a metal- 
lic resistor, it makes no difference whether the cur- 
rent is flowing from A to B or from B to A, if a direct 
current, or flowing either way if an alternating cur- 
rent. These devices do not involve motion. The utility 
of such a device depends entirely on the resistor and 
not upon the direction of flow of the current. 
It is well to dip the resistance coils in shellac to 
prevent the oxidation of the metal but this coating of 
shellac should be scraped off wherever contacts are to 
be made, Climax and other kinds of resistance wire 110 
PRACTICAL DENTAL METALLURGY 
have been tried out in the resistance coils, but crystal- 
lization and oxidation undoubtedly aided by the pas- 
sage of the current causes a number of breaks in the 
wire which may cause trouble at any time. When the 
conductors from the resistance coils are connected to 
the proper contact buttons and the marble slab securely 
fastened to the iron base, we are ready to proceed with 
the muffle. 
The muffle case is of cast bronze 3%x4%x3% inches 
milled and buffed. It consists of two parts, viz., a 
base with four legs screwed to the marble slab. Near 
the muffle terminals two holes are drilled through the 
base which carry refractory insulating tubes through 
which the muffle leads pass to the terminals. The other 
part is a cap carrying a shelf at the base of door. 
This cap is fastened to the base by two machine screws 
on either side. After the muffle is made, it is carefully 
packed in this muffle case with dry fibrous asbestos or 
magnesite so that the floor of the muffle is on a level 
with the shelf, the muffle leads are then passed through 
the insulating tubes, and connected to the terminals, the 
cap fastened to the base, and the completed furnace is 
ready for use. (See Fig. 38.) 
Muffle.—The muffle is the most important part of the 
furnace and care should be used in its design and con- 
struction. The important thing to consider is to obtain 
the maximum amount of heat uniformly distributed 
with as little loss by radiation as is possible. The size 
of the muffle may vary to suit the needs or inclinations 
of the maker. The muffle used in this furnace is D- 
shaped, 2" long x \x/2" high x 1%" wide con- 
stricted at the top. It may be made by taking a 
split wood, wedge shaped, pattern, or core of the de- MELTING METALS 
111 
sired size, from two to four inches longer than the 
muffle for convenience in handling, and covering it 
with glazed or waxed paper held in place by pins. The 
split wedge shaped core allows the center part to be 
easily drawn away when the sides will collapse, and 
thus allow the removal of the paper. Eleven feet of 
28-gauge platinum wire is used as a resistor and it has 
been found to meet all the requirements in fusing 
Fig. 35. 
2560° F. S. S. W. body. Beginning at one end near 
the muffle terminal side, the wire is fastened to one of 
the pins, allowing about four inches for a two-ply con- 
nection to the terminals, and is then wound around 
the core about one and one-half millimeters apart at 
the ends and about two millimeters apart in the center 
until the other terminal is reached, with another allow- 
ance made for a two-ply terminal at the end. The 112 
PRACTICAL DENTAL METALLURGY 
object of folding about two inches of the platinum wire 
back upon itself and twisting it, is because it decreases 
the resistance gradually instead of suddenly and there 
is less danger of a burn out. 
One may carve a block of plaster of Paris of the 
desired shape and size and then make shallow grooves 
or scratches longitudinally in it, after which the plati- 
num wire may be wrapped around it just as with the 
wooden core. 
The wire is now ready to be coated with a refractory 
material which will resist high temperatures without 
change of form, and have no bad effect upon the plati- 
num. Various combinations of silex, fireclay, ground 
firebrick and asbestos have been discontinued and an 
artificially prepared refractory is now used with very 
satisfactory results. It is alundum R. A. 162, a high 
grade aluminum oxide to which has been added a bind- 
er to hold the mass together while molding or com- 
pressing into shape. The powder is moistened with 
water just enough to mold it easily and then applied 
to the core, covering the wires to a depth of one- 
sixteenth of an inch, gradually drying the muffle near 
a Bunsen flame as the alundum is applied. When com- 
pleted and the ends are squared up, the muffle is dried 
out until it becomes set enough to withdraw the wooden 
core and paper, after which the muffle is heated to 
redness in the Bunsen flame. If a plaster core is used, 
it can be placed over the Bunsen just as soon as all 
volatile moisture has passed off and then heated to 
redness. Care must be taken not to heat a moist core 
over a flame too quickly as the steam generated within 
the core may explode and damage the entire mass. 
The plaster core will contract sufficiently with this heat MELTING METALS 
113 
to permit of its being withdrawn easily. The inner 
surface of the muffle should now be carefully examined 
for checks, or exposed wires and these places should be 
coated with the alundum paste. The muffle is now con- 
nected up with a rheostat and the current turned on un- 
til it produces a white heat. This hardens the alundum 
muffle and permits of its being handled with only ordi- 
nary care. 
Alundum is a much better conductor of heat than 
Fig. 36. 
other types of refractories and one should take pre- 
cautions to see that none of this heat is lost by radia- 
tion. Therefore, an infusible nonconducting refractory 
is desirable to insulate the muffle from the outer air. 
If possible an air space should be provided between 
these two materials, since dry air is the best noncon- 
ductor obtainable. Fibrous asbestos of a good grade that 
is now combined with low grade silicious compounds 
used in the making of asbestos paper or felt is very 
satisfactory. Silicon or carbon in any of their forms 
should not be placed in contact with platinum when it 114 
PRACTICAL DENTAL METALLURGY 
is heated to high temperatures, since they combine quite 
readily with the latter and favor crystallization of the 
metal. Fig. 36 shows different types of muffles. No. 1 
is the ordinary fireclay-silex mixture. No. 2 is an alun- 
dum tube with an additional concentric ring of the 
same material at either end. This was prepared so that 
the wire could be wrapped around the outside of the 
tube and then asbestos paper wrapped about the tube, 
allowing for an air space, as an insulator. It was un- 
satisfactory, first, because the bottom and sides were 
curved, and, second, the asbestos fused and when it 
came in contact with the heated platinum wires, it 
Fig. 37. 
produced a short circuit and the wires were burned 
out as in No. 4. No. 3 is talc grooved while in the 
natural state, and then subjected to a high temperature 
to vitrify it. It cannot be turned or milled thin 
enough to permit of the passage of heat from the coil 
to the inside of the muffle and it is a very poor conduc- 
tor as compared with alundum. Fig. 37 is the type of 
muffle adopted for use in this school. It simplifies 
construction and repairs very materially. The wire is 
wrapped on the outside in the grooves, the ends fas- 
tened securely, the muffle placed in a case surrounded 
by magnesite or fibrous asbestos and fireclay molded MELTING METALS 
115 
so that there is a definite air space about it, terminals 
connected and it is ready. In the event of a burn-out, 
it can be removed, the ends electro welded or twisted 
together, and replaced very quickly. Fig. 38 shows 
the completed furnace without the muffle in place. The 
door to the muffle should be closed with a block of 
Fig. 38. 
asbestos and alundum, one-half inch thick, formed to 
fit the opening with a convenient spnr for handling 
with the furnace tongs. 
A number of different substitutes for the platinum 
coil have been tried but none have proved to meet all 
the requirements. Nickel wire when protected from 
the air will give service up to 1000° C. Nichrome and 116 
PRACTICAL DENTAL METALLURGY 
French armor plate wire have been successfully used 
at about the same temperature, but none of these ele- 
ments or alloys will produce the heat required to fuse 
porcelain, viz., 1260°-1450° C. Tungsten is capable 
of producing satisfactory temperatures, and is much 
less expensive than platinum but is very easily oxi- 
dized at high temperatures. In an atmosphere of hy- 
drogen it is very satisfactory, but it is impractical to 
set up a hydrogen generator in a dental office every 
time one wants to fuse porcelain. The resistance of- 
fered by any electrical conductor to the passage of the 
current is directly proportional to its length and 
inversely proportional to its cross-sectional area. It 
is obvious therefore that the shorter the length of wire, 
the less heat will be produced within certain limitations. 
Further, the resistance of any conductor varies with the 
temperature, and this is known as the “temperature co- 
efficient.” The resistance of platinum wire increases 
0.0025 with every degree Centigrade. 
In using the older furnaces the workman had to de- 
pend solely upon visual judgment in determining when 
the porcelain was properly fused. Some made use of 
a pellet of pure gold, in working with the high-fusing 
bodies, placing it in the muffle and keeping the piece 
of work in the heat a definite time after the gold was 
seen to fuse (1063° C.). This principle is utilized by Le 
Cron in his pyrometer, in which by varying the pro- 
portions of gold and platinum in his pellet, the tem- 
perature of any given one of the high-fusing bodies 
may be judged, and, having been determined, the body 
may be baked at that temperature. CHAPTER V 
ALLOYS 
AN ALLOY is a compound or mixture or a solid 
solution of two or more metals effected by fusion. 
AN AMALGAM is an alloy of two or more metals, 
one of which is mercury. 
Few metals are employed in the pure state, with the 
exception of iron, copper, lead, tin, zinc, platinum and 
aluminum; they are more frequently used for technical 
purposes in the form of alloys. Every industrial ap- 
plication requires special qualities that may not exist 
in any single metal, hut which may he produced by the 
proper mixture of two or more. For example: silver 
and gold are much too soft and pliable for plate, coin 
or jewelry, but by the addition of certain amounts of 
copper they are rendered harder and more elastic, 
while their color and other valuable qualities are not 
impaired. Copper is also too soft and tough to be 
wrought in a lathe, but when alloyed with zinc, it 
forms a hard, beautiful, yellow-colored alloy known as 
brass, of great usefulness, and more easily worked than 
the pure metal. 
Alloys are equally interesting, from a scientific stand- 
point, for they may be regarded not only as mere mix- 
tures of metals, but in many instances as true chemical 
compounds. Matthiessen* regarded it as probable that 
the condition of an alloy of two metals in a melted state 
may be either that of: (1) A solution of one metal in 
another; (2) a chemical combination; (3) a mechanical 
‘British Association Reports, 1863, p. 97. 
117 118 
PRACTICAL DENTAL METALLURGY 
mixture; or, (4) one consisting of two or all of 
the above; and that similar differences may exist as to 
its condition in the solid state, defining a solid solution 
as “a perfectly homogeneous diffusion of one body 
in another.” 
Each of these four types of alloy presents a charac- 
teristic appearance when polished, etched and exam- 
ined under the microscope. An alloy forming a solid 
solution when properly treated with etching reagents 
will not be distinguishable from a pure metal, while an 
alloy coming under the division of a mechanical mix- 
ture will appear totally different. The type of alloy 
formed by melting two metals together can be deter- 
mined by an examination of the temperature-composi- 
tion diagram. This diagram shows the relation be- 
tween the composition of the alloy and the solidifying 
temperatures. It is prepared by measuring the rate 
at which alloys of different composition of the same 
metals solidify. These are called cooling curves and 
the shape of these lines shows the type of alloy that 
is being used. 
1. A Solid Solution of One Metal in Another.—Some 
metals when melted together will unite in the same 
manner that water mixes with alcohol in all propor- 
tions and will appear perfectly homogeneous. They 
exhibit little tendency to separate on cooling. The 
alloy thus formed will vary continuously as regards 
chemical and physical properties. Gold and silver form 
such an alloy. The temperature-composition diagram 
of gold and silver is given in Fig. 39. 
The portion above the curves is a liquid solution; 
that between the lines is composed of solid crystals 
and liquid solution, and that below the curves is com- ALLOYS 
119 
pletely solidified. For example, an alloy containing 
90 per cent silver and 10 per cent gold would be totally 
liquid at a temperature of 1000 degrees. An alloy of 
50 per cent gold and 50 per cent silver at this tem- 
perature would be partly solidified but would still 
have some liquid solution. An alloy of 90 per cent gold 
and 10 per cent silver, however, would be completely 
solidified at the same temperature. 
Combos/ t/o/v 
Fig. 39. 
2. A Chemical Combination.—Other metals when 
melted together do, without doubt, form true chemical 
compounds. In the phenomena which accompany such 
union, and in the properties of the resulting products, 
we observe that which characterizes the manifestation 
of affinity, that is, an evolution of heat and light, result- 
ing in the formation of substances having a definite com- 
position, distinct crystalline form, and a variety of prop- 
erties different from those of the constituents. Thus, 
if a piece of clean sodium be rubbed in a mortar with a 120 
PRACTICAL DENTAL METALLURGY 
quantity of dry mercury, the sodium combines with a 
hissing sound, and a considerable increase of mass tem- 
perature is noticeable on the addition of each succes- 
sive piece of sodium. 
EXPERIMENT: Throw a small piece of clean, dry sodium, 
upon the surface of a small amount of clean, dry, and warmed 
mercury; a chemical union takes place immediately, accompanied 
by heat and incandescence, forming crystalline amalgam. 
When the mass cools, long needles of a white, bril- 
liant alloy of definite composition crystallize from the 
middle of the liquid, and the excess of mercury may be 
separated by decantation. Platinum, iridium, gold, and 
silver unite with tin, accompanied by an evolution of 
heat. If the tin is in excess, upon cooling, the mass 
very much resembles that metal, but if the ingot be 
treated with strong hydrochloric acid, the excess of tin 
is dissolved, and crystals of a definite alloy of tin and 
the precious metals remain.* Several other metals, 
such as iridium and osmium, as iridosmine, palladium, 
and platinum and others occur as native alloys. These 
compounds act much the same as pure metal in re- 
spect to the result on the temperature-composition dia- 
gram. The alloy that forms chemical compounds often 
forms double eutectics, one on either side of the com- 
pound. The dental amalgams are generally this type 
of alloy and the setting of the amalgam is due to the 
formation of these compounds. Fig. 40 shows the 
typical temperature-composition diagram of the alloys 
forming definite chemical compounds. The maximum 
point in the diagram shows the composition of the 
compound and these always occur in simple molecular 
proportions. 
*See chapter on Tin. ALLOYS 
121 
3. A Mechanical Mixture.—Just as some substances 
like camphor and water are not mutually soluble so 
some metals separate on solidification. Copper and 
silver exhibit such properties. Upon polishing and 
etching such an alloy two distinct crystalline forms can 
be distinguished. One of these is usually composed of 
crystals of one of the pure metals and the other is the 
eutectic mixture. The temperature-composition dia- 
gram of copper and silver is given in Fig. 41. 
7kr-rp£r?flT-£j/=!£r 
Cv^S'T'Or* 
Fig. 40. 
An alloy containing 70 per cent copper and 30 per 
cent silver would begin to solidify at about 900° C. and 
the crystals forming at that temperature would be pure 
copper. This solidification would continue as the alloy 
cooled until the liquid remaining would have the com- 
position of 28 per cent copper and 72 per cent silver 
which is the eutectic mixture. At this point the tem- 
perature remaining constant at 780° C., the entire 122 
PRACTICAL DENTAL METALLURGY 
liquid mass would solidify. In this diagram, as before, 
the portion above the lines is liquid; that between the 
lines part solid, part liquid, and that below the lines 
is solid. 
4. An Alloy Consisting of Two or All of the Above.— 
A large majority of the alloys fall into this classifica- 
tion. The alloy of gold and copper forms a series of 
solid solutions at the melting points of the alloys of 
varying composition and also forms two chemical com- 
cVowposrr/o/v 
Fig-. 41. 
pounds at about 400° C. The properties of these com- 
pounds following the general rule are different from 
those of the solid solution and also appear different on 
microscopic examination. Advantage is taken of this 
fact in the annealing and also the hardening of gold 
copper alloys of high gold content. The solid solution 
forms a soft malleable alloy while the compound is 
hard and brittle. In order, then, to anneal such an 
alloy the metal must be heated almost to the melting ALLOYS 
123 
point and cooled rapidly. In order to harden such 
an alloy the temperature should be raised to 400° C. 
and held at that temperature for some time, allowing 
the compounds to form. The temperature-composition 
diagram is shown in Fig. 42. 
Fig. 42. 
THE PHYSICAL PROPERTIES OF ALLOYS can 
not be anticipated, and are only determinable by actual 
experiment. Very minute proportions of some metals 
added to others will produce an alloy with properties 
foreign to either of the constituents. Thus, a small 
quantity of lead fused with gold will produce a brittle 
alloy, though each metal is malleable. 
Specific Gravity.—If this property be calculated from 
that of the components—assuming that there is no con- 
densation of volume—the resulting number may be 
greater than, equal to, or less than, the experimental 
result. Thus, the alloys of silver and gold have a less 
specific gravity than the theoretical mean of the com- 
ponents ; whereas copper and zinc vary in the opposite 
direction. 124 
PRACTICAL DENTAL METALLURGY 
The following table,* by Thenard, shows examples 
of this variation: 
Alloys Possessing a Greater Specific 
Gravity than the Mean of Their 
Components 
Alloys Having a Specific Gravity 
Inferior to the Mean of Their 
Components 
Gold 
and 
Zine 
Gold 
and 
Silver 
( t 
i < 
Tin 
6 ( 
i C 
Iron 
< l 
C C 
Bismuth 
u 
i i 
Lead 
( ( 
i t 
Antimony 
c c 
( ( 
Copper 
6 i 
c c 
Cobalt 
( c 
C ( 
Iridium 
Silver 
< c 
Zinc 
(( 
( c 
Nickel 
( ( 
c c 
Lead 
Silver 
( c 
Copper 
C ( 
c < 
Tin 
Coppei 
c c 
Lead 
( i 
t c 
Bismuth 
Iron 
(t 
Bismuth 
6 ( 
(( 
Antimony 
C ( 
i c 
Antimony 
Copper 
C ( 
Zine 
( < 
i ( 
Lead 
( ( 
(( 
Tin 
Tin 
C ( 
Lead 
( c 
(( 
Palladium 
( C 
(( 
Palladium 
(i 
( c 
Bismuth 
( c 
( c 
Antimony 
i c 
It 
Antimony 
Nickel 
( c 
Arsenic 
Lead 
( c 
Bismuth 
Zinc 
t c 
Antimony 
c c 
i l 
Antimony 
Platinum 
( c 
Molybdenum 
Palladium 
(( 
Bismuth 
It is common among authorities who publish determi- 
nations upon specific gravities of the alloys to give the 
calculated as well as the observed specific gravity. 
The color of an alloy usually resembles that of the 
metal which predominates. Some few exceptions are 
quite notable, for instance gold 2 to 6, and silver 1 part 
produces an alloy of a greenish color, and it is said that 
1/24 part of silver is sufficient to modify the color of 
gold. Nickel and copper form alloys varying from 
copper-red to the bluish-white of nickel. With a con- 
tent of 30 per cent of nickel the alloy is silver white; 
while with zinc, copper yields a variety of shades, from 
the silver white of brass consisting of copper 43, and 
zinc 57 parts, to that of red brass, which contains 80 
per cent or more of copper. 
‘Phillip’s Metallurgy. ALLOYS 
125 
Malleability, Ductility, and Tenacity.—These prop- 
erties are generally very much modified by alloying. 
As a rule the malleability and ductility are decreased, 
even when two malleable and ductile metals, such as 
gold and lead, are alloyed together—a very small con- 
tent of lead destroying the malleability and ductility of 
the noble metal. Again, copper 94 and tin 6 parts form 
an exceedingly brittle alloy. Generally the ductility 
decreases, while the hardness, as compared with that 
of the constituent metals, increases to a considerable 
extent, for example, gold and platinum, two very 
ductile and soft metals, afford an alloy much harder 
and of greater elasticity than either. Gold and silver, 
being too soft for currency, are alloyed with 10 per 
cent of copper, which gives them the required hard- 
ness. A few metals, antimony, for instance, possess 
the property of making metals harder. Mr. Makins 
states that l-1900th part of this brittle metal will make 
gold quite unworkable. As a rule, a brittle and a 
ductile metal afford a brittle alloy; yet copper and zinc 
yield a malleable and ductile brass. 
The tenacity is generally very much increased, as is 
shown by the following results of Matthiessen’s experi- 
ments. "Wires of the same gauge were employed, and 
the weights causing their rupture before and after 
alloying noted as follows: 
Lbs. at Rupture 
Copper, unalloyed 25 to 30 
Tin, “ under 7 
Lead “ “ 7 
Gold, “ 20 to 25 
Silver, 11 45 to 50 
Platinum, “ 45 to 50 
Iron, lt 80 to 90 126 
PRACTICAL DENTAL METALLURGY 
Lbs. at Rupture 
Copper, alloyed with 12 per cent Tin 80 to 90 
Tin, “ “ “ Copper 7 
Lead, “ “ Tin 7 
Gold, “ “ Copper 70 
Silver, “ “ Platinum 75 to 80 
Steel (iron compounded with carbon) above 200 
Fusibility.—The fusing point of an alloy is always 
lower than the highest fusing metal entering into its 
composition, and is sometimes lower than that of any of 
the components. Thus an alloy composed of 10 parts 
lead and 4 parts tin fuses at 243° C., melting lower than 
the less fusible lead (327° C.), but at a greater tempera- 
ture than tin (232° C.) ; and an alloy composed of 25 
parts lead, 12.5 parts tin, 50 parts bismuth, and 12.5 
parts cadmium (Wood’s metal) melts at 65.5° C., 
lower than that of any of its constituents—tin being the 
most fusible (232° C.). Alloys of lead and silver, con- 
taining a small quantity of the latter, are more fusible 
than lead, and sodium and potassium form an alloy 
fluid at ordinary temperatures. 
Matthiessen* explains why the fusing point of alloys 
is uniformly lower than the mean of those of their con- 
stituents: “It is generally admitted 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 attrac- 
tion. Let us assume that similar particles of matter 
attract each other more powerfully than dissimilar ones; 
it will then follow that the attraction subsisting be- 
tween the particles of a mixture will be sooner over- 
come by repulsion than will the attraction in the case 
*Makins’ Metallurgy, p. 65, ALLOTS 
127 
of a homogeneous body; hence, mixtures should fuse more 
readily than their constituents. ’ ’ 
Sonorousness.—This property is most wonderfully 
developed in some instances. Copper and tin, two 
metals which possess the quality in but a small degree 
comparatively, unite to form an alloy known as “bell 
metal,” the normal composition of which is, copper 74 
or 85, and tin 26 or 15, respectively. Copper and alum- 
inum also yield alloys of remarkable sonorousness. 
Conductivity.—The property of conductivity, either 
for electricity or heat, in an alloy is much inferior to 
that of the pure metals. Advantage is taken of the 
high electrical resistance in some of the alloys, such 
as German silver, for measuring the resistance of long 
lines of telegraph wire, the electromotive force or work- 
ing power of batteries, for making rheostats and other 
apparatus for controlling the electric current, etc. 
Decomposition.—Heat decomposes alloys containing 
volatile metals like mercury or zinc. It requires a tem- 
perature much above the boiling point of the metal, 
however, to completely separate all traces of it from an 
alloy, and in most instances this cannot be accom- 
plished even then without the assistance of a chemical 
agency. When gold is contaminated with tin, the lat- 
ter cannot be removed entirely by roasting; but if 
heated with small quantities of potassium nitrate, which 
serves to oxidize the base metal, it may be entirely re- 
moved. Mercury may be completely separated by 
roasting; it volatilizes at about 357.3° C. When en- 
deavoring to expel it from old amalgam fillings, how- 
ever, the plug should be heated bright red. 
ANNEALING AND TEMPERING.—Annealing is a 
process employed in the working of various metals and 128 
PRACTICAL DENTAL METALLURGY 
alloys to reduce the brittleness and stiffness usually 
resulting from a rapid or important change of molecu- 
lar structure, such as is produced by hammering, long 
continued vibration, rolling, and sudden cooling. Bell 
metal is brittle, and cracks under the hammer, cold 
as well as heated. If it be repeatedly brought to a 
dark-red heat and quickly cooled by immersion in 
water, its brittleness is so far decreased that it can be 
hammered and stamped. 
The dentist, in swaging a flat sheet of gold alloy to 
conform to his dies, must stop at intervals and anneal 
the piece of metal to prevent its splitting under his 
blows and pressure. 
It is said sudden changes of temperature have the 
effect, almost invariably, of rendering metals brittle. 
Gold, silver, platinum, etc., should be heated for a re- 
arrangement of their molecular structure and allowed 
to slowly cool, rather than to be immediately plunged 
into a cold bath, if the best results are desired. Lead, 
tin, and zinc are annealed by immersion in water, which 
is made to boil and then cool slowly. Steel should not be 
annealed in an open fire, as the carbon which enters the 
iron as an element, combines with the oxygen of the 
air to the detriment of the steel. 
Annealing may be said to be the inverse process of— 
Tempering, which latter is the fixing of the molecular 
condition of steel by more or less sudden cooling from 
a particular temperature. 
Oxidation.—Alloys are usually more easily oxidized 
than their constituents. 
Nearly all metals in a state of fusion have a tendency 
to dissolve a greater or less amount of their oxides, 
and this is particularly true of alloys, for then the metals ALLOYS 
129 
are in a state of solution, a condition most favorable to 
chemical change. 
The best preventive against this formation of oxides 
and their subsequent absorption is to protect the molten 
alloy by a layer of pulverized charcoal or some of the 
fluxes. A reduction of much of the oxide formed may 
be effected by vigorous stirring with a stick of green 
wood. The careful addition of not more than 0.008 to 
0.0010 parts of phosphorous has been found an excel- 
lent agent for the deoxidation of the oxides dissolved 
in bronze. 
The zinc and alloys used in the dental laboratory for 
making dies, after repeated melting and casting in con- 
tact with the air, often become thick and mushy from 
dissolved oxides; and their valuable working qualities 
are so seriously impaired that they fail to copy the fine 
lines of the mold and produce a perfect die. Their 
properties may be restored to a great extent by melting 
under pulverized charcoal or tallow, and vigorously 
stirring with a stick of green wood, or by dissolving in 
the molten metal a small quantity of aluminum. 
INFLUENCE OF CERTAIN METALS IN ALLOYS. 
—Certain metals when present in an alloy confer upon 
it definite properties which are in many instances char- 
acteristic; thus, in a general way, mercury, cadmium, 
and bismuth increase fusibility; tin, hardness and 
tenacity; antimony and arsenic, hardness and brittle- 
ness. 
A SOLDER is an alloy or metal used for cementing 
or binding metallic surfaces or margins together, and 
the process is usually effected by heat. Ordinary sol- 
ders are divided into hard and soft classes. 130 
PRACTICAL DENTAL METALLURGY 
The Hard Solders comprising those which require a red 
heat for their melting. 
The Soft Solders being those used by plumbers and 
tinsmiths, and consisting principally of lead and tin. 
with sometimes an addition of bismuth. 
Brazier’s Solder, for uniting the surfaces of copper, 
brass, etc., is usually composed of copper and zinc, 
nearly equal parts, with a small addition of tin, and 
sometimes antimony. 
Silver is the proper solder for German silver articles, 
and gold or an alloy of gold and platinum for platinum. 
In Soldering, the surfaces or edges to be united must 
be kept free from oxidation and dirt. To keep them 
deoxidized during the operation several fluxes are used, 
such as dehydrated borax, or some of the reliable pre- 
pared compounds on the market, for gold, silver, 
brass, or copper soldering; rosin, or a solution of zinc 
chloride, for tin plate; zinc chloride for zinc, hydro- 
chloric acid for galvanized iron, and rosin and tallow 
for lead and tin. 
Burnley’s soft soldering paste consists of 2 oz. of a 
saturated solution of zinc chloride mixed with one 
pound of petrolatum or vaseline. It is most conven- 
ient when placed in a container like a tooth paste tube 
with a long aluminum nozzle. 
Among the requirements of a good gold solder the 
most important are carat, color, strength, and fusing 
point. In fineness it should be equal, or nearly equal, 
to the plate, its color and strength as nearly as possible 
the same, while the fusing point should be a trifle 
lower—the nearer the melting point of the plate the 
better the results. 
To obtain these qualities it is necessary to prepare a ALLOYS 
131 
solder by the addition of some metal which will fuse at 
a lower temperature than any of the constituents of the 
plate. Zinc is admirably suited for this purpose, and 
is generally used, since it permits of a solder as fine, or 
nearly as fine as the plate. In addition to this it also 
possesses the advantage of yielding a less fluid solder 
than that of copper and silver, permitting it to bridge 
over slight spaces. This is very probably on account of 
the oxidation or volatilization which takes place, for it 
is observable that any subsequent fusing requires a 
greater heat. An advantage is also obtained here in 
this fact, since it enables more perfect second solder- 
ings with the same alloy. 
The process of soldering is a cementation by super- 
ficial alloying, and is admirably illustrated in the in- 
stance of soldering platinum bases with pure gold for 
continuous-gum dentures. By means of the blow pipe 
the gold is flowed over the surfaces of platinum, joining 
them, but if the joint is not well made, and the inter- 
vening space is filled with gold, it is not as strong as 
it might be. This, however, is all remedied during the 
process of baking the body and enamel, as the high heat 
required for this so diminishes the cohesive power of 
the platinum that it readily and completely alloys with 
the gold, producing a stronger joint of a platinum-gold 
alloy, which is observed to be the same color as the 
platinum. 
Soldering iron or steel, except galvanized iron, is 
more difficult than any of the soldering operations, 
aluminum excepted. It is due to surface oxidation and 
lack of affinity. Before soldering iron, it is necessary 
to tin it when soft solder is used. This is like a plat- 
ing process. The surface must be free from oxides. 132 
PRACTICAL DENTAL METALLURGY 
This may be accomplished by first immersing in ben- 
zine, or potassium hydroxide or lye solutions until the 
grease is removed, then placed in a 10 per cent solution 
of sulphuric acid until the oxide is removed, and 
finally immersing in strong solution of sodium hydrox- 
ide. The iron may now be coated with a light coat of 
copper by immersing in a copper sulphate solution, 
after which it may be tinned by heat in the usual man- 
ner or it may be tinned without first depositing copper. 
The former method gives a more adhesive coat of tin 
and lead. 
Autogenous Soldering is a process of uniting by 
direct fusion of the contiguous parts, without the inter- 
vention of a more fusible alloy. It is extensively used 
in uniting ends of bands for collar crowns. 
PREPARATION OF ALLOYS.—This would seem 
but a simple task, but in order to produce an accurate 
result it is far from being as easy as it may seem. 
Most alloys are prepared by directly melting the metals 
together, but much skill, judgment, and experience are 
required to determine when it is best to add each con- 
stituent, and the amount of each to be used—to protect 
the molten mass, and to handle it generally. 
The metal having the highest fusing point is gen- 
erally melted first, and the others are added in accord- 
ance with their points of fusibility. To obtain as homo- 
geneous an alloy as possible, the metals, while in a state 
of fusion, must not be allowed to remain quiescent, but 
an intimate mixture effected by vigorous stirring, sticks 
of dry soft wood being used for the purpose. By stir- 
ring the fused mass with one of these sticks, the wood 
is more or less carbonized according to the tempera- 
ture of the mass, gases are evolved from the carbon- ALLOYS 
133 
izing wood, which, by ascending in the fused mass, 
contribute to its intimate mixture. The stirring should 
continue for some time and the alloy then cooled as 
rapidly as possible. 
The varying densities of the metals to be combined 
frequently render the formation of a homogeneous mass 
very difficult. In some instances the heavier metal 
tends to sink to the bottom, carrying with it a small 
quantity of the other, while the lighter, floating above, 
retains a small quantity of the heavier. For instance, 
only a small proportion of zinc will unite with lead, or 
aluminum with bismuth; but, as a rule, metals mix per- 
fectly in the fluid state. When, however, the fluid 
mixture is poured into the ingot mold, it rarely happens 
that the solidified mass is perfectly homogeneous. The 
reason of this is that the addition of one metal to an- 
other produces an alloy, the solidifying point of which 
is usually lower than it should be according to calcula- 
tions based upon the proportionate amounts and fus- 
ing points of the constituents. One particular mixture 
has a lower fusing point than any other possible mix- 
ture of the metals employed, and this is termed the 
eutectic alloy of that series. Aside from those pos- 
sibly true chemical combinations of metals, a fluid mix- 
ture of two metals may be expected to begin deposit- 
ing its less fusible constituent first, and, as the tem- 
perature falls, more and more of this element will be 
separated, the other constituent concentrating in the 
fluid residue until this has acquired the eutectic com- 
position, when it will solidify as a whole in the spaces 
left between the already solidified particles. The more 
slowly the material solidifies, the more marked will be 
the separation that occurs. 134 
PRACTICAL DENTAL METALLURGY 
EUTECTIC ALLOYS.—In 1884 the late Professor 
Guthrie introduced the term eutectic to denote the 
most fusible alloy of two or more metals. He com- 
pared it to the mother liquor of a salt solution, which 
remains fluid after the bulk of the salt has separated 
out. At a temperature near the melting point of lead 
a mixture of equal parts of Pb and Sn would be fluid. 
If the alloy were cooled down to 220° C., the lead 
would crystallize out, and a solid lead would exist in 
contact with liquid lead. As the mixture cooled, more 
and more lead would crystallize out until at 180° C. 
the whole would solidify. The residue would now 
consist of about 70% tin and 30% lead. This, therefore, 
is the eutectic alloy. The reverse would happen if 
there was more tin than lead in the alloy; then the tin 
would separate out. The minute structure of the cold 
alloy would appear as a mass of lead crystals in the 
eutectic of lead and tin. 
Eutectics are not always as simple as this, for if there 
is more than one solution and each solution on cooling 
will give a deposit and a eutectic, the eutectic is not a 
chemical compound, for it is never in molecular pro- 
portions. 
Authorities differ on this point, as Flavitzkii (Phys. 
Chem. Soc. 42, 428-34) considers cryohydrates and eu- 
tectics to be definite chemical compounds. Conversely, 
many chemical compounds might be regarded as eutec- 
tics. If the determination of eutectics depends entirely 
on the lowest fusing point of alloys of certain metals in 
definite chemical proportions, then the results of some 
experiments would tend to disprove Flavitzkii’s state- 
ment. (See table on page 135.) ALLOYS 
135 
Lead 
Tin 
Bismuth 
Cadmium 
Fusing point, C. 
25.00 
12.50 
50.00 
12.50 
55.5 
12.00 
216.00 
60.00 
12.00 
55.5 
34.97 
9.90 
35.13 
90. 
31.25 
18.75 
50.00 
90. 
16.67 
41.67 
41.66 
100. 
25.00 
25.00 
50.00 
100. 
For making large quantities of an alloy the reverber- 
atory furnace is used, special precautions being taken 
to preserve a deoxidizing flame within the furnace. 
For preparing alloys in a small way a crucible is 
used, and the alloy is covered with a suitable flux to 
protect it from the action of atmospheric air. Four 
sources of loss must he guarded against: (1) loss by 
oxidation; (2) loss by volatilization; (3) loss by chem- 
ical combination with the flux; (4) loss by fracture or 
solution of the crucible. 
The first may he prevented by the use of one of the 
various fluxes,# or covering the surface with pulverized 
charcoal. The second loss usually occurs through an 
endeavor to alloy a metal of a high fusing point with 
one which fuses at a low temperature. Under such 
circumstances the one requiring a high temperature 
should be fused first and well covered with flux melted 
to extreme fluidity; the more fusible metal should then 
be added in as large a piece as convenient and quickly 
thrust beneath the molten surface. The third source 
of loss is principally caused by the use of borax as a 
flux for some base metals. It is well known that in 
much borax a portion of the boric acid is not perfectly 
saturated, and this is especially true of the prepared 
article; and if melted with some base metals, the free 
*See chapter on Melting Metals. 136 
PRACTICAL DENTAL METALLURGY 
acid is absorbed, which, with the sodium borate, forms 
double salts of a glassy nature. Hence, by fusing some 
metals and alloys under borax, a certain portion will be 
lost in chemical combination. The fourth cause is 
guarded against by careful selection of crucibles. If 
alloys of low fusing metals are to be made, the ordi- 
nary clay or Hessian crucible is all that is necessary, 
and, indeed, with proper care, noble metals may be 
alloyed in it without danger of loss; but it is liable to 
perforation by corrosive fluxes, allowing the molten 
alloy to escape. Therefore, for the preparation of ex- 
pensive alloys from noble metals, the employment of 
tried graphite or graphite and clay crucibles often 
saves much trouble and expense. 
In some instances, especially when metals are known 
to form chemical combinations, it may be best to melt 
the one of lowest fusing point first, and then dissolve 
the other components in it. Or, those of low fusing 
point may be melted in one crucible, while those more 
difficult of fusion are melted in another, then combined 
in the molten state. 
When two metals of varying specific gravity are 
alloyed, the mass should not be allowed to become 
quiescent just before pouring. And if any incompati- 
bility exists between the metals, such as in the case of 
zinc and lead, accompanied by a great difference in 
specific gravity, an intimate admixture should be 
effected by vigorously stirring the molten mass with 
sticks of soft, dry wood, which become more or less 
carbonized, according to the temperature of the mix- 
ture. In consequence of this dry distillation of the 
wood there is evolved an abundance of gases, which 
by ascending in the fused mass, contribute to its inti- ALLOYS 
137 
mate mixture. The stirring should be continued for 
some little time, and the alloy poured as quickly as 
possible. 
“Many alloys,” says Mr. Brannt,* “possess the 
property of changing their nature by repeated remelt- 
ing, several alloys being formed in this case, which show 
considerable differences, physically as well as chem- 
ically. The melting points of the new alloys are gen- 
erally higher than those of the original alloy, and their 
hardness and ductility are also changed to a consid- 
erable extent. This phenomenon is frequently con- 
nected with many evils for the further application of 
the alloys, and in preparing alloys showing this prop- 
erty the fusion of the metals and subsequent cooling 
of the fused mass should be effected as rapidly as 
possible.” 
Although most of the heavier metals are at present 
used in the preparation of alloys, copper, zinc, tin, 
lead, silver, and gold are more frequently employed 
than all others. Alloys containing nickel have become 
of great importance, as well as those in which alumi- 
num forms a constituent. 
Mr. Brannt recommends for experimentation that 
metals be added to each other in certain quantities by 
weight, which are termed atomic weights, and claims 
that in this manner alloys of determined, characteristic 
properties are, as a rule, produced; or, if such does not 
answer the demands of the alloy, the object may be 
attained by taking two, three or more equivalents of 
the metal, exception being made in the cases of arsenic 
and such elements. 
‘Metallic Alloys, p. 87. CHAPTER VI 
LEAD 
Plumbum. 
Valence, II, IV. 
Atomic weight, 207.2. 
Melting Point, 327° C. 
Ductility, 10th rank. 
Conductivity (heat), 8.36. 
Symbol, Pb. 
Specific gravity, 11.34. 
Malleability, 7th rank. 
Tenacity, lowest (8th) rank. 
Chief ore, galenite. 
Conductivity (electricity), 8.4. 
(Silver being 100.) 
Specific heat, 0.0310. 
Color, bluish-white. 
Crystals, octahedral. 
OCCURRENCE.—This abundant and very useful 
metal is almost wholly obtained from its native sul- 
phide, (1) Galenite (PbS) or galena, and is rarely, if 
ever, found free. Its other more widely distributed ores 
are (2) Cerusite (PbC03), lead carbonate, sometimes 
called white-lead ore, and (3) Crocoisite (PbCr04), lead 
chromate. There is also a (4) Wulfenite (Mo04Pb) and 
a (5) Sulphate (PbS04). Galenite often carries silver, 
as AgS, in sufficient quantities to be well worth ex- 
tracting, the proportion of the noble metal varying 
from about 0.01 to 0.03 per cent, and in rare cases 
amounting to 0.5 or 1 per cent. Such ore is called 
Argentiferous Galena. Lead ore frequently occurs ac- 
companied by copper, iron pyrites, and zinc-blende. 
Galenite is found in the United States, Great Britain, 
Spain and Saxony. The largest mines in the world are 
located in Idaho. 
REDUCTION OF GALENITE is effected in a rever- 
beratory furnace, into which the crushed lead ore is 
138 LEAD 
139 
introduced and roasted for some time at a dull-red 
heat. In the roasting a portion of the lead sulphide is 
oxidized to the oxide and sulphate— 
PbS + 30 == PbO + S02 and 
PbS + 04 = PbS04. 
The contents of the furnace are then thoroughly 
mixed and the temperature raised, whereupon the sul- 
phate and oxide react with the remaining sulphide, 
forming sulphurous oxide and metallic lead— 
2PbO + PbS = S02 + 3Pb and 
PbS04 + PbS = 2S02 + 2Pb. 
Contaminating metals, which render the lead hard, 
are removed by melting and partially oxidizing in a re- 
verberatory furnace with a cast-iron bottom. 
PROPERTIES.—Pure lead is a feebly lustrous, blu- 
ish-white metal, endowed with a high degree of.soft- 
ness and plasticity and almost entirely devoid of elas- 
ticity. It is said to be the least tenacious of all metals 
in common use. A wire 0.1 inch in thickness is rup- 
tured by a weight of about thirty pounds. Its specific 
gravity is 11.34. It melts at 327° C. At a bright-red 
heat it vaporizes, and at a white heat (1580° C.) it boils. 
Its specific heat is .0310, that of water at 0° C. being 
taken as a unit. Lead exposed to ordinary air is 
rapidly tarnished, forming a suboxide. The same sup- 
posed suboxide is formed upon lead kept in a state 
of fusion in the presence of air, when at the same time 
the metal rapidly absorbs oxygen; then the monoxide 
(PbO) is formed, the rate of oxidation increasing with 
the temperature. By slowly cooling lead may be ob- 140 
PRACTICAL DENTAL METALLURGY 
tained in octahedral crystals. Dilute acids, with the 
exception of nitric, act but slowly on lead. 
DENTAL APPLICATIONS.—Its chief dental use is 
in the laboratory as a connterdie. It may be rolled into 
a thin foil, and at one time was used for filling carious 
teeth, and in conical points was used in filling the 
apices of pulp-canals. It is an important component 
of soft solders and various alloys. 
COMPOUNDS WITH OXYGEN.—There are four 
compounds of lead and oxygen: 
The Diplumbic Oxide, or Lead Suboxide, Pb20, a 
gray pulverulent substance, is formed when the monox- 
ide is heated to a dull redness in a retort, and is sup- 
posed to correspond with the dull coating formed on 
bright, freshly cut surfaces of lead when left exposed 
to the air. 
The Monoxide, Litharge or Massicot, PbO, is very 
heavy, and of a delicate straw-yellow color, slightly 
soluble in water, melting at a red heat, with a tendency 
to crystallize on cooling, and is easily reduced when 
heated with organic substances of any kind containing 
carbon or hydrogen. It is the product of the direct 
oxidation of the metal, but is more conveniently pre- 
pared by heating the carbonate to dull redness. 
PbC03(+ heat) = PbO + C02. 
The Dioxide, Puce or Brown Lead Oxide, Pb02, is a 
heavy brown powder, insoluble in water, having an acid 
reaction, and may be regarded as the anhydride of 
plumbic acid, II4Pb04. It is easily obtained by digest- 
ing the red oxide in nitric acid. 
Red Oxide, or Red Lead, is a compound of the mon- 
and dioxides, not very constant in its composition, but LEAD 
141 
is generally regarded as having the formula 2PbO, 
Pb02 = (Pb304). It is a heavy, bright-red powder, and 
may be regarded as lead plumbate, Pb2Pb04. It is 
used as a cheap substitute for vermilion. When 
treated with dilute nitric acid the monoxide dissolves, 
forming soluble lead nitrate, leaving the puce-colored 
oxide behind. It is prepared by exposing the monoxide, 
which has not been fused, for a long time to the air 
at a very faint red heat. 
ACTION OF ACIDS ON LEAD.—The presence of 
carbonic acid in a water does not affect its action on 
lead. Aqueous nonoxidizing acids generally have lit- 
tle or no action on lead in the absence of air. 
Sulphuric Acid, when dilute (20 per cent solution or 
less), has no action on lead, even -when air is present, 
nor on boiling. The stronger acid does act, slowly in 
general, but appreciably, the more so the greater its 
concentration and the higher its temperature. Pure 
lead is more readily acted upon than that contaminated 
with antimony or copper. Boiling concentrated sul- 
phuric acid converts lead into the sulphate, with the 
indirect evolution of sulphurous oxide. 
Pb + H2S04 = PbS04 + 2H 
2H + H2S04 = 2H20 + S02 
The hydrogen formed reacts with sulphuric acid to 
produce S02. If there is sufficient hydrogen it will re- 
duce H2S04 to H20 + S. 
Nitric Acid.—The metal is readily dissolved in di- 
lute nitric acid, nitrogen dioxide being evolved and 
plumbic nitrate formed. 
Hydrochloric Acid.—Strong and hot hydrochloric 142 
PRACTICAL DENTAL METALLURGY 
acts but slowly upon lead, forming the dichloride and 
liberating hydrogen. 
Water, when pure, has no action on lead per se. In 
the presence of free oxygen (air), however, the lead is 
quickly attacked, forming a hydrated oxide, Pb(OH)2 or 
PbOH20, which is appreciably soluble in water, ren- 
dering the liquid alkaline. When carbonic acid is 
present the dissolved oxide is soon precipitated as basic 
carbonate—PbC03 (which is slightly soluble in water 
containing carbon dioxide)—so there is room made, so 
to say, for fresh hydrated oxide, and the corrosion of 
lead progresses. Now, all soluble lead compounds are 
strongly cumulative poisons; hence the danger in- 
volved in using lead pipes or cisterns in the distribu- 
tion of PURE waters. We emphasize the word “pure, ” 
because experience shows that the presence in water of 
even small proportions of bicarbonate or sulphate of 
lime prevents its action on lead. These sulphates or car- 
bonates almost invariably present, cause the deposition 
of a very thin but closely adherent film of sulphates or 
carbonates upon the surface of the metal, which protects 
it from further dissolution. 
ALLOYS.—Pure lead unites with almost all metals. 
Mercury readily amalgamates with it, and, in proper 
proportions, crystallizes, forming a very white but brit- 
tle alloy. This union is said to be of a definite chem- 
ical proportion, and is expressed as Pb2Hg. Very 
small quantities of lead admixed with the noble metals 
destroy completely their malleability, and hence ren- 
ders them unworkable. It is said that l-1920th part 
of lead in gold will greatly impair its coining property, 
and that gold containing l-500th part of lead is “ren- 
dered unfit for coinage.” The gold drawer in the LEAD 
143 
dental laboratory is often so situated that it is almost 
impossible to prevent particles of lead from accumu- 
lating with the gold scraps and filings. These, however, 
may be easily removed by roasting with potassium 
nitrate and sulphur.* 
Silver in certain proportions with lead forms an alloy 
which has a lower fusing point than that of lead. Pat- 
tinson, taking advantage of this fact, invented his pro- 
cess for recovering the silver from argentiferous ga- 
lena. A quantity of the silver-lead ore is melted in one 
of a series of iron pots. After complete fusion it is 
allowed to slowly cool, when the poorer lead crystal- 
lizes and is ladled off to another pot, leaving the rich 
silver-bearing lead behind. This is carried on through 
the whole series of some twelve pots, until the lead-sil- 
ver alloy has been reduced to proportions by which the 
noble metal may be recovered by the process of cupel- 
lation.f 
Platinum with equal weight of lead gives a purplish- 
white, brittle, and granular alloy. So great is the af- 
finity these metals have for each other that lead oxide 
heated in a platinum crucible with reducing flux is 
broken up and the lead combines with the platinum 
vessel. Lead can only be separated from platinum by 
the humid process of refining platinum. 
Palladium and lead form a green alloy which is very 
hard and brittle. 
The more common alloys of lead are those with tin, 
antimony, etc. 
Tin unites with lead in almost any proportion with 
slight expansion.J 
*See chapter on Gold. 
fSee chapter on Silver. 
JKuppfer. 144 
PRACTICAL DENTAL METALLURGY 
The following table gives an idea of the melting 
points of alloys of lead and tin: 
An Alloy 
of— 
Fuses at— 
Lead 1, 
Tin 
2 
171.° C. 
“ 1, 
C ( 
6 
“ 2, 
c e 
1 
227.7° C. 
“ 4, 
( c 
1 
259.° C. 
“ 17, 
( c 
1 
289.° C. 
With tin 1 part and lead 5 parts* Dr. Haskell makes 
counterdies to be used with his Babbitt-metal dies. 
It fuses at a lower temperature than the die alloy, and 
also has the advantage of being harder than lead, which 
he claims is too soft for counterdies. Tin-lead alloys 
are used largely in soldering. 
The following are compositions and melting points 
of frequently used compounds:! 
Grade 
Tin 
Cead 
Melts at— 
Fine Solder.. .. 
... 2 
... 1 
.. .171.° 
C. 
Common “ .. .. 
... 1 
.... 1 
...188.° 
c. 
Coarse “ .... 
... 1 
.... 2 
.. .227.7° 
c. 
Pewter may be said to be substantially an alloy of 
the same two metals; but small quantities of copper, 
antimony, and zinc are frequently added. Common 
pewter contains about 5 parts of tin for 1 of lead. In 
France a tin-lead alloy, containing not over 18 per 
cent of lead, is recognized by law as being fit for 
measures for wine or vinegar. “Best pewter” is sim- 
ply tin alloyed with a mere trifle (i/2 per cent or 
less) of copper. 
Antimony.—Lead contaminated with small propor- 
tions of antimony is more highly proof against vitriol 
*The author has found the fusing point of this alloy to be 192.2° C. 
fTomlinson. LEAD 
145 
than the pure metal. An alloy of 83 parts of lead and 
17 parts of antimony is used as type metal; other pro- 
portions are used, however, and other metals added 
besides antimony (e. g., tin, bismuth) to give the alloy 
certain properties. 
Arsenic renders lead harder. An alloy made by the 
addition of about of arsenic is used for making 
shot. 
Lead forms a very important part in “fusible al- 
loys.”* 
TESTS FOR LEAD IN SOLUTION.—In testing va- 
rious solutions, first pour about three c.c. of the solu- 
tion to be tested in a test tube, and add a few drops of 
the selected reagent. Sometimes the precipitate is 
soluble in an excess of this reagent, and sometimes in 
excess of either solution or reagent. If there be reason 
to suspect either, proceed cautiously, adding but a 
drop at a time, until a sufficient precipitate has been 
thrown down. If the first few drops of the reagent 
added cause a precipitate which is immediately redis- 
solved, it shows that it is soluble in an excess of the 
solution, and if it be also soluble in an excess of the 
reagent, an equilibrium must be attained. After the 
precipitate has thoroughly settled, note its color and 
general appearance; then decant the supernatant liquid 
as thoroughly and carefully as possible, and divide the 
precipitate in as many other test tubes as may be 
desired for testing its solubility in the various reagents. 
Hydrogen sulphide is one of the most important 
reagents used in tests for salts of metals in solution. 
To the suspected solution add, drop by drop, the satu- 
rated solution of hydrogen sulphide (H2S); a black 
*See chapter on Bismuth. 146 
PRACTICAL DENTAL METALLURGY 
precipitate is quickly formed, which is insoluble in an 
excess of the reagent. To the suspected solution add a 
few drops of ammonium sulphide, (NH4)2S; a black 
precipitate, insoluble in an excess of the reagent, is 
formed. This is a characteristic test for lead in solution. 
Potassium hydroxide or ammonia throws down a 
white precipitate—hydrated oxide. This is soluble in 
an excess of the potassa, but not of the ammonia. 
Alkaline carbonates precipitate the white plumbic 
carbonate, which is quickly blackened by hydrogen 
sulphide. 
Sulphuric acid is a characteristic test, precipitating 
a white sulphate. 
Hydrochloric acid or a chloride gives a white precipi- 
tate soluble in an excess of potassa. 
BLOWPIPE ANALYSIS.—A lead-salt is easily re- 
duced on a piece of charcoal before the blowpipe, a 
bead of lead ultimately resulting in the center of the 
point of fusion, around which the charcoal will be seen 
to have absorbed a portion of the yellow monoxide of 
lead. The bead may be readily recognized as metallic 
lead, which is soft and may be readily flattened or cut 
with a knife. “If the lead contains silver, the latter 
is easily detected by the use of bone-ash. Fill a bowl- 
shaped cavity in the charcoal with finely powdered 
bone-ash, pressed down well, so as to fill the cavity 
with a compact mass, smooth, and slightly hollowed on 
the surface. In this, place a small quantity of the lead, 
hold the charcoal horizontally, and direct the extreme 
point of the outer (oxidizing) flame upon the metal. 
The bone-ash will absorb the lead oxide formed, leaving 
a metallic globule of silver. The latter may be cov- 
ered with a thin film of oxide, showing rainbow tints. 
When the color ceases, and the globule no longer dimin- LEAD 
147 
ishes in size, it is pure silver. The process is hin- 
dered by the presence of tin. 
On charcoal in either flame lead is reduced to a malle- 
able metal, and yields near the assay a dark lemon- 
yellow coat, sulphur-yellow when cold, and bluish- 
white at border. 
With bismuth flux: On plaster, a chrome-yellow coat, 
blackened by ammonium sulphate. 
Interfering1 Elements.—Antimony.—Treat on coal 
with boracic acid, and treat the resulting slag on plas- 
ter with borax flux. 
Arsenic Sulphide.—Remove by gentle oxidizing flame. 
Cadmium.—Remove by reducing flame. 
Bismuth.—Usually the bismuth flux test on plaster is 
sufficient. In addition the lead coat should color the 
reducing flame blue. 
ELECTRODEPOSITION OF LEAD.—In a solution 
of nitrate or acetate of lead, zinc receives a coating, 
or its place may be taken entirely by the lead. 
EXPERIMENT: Dissolve one gram of the nitrate or ace- 
tate of lead in about 500 c.c. of distilled water and put the 
solution in a bottle. Suspend a piece of granulated zinc or a 
spiral of zinc wire in the center of the solution and let it stand. 
The lead will be deposited slowly in a crystalline form, known as 
arbor plumbi. At the same time the zinc will pass into solution, 
the lead simply replacing the zinc. After the tree has been 
formed, filter off some of the solution and see whether or not zinc 
is contained in it. There will probably be some lead left. In 
order to detect the zinc, the lead will have to be removed. This 
may be done by adding sulphuric acid (forming the sulphate) 
and alcohol (to prevent its being redissolved). Filter off the 
lead sulphate, and to the filtrate add just enough ammonia to 
neutralize the sulphuric acid, and then test with ammonium hy- 
drosulphide; white zinc sulphide is precipitated. 
*Dr. Clifford Mitchell. CHAPTER VII 
ANTIMONY 
Stibium. 
Valence, III, V. 
Atomic weight, 120.2 
Melting point, 630° C. 
Ductility, brittle. 
Specific heat, 0.0495. 
Conductivity (heat), 3.6. 
Color, bluish-white. 
Symbol, Sb. 
Specific gravity, 6.69 
Malleability, brittle. 
Tenacity, brittle. 
Chief ore, stibnite. 
Crystal, rhombohedral. 
Conductivity(electricity), 4.42 
OCCURRENCE.—Antimony is found in the metallic 
state to a small extent in many of the localities from 
which its ores are derived. It occurs alloyed with other 
metals, such as silver, nickel, copper, and iron, and 
usually contaminated with arsenic. Commercial anti- 
mony is obtained almost entirely from its chief ore, 
stibnite, the sulphide, Sb2S3, which is found in great 
abundance in Borneo, New Brunswick, and Nevada. 
This ore usually occurs in veins, and has a leaden-gray 
color, with a metallic, sometimes iridescent, luster. 
REDUCTION.—The metal is easily reduced by heat- 
ing the ore in a furnace with about half its weight in 
scraps of metallic iron, whereupon it gives up its sul- 
phur, which unites with the iron, forming ferrous sul- 
phide, and liberates antimony. 
Sb2S3 + 3Fe = 2Sb + 3FeS. 
The process is usually carried on in perforated tubes 
or kettles to allow the antimony to separate from the 
gangue. 
148 ANTIMONY 
149 
The metal is so frequently contaminated with arsenic 
that it cannot be safely used for dental purposes until 
it has gone through a refining process. 
PROPERTIES.—Pure antimony is a brilliant, some- 
what iridescent, bluish-white metal, readily crystal- 
lizing in rhombohedrons, which form large stellate 
figures on the fused surface when cooled. It fuses at 
630° C., and may be distilled at a white heat in an 
atmosphere of hydrogen. When heated to redness it 
takes fire, burning with a brilliant white flame. It un- 
dergoes no change in air at ordinary temperatures, but 
is easily oxidized when heated to fusion. It is an im- 
portant metal in the manufacture of alloys, increasing 
their hardness even when mixed in very small quanti- 
ties, and Roberts-Austen states that it is one of the two 
metals which expand on solidification, the other being 
bismuth. The finely powdered metal takes fire spon- 
taneously when thrown into chlorine gas, forming 
chlorides. 
COMPOUNDS WITH OXYGEN.—Antimony forms 
two distinct oxides: 
The Trioxide, or Antimonous Oxide, Sb203, occurs 
native, though rarely. It may he prepared by burning 
metallic antimony at the bottom of a large red-hot cruci- 
ble. It is a pale huff-colored powder, fusible, volatile, of 
basic reaction, and having double molecules (Sb203)2 
like arsenic, it readily absorbs more oxygen changing 
to Sb204. When boiled with potassium bitartrate, it is 
dissolved, and the solution yields on evaporation crystals 
of tartar emetic, KSb0C4H406. 
The Pentoxide, or Antimonic Oxide, Sb205, is obtained 
by the action of strong nitric acid on antimony. It is 
a pale straw-colored powder, of acid reaction, insoluble 150 
PRACTICAL DENTAL METALLURGY 
in water or acids, decomposes on being heated, passing 
to the intermediate oxide, Sb203,Sb205. 
The Intermediate Oxide, or Tetroxide, Sb204, as it is 
sometimes called, Sb203, Sb205, is obtained by heating 
the pentoxide in the air, and is recognized as an infus- 
ible, nonvolatile and insoluble, grayish-white powder. 
ACTIONS OF ACIDS ON ANTIMONY.—Hydro- 
chloric acid, boiling and concentrated, slowly dissolves 
powdered antimony, forming antimonous chloride and 
liberating hydrogen— 
Sb + 3HC1 = SbCl3 + 3H, 
but when the metal is in the compact state, it resists 
this acid. 
Sulphuric acid, boiling and concentrated, slowly con- 
verts it into antimonous sulphate with an evolution of 
sulphur dioxide— 
2Sb + 6H2S04 = Sb2(S04)3 + 6H20 + 3S02. 
Nitric acid rapidly oxidizes the metal, the dilute acid 
forming chiefly antimonous oxide— 
2Sb + 2HN03 = Sb203 + H20 + 2NO, 
while the concentrated form yields some antimonic 
oxide 
6Sb + 10HNO3 = 3Sb205 + 5H20 + 10NO. 
For the most part the intermediate is the result of this 
action— 
6Sb + 8HN03 — 3Sb20 + 4H20 + 8NO. 
Nitro-hydrochloric acid converts it into soluble anti- 
monous chloride and insoluble oxides, and is the only 
satisfactory solvent. ANTIMONY 
151 
Tartaric acid in a boiling solution slowly dissolves 
precipitated antimony— 
2Sb+ H2(C4H406) +2H20 = (SbO)2C4H406 + 6H. 
Alkalies do not dissolve it. 
ALLOYS.—The metal is chiefly valuable for the al- 
loys it yields with other metals, and, as has been said, 
possesses the quality of increasing the hardness of 
those alloys. Antimony also causes expansion in most 
alloys, if in excess of 22 parts per 100, thereby copying 
fine lines and sharp casts; hence, its great value in the 
manufacture of type. In many cases it renders the 
alloy very brittle, and is especially injurious to the 
noble metals or copper, destroying their malleability, 
ductility, etc. 
Mercury.—The amalgam of antimony is soft and 
easily decomposed. Experiments have been made, with 
a view to using this element in dental-amalgam alloys, 
but to no profit. 
Gold.—One grain of antimony to 2000 will greatly 
injure the malleability of gold. 
Copper containing 1/1000 of this metal can no longer 
be worked for sheet-brass. 
Tin.—Antimony is added to tin alloys to give hard- 
ness and expansion, but renders most of them very 
brittle. 
Bismuth forms with antimony a grayish, brittle and 
lamellar alloy. In order to remove the brittleness 
varying quantities of tin are added, as is also lead, or 
both. The fusibility then rather increases, instead of 
decreasing. 
Some alloys containing antimony: 
Cliche metal, tin 48, lead 32.5, bismuth 9, and anti- 
mony 10.5. 152 
PRACTICAL DENTAL METALLURGY 
Babbitt metal, copper 4, tin 12, and antimony 8, 
melted separately. The antimony is added to the tin, 
then the copper, and 12 parts more tin after fusion. 
TYPE METAL—TABLE OF COMPOSITION* 
Metal 
Parts 
I 
II 
III 
IV 
V 
Lead 
3 
10 
70 
6 
100 
Antimony 
1 
2 
18 
30 
Copper 
2 
4 
8 
Bismuth 
1 
2 
Zinc 
90 
Tin 
10 
20 
Nickel 
8 
Britannia Metal (Wagner’s).-—Tin 85.64, antimony 
9.66, copper 0.81, zinc 3.06, and bismuth 0.83. 
Queen’s Metal.—Tin 88.5, antimony 7.1, copper 3.5, 
and zinc 0.9. 
TESTS FOR ANTIMONY IN SOLUTION—Hydro- 
gen Sulphide added to an acidulated solution of anti- 
mony occasions an immediate precipitate of very char- 
acteristic orange-red color. 
Potassium hydroxide or ammonium hydroxide or 
the carbonates of sodium or ammonium, throw down 
a bulky white hydrate, of which that formed by potas- 
sium hydroxide is soluble in excess of alkali, but the 
hydrate formed by the ammonium hydroxide or al- 
kaline carbonates is nearly insoluble. 
If a hydrochloric acid solution be treated with a 
quantity of water, an immediate precipitate of oxy- 
chloride falls, soluble in tartaric acid, distinguishing it 
from bismuth. 
SbCl, + H20 = SbOCl + 2I1C1. 
*Table from Brannt. CHAPTER VIII 
TIN 
Stannum. 
Valence, II, IV. 
Atomic weight, 118.7. 
Melting point, 232° C. 
Ductility, 9th rank. 
Conductivity (heat), 15.28. 
Symbol, Sn. 
Specific gravity, 7.29. 
Malleability, 5th rank. 
Tenacity, 7th rank. 
Chief ore, tinstone. 
Conductivity (electricity), 14.4. 
Specific heat, 0.0559. 
Color, brilliant white. 
(Silver being 100.) 
Crystals, isometric and quadratic. 
OCCURRENCE.—Tin occurs chiefly as tinstone, cas- 
siterite, or native oxide, Sn02, which forms in very 
hard quadratic crystals, usually dissolved by the 
presence of ferric or manganic oxide. The pure ore is 
colorless and very scarce. Another native form known 
as “wood tin” occurs in roundish masses, with a fibrous, 
radiating fracture. The metal is rarely, if ever, found 
free. The ore is mined from veins or layers within the 
older crystalline rocks and slates, associated with cop- 
per ore, iron arsenide and other minerals, and as allu- 
vial deposits, mixed with rounded pebbles, in the beds 
of streams. The former is called mine-tin, and the lat- 
ter stream-tin. The only lode and placer tin mines in 
North America are in Alaska. 
REDUCTION.—The ore is first washed to separate it 
from earthy impurities, and then stamped, and again 
washed to separate the lighter gangue. It is then 
roasted at a low heat to volatilize the arsenic and sul- 
phur, without at the same time fusing the ore. The 
153 154 
PRACTICAL DENTAL METALLURGY 
copper ore, copper pyrites, is, during this time, joined 
with subsequent exposure to air and moisture, changed 
to copper sulphate, and is then dissolved out by water, 
the copper afterwards being reduced by iron and 
thereby saved. The ore is finally washed to separate 
all lighter oxides, and is then ready for smelting. The 
purified ore, known as black “tin,” is mixed with about 
15 to 20 per cent of anthracite “smalls,” the mixture 
moistened to prevent its being blown off by the draft, 
then fused in a reverberatory furnace for five or six 
hours, and, after thorough stirring, the metal is run 
off— 
Sn + 2KOH + H20 = K2Sn03 + 4H. 
The tin obtained from Malacca is almost chemically 
pure, while that from England almost invariably con- 
tains traces of arsenic and copper. Most of the tin 
consumed in this country is shipped from Singapore, 
having been mined in the Malacca regions. Two varie- 
ties of the commercial metal are known, called grain and 
bar tin. The first is the better; it is prepared from the 
stream ore. 
Pure Tin.—Tin used in dental operations should be 
chemically pure. Much of that which we have just de- 
scribed is still greatly contaminated with arsenic, cop- 
per, iron, etc., and to obtain it pure a further refining 
process must be gone through with. For this purpose 
good commercial tin may be dissolved in hydrochloric 
acid. Hydrogen is evolved, and the metals are all con- 
verted into chlorides, with the exception of antimony 
and arsenic. If either of these be present, it will com- 
bine with hydrogen, forming a gas and be evolved. 
The liquid is now evaporated to a small bulk, and to it TIN 
155 
is added nitric acid, which, will convert the tin into 
the insoluble, white, crystalline, metastannic acid, 
H10Sn6O15. The whole is now evaporated to dryness, 
washed with water acidulated with hydrochloric acid, 
filtered, rewashed, dried, and melted in a crucible with 
charcoal, when a button of pure tin will result. 
PROPERTIES.—Pure tin is white (except for a slight 
tinge of blue); it exhibits considerable luster and is 
not subject to tarnishing on exposure to normal air. 
It is soft and exceedingly malleable; indeed, it is said 
it may be beaten into foil %0 of a mm. in thickness; 
at 100° C. it may be drawn into wire, but it is almost 
devoid of tenacity. That it is elastic, within narrow 
limits, is proved by its clear ring when struck with a 
hard body under circumstances permitting free vibra- 
tion. Though it is seemingly amorphous, it has a crys- 
talline structure, hence the crackling noise known as 
the “tin cry” which a bar of tin emits on being bent. 
The crystalline structure must also account for the 
strange fact that an ingot, when exposed to the tem- 
perature of—39° C. for a sufficient length of time, be- 
comes so brittle that it falls into powder under pestle 
or hammer. At some temperature near its fusing point 
it again becomes brittle. Tin fuses at 232° C. At a 
red heat it begins to volatilize slowly; at 1450° to 1600° 
C. it boils and may be distilled. The hot vapor pro- 
duced combines with the oxygen of the air, forming the 
white oxide, Sn02. The specific gravity is 7.29. Its 
specific heat is 0.0559. 
DENTAL APPLICATIONS.—Tinfoil has been used 
as a filling material for carious teeth because of its 
comparatively low conducting power of heat. The 156 
practical dental metallurgy 
combination of tin and gold foil is said to have a very 
low conducting power of heat. 
Casts of tin are used to vulcanize upon, and plaster 
casts are often covered with tin-foil to give a clear and 
finished appearance to the denture after the process of 
vulcanization. 
COMPOUNDS WITH OXYGEN.—There are twc 
oxides of tin: 
Tin Monoxide, or Stannous Oxide, SnO, is a blackish- 
brown powder of feeble basic reaction prepared by 
heating stannous hydrate, Sn(OH)2, in an atmosphere 
of carbon dioxide. It is unstable, and burns when 
heated in the air, becoming stannic oxide. 
Tin Dioxide, or Stannic Oxide, Sn02, occurs native 
as tinstone, or cassiterite, the common ore of tin, and is 
easily formed by heating tin, stannous oxide, or stan- 
nous hydrate, in contact with air. According to the 
manner in which it may be prepared, it is either a 
white or yellowish-white amorphous powder, or it may 
be obtained crystalline. It is infusible and insoluble in 
the acids or alkalies, and is known as “polishing 
putty,” being used for polishing glass, hard metals, 
granite, and similar substances. It forms two isomeric 
hydroxides (stannic and metastannic), which differ 
somewhat in their properties; both, however, are acids, 
and capable of exchanging their hydrogen for metal, 
thereby forming salts. 
Stannic Acid, H2Sn03, is precipitated by an alkali 
from stannic chloride as a white powder, soluble in the 
stronger acids and alkalies, and is capable of exchang- 
ing the whole of its hydrogen for metal forming stan- 
nates, as: Na2Sn03. These salts are quite stable. TIN 
157 
Metastannic Acid, H10Sn5O15, may be written 
(H2Sn03)5, is prepared as a white crystalline powder 
by the action of dilute nitric acid upon tin. It is insol- 
uble in water and the acids, but dissolves slowly in the 
stronger alkalies, and has the property of exchanging 
only one-fifth of its hydrogen for metal-forming 
metastannates, very unstable, as K2H8Sn5015. 
ACTION OF ACIDS ON TIN.—The three mineral 
acids act upon tin. 
Sulphuric acid, concentrated, acts rather energet- 
ically at first, but, owing to the stannic sulphate coating 
which is soon formed, its action is greatly hindered. 
The dilute form acts slowly, but converts the whole of 
the tin into stannous sulphate with a liberation of hy- 
drogen. 
Sn + II2S04 = SnS04 + 2H. 
Nitric Acid.—In its dilute form this acid acts but 
feebly upon tin, and, if heated, produces the nitrate; 
but the concentrated is energetic, and, instead of dis- 
solving, oxidizes it into the crystalline powder, hydrox- 
ide, known as metastannic acid—H10Sn5O15. 
3Sn + 4HN03 == 3Sn02 + 2H20 + 4NO, and then 
5Sn02 + 5H20 = Hj0Sn5O15. 
Hydrochloric Acid.—Strong, warm hydrochloric acid 
acts energetically upon tin, the cold and dilute forms 
acting more slowly, but converting it into stannous 
chloride and liberating hydrogen. 
Sn + 2HC1 = SnCl2 + 211. 
Nitro-hydrochloric acid dissolves tin very ener- 
getically, producing stannic chloride, SnCl4. 158 
PRACTICAL DENTAL METALLURGY 
Sn + 4C1 = SnCl4. 
Caustic Alkalies.—Boiling solutions of caustic soda 
or potassa act upon tin, producing stannates with an 
evolution of hydrogen. 
Sn + 2KOH + H20 = K2Sn03 + 4H. 
ALLOYS.—Mercury and tin readily unite as an amal- 
gam, under ordinary circumstances, and, it is said, 
form a definite chemical compound having the formula, 
Sn2Hg. 
Tin is a very important component of dental-amalgam 
alloys.* Of it Dr. J. Foster Flagg says, in his work on 
Plastics and Plastic Filling: “All such alloys as 1 
should favorably regard, have from 35 to 48 per cent 
of tin; it is found that by the addition of copper and 
gold, both antagonists of “shrinkage,” the most dele- 
terious of the effects of tin can be counterbalanced; 
that under this control sufficient silver can be used to 
obviate a detrimental loss of edge-strength; that the 
retardation of “setting” is prevented, and that the tin 
not only loses its power for harm, but becomes an in- 
gredient of manifold utility; it greatly augments the 
facility of amalgamation; it aids in producing a good 
color and in preventing discoloration; and it diminishes 
conductivity.” 
The amalgam of tin is also largely used in the man- 
ufacture of mirrors. 
Gold and tin form a malleable alloy, provided the 
tin be pure and does not exceed in quantity 10 per 
cent. 
*See chapter on Amalgams. TEST 
159 
Platinum and tin in equal proportions form a hard, 
but brittle, alloy, fusing at a comparatively low tem- 
perature. 
Palladium, says Mr. Makins, forms a very brittle 
alloy with tin. 
In view of the fact that gold, platinum, and palla- 
dium so readily unite with tin to form alloys whose fus- 
ing points are so comparatively low, and in view of the 
behavior of tin with other metals, and of metals in 
general toward each other, there is little reason to 
doubt a chemical affinity of tin for these metals. The 
affinity of tin for gold in particular has been clearly 
demonstrated by Dr. Matthiessen. Into a crucible of 
molten tin a rod of gold and one of copper were 
dipped, the latter having been previously tinned to 
ensure perfect contact. The gold united readily and 
rapidly with the tin, while the copper rod remained 
unaffected. A gold wire which has been superficially 
tinned will melt like one of tin when held in the flame 
of a Bunsen burner. A wire of tinned copper exposed 
to the same heat, under like circumstances, remains un- 
affected, except that the tin is burned off. The affinity 
of tin for platinum is so great, states Clarke, that if tin 
and platinum foils be rolled together and heated before 
the blowpipe, combination takes place explosively. 
The affinity of tin for gold is unquestionably an interest- 
ing subject for the dentist, in view of the place these 
two metals occupy in operative dentistry. 
Silver alloys with tin, and, in the proportion of 80 
of the former to 20 of the latter, it is said produces a 
very tough alloy. 160 
PRACTICAL DENTAL METALLURGY 
Dr. G. F. Rees’s alloy for artificial dentures, con- 
structed by the cheoplastic process, is composed of tin 
20, gold 1, and silver 2 parts.* Other alloys much used 
in cheoplastic work are composed largely of tin. 
Bean’s alloy, intended for casting lower dentures, is 
composed of tin 95, and silver 5 parts. 
Antimony 1 and tin 16 parts forms another alloy, 
which is intended for the same purpose, and was intro- 
duced by Dr. William B. Kingsbury. 
Britannia metal is made under a great variety of for- 
mula;; one known as English is composed of antimony 
7.8, tin 90.7, and copper 1.5. It sometimes contains 
lead or bismuth. 
Type metal, generally speaking, consists of lead, anti- 
mony and tin—lead 55, antimony 30, and tin 15 parts. 
Dr. L. P. Haskell’s Babbitt metal for dies is com- 
posed of the following: “Copper 1 part, antimony 2 
parts, tin 8 parts. These should be melted in the order 
named, as tin would oxidize badly before the first was 
melted, if all were placed in the crucible together. 
Melt, and turn off into ingots, and remelt. If it should 
not be found to run freely from the ladle, when mak- 
ing a die, add a small amount of tin, as it is presumable 
that some of that metal has oxidized.”! 
Babbitt metal is made under a great variety of for- 
mula ; but one made in the following proportions 
(tin 12 parts, antimony 3 and copper 2 parts) is given 
by Dr. Essig, wdiich, he states, is sometimes used in the 
dental laboratory for dies, and is thought by many to 
be superior to zinc for that purpose.| 
*“Amalgams and Alloys Chemically Considered,” by J. Morgan Howe, 
M.D., Transactions New York Odontological Society, 1880. 
fDr. L. P. Haskell. 
JDental Metallurgy. TIN 
161 
Copper and tin form a large number of alloys of 
great importance. 
Bronze.—Copper and tin unite in almost any propor- 
tion to form bronze. 
Copper 
Tin 
Phosphorus 
Zinc 
U. S. Ordnance Bronze.. 
Phosphor Bronze 
Statuary Bronze 
90. 
90.34 
84.42 
10. 
8.90 
4.30 
0.76 
11.28 
Actual speculum-metal is supposed to have the for- 
mula, Cu4Sn, and the centesimal composition of cop- 
per 66.6 parts and tin 33.4 parts. 
Bell metal is copper 74 to 85 parts, and tin 26 to 15 
parts. 
With iron, in the process of tin-plate manufacture, 
tin is said to alloy. 
Lead and tin alloy freely in all proportions, tin gen- 
erally imparting greater resistance to the lead. The 
strongest alloy of lead and tin is Pb-1; Sn-3. Such 
alloys constitute certain forms of pewter, an important 
class called “soft solders,” and counterdies.* 
TESTS FOR TIN IN SOLUTION.—To the suspected 
solution add a few drops of potassium hydroxide or 
sodium hydroxide. A white precipitate is thrown 
down, soluble in excess of the reagent. 
Ammonia also gives a white precipitate insoluble in 
excess of the reagent. 
Ammonium or hydrogen-sulphide throws down a 
brown, in the case of stannous, and yellowish-brown 
precipitate with stannic chloride, both of which are 
soluble in excess of the reagent. 
*See Lead Alloys. 162 
PRACTICAL DENTAL METALLURGY 
Gold trichloride added to a dilute solution of the tin 
chlorides gives the characteristic purple precipitate, 
known as the purple of Cassius.* 
Final Test: Add hydrogen sulphide, H2S, to an 
acidified solution of a salt of tin and filter. Wash the 
precipitate with water and add ammonium sulphide, 
(NH4)2S, and filter. Acidify the filtrate with hydro- 
chloric acid, HC1. A yellow or brown precipitate sol- 
uble in concentrated hydrochloric acid, HC1, shows tin 
as a sulphide; SnS; SnS2. 
ELECTRODEPOSITION OF TIN.—Tin is easily de- 
posited upon small articles of brass or copper by simple 
immersion, as by the following experiment: 
EXPERIMENT: Place the articles in layers between sheets 
of tin foil in a saturated solution of potassium bitartrate 
and boil. A little stannous chloride may also be added, if nec- 
essary. 
The metal may be crystallized out of its solution and 
rendered pure by the following: 
EXPERIMENT: Immerse a bar of tin in a strong solution 
of stannous chloride and pour on carefully, so as not to dis- 
turb the tin solution, some distilled water. Pure tin will be 
deposited on the bar of tin at the point of junction of the water 
and tin solution. 
*See chapter on Gold. CHAPTER IX 
BISMUTH 
Bismuthum. 
Valence, III, V. 
Atomic weight, 209. 
Melting point, 269. 
Ductility, brittle. 
Conductivity (heat), 1.77. 
Symbol, Bi. 
Specific gravity, 9.7474. 
Malleability, brittle. 
Tenacity, brittle. 
Chief ore, native metal. 
Conductivity (electricity), 1.4. 
Specific heat, 0.03013. 
Color, white with reddish tint. 
(Silver being 100.) 
Crystals, rhombohedral. 
OCCURRENCE.—Practically the only ore of this 
element is the Native Metal found disseminated in veins 
through slate rock associated with the ores of copper, 
iron, cobalt, nickel, silver, gold, and arsenic. It is a 
comparatively rare metal, inasmuch as the supply has 
not kept pace with the demand, and its commercial 
value has risen considerably. It is found chiefly in 
Saxony, Transylvania, United States, England, Peru, 
Norway and Sweden. 
REDUCTION.—This is simple and may be accom- 
plished by a process of sweating. The crushed ore is 
introduced into large iron tubular retorts, built in the 
furnace. These tubes are placed in an inclined position 
over a wood fire. At the upper end the ore is intro- 
duced, and as the metal is sweated out it accumulates 
at the lower end, where it is drawn off into iron ves- 
sels. The siliceous residue is then raked out of the tube 
at its upper end and the retort recharged. 
Commercial bismuth frequently contains arsenic and 
163 164 
PRACTICAL DENTAL METALLURGY 
iron, besides gold and silver, hence is not fit for dental 
usage until it is purified. When silver exists in bis- 
muth in sufficient quantity to repay for extracting, it 
is cupellated just as lead is, while the bismuth is 
oxidized, leaving the silver as a molten button on the 
cupel. From the oxide the bismuth is afterwards re- 
covered by strongly heating under powdered charcoal. 
At the same time the arsenic is got rid of, in that it 
volatilizes. 
PROPERTIES.—Bismuth is a highly crystalline, 
hard, and very brittle metal, having a grayish-white 
color, with a decided reddish tint. Its specific gravity 
is 9.747 and fuses at 269° C. It expands about %2 
of its volume when solidification takes place and im- 
parts this property to its alloys. It crystallizes in large, 
beautiful iridescent rhombohedra, which nearly ap- 
proach a cube. These crystals may be obtained by 
melting a quantity of the metal and allowing the bulk 
to cool slowly, the surface being prevented from more 
rapid solidification by covering the pot with a sand 
bath filled with glowing coals. As soon as a crust has 
formed on the sides and top, it is pierced with a hot 
iron, and the still molten metal poured out. When 
quite cold the upper surface is sawed off, exposing the 
beautiful crystals in the interior. The metal volatilizes 
at a high temperature, and has a specific heat of 
0.0301. It is the most diamagnetic of all substances. 
Exposed to the air at ordinary temperatures, it is un- 
affected, but when heated to a red heat it rapidly oxi- 
dizes, producing a beautiful play of colors. 
COMPOUNDS WITH OXYGEN.—Bismuth combines 
with oxygen to form two stable oxides; Bi203 and 
Bi205. The oxides Bi202 and Bi204 also may be formed. PlSMUTH 
165 
Bismuthous Oxide, the Trioxide, Bi203 is found na- 
tive as bismuth ochre, and may be prepared by roasting 
the metal in air or by gently igniting its nitrate. It is 
a straw-yellow powder, insoluble in water and fusible 
at a high temperature. 
Bismuthic Oxide, the Pentoxide, Bi205, may be ob- 
tained by dissolving the trioxide in caustic potash and 
passing chlorine through the liquid; the water decom- 
poses, forming hydrochloric acid, and the trioxide is 
converted into the pentoxide. It is then washed with 
dilute nitric acid to separate any remaining trioxide. 
The pentoxide is a reddish-brown powder, which is 
insoluble in water. The bismuthyl radical - Bi = 0 
acts like a monad, giving bismuthyl salts or the 0 may 
be replaced, giving normal salts. 
ACTION OF ACIDS ON BISMUTH.—Sulphuric acid 
when cold has but slight action on bismuth, but dis- 
solves it more readily when heated, forming the sul- 
phate, and giving off sulphur dioxide. 
Hydrochloric acid, hot or cold, but feebly attacks 
bismuth. 
Nitric acid dissolves bismuth very energetically, form- 
ing the nitrate or ternitrate, as it is generally termed, 
Bi(N03)3, which is a white crystalline, soluble mass. 
If the ternitrate be added to a large quantity of wa- 
ter, a white precipitate is thrown down known as the 
subnitrate of bismuth, BiON03, which is much used in 
medicine and as pearl white or l)lanc de fard in cos- 
metics. It is a heavy white powder, insoluble in water 
or alcohol. It is darkened by sulphuretted hydrogen. 
ALLOYS.—Bismuth unites readily with other metals, 
the alloys being remarkable for their ready fusibility, 166 
PRACTICAL DENTAL METALLURGY 
and for their property of expanding on solidification. 
These two properties render it most valuable as an in- 
gredient to alloys used for making casts or dies where 
it is essential to copy fine lines, and in alloys when a 
very low fusing point is desirable. A great many com- 
binations of lead, tin, bismuth and cadmium produce 
alloys possessing the latter property, some fifty-eight* 
being known that fuse at or below 100° C., and an 
alloy of lead 25.00, tin 12.50, bismuth 50.00 and cad- 
mium 12.50 will fuse at 55.5° C. Generally 50% of 
the low fusing alloy is bismuth. (See table p. 196.) 
With tin bismuth alloys in any proportion. A very 
small quantity of the metal imparts to tin more hard- 
ness, sonorousness, luster, and a fusibility lower than 
either of the metals taken separately possesses. An 
alloy of equal parts of the two metals fuses at 212° C. 
With lead bismuth alloys very easily, producing an 
alloy which is malleable if the proportion of bismuth 
does not exceed that of lead. The specific gravity is 
greater than the mean of the two taken separately. 
These alloys are white, lustrous, harder than lead, and 
more malleablef up to a certain proportion. Bismuth 
1 and lead 2 gives a very ductile and malleable alloy 
fusing at 165.5° C. 3Pb + 2Bi forms an alloy having 
ten times the hardness and twenty times the tenacity 
of lead. 
With copper it forms a pale-red, brittle alloy. 
With zinc it easily unites, producing an alloy, some- 
times employed in the dental laboratory for the forma- 
tion of dies, such an alloy having a lower fusing point 
•William T. Brannt. 
tjour. Soc. Chem. Ind., xxv, p. 1221. BISMUTH 
167 
than pure zinc, and being free from contraction on 
cooling. 
m 
Sb 
Sn 
Pb 
9. 
10.5 
48. 
32.5 
‘ ‘ Type-metal... 
8. 
1. 
4. 
5. 
i ( ( ( 
1. 
3. 
8. 
Alloys of bismuth, tin, and lead are known as the 
triple alloys, and are very numerous and useful. 
Newton’s alloy, improperly called “Melotte’s Metal,” 
consists of bismuth 8, lead 5, and tin 3 parts, and 
fuses at 94.4° C. 
Rose’s fusible alloy is composed of 
i. ii. 
Bismuth 2 8 parts 
Tin 1 3 “ 
Lead 1 8 “ 
The first fuses at 93° C. and the second at 94° C. 
They were used as safety-plates and inserted in the top 
of steam boilers, intended to prevent the explosion of 
boilers by allowing the steam to escape at a certain 
tension. 
Wood’s metal consists of lead 4, tin 2, bismuth 5 to 
8, and cadmium 1 to 2, melts at 60° C. to 66.4° C., in 
color resembles platinum, and, is, to a certain extent, 
malleable. 
Onion’s fusible alloy contains lead 3, tin 2, and bis- 
muth 5 parts, and melts at 91.6° C. 
“La Nation” describes a fusible alloy, of which the 
following is the formula: Bismuth 48, cadmium 13, 168 
PRACTICAL DENTAL METALLURGY 
lead 19, and tin 26. It melts at 70° C. and resists 
great pressure. 
Hodgen’s fusible alloy, for making dies and coun- 
terdies by the dipping process, is composed of the fol- 
lowing: Bismuth 8, lead 5, tin 3, and antimony 2. It 
is a light, lustrous alloy, very hard, slightly malleable, 
expands slightly on cooling, copying the finest of 
lines, takes a high polish and resists great pressure, 
melting at 106.6° C. 
Dr. Mathews’ Fusible Alloy.—This alloy is com- 
posed of bismuth 48, cadmium 13, and tin 19 parts. It 
melts below the boiling point of water and may be 
packed with the fingers. It may be poured into plaster 
impressions immediately after they have been taken, 
producing sharp, bright, hard dies, with which shot 
may be used for the counterdie. 
Darcet’s fusible alloys are a series of proportions 
of bismuth, tin, and lead, and their melting point 
varies as per the following table: 
Parts 
Melts 
Bismuth 
Tin 
Lead 
7 
4 
2 
100° c. 
16 
7 
4 
100° c. 
8 
2 
6 
96° C. 
Most of these fusible alloys are of much value in 
the dental laboratory in the hands of a practical, re- 
sourceful man. The cleaner ones may, when lack of 
time will not permit of a more perfect repair, be used 
to mend a denture or replace a tooth or block of teeth 
on a vulcanite plate, and the more fusible ones may be 
used for the same purpose, even though the base be cel- BISMUTH 
169 
luloid. In replacing teeth undercuts may be made with 
a file, or preferably with a large bur in the engine, the 
tooth placed in position and the alloy packed in with 
warm instruments, smoothed and afterward polished. 
These alloys are also valuable baths for tempering 
steel instruments. They give a very exact tempera- 
ture, which may be adjusted to the purpose intended. 
They are used, according to Thurston,* by placing 
the articles on the surface of the unmelted alloy and 
gradually heating until fusion occurs and they fall 
below the surface, at which moment their temperature 
is right; they are quickly removed and cooled in 
water.f “An alloy of 3 parts each bismuth, fine gold, 
and platinum with 15 of fine silver, and 10 of tin, is 
very similar to precipitated palladium, and has been 
used as a substitute for this costly metal. One curious 
point about this alloy is, asserts Mr. Fletcher, that if 
it contains the merest trace of palladium, it is almost 
worthless; and as ordinary fine silver is rarely, if ever, 
free from palladium, this alloy can only be made from 
silver reduced direct from the chloride.” 
In amalgams.—“The addition of bismuth to amal- 
gams makes them excessively sticky and adhesive ne- 
cessitating, at the same time, an increase in the propor- 
tion of mercury required. 
The same author, continuing, says: “Amalgams 
containing a trace of bismuth will build and adhere to 
a flat dry surface, and may be used as a metallic ce- 
ment for joints in apparatus which require to be per- 
fectly air tight and to stand heavy pressures. A 
good alloy for this purpose is 1 bismuth, 15 tin, 15 
*Brasses, Bronzes, and other Alloys. 
tMetallic Alloys, Brannt. 
{Dental Metallurgy, Thomas Fletcher, p. 65. 170 
PRACTICAL DENTAL METALLURGY 
silver, fused and filed up, and then mixed in the pro- 
portion of 1 alloy to 4 of mercury. This alloy is so 
excessively sticky as to be useless for fillings.”* 
Commenting on the above, Dr. Kirk says:f “The 
effect of bismuth in dental-amalgam alloys does not 
seem to have been fully studied.” And, further, “it 
would seem that the power of bismuth to overcome the 
contraction of alloys in solidifying would render it 
valuable as an ingredient in certain dental-amalgam 
alloys if it conferred no objectionable qualities other 
than adhesiveness upon them.” 
TESTS FOR BISMUTH IN SOLUTION.—Makins 
states: “The salts of this metal are for the most part 
devoid of color; some are soluble, others insoluble, the 
soluble salts redden litmus paper.” 
Hydrogen sulphide or ammonium sulphide when 
added to a solution produces a black precipitate—sul- 
phide of bismuth—insoluble in dilute acids or alkalies, 
but dissolves in strong hot nitric acid. 
The alkalies precipitate from bismuth solutions—in 
the absence of certain organic substances—the white 
bismuth hydrate, Bi(OH)3, insoluble in excess of the re- 
agents, converted by boiling to the yellowish-white 
oxide, Bi203. 
The carbonates—as K2C03—precipitate the white 
basic bismuth carbonate, Bi202C03, insoluble in excess 
of the reagents. 
Water precipitates from acidulated bismuth solutions 
white basic salts, which contain less of their acid rad- 
icals in proportion as greater quantities of water are 
added, as— 
Bi(N03)3 + 2H20 = BiON03 + H20 + 2HNOb. 
*Dental Metallurgy, Thomas Fletcher, p. 65. 
fAmerican System of Dentistry, iii, p. 931. CHAPTER X 
ZINC 
Zincum. 
Valence, II. 
Atomic weight, 65.37. 
Melting point, 419° C. 
Ductility, 8th rank. 
Specific heat, 0.09356. 
Conductivity (heat), 26.53. 
Color, bluish-white. 
Symbol, Zn. 
Specific gravity, 7.142 at 16°. 
Malleability, 8th rank. 
Tenacity, 6th rank. 
Chief ore, calamine. 
Crystals, rhombohedral. 
Conductivity (electricity), 29.6. 
OCCURRENCE.—Zinc is a somewhat abundant 
metal, but never occurs in the native state. It is found 
as a carbonate, sulphide, silicate, etc., associated with 
lead ores in many districts; large supplies are obtained 
from Silesia and from the neighborhood of Aachen. 
(1) The native carbonate, Calamine, Smithsonite, 
ZnC03, is the most important of its ores. As a rule 
this ore is a light-gray, yellow, or buff in color. (2) 
Zinc blende, the sulphide, ZnS, is second in importance 
only to the carbonate; it is extensively mined and 
much of the zinc of commerce is procured from this ore. 
Its color is green, yellow or red but mostly brown. 
There is also a (3) Red Zinc Ore, an impure oxide, 
ZnO; an (4) Electric Calamine, one of the silicates, 
Zn0.Si02 + H20 and (5) Willemite, an anhydrous sili- 
cate, ZnO.Si02. 
REDUCTION.—Calamine, ZnC03, is generally re- 
duced by first roasting, to expel the water and carbon 
(Silver being 100.) 
171 172 
PRACTICAL DENTAL METALLURGY 
dioxide. This leaves the oxide, ZnO, which is then 
mixed with fragments of coke or charcoal, and dis- 
tilled at a full red heat in a large earthen retort. The 
carbon unites with the oxygen to form carbon monox- 
ide and escapes, while the reduced metal volatilizes 
and is condensed by suitable means, generally con- 
taminated with minute quantities of arsenic. Metals 
having a lower boiling point such as cadmium, arsenic, 
lead and antimony, come over first and with some zinc 
form what is known as zinc dust largely used in paints. 
Zinc blende is roasted to drive off the sulphur, but 
Fig. 43.—A furnace for purifying zinc. Patented by Richard Ziesing. 
Consists of two chambers / and 2. It may be heated in any manner though 
this type is heated by resistance elements at 6 and // in the diagram. Zinc 
contaminated with impurities having a heavier sp. gr. is charged into cham- 
ber 2 through the hopper, and heated until the molten metal nearly reaches 
the level of the outlet to the condensing chambers at p. During this time 
the heavier metals sink to the bottom and are drawn off at 3. When the 
furnace is fully charged, the temperature is increased and the metal is 
distilled over at p and condensed in metallic form. 
when it contains any foreign sulphide, as of lead, it 
is more difficult and requires several hours roasting. 
Old zinc may be refined or cleansed for use again in 
the laboratory by heating with pulverized charcoal or 
some hydrocarbon, as wax, etc. 
PROPERTIES.—Zinc is a bluish-white metal, which 
but slowly tarnishes in moist air, usually forming a 
superficial carbonate which prevents further disinte- ZINC 
173 
gration; it has a lamellar, crystalline structure, a spe- 
cific gravity of 7.142, and is, under ordinary circum- 
stances, quite brittle, but when heated to 100° or 150G 
C. it may be rolled by passing through heated rolls or 
hammered into thin sheets, or drawn into wire; and, 
what is very remarkable after such treatment, it re- 
tains its malleability when cold; the sheet zinc of com- 
merce is thus made. The addition of any of the fol- 
lowing metals is harmful to sheet zinc during manu- 
facture: Cd. 0.25%; As, 0.02—0.03% impossible to 
work; Sb 0.07%; Sn 0.01%; Cu 0.08—0.19% unwork- 
able; Fe, 0.12% ; Pb, 1.00—1.25% does not interfere, but 
does not alloy, leaving patches. If the temperature be 
carried to 205° C. it again becomes so brittle that it 
may be easily poAvdered in a mortar. Care should be 
exercised in handling hot zinc dies, for if by accident 
one be dropped upon a hard surface it is likely to be 
ruined. The metal melts at 419° C. It boils at 918° C. 
and, if air be admitted, burns with a splendid greenish 
incandescence, forming the oxide. In boiling water 
zinc is said to be attacked appreciably, but no more, 
forming the hydroxide, Zn(OH)2, with evolution of hy- 
drogen. Zinc is electro-positive to all ordinary metals 
except aluminum and therefore will precipitate most of 
these metals out of their salt solutions. Possessing 
distinct galvanic properties, it is extensively used in 
both wet and dry batteries and its use in the mouth in 
any form influences galvanic action. 
Zinc is ionized in simple and complex form, the 
+ + 
former being Zn while the latter we have the zincate 
— + + 
ion ZnO and zinc ammonia ions. Zn(NH3)n. The 
hydroxyl ion in combination with a zinc salt in solution, 174 
PRACTICAL DENTAL METALLURGY 
precipitates white Zn 02H2 which exhibits both acidic 
+ + 
and basic properties, for it may dissociate into Z11 
and (OH)2 ions, in which case the Zn ions act as 
+ + 
metallic ions or it may dissociate into H2 ions and 
Zn02 ions in which case zinc acts as an acid forming 
element. 
Zn 02H2 + 2 H -Cl = Zn Cl2 + H2(OH)2 or 2H20 
+ + 
zA 02H2 + 2 NaOH = £Ja I Q/Zn + H2(OH) 2 or 2H20 
The phosphate ion (P04) precipitates white Zn3(P04)2 
which is quite soluble in acids even in acetic acid. The 
chloride ion Cl produces no precipitate. ZnCl2 is so ex- 
tremely soluble that it melts in its own water of crystal- 
lization or being hygroscopic quickly absorbs moisture 
from the air and on going into solution tends to be- 
come cloudy, due to hydrolysis forming the basic 
salt Zn/ 
\G1 
Cl OH a basic chloride. 
/ / 
Zn + HHO = Zn + HC1 
\ \ 
Cl Cl 
OH OH OH 
/ / / 
Zn + HHO = Zn + HC1 : Zn + heat = ZnO + H20. 
\ \ \ 
Cl OH OH 
IN THE ARTS.—Zinc meets with extensive applica- 
tion. It is much used for the positive element in gal- ZINC 
175 
vanic batteries, and in the form of sheet zinc it is 
greatly employed in manufacturing industries. 
DENTAL APPLICATIONS.—Zinc has long been 
very extensively used in the dental laboratory for mak- 
ing dies. Its comparatively low fusibility, hardness, 
and other properties eminently fit it for this purpose. 
DIES.—“In passing from a low to a higher tempera- 
ture zinc increases in volume in a greater ratio than 
any of the metals in common use. The coefficient of 
its cubical expansion between zero and 100° C., which 
represents the rate of increase of its unit volume be- 
tween these temperatures, has been found to be 
0.000088251, or nearly three times that of cast iron. 
The rate of expansion of liquids being greater than that 
of solids, and as this rate is not constant, but increases 
with the temperature, the rate of increase in volume 
which zinc undergoes in passing from the solid to the 
fluid condition would be represented by a figure some- 
what higher than that given above. From the fact that 
metal plates for entire dentures which have been 
swaged upon dies made of zinc generally fail to fit the 
plaster model accurately, it is held by some practition- 
ers that the high rate of expansibility of zinc is an 
undesirable feature; but as the absolute contraction 
in the size of a zinc die is but slight, and as the dif- 
ference in the size of a plate made upon it and that of 
the mouth for which it is intended is to a certain ex- 
tent reduced or counteracted by the expansion which 
the plaster model undergoes in setting, it is question- 
able whether the contraction which takes place in zinc 
on passing from the fluid to the solid condition is of 
any detriment. It is held by many, and for potent 176 
PRACTICAL DENTAL METALLURGY 
reasons, that in most cases the contraction which occurs 
in a zinc die is of positive benefit. A plate swaged 
upon a zinc die is, by reason of the contraction which 
the metal undergoes in passing from the fluid to the 
solid state, slightly smaller than the mouth it is in- 
tended to fit, thus bringing the greatest pressure to bear 
upon the alveolar ridge. Should the plate be made 
to fit upon the plaster cast, it would be a trifle larger 
than the mouth, as plaster expands in setting, and two 
expansions have taken place in taking the impression 
and making the cast. The pressure exerted by such a 
plate would be expended upon the bony arch of the 
hard palate. Usually the tissues covering the alveolar 
ridge are thicker, and therefore more yielding, than 
those covering the hard palate, and a plate swaged 
upon a zinc die would be of positive advantage, as the 
slight absorption of the tissues covering the alveolar 
ridge which result from the increased pressure, would 
soon bring about a perfectly uniform bearing over the 
entire area covered by the plate. But one class of 
cases arises, and their occurrence is infrequent, where 
the quality of expansibility of zinc is detrimental to the 
fit of a plate when swaged upon it—namely, where the 
tissues covering the bony arch of the hard palate are 
thick and spongy, while the alveolar ridge is hard and 
covered by a thin unyielding membrane. When this set 
of conditions presents, it is usually in combination with 
a high Y-shaped arch. In such cases a die of Babbitt 
metal gives better results, though even with a zinc die 
the difficulty can be readily overcome and a proper 
adaptation secured by properly manipulating the plaster 
cast or impression, i. e., by scraping those portions of 
the cast which represent the soft, yielding portions, or ZINC 
177 
by treating the impression in like manner at those 
positions which represent the hard or unyielding parts 
of the ridge.’ 
Counterdies.—Zinc is frequently used for making 
the counterdie as well; being hard and unyielding, 
copying the finest lines, it secures a perfect and ready 
adaptation of the metal to the die. In working platinum- 
gold or iridio-platinum the lead die is entirely inade- 
quate to perfectly swage the metal to the die, espe- 
cially where the palatine arch is very high or the rugae 
prominent, and it is then that a zinc counterdie is 
especially serviceable. It is also of great assistance in 
conforming plates to dies for partial dentures, as it 
more perfectly forces the metal snugly about the necks 
of the teeth than lead can be made to do. 
The zinc counter is formed similarly to the manner 
of making a lead counter, except that the die should 
be quite cool—not cold—and thinly coated with a 
solution of whiting, which is allowed to dry, or with 
a deposit of carbon, obtained by smoking the die over 
a candle flame. In experienced hands the coating may 
be dispensed with and zinc heated just to complete 
fusion, and quickly poured in an uninterrupted stream 
upon the cool die. 
ZINC OXIDE.—ZnO is the only known compound of 
this metal and oxygen. It is a strong base, forming 
salts isomorphous with those of magnesium. It may 
be prepared by heating the metal to 918° C., exposed 
to the action of the atmospheric oxygen. Soon after 
melting it begins to be covered with a film of gray 
oxide. Just before the temperature reaches redness 
it takes fire and burns with an intense greenish-white 
*Dr. p. C. Kirk, Am. System of Dentistry, iii, p. 922, 178 
PRACTICAL DENTAL METALLURGY 
light, forming a very light, white, flocculent oxide re- 
sembling carded wool, which quickly fills the crucible, 
and is in part driven into the atmosphere by the cur- 
rent of air. It may also be prepared by heating the 
carbonate, ZnC03, to redness, driving off the water 
and carbon dioxide, C02. Too high a temperature will 
discolor the oxide a light yellow, and, partially vitri- 
fying it, will give to it a harsh, gritty feel. A good 
Fig. 44.—The interior of a bag house where the oxides of metals, par- 
ticularly of zinc, are collected for commercial use. The metals are oxidized 
in a roasting or reverberatory furnace. Passing through long horizontal 
stacks to be cooled, finally reaching the bag house where the oxides are 
collected in bags from 25 to 50 feet long and 2 feet in diameter, the 
bases being attached to metal bins. Most of the zinc oxide of commerce 
is obtained in this manner. 
quality should present a soft, white, flaky, impalpable, 
amorphous powder, permanent in air, odorless and 
tasteless, insoluble in water or alcohol, but soluble in 
acids without effervescence; also soluble in ammonia- 
water and ammonium carbonate solutions. When 
strongly heated (calcined), the oxide assumes a deep ZINC 
179 
lemon color, but turns nearly white again on cooling. 
At a low white heat it fuses, and at a full whiteness 
sublimes. If it be contaminated with white lead or 
chalk, it will not be entirely soluble in dilute sulphuric 
acid, but an insoluble sulphate of lead or of lime will 
remain. If zinc oxide exhibits any effervescence on 
the addition of hydrochloric acid, a content of zinc 
carbonate is suspected and its presence is probably 
due to improper calcining. 
ZINC CEMENTS.—No material is more generally 
used in dentistry than dental cements, and of all classes 
the zinc phosphates are the most common. They are 
most frequently spoken of as zinc oxyphosphates 
which is a misnomer, for there is no salt of zinc ex- 
hibiting a formula which would comprehend such ter- 
minology. From all chemical evidence obtainable we 
have, in mixing zinc oxide and phosphoric acid, a salt, 
viz., zinc phosphate or phosphite. If there is an ex- 
cess of acid present, it remains as such until neutralized, 
and if there is an excess of the oxide present, it re- 
mains as such, probably accounting for the above term, 
oxyphosphates. 
Since this material is of such importance, it is well 
to bear in mind the physical and chemical properties of 
the elements which go to make up dental cements.* 
The oxide of zinc is found in nature at Franklin 
Furnace, N. J., where it is extensively mined. It is 
prepared commercially by heating the hydroxide, car- 
bonate, nitrate, sulphide, or acetate, or by heating the 
metal to 918° C. in the presence of air. For commer- 
cial purposes the latter is the customary method of 
preparation, for medicinal purposes it is prepared by 
*§pe properties of zinc and copper. 180 
PRACTICAL DENTAL METALLURGY 
heating the carbonate, and for dental purposes it is 
prepared, according to some authorities, by heating the 
nitrate, it being stated that an oxide of heavier specific 
gravity is thus obtained. 
Zinc oxide is an amorphous, white, tasteless powder, 
insoluble in water, and when in a pure dry state is 
absolutely neutral in reaction. It is soluble in all the 
solvents of the pure metal, thus differing from the 
oxides of the other common metals. For dental ce- 
ments, zinc oxide is calcined at a temperature of about 
1400° C. for several hours. Usually an electric fur- 
nace of the muffle type, specially designed for this 
purpose, is used since it protects the oxide from pos- 
sible contamination with the products of combus- 
tion.* Dr. Marcus L. Ward conducted a series of 
interesting experiments on cements in 1914-15, which 
have cleared up our hazy knowledge of the subject. 
He found by analysis and synthesis that the powder of 
the principally used cements, (Ames, Justi’s, Fellow- 
ship, and Caulk’s) consisted of zinc oxide with traces 
of silicon oxide and magnesium oxide, except that 
Caulk’s Petroid was modified by the addition of mag- 
nesium oxide and bismuth oxide, (Z11O, 84., MgO, 10., 
Bi203, 6.) and a trace of ferric oxide. 
After calcination the oxide is found to be greatly 
contracted in mass, semivitreous, and the color has 
changed to a light yellow, which is probably due to a 
partial fusion. Ward states that calcining from eight 
to fourteen hours is the period of time best suited to 
duplicate the manufactured products, the tempera- 
ture approximating 1400° C. Also, that the longer the 
zinc oxide was fired, the slower it reacted with the 
*Jour. N. D. A., ii, pp. 3S4-370. zinc 
181 
cement liquids. The calcined mass is then reduced to 
a powder in a ball-mill, and bolted through bolting 
cloth, depending upon the service for which the cement 
is to be used, the coarser grades being used for filling 
purposes, and tbe finer grades being used for setting 
inlays. 
Color modifications are produced by adding various 
oxides, as ferric oxide, cobalt oxide, copper oxide, 
which in themselves possess certain cement making 
properties. It is quite generally understood that the 
permanent yellow tints in zinc cement powders are not 
obtained wholly by calcination. 
ORTHOPHOSPHORXC ACID is the acid used 
chiefly in zinc cements. Phosphorous in combination 
with oxygen forms P203 and P205 besides the lesser 
important oxides P40 and P204. P203 is an acid anhy- 
dride and with water readily forms metaphosphoric 
acid, H P03. It also combines with two more atoms 
of oxygen to form the pentoxide P205 which has such 
a strong affinity for water that it is the best dehydrat- 
ing agent known to science. When the pentoxide and 
water stand for a long time a pentahydroxide 
[P(OH)5]2 is formed which forms orthophosphoric 
acid quite readily when attempts to isolate it are made. 
/OK 
//Oil HO 
? OH = HO P = 0 + Ha0 
ho' 
'OH 
If this compound be gently heated to about 255° C., 
it loses water and forms pyrophosphoric acid. 182 
PRACTICAL DENTAL METALLURGY 
rH0\ eo 
2 ■] HO = 0 + Heat = >sSp = 0 
/ | 
H0 0 + H,0 
HO. | 4 
>P= 0 
HCK 
Heating pyrophosphoric acid gives two molecules of 
metaphosphoric acid and water. 
Orthophosphoric acid, the most common type, is made 
by adding nitric acid to phosphorus and heating, grad- 
ually adding more acid until all the phosphorus has 
been oxidized. 
5HN03 + 3P + 2H20 = 3H3P04 + 5NO. 
Glacial phosphoric acid, formerly used for the manu- 
facture of cement liquids, is made by volatilizing meta- 
phosphoric acid and condensing the vapors. The com- 
mercial product is made by adding sodium metaphos- 
phate, in some instances nearly sixty per cent, to meta- 
phosphoric acid, to give hardness and transparency, 
Orthophosphoric acid may be obtained from this by 
adding distilled water and boiling down, when the 
meta compound takes up water to form the ortho com- 
pound, with sodium metaphosphate still present. 
Dr. Ward found that the liquids of the most com- 
monly used cements consist of orthophosphoric acid, 
modified by the addition of hydrated aluminum oxide 
and water in varying proportions, depending on the 
rapidity or slowness of setting desired. Poetschke 
states that occasionally salts of nickel and iron, and 
oxides of bismuth and magnesium are added as modi- 
fiers. 
Since zinc produces only one series of compounds, 
it is logical to suppose that no matter which phos- ZINC 
183 
phoric acid is used, the ultimate phosphate formed 
will be Zn3 (P04)2 if the reaction runs to completion. 
It has been stated that a basic salt is formed. A basic 
salt is one that partakes more of basic properties than 
acid or neutral. How can we form a basic salt from 
a bivalent compound and a trivalent acid? There are 
three replaceable hydrogen atoms in orthophosphoric 
acid. Since zinc in an aqueous solution tends to de- 
compose the water and form Zn Oj,H2, and since we use 
an aqueous or diluted solution of orthophosphoric acid, 
the following reactions may express graphically the 
several changes which take place in the production of 
a normal phosphate of zinc by the addition of small 
quantities of zinc oxide to orthophosphoric acid. 
The presumed basic salt is therefore merely an ex- 
cess of zinc oxide with normal zinc phosphate. 
SZnfOHlj— Zn3fP0^)t— 6Ht0. 
rUO 
Zn <T \ \ 
JhO—OP—O xO —)-P — 0 
<0H Uo' ✓(r 
>4- Zn<T + 6H.0 
OH /HO. X0. 
<0H < — 0 /CAP = 0 
/ / 
OH' 1ho/ x 0' 
L0--h—H—lo. 
Zn<4 > \ 
\0--H--H—0 —= o 
<0—H H— O' 
0 H H 0'S. 
0 H H—0—>P = 0 
Zn<C / 
Thus in the elimination of six molecules of water, 
by gradually incorporating the powder into the liquid. 184 
PRACTICAL DENTAL METALLURGY 
as shown above, we may produce five different salts 
of zinc before the normal phosphate is formed. Dr. 
Ames states that different grades of basic phosphate 
require different amounts of water of crystallization, 
and that in proportion to the normal phosphate formed 
during the mix, will the setting be retarded or modi- 
fied. Segerblom gives us five phosphatic compounds 
of zinc: 
1. Zn(H2P04)2, 2H20., acid zinc phosphate. 
2. Zn(P03)2, 4H20., zinc metaphosphate. 
3. Zn2P207, zinc pyrophosphate. 
4. X, ZnO, Y, P205, Z, H20, basic zinc phosphate. 
5. 2ZnHP03, 5H20., zinc phosphite. 
The last one only is readily soluble in water. 
MIXING CEMENTS.—The technic of mixing ce- 
ments is very easily acquired. It does not require pre- 
cision or strength or delicate manipulative skill, but 
it does require attention to detail and careful handling 
of the materials in hand. We are dealing with a 
chemical problem in a physical way. The end prod- 
ucts would be just about the same if we poured a bot- 
tle of cement powder into a bottle of cement liquid, 
but the material could not be used for the purposes 
for which it was intended. It requires manipulation 
in order to render the mass plastic and thereby adapted 
to our needs. 
Definite orders of procedure should be established. 
First, use a clean polished plate glass slab, free from 
scratches and ground surfaces and heavy enough to 
permit of mixing a creamy mix without holding it if 
the occasion demands it. Any accumulation of ce- ZINC 
185 
ment crystals from a previous mix, that may remain 
on the surface or in the scratches, materially hastens 
the setting of a new mix. Second: use a broad stiff 
spatula, preferably of one of the nickel, copper, zinc 
alloys, variously known as German Silver, Nickel Sil- 
ver, or Platinoid, or a bone or agate spatula, the lat- 
ter being especially indicated for the silicious cements. 
Steel spatulas are so readily oxidized by the cement 
liquids that they modify the color of the cement to a 
considerable degree, and may bring about a failure in 
setting porcelain inlays. 
Third: the liquid, which should be kept in a special 
bottle with a telescoping ground glass stopper, is 
placed on the slab, by means of a glass stirring rod 
which can be washed after each operation. The ac- 
cumulation of crystals around a common cork or in a 
pipette are unsightly and tend to modify the setting 
qualities of the liquid. Fourth: the powder should be 
kept in a well corked bottle at all times, for zinc 
oxide, as do all oxides, absorbs carbon dioxide from 
the air, and we are then dealing with a carbonate 
instead of the oxide, with unsatisfactory results. Place 
the powder on the clean slab and divide it into four 
or five portions. Then incorporate one portion at a 
time, thoroughly spatulating the mass until it is homo- 
geneous before adding a second portion. Continue in 
this way until the desired consistency is obtained. The 
rationale of this process is to produce as large a 
quantity of normal zinc phosphate as is possible, to 
retard the setting and give time for manipulation. If 
we add a large amount of powder to the liquid with 
very little spatulation, we produce a large amount of 186 
PRACTICAL DENTAL METALLURGY 
basic zinc phosphate which hastens setting and gives 
a flaky or clotty mix. If under such conditions we re- 
sort to excessive spatulation we may produce an ex- 
cess of normal phosphate and retard the setting dis- 
astrously. It is better to discard the mix. 
If, on the other hand, we do not add enough powder 
to thoroughly neutralize the liquid, we will have an 
acid phosphate, with the possibility of some free acid 
remaining which is very likely to attack the tooth 
structure as well as lessening the cementing qualities 
of the mix. In the end we have a mixture consisting of 
zinc and other oxides held by an agglomerating me- 
dium, normal zinc phosphate, provided the liquid is 
fully saturated by the powder. 
Other classes of cements include chiefly copper ce- 
ments and silicious cements. The former are either the 
black oxide of copper (cupric) or the red oxide (cu- 
prous) or a combination of either of these with zinc 
oxide, or zinc oxide modified by the addition of cu- 
prous iodide (Cu2I2), cupric phosphate (CuHPOJ, or 
cupric silicate, (CuSi03). They are primarily intended 
for use in the deciduous teeth, for which they are par- 
ticularly suited, and while much is claimed for their 
germicidal value, they should not be relied upon as 
germicides, per se. The silicious cements are com- 
pounds of calcium and aluminum silicates, with in one 
instance a silicate of a rare element. The liquids are 
similar to the liquids used for the zinc cements, the 
chief difference being in the modifying agents. Little 
experimental work has yet been done by the profes- 
sion on this problem. Properly manipulated, these 
compounds are more durable than the other classes of 
cements and they harmonize with the tooth structure ZINC 
187 
and color better. They are unaffected by the acids or 
alkalies, except sulphuric acid, and the various kinds 
of powders and liquids are interchangeable. This 
may be determined by simple experimental mixes. 
ACTION OF ACIDS ON ZINC.—Pure zinc dissolves 
very slowly in acids or alkalies, unless in contact with 
copper, platinum, or some less positive metal. Any 
metallic impurity in zinc renders it quite soluble in the 
acids or alkalies. It is rapidly oxidized in water 
containing air, when in contact with iron, but the water 
does not dissolve it, unless aided by certain salts. All 
agents which dissolve the metal, also dissolve its oxide 
and hydroxide. 
In Sulphuric acid dilute, it dissolves slowly, forming 
zinc sulphate, and evolving hydrogen. 
Zn + H2S04 = ZnS04 + H2. 
In strong sulphuric a coating of zinc sulphate is 
quickly formed over the metal, retarding, if not alto- 
gether preventing further action. 
In Hydrochloric acid it is also slowly dissolved when 
pure, more rapidly when contaminated, forming the 
chloride of zinc and evolving hydrogen— 
Zn + 2HC1 = ZnCl2 + H2. 
The Chloride is a nearly white, translucent, fusible 
substance, very soluble in water and alcohol, and very 
deliquescent. It is used in dentistry when melted, or 
melted and diluted as liquid for oxychloride cement; 
as an obtundent to sensitive dentine, an antiseptic, dis- 
infectant, etc. 188 
PRACTICAL DENTAL METALLURGY 
In Acetic acid zinc slowly dissolves, forming the 
acetate, and evolving hydrogen— 
Zn + 2HC2H302 = Zn(C2H302)2 + H2. 
In Nitric Acid.—In very dilute nitric acid it dissolves 
without evolution of gas— 
4Zn + 10HNO3 = 4Zn(N03)2 + II4NN03 + 3H20, 
forming the nitrates of ammonium and zinc. 
In moderately dilute cold nitric acid, it dissolves 
with evolution of nitrous oxide— 
4Zn + 10HNO3 = 4Zn(N03)2 + N20 + 5H20. 
In a less dilution it dissolves with evolution of nitric 
oxide— 
3Zn + 8HN03 = 3Zn(NOs)s + 2NO + 4H20. 
In concentrated nitric acid zinc is but slightly soluble. 
IN ALKALIES.—In Potassium Hydroxide, and in all 
the caustic alkalies, zinc slowly dissolves, evolving 
hydrogen— 
Zn + 2KOH = Iv2Zn02 + H,. 
ALLOYS.—Mercury and zinc amalgamate quite 
readily to form a definite compound, having the form- 
ula Zn2Hg.# 
With Gold, zinc readily unites. The malleability, 
brilliancy, and color of gold is impaired by a content 
of zinc. 
Platinum.—Small pieces of platinum may be dis- 
solved in molten zinc, and the union is attended with 
*See chapter on Amalgams. ZINC 
189 
considerable energy, owing to the formation of a definite 
chemical compound. The alloy is hard and brittle. An 
alloy may be prepared of platinum, 16; copper, 7; and 
zinc, 1; which very much resembles gold in color, spe- 
cific gravity and ductility. 
Silver and zinc have a great affinity for each other. 
This fact, with the knowledge that zinc and lead are so 
comparatively incompatible, led to the process of desil- 
vering lead by the assistance of zinc. The alloy of sil- 
ver and zinc is best obtained by throwing the required 
quantity of zinc wrapped in paper into molten silver, 
stirring thoroughly with an iron rod, and pouring the 
fused mass at once. The alloy of two parts zinc and 
one part silver is flexible, ductile, and has nearly the 
color of pure silver. Larger proportions of zinc pro- 
duce brittle alloys. 
Copper and Zinc Alloys.—(See chapter on Copper.) 
Iron and zinc unite to form a very interesting as 
well as somewhat useful and brittle alloy. Iron plate 
and ware when perfectly cleaned may be immersed in 
molten zinc and the surface alloyed slightly, forming 
what is known as “galvanized iron.”* Zinc alloys with 
the iron melting pots of the laboratory; the admixture 
rendering the zinc less fluid when molten and more 
difficult to fuse. This contamination may be prevented 
by coating the pot with whiting. 
With Lead zinc does not alloy, except to a very slight 
degree. “ Matthiessen foundf that on melting equal 
parts of zinc and lead, and, after well mixing, allowing 
the alloy to cool slowly, they separate, but the heavier 
lead on subsiding retains 1.6 per cent of the zinc al- 
’'See chapter on Iron. 
fMakins’ Metallurgy, p. 62. 190 
PRACTICAL DENTAL METALLURGY 
loyed with it; while, on the other hand, the upper 
layer of zinc thrown out retains 1.2 per cent of lead.” 
It often occurs that lead and zinc will become mixed 
in the laboratory, and is seldom discovered until the 
molten mixture is poured. Then the lead, owing to its 
greater specific gravity, falls to the bottom of the 
mold, forming the alveolar ridge of the die, rendering it 
worthless. Many times the counterdie is poured before 
the mistake is noticed, resulting in a union of the die 
and counterdie. 
Tin and zinc alloy in almost any proportion. Mr. 
Fletcher recommends an alloy of zinc 2 parts and tin 
1 part for making dies for swaging, claiming the im- 
pression from the sand is much finer, and the shrink- 
age on cooling is greatly reduced. It melts much lower 
than zinc alone, hence some care must be exercised in 
pouring the counterdie. The die should be perfectly 
cold and the lead should be just hot enough to pour, 
but not sufficiently heated to char a slip of paper. 
Bismuth and zinc are almost immiscible in either a 
solid or liquid state except in alloys having less than 
three per cent of zinc by weight. Other alloys will not 
mix under 800° C. 
Cadmium and zinc are miscible in all proportions in 
a liquid state, and they unite to form a definite chem- 
ical compound. An eutectic of Zn, 82.4; Cd, 17.6, 
melts at 260° C. 
TEST FOR ZINC IN SOLUTION.—Potassium hy- 
droxide and sodium hydroxide all precipitate the white 
hydroxide of zinc, Zn(OH)2, soluble in excess of either 
precipitant with the formation of sodium zinc oxide. 21NC 
191 
ZnCl2 + 2NaOH = Zn(OH)2 + 2NaCl. 
Zn(OH)2 + 2NaOH = Na2Zn02 + 2H20. 
Ammonium sulphide completely precipitates zinc as 
a sulphide. 
Alkaline carbonates precipitate it as basic carbonate 
soluble in ammonia. 
Final Test: make zinc solution slightly acid with 
hydrochloric acid, HC1. Add hydrogen sulphide, H2S, 
and filter. To the filtrate add ammonium hydroxide, 
NH40H, and pass in H2S and filter. Dissolve the pre- 
cipitate in HC1, add NH40H and filter. Acidify the 
filtrate with acetic acid, HC2H302, and add H2S. A 
white precipitate shows the presence of zinc sulphide, 
ZnS. CHAPTER XI 
CADMIUM 
Cadmium. 
Valence, II. 
Atomic weight, 112.40. 
Melting point, 320° C. 
Tenacity, 9th rank. 
Specific heat, 0.0548. 
Conductivity (heat), 22.13. 
Color, tin-white. 
Symbol, Cd. 
Specific gravity, 8.642 at 17°. 
Malleability, 10th rank. 
Ductility, 11th rank. 
Chief ore, greenockite. 
Crystals, octahedral. 
Conductivity (electricity), 24.4. 
(Silver being 100.) 
OCCURRENCE.—This metal does not occur native. 
There is but one mineral known which could be called 
an ore of cadmium, and which contains it in any quan- 
tity; namely, the sulphide, CdS, greenockite, which is 
found near Bishopstown, Renfreivshire. This ore is 
crystalline, belonging to the hexagonal system, and is 
of an orange-yelloAV color. Cadmium is, however, 
often associated Avith the zinc blende, ZnS, and Cala- 
mine ZnC03, and from these tAvo ores it is principally 
obtained, varying in amount from 1 to 5 per cent. 
Practically the entire output in the United States comes 
from the zinc ores found in the Joplin district in Mis- 
souri, which contain about 0.3 per cent of cadmium. 
The metal very much resembles zinc, especially in its 
chemical properties. 
REDUCTION.—A humid method (Stromeyer’s) is 
to dissolve the zinc ore containing cadmium in dilute 
sulphuric acid and precipitate the metal as the orange- 
yelloAV sulphide by means of sulphuretted hydrogen. 
192 CAbMiUM 
193 
The sulphide is then dissolved in hydrochloric acid, the 
excess of the solvent evaporated, and the cadmium 
thrown down as the carbonate by adding ammonium 
carbonate. By heating this to redness the carbon diox- 
ide is driven off, leaving the oxide, which is mixed with 
carbon and distilled from an earthen retort. Most of 
the cadmium on the market, however, is obtained by 
roasting the zinc ores below the volatilizing point of 
zinc, usually during the first hour and a half. The 
retorting is frequently repeated to obtain the cadmium. 
PROPERTIES.—Cadmium is a tin-white lustrous 
metal, tough, very volatile (next to mercury), and some- 
what harder than tin, which it very much resembles 
physically. It fuses at 321.7° C. and boils at 778° C., 
giving off a yellowish-brown colored vapor. Its specific 
heat is 0.0548, electric conductivity somewhat lower 
than that of zinc, and its specific gravity 8.642 at 17°. 
It is malleable, ductile, and somewhat tenacious, break- 
ing under an increasing strain, with fibrous scaly frac- 
ture; may be readily crystallized in regular octahedra; 
is unalterable in the air at ordinary temperatures, but 
when heated strongly in the presence of air, burns, emit- 
ting the yellowish-brown fumes of cadmium oxide, CdO. 
COMPOUNDS WITH OXYGEN.—Cadmium forms a 
single oxide, CdO, a yellowish-brown powder, which is 
easily volatilized, or may be readily reduced with hy- 
drogen or carbon, at a high temperature, but below that 
point necessary for the reduction or volatilization of 
zinc oxide. It is strongly basic and forms a series of 
salts similar in constitution to those formed by the 
oxide of zinc. It may be formed by burning the metal 
in the air, or by calcining the nitrate or carbonate, dif- 194 
PRACTICAL DENTAL METALLURGY 
fering somewhat in shade according to the manner of 
preparation. 
ACTION OF ACIDS ON CADMIUM.—In hot sul- 
phuric or hydrochloric acid, moderately diluted, it is 
slowly dissolved, forming the salts CdS04, or CdCl2, 
and liberating hydrogen. 
In Nitric acid it is readily soluble, forming the ni- 
trate, and generating nitrogen oxides. 
COMPOUNDS OF CADMIUM.—The most important 
of these is the sulphate, CdS04, which is used in medi- 
cine as an astringent and stimulating remedy, especially 
in diseases of the eye. The next of importance is the 
sulphide, CdS, which occurs native as greenockite, and 
is used as a superior yellow pigment by artists. The 
iodide, Cdl2, is used in photography. 
ALLOYS.—The metal is of little use except as a 
constituent of certain alloys, especially those fusing 
at a low temperature. 
With mercury cadmium combines to form a silver- 
white mass, which readily crystallizes, and under cer- 
tain circumstances is said to be malleable. When intro- 
duced into a dental-amalgam alloy, it imparts the 
property of malleability. Such dental alloys, however, 
cannot be too strongly condemned. 
“In 1848, Dr. Thomas W. Evans of Paris introduced 
his amalgam, which was composed of pure tin, cad- 
mium and mercury; but it was soon found that cadmium 
was one of the very worst metals that could be used in 
a dental alloy, and its use was soon discontinued. * ’* 
Of it Dr. J. Foster Flagg, Philadelphia, says: “The 
‘Relative Merits of Filling-materials, by E. T. Darby, M.D., D.D.S., 
Dental Cosmos, xxxvi, p. 178. CADMIUM 
195 
promises of this alloy were certainly alluring. It was 
easily amalgamated; the amalgam was readily inserted; 
it did not discolor; it ‘set’ with surprising celerity; it 
made a sufficiently resisting filling. What wonder, 
then, that the gentleman who introduced it was pleased 
with the material! * * * My satisfaction was, 
however, very short-lived, for only three or four months 
passed before sundry indications presented, which 
aroused my suspicions as to the uniform integrity and 
durability of the material—these were, an occasional, 
but evident crevicing at edges; a gradual softening and 
disintegration of some fillings; and the yellowish dis- 
coloration sometimes apparent in adjoining tooth struc- 
ture.” He further states that in some cases the “den- 
tine had become thoroughly decalcified, and stained to 
a bright orange-yellow color—sulphide of cadmium.” 
He explains that pulps under such fillings were “de- 
vitalized,” except “where thick septa of dentine existed 
between the bottoms of the cavities of decay and the 
pulp cavities.”* 
“Cadmium shares with bismuth the property of 
greatly reducing the melting points of alloys, there 
being some whose melting points are so low that they 
may be liquefied in hot water. But while bismuth alloys 
are nearly all brittle, many alloys of cadmium possess 
considerable ductility, and may be worked under the 
hammer as well as between rolls. They act, however, 
very differently in this respect, there being alloys 
which are ductile, and others again, though containing 
besides cadmium the same metals, only in different 
proportions, which are very brittle.”! 
*Plastics and Plastic Fillings, p. 54, First Edition. 
tMetallic Alloys, Brannt, p. 297. 196 
PRACTICAL DENTAL METALLURGY 
These alloys are usually made up of cadmium, tin, 
lead, bismuth, and sometimes mercury, the latter being 
added chiefly to lower the melting point still more. 
The following are a few cadmium alloys with their 
melting points: 
Observer or 
Special name* 
Lead 
Tin 
Bismuth 
CAD- 
MIUM 
Fusing 
point C. 
Lipowitz 
26.70 
13.30 
50.00 
10.00 
60-68. 
Wood 
28.60 
14.30 
50.00 
7.10 
70. 
Y. Hauer 
34.38 
9.37 
50.00 
6.25 
76.5 
Wood 
42.86 
50.00 
7.14 
82.0 
33.33 
50.00 
16.67 
89.5 
V. Hauer 
28.00 
47.00 
25.00 
132. 
Rudberg 
.... 
.... 
78.80 
21.20 
146.3 
*Van Nostrand’s Chem. Annual, 1909. 
TESTS FOR CADMIUM IN SOLUTION.—Hydro- 
gen sulphide throws down the yellow sulphide, CdS, 
from acid solutions, distinguishing' the metal from zinc. 
The Caustic Alkalies precipitate the white hydrated 
oxide, Cd(OH)2, soluble in excess of ammonia, but in- 
soluble in potassa or soda. 
Final Test: add hydrogen sulphide, H2S to an acidi- 
fied solution and filter. Treat the precipitate with am- 
monium sulphide, (NH4)2S, and filter. Dissolve the 
precipitate in nitric acid, HN03, add sulphuric acid, 
H2S04, filter, make alkaline with ammonium hydroxide, 
NITjOH and add potassium cyanide,* KCN, and pass in 
H2S. A yellow precipitate shows cadmium sulphide, 
CdS. 
*Potassium Cyanide is a deadly poison and great care should be exer- 
cised in its use. CHAPTER XII 
COPPER 
Cuprum. 
Valence, I, II. 
Atomic weight, 63.57. 
Melting point, 1083° C. 
(1065° in air) 
Ductility, 4th rank. 
Conductivity (heat), 71.98. 
Symbol, Cu. 
Specific gravity, 8.93-8.95. 
Malleability, 3d rank. 
Tenacity, 2d rank. 
Chief ore, copper pyrites. 
Conductivity (electricity), 97.6. 
(Silver being 100.) 
Specific heat, 0.0936 
Color, red. 
Crystals, isometric. 
OCCURRENCE.—This exceedingly interesting and 
useful metal has been known and used by the human 
race since the most remote periods. Its alloy of tin- 
bronze was the first metallic compound used by man. 
The Smithsonian report (1868) mentions the use of 
native copper by the aborigines of North America, who 
obtained it from the southern shores of Lake Superior. 
Only the early inhabitants of Mexico and southern 
United States knew how to make bronze. It is found 
in the metallic state, in masses of irregular form, in 
rocky fissures; and often crystallized in the Lake Su- 
perior region known as Lake copper and in Virginia, 
the southwestern portion of the United States, in Mex- 
ico, Chile, Cornwall, and many other parts of the world. 
Native copper is obtained in pieces of monstrous weight 
on the shores of Lake Superior, many times weighing 
from 100 to 200 tons. The principal ores are, how- 
197 198 
PRACTICAL DENTAL METALLURGY 
ever, chalcopyrite, copper pyrites, a sulphide of copper 
and iron, CuFeS2, which when pure contains 34.6 per 
cent copper; bornite, another copper-iron sulphide, 
A 
B. 
Fig. 45.—Specimens of native copper from Fake Superior district. A i3 
a crystallized mass of irregular form while B is a shaving produced by 
cutting a large mass into smaller masses by means of a sledge hammer and 
long cold chisel. The reverse side is smooth while the obverse side shows 
the condensing effect of repeated blows of the hammer. 
Fig. 46.—A vertical section of a copper mine in the Fake Superior district 
showing the method of driving the shafts and stoping along the lode. 
Cu5FeS4, 63.3 per cent copper; chalcocite, copper 
glance; the sulphide, Cu2S, 79.8 per cent of copper; 
covellite, a beautiful indigo-blue sulphide, CuS, a rare COPPER 
m 
mineral; enargite, a copper arsenic sulphide, Cu3AsS4, 
4.83 per cent copper. These are the chief ores found in 
Butte, Montana, where one-sixth of the world’s pro- 
duction and one-third of the quantity produced in the 
United States is mined. In addition the following ores 
furnish this metal: Cuprite, the red oxide, Cu20; 
melaconite, the black oxide, CuO; malachite, green car- 
bonate, CuC03, Cu(OH)2. 
REDUCTION.—This metal is obtained from its ores 
by three different methods, the dry, humid, and electro- 
metallurgic. The process, of course, varies according 
to the nature of the ores treated and local circumstances. 
Fig. 47.—The Calumet and Hecla mine has been one of the largest and 
best producers of copper the world has ever known and has only been 
eclipsed in recent years by the mines in Utah and Montana. 
At the Anaconda works the ore ranging from dnst 
to masses fifteen iches in diameter is delivered from 
bins through shaking perforated feeders to crushers. 
The smaller particles pass through the perforations. 
The process is repeated with various sizes and types of 
machinery until the valuable ore is practically reduced 
to a slime. 
If the ore is to be treated in a blast furnace larger 
sizes ranging from three-eighths of an inch to two 200 
PRACTICAL DENTAL METALLURGY 
inches may be used. The ore masses less than one- 
sixteenth of an inch in diameter go to classifiers where 
the slime overflows and the sand passes to Wilfley 
tables. Here part of the concentrate is recovered and 
goes back to the mills for finer grinding. The ore 
finally reduced to masses ranging from two one- 
hundredths of an inch to slime passes to the flotation 
machine with some concentrate saved for smelting. 
By ingenious methods in the jigs, the heavier and 
more valuable minerals settle to the bottom where they 
pass out as concentrate through a trapped gate to 
Wilfley tables. The peculiar jerking motion of these 
tables carries the concentrate forward more rapidly 
and settles it below the middling' which is washed over 
the lower edge of the table. 
The flotation process used combines both film and 
froth methods. The heavier metallic minerals with the 
thin film of oil rise to the surface while the lighter non- 
metallic minerals settle as a sludge. The success of the 
flotation process depends on grinding the ore to a very 
impalpable slime. Particles three one-thousandths of 
an inch in diameter give no satisfactory results unless 
mixed with slime. A small quantity of sulphuric acid 
aids in the selective action. In the concentrator 95 per 
cent of the copper is obtained by these relatively cheap 
methods while two-thirds of the ore is discarded. 
The dry method is ordinary smelting, and is used for 
ores containing not less than 4 per cent of the metal, 
the wet method being preferred for the poorer ores. 
In the former method the ore is roasted in a reverbera- 
tory furnace, by which much of the iron sulphide is 
converted into oxide, while the copper sulphide re- COPPER 
201 
mains unaltered, and any arsenic that may be present 
is volatilized. The process at the Anaconda smelters is 
representative of the modern method of reverberatory 
furnace procedure. The charge contains the sulphides 
and oxides of copper and iron together with lime sili- 
con and aluminum. The silicon and aluminum com- 
bine with the iron oxide to form a fusible slag, and 
separates from the heavier copper compound. Copper 
in the fused state has a greater affinity for sulphur 
than other metals have. With iron sulphide it settles 
to the bottom of the furnace and is drawn off as matte. 
It is then transported in large steel ladles to the con- 
verters, sixty-five tons to the charge. Air is blown 
through the molten mass, burning the iron and sulphur 
until a rich copper alloyed with gold and silver re- 
mains. This is sent to the refiners for further purifica- 
tion. The carbonates and oxides are reduced in much 
the same manner, the former being heated to drive off 
the C02, thereby reducing it to an oxide, which, with 
the latter, is further reduced by the aid of a raised 
temperature and added carbon. 
Blast furnace operations are somewhat similar to 
the reverberatory furnace methods, except that a 
coarser ore is used and a strong blast of air is forced 
through the stack from the tuyeres burning the sul- 
phur, iron and coke. The combustion of the sulphur 
and iron saves a great deal of fuel. The matte is 
drawn off through tap holes at suitable intervals and 
then sent to the converter. 
The wet method, which, as previously hinted, is de- 
sirable for ores too poor to yield a profitable quantity 
by the dry method. This method is frequently em- 
ployed in working over what is technically known qs 202 
PRACTICAL DENTAL METALLURGY 
“blue billy,” or burnt pyrites, which remains as a resi- 
due in the manufacture of sulphuric acid from iron 
pyrites. Mixed with rock-salt and calcined, the small 
amount of copper contained in the iron oxide residue is 
converted into soluble cupric chloride, CuCl2, and on 
lixiviating the calcined mass with water a solution is 
obtained from which the copper may be thrown down 
in the metallic state by scrap-iron. 
Pure Copper.—The electrolytic method is used very 
extensively, as it yields a purer quality of the metal, 
which is much in demand in electrical engineering. The 
cathode is a thin sheet of pure copper, the anode a bar 
or pig of impure copper, and the bath an acid solution 
of copper sulphate. The pure copper is precipitated on 
the cathode in a highly crystalline form; the other base 
metals are not precipitated, but held in the acid solu- 
tion, while the silver and gold are deposited in the 
slime and subsequently recovered. 
Commercial Copper is quite pure, yet it frequently 
contains a small percentage of base metals and silver. 
Arsenic and antimony very materially injure the work- 
ing properties of copper, while tin, producing a bronze, 
increases its tenacity and hardness. The impurities 
are of three classes: 
1. Those which depress conductivity, as arsenic and 
antimony. 
2. Those which impair ductility, as lead bismuth, 
tellurium. 
3. Those which have a reclaiming value, as gold, 
silver, platinum and palladium. 
PROPERTIES.—Copper, or cuprum, in name is de- 
rived from kupros, the Greek spelling of Cyprus, an 
island where it was extensively mined. Its symbol is COPPER 
203 
the planet Venus, as the isle of Cyprus was sacred to 
that goddess. It is a peculiar red-colored, brilliant 
metal, differing in this respect from all other metallic 
elements, except, perhaps, titanium. Its atomic weight 
is 63.5, and its specific gravity, 8.91. It takes a bril- 
liant polish, and is very malleable and ductile, being 
second to iron in point of tenacity. It may be rolled 
into thin sheets or drawn into very fine wire. A copper 
wire, hard drawn, having a sectional area of a square 
millimeter, sustained a weight of 90.20 pounds at the 
moment of rupture. The same wire, annealed, broke 
under a weight of 69.52 pounds.* The melting point 
of copper is probably best stated at 1084°-1065° in air, 
and it expands slightly on passing from the molten to 
the solid state. It is unaffected by dry air, but in a 
moist atmosphere it becomes coated with a green car- 
bonate, malachite, which is also found native in most 
beautiful shades, takes a high polish, and is used for 
ornamental articles. When heated or rubbed with 
much friction, it emits a peculiar, disagreeable odor. 
In the conductivity of heat (71.9) and electricity (97.6) 
it is second only to silver (100). 
DENTAL APPLICATIONS.—Metallic copper has 
long been used for various purposes in the mouth, and 
was formerly used in the form of an attenuated, cone- 
shaped point known as canal points, for filling pulp 
canals, accompanied with a coating of some plastic- 
filling substance, such as chloropercha. Very thin 
sheet copper is cut into narrow strips about an inch 
and one-half long, and used for obtaining the circum- 
ferential measurement of teeth or roots before crown- 
ing. Copper bands of the same gauge and diameter 
*Gannot. Elements de Physique. 204 
PRACTICAL DENTAL METALLURGY 
as seamless gold shells are now furnished for the con- 
venience of the operator, thus saving much time. These 
bands are also adapted to broken down teeth in the 
mouth, for introducing large contour amalgam fill- 
ings, thus lessening the danger of fracturing the amal- 
gam during the setting stage. 
Dr. Charles B. Atkinson recommends swaging copper 
plate as retaining caps secured by copper wire in the 
treatment of pyorrhea alveolaris.# It is further used 
as concave disks for the protection of exposed pulps, 
and the wire as a ligature for retaining the rubber-dam 
in position. 
The foil in the form of pellets or ropes has been used 
as a filling material, inserted beneath gold surfaces; 
also to finish off the amalgam fillings, absorbing the 
surplus mercury. 
Copper pans are used for subjecting gold bases dur- 
ing the course of construction to the action of boiling 
dilute sulphuric acid. 
Copper poisoning shows a red, or purple-red or “some- 
times greenish-brown” (Hirt), line near the margin of 
the gums, says Professor W. D. Miller, and further, 
teeth of copper workers * * * show a more or less 
pronounced greenish discoloration. * * * Teeth 
filled with copper amalgam often show a greenish sur- 
face discoloration.! 
COMPOUNDS WITH OXYGEN.—Copper forms two 
oxides of importance, each of which is found native: 
Copper monoxide, Cupric oxide or Black oxide, CuO, 
is prepared by calcining metallic copper at a red heat 
in the presence of air, or by heating the nitrate to 
‘Dental Cosmos, xxxii, p. 549. 
tDental Cosmos, xxxvi, p. 265. COPPER 
205 
redness, driving off the N02. It forms a series of very 
important blue and green cupric salts, isomorphous 
with the salts of magnesium. It imparts a green color 
to glass, and is much used in the chemical laboratory 
as a means of supplying oxygen for the combustion of 
organic substances. When a caustic alkali is added to 
a cupric salt, a light blue precipitate, hydrated copper 
oxide, Cu(0H)2, is formed, which, if heated to 100° C., 
loses its water of crystallization and falls as a black 
oxide. This oxide is soluble in acids. 
Cuprous oxide, Red Oxide Cu20, occurs, in nature as 
a ruby-red octahedral crystal. It may be prepared by 
heating in a covered crucible 5 parts of the black oxide 
and 4 parts of fine copper filings. It gives to glass a 
beautiful ruby-red color. 
The most important cuprous salt is the chloride, 
CuCl, a white solid obtained by dissolving a mixture 
of cupric oxide and metallic copper in hydrochloric 
acid. It possesses a remarkable property of absorbing 
carbon dioxide. 
ACTION OF ACIDS ON COPPER.—Copper does not 
dissolve in acids with evolution of hydrogen. 
In nitric acid it dissolves most readily, chiefly with 
the evolution of nitric oxides— 
3Cu + 8HN03 = 3Cu(N03)2 + 4H20 + 2NO, 
and forms copper nitrate. 
In sulphuric acid, hot and concentrated, it also dis- 
solves readily, with evolution of sulphorous anhy- 
dride— 
Cu + 2H2S04 = CuS04 + 2H20 + S02 
and forms copper sulphate—blue vitriol. 206 
PRACTICAL DENTAL METALLURGY 
In hydrochloric acid copper is slowly soluble. 
EXPERIMENT.—In test tubes containing each of the above 
acids drop small strips of copper plate; heat and note reaction. 
ALLOYS.—The preparation of copper alloys is gen- 
erally attended with many difficulties, on account of 
the high fusing point of the metal and the almost in- 
variable presence of small quantities of other elements. 
An analysis of electrolytic copper having a conductiv- 
ity of 100% showed the presence of the following ele- 
ments: 
Cu 99.93 
Ag 001 
Au . .. .00001 
S 003 
O 04 
Fe 0035 
Ni 004 
As , 002 
Sb 003 
A1 ' 001 
P trace 
Fb 002 
Bi trace 
Si 0005 
Te 0005 
99.99051 
Copper must always be protected from oxidation in 
fusing for the cupric oxide formed tends to dissolve 
in the melted metal and make it springy. 
Mercury with copper readily forms an amalgam of 
definite chemical proportions, having the formula Culig. 
It crystallizes easily and, on solidifying becomes very 
hard and takes a fine polish. It is also malleable, and COPPER 
207 
can be worked under the hammer and between the 
rollers. It retains its metallic luster though for some 
time exposed to air, but blackens quickly when in con- 
tact with air containing sulphuretted hydrogen. It 
may be softened by heat, and is again plastic and flex- 
ible, solidifying subsequently. 
These peculiar properties, together with others, led 
to its introduction as a binary dental amalgam, first 
known as Sullivan’s Amalgam or Cement * 
Gold and copper alloy readily, the latter giving a 
desirable hardness to gold and deepening its color. 
If, however, any considerable proportion of copper be 
added to gold, the alloy is apt to be brittle, especially 
if the copper be not absolutely pure. For United States 
gold coins 10 per cent of copper is added to pure gold, 
giving it a carat fineness of 21.6, and a proper degree 
of hardness for durability. 
Silver and copper also alloy readily, and the copper 
again gives hardness with a slight change of color. Ten 
per cent of copper is added to silver for United States 
coin. 
Platinum and copper alloy at an intense white heat, 
giving an alloy much resembling gold in color and spe- 
cific gravity. 
Lead added to copper from .001 to .003 somewhat 
increases its ductility and malleability, but the pres- 
ence of 0.001 renders the metal unfit for preparation 
of malleable or ductile brass. 
Iron to the amount of .003 also has an injurious 
effect upon the properties of copper, rendering it hard 
and brittle. 
*See chapter on Amalgams, p. 368. 203 
practical dental metallurgy 
Antimony, bismuth and arsenic in small quantities 
have a very injurious effect upon copper. 
Zinc alloys with copper in any proportion, all the al- 
loys of which are included under the term brass. Alloys 
of copper and zinc were known in the time of Aristotle, 
and the manufacture of brass was first introduced in 
Germany in 1550, but was probably not produced by 
the direct union of the two metals until 1781 in Eng- 
land, as the art of obtaining zinc in the metallic form 
became known but a short time previous to that period. 
Notwithstanding copper and zinc may be alloyed in any 
proportion, the product is always serviceable. “Gen- 
erally speaking, it may be said that with an increase 
in the percentage of copper the color inclines more 
toward a golden, the malleability and softness of the 
alloy increasing at the same time. With an increase 
in the percentage of zinc, the color becomes lighter 
and lighter, and finally shades into a grayish-white, 
while the alloy becomes more fusible and brittle and at 
the same time harder.”* Alloys containing from 15 to 
20 per cent zinc are the most ductile. Those of 36 to 
40 of zinc can be worked cold as well as hot, while those 
containing 60 to 70 of zinc are so brittle that they 
cannot be worked at all. Raising this percentage to 
from 70 to 90 of zinc, the alloy again becomes ductile, 
and can be worked quite well when hot, but not when 
cold. An alloy of copper 75 and zinc 25 fuses at 
960° C. 
When cupric oxide is heated with powdered zinc in 
equal proportions, zinc oxide is formed and copper is 
freed. When zinc oxide and copper are heated to the 
melting point of copper, there is no loss of weight of 
*Brannt, Metallic Alloys. COPPER 
209 
copper. Therefore the oxide in brass is presumably 
zinc oxide. It is not dissolved in brass and therefore 
must be mechanically entangled. 
Good sheet brass may be made according to many 
formulae; two are cited: 
Rosthorn (Vienna)—Copper 68.1 and zinc 31.9 parts. 
Romilly—Copper 70.1, zinc 29.26, lead 0.38, and tin 0.17 parts. 
For wire, the following: 
England—Copper 70.29, zinc 29.26, lead 0.28, and tin 0.17 parts. 
Neustadt—Copper 71.5 and zinc 28.5 parts.* 
Alloys containing as high as 37 per cent of zinc are 
used as ductile and malleable products. 
The brass trade classes brass as (1) high brass, (2) 
low brass, (3) Muntz metal, (4) gilding, and (5) bronze. 
High brass is the most extensively used, and is known 
as “common brass.” It carries from 61 to 70 per cent 
of copper, the remainder being zinc. Spinning brass, 
cartridge brass, dipping brass, and screw rod brass are 
all high brass, although the last mentioned contains some 
lead to allow it to cut freely. Low brass is softer and has 
more stretch. It is used for drawing and spinning, 
and for brazing. It carries from 75 to 80 per cent of 
copper, the rest being zinc, and the color is usually a 
greenish yellow. All brasses carrying over 40 per cent 
zinc are known as Muntz metal. They will roll hot and 
are used for the cheaper grades of brass products. 
Gilding is a gold-colored mixture of copper 90, and 
zinc 10, used in cheap imitation jewelry. Bronze con- 
sists of this gilding alloy with some tin, usually, Cu 90, 
Zn 9, Sn 1, and is the best formula for rolling. 
Fine cast brass usually contains from 20 to 50 parts 
’Figures from Brannt, Metallic Alloys. 210 
PRACTICAL DENTAL METALLURGY 
of zinc to 100 parts copper, together with lead, or tin, 
or both in the proportion of 0.25 to 3 per cent of each.* 
Gun metal is classed as a brass alloy. For work re- 
quiring the highest tensile strength, (30,000 lbs. per 
square inch) the formula is Cu 88, Sn 10, Zn 2. For 
free turning gun metal the formula is Cu 86, Sn 10, Zn 
2, Pb 2. It casts exceptionally well with a small amount 
of shrinkage, is stiff, strong and noncorrosive. 
“The most malleable of the brasses is Dutch metal, 
composed of copper 11, zinc 2 parts; it can be rolled out 
into thin sheets and afterward beaten into leaves of ex- 
treme tenuity, and is used in this form for decorative 
purposes under the name of Dutch leaf-gold, or reduced 
to powder by levigation with a small quantity of oil or 
honey, it is sold as bronze powder.”! 
Pinchbeck, an alloy of copper 88.8 and zinc 11.2 
parts, very much resembles gold; is very ductile and 
malleable; used for cheap jewelry. 
Mosaic gold, a term sometimes applied to tin sul- 
phide, is composed of about equal parts of copper and 
zinc. 
Copper coins.—Those of the United States are com- 
posed of copper 95, tin 3, zinc 2 parts. 
Nickel and copper unite in all proportions, the color 
varying from the red of copper to the blue-white of 
nickel, according to the proportions of the respective 
metals. 
Copper with 10 per cent of nickel gives a light cop- 
per-colored alloy, very ductile; with 15, the color is a 
very pale red, but the alloy is still quite ductile; with 
25, a nearly white alloy, and 30, a silver-white alloy. 
•Figures from Brannt, Metallic Alloys. 
tKirk, American System of Dentistry. COPPER 
211 
United States nickel coins are composed of copper 75, 
and nickel 25 parts. 
Nickel, copper and zinc alloys are called German 
silver, argentan, etc. They are in reality brasses with 
nickel added, which gives them a white color and 
much hardness. 
These compositions vary greatly as may be noticed: 
Copper 50 to 66 parts 
Zinc 19 “ 30 “ 
Nickel 13 “ 18 “ * 
White metal.—A variety of alloys consisting of cop- 
per and a large proportion of zinc. They are very 
white, or, depending upon the proportion of copper, 
may be a pale yellow; melt at a low point, may be cast, 
and are somewhat malleable and ductile. 
Aluminum alloys easily with copper, producing alu- 
minum bronze, the alloys showing different properties, 
according to the quantity of aluminum they may con- 
tain. It makes copper harder and tougher without af- 
fecting its ductility, but renders it more liable to absorb 
oxygen. With 60 to 70 per cent aluminum, a very brit- 
tle alloy is produced; with 50 per cent, one quite soft, 
but less than 30 per cent of aluminum, the hardness 
returns. The bronze composed of copper 95, aluminum 
5, is a beautiful gold color, takes a fine polish, casts well, 
is malleable hot or cold, and is very strong, especially 
after hammering. With 7.5 per cent aluminum, the 
color is a greenish golden. The most common alloy is 
10 per cent aluminum, having a bright golden color 
which is not tarnished in air, may be engraved, pos- 
sesses, it is said, greater elasticity than steel, and may be 
*Brannt, Metallic Alloys. 212 
PRACTICAL DENTAL METALLURGY 
soldered with 20-carat gold solder. It melts at about 
927° C. 
Tin and copper form a very important series of al- 
loys termed bronze. (See chapter on Tin.) 
Brazier’s Solder.—An alloy composed of copper, 
zinc, tin and lead in variety of proportions, according 
to color and fusibility. 
Dr. Kirk gives the following table: 
Copper 
Zinc 
Tin 
Lead 
A. GoldeD Yellow 
53.50 
43.33 
50.58 
2.12 
B. Medium light 
43.75 
3.75 
1 
C. White .. .7 
57.50 
27.90 
14.90 
trace 
It is used in soldering brass and copper, which may 
also be soldered with the ordinary soft solder, spelter 
(zinc), or silver solder. 
Solders.—Copper is a constituent of most hard sol- 
ders; its proportion varying according to the purpose 
for which they are to be used. (See chapters on Silver 
and Gold.) 
DENTAL-AMALGAM ALLOYS.—Copper is a valu- 
able ingredient in these alloys, and is generally used in 
a proportion varying from 1 to 8 per cent. (See Amal- 
gams.) 
TESTS FOR COPPER IN SOLUTION.—Hydrogen 
sulphide added to either acid, alkaline, or neutral 
solutions of copper throws down a brownish-black pre- 
cipitate of cupric sulphide, insoluble in dilute acids or 
alkalies, but soluble in potassium cyanide. 
Potassium hydroxide or sodium hydroxide throws 
down a light blue cupric hydrate, Cu(OH)2, insoluble COPPER 
213 
in excess of either reagent, but, if heated, falls as the 
black cupric oxyhydrate, (Cu02) Cu(OH)2. 
Ammonia, or its carbonate, gives a blue precipitate, 
soluble in excess, producing a deep blue solution. 
Potassium ferrocyanide yields a characteristic brown 
precipitate, soluble in ammonia and decomposed by 
potassium hydroxide. 
Metallic iron placed in a solution containing copper 
precipitates the latter upon itself in the metallic state. 
Zinc or tin precipitates it as a black powder. 
Final Test: Add hydrogen sulphide to an acidified 
solution of a copper salt and filter. Dissolve the pre- 
cipitate in nitric acid, HN03, and add ammonium hy- 
droxide, NH4OH. Deep blue color shows copper, 
Cu(NH3)4. 
ELECTRODEPOSITION OF COPPER.—Copper may 
be deposited by simple immersion from a sulphate 
solution. The same solution is used for coating all 
metals and alloys, such as brass and German silver; 
but zinc, iron, lead, steel, tin, Britannia metal, type 
metal, etc., which precipitate it from its solutions by 
simple immersions, are coated in the cyanide or other 
alkaline solutions. Fruits, flowers, insects, etc., may 
be coated with a film of copper from the sulphate so- 
lution and a single cell. 
Plaster casts of the mouth are easily coated by first 
boiling in wax and coating when cold with plumbago 
and tin bronze. CHAPTER XIII 
IRON 
Ferrum. 
Valence, II, III. 
Atomic weight, 55.84. 
Melting point, pure 1505° C. 
Ductility, 5th rank. 
Conductivity (heat), 16.65. 
Symbol, Fe. 
Specific gravity, pure 7.85-7.88. 
Malleability, 9th rank. 
Tenacity, 1st rank. 
Conductivity (electricity), 14.6. 
Specific heat, 0.1162. 
Color, grayish-white. 
(Silver being 100.) 
Chief ores, hematite, magnetite, 
and siderite. 
Crystals, cubical. 
OCCURRENCE.—Iron is widely and abundantly dis- 
tributed throughout nature, being found in nearly all 
forms of rock, clay, sand and earth; its presence in these 
being commonly indicated by their colors, for iron is 
the commonest of all natural mineral coloring ingre- 
dients. 
Meteoric Iron—Metallic iron is very rarely found in 
nature, nearly all of which is probably of meteoric ori- 
gin, with the exception of ferruginous metallic plati- 
num. True meteoric iron usually, if not invariably, 
contains nickel to the extent of 1 or 2 per cent. 
Ores of Iron.—The chief combinations in which iron 
is found in sufficient quantity to render them available 
sources of the metal are shown in the table* on page 215. 
Magnetic Iron—Magnetite, or loadstone, Fe304, is 
found massive in very large quantities in Norway, 
United States, Canada, New Zealand, and India. The 
“Bloxam’s Chemistry Inorganic and Organic, p. 332. 
214 IRON 
215 
1 
Common Name 
Chemical Name 
Composition 
Magnetic iron ore. 
Protosesquioxide of Iron... 
Fe304. 
Bed hematite 
Sesquioxide of Iron 
Fe203. 
Specular iron 
Sesquioxide of Iron 
Fe203. 
Brown hematite... 
Hydrated sesquioxide of Iron 
2Fe203.3H20. 
Spathic iron ore. . 
Carbonate of Iron 
FeO.C02. 
Clay iron-stone... 
Blackband 
Carbonate of Iron, with clay 
| Carbonate of Iron, with clay 
and bituminous matter... 
Iron pyrites 
Bisulphide of Iron 
FeS2. 
ore of Norway furnishes the Swedish iron of such 
excellent quality, and the sands of New Zealand and 
India the excellent Wootz steel. It contains, when 
pure, about 72 per cent of iron. 
Red hematite, Fe203, is found in abundance in Eng- 
land, occurring in hard, shining, rounded masses of a 
dark red-brown color. It is a very characteristic ore 
of iron, containing from 47 to 70 per cent of the metal. 
Specular Iron, like red hematite, is an anhydrous 
sesquioxide (Fe203), but differs greatly in appearance, 
being of a steel-gray color and brilliant luster. It oc- 
curs chiefly on the island of Elba, but is also found in 
Germany, France, and Russia. The excellent quality 
of iron obtained from this is probably due to the purity 
of the ore, and to the fact that charcoal, instead of 
coal, is employed in smelting it. It contains about 62 
per cent of iron. Red ochre is a soft variety of this ore, 
containing clay. 
Brown Hematite, limonite, 2Fe203.3H20, is the hy- 
drated sesquioxide. It is of a distinctly sedimentary 
character, forming beds, but is also found in veins. It 
occurs principally in Belgium and France, and contains 216 
PRACTICAL DENTAL METALLURGY 
about 15 per cent water, and, when pure, about 59 per 
cent iron. Yellow ochre is a variety of this ore. 
Spathic ore, siderite, ferrous carbonate, FeO.C02, or 
FeC03. The value of this ore depends as much upon 
the nature of its impurities as upon the percentage of 
iron. It is found in Saxony of a crystalline character, 
light brown or gray in color, having a pearly luster, 
and when pure contains about 48 per cent iron. 
Iron pyrites, FeS2, is particularly remarkable for its 
yellow color, brilliant metallic luster, and crystalline 
structure, from which facts it has been termed “fools 
gold.” It does not form a direct source of iron, but 
the residue left after burning pyrites to make sulphuric 
acid, and extracting the copper,* is almost entirely of 
ferric oxide, from which iron is ultimately reduced. 
REDUCTION.—If the ore is a carbonate, or contains 
any carbonate, it is usually first calcined to expel the 
water and carbon dioxide, by roasting in a kiln or in 
long pyramidal heaps, resting upon foundations of 
large lumps of coal. This process reduces the ore to 
a dry, porous mass, and the iron to an oxide. Much 
of the sulphur, nearly always present, is driven off as 
sulphur dioxide at the same time. 
The calcined ore is then mixed with a certain propor- 
tion of limestone (calcium carbonate) as a flux, which is 
to induce the earthy part of the ore to flow, in order to 
liberate the iron. With the proper quantity of coal, 
coke, or charcoal, it is then introduced into one of the 
great blast-furnaces.f 
It would be very easy to reduce the oxide contained 
*See chapter on Copper. 
fSee chapter on Melting' JkJet^ls, IRON 
217 
in the calcined ore to metallic iron in such a furnace 
when heated with carbon; but the metallic iron fuses 
Fig. 48.—A crude type of blast furnace used by the native Filipinos 
for the reduction of iron. The principles involved are much the same as 
are used in the modern blast furnace. 
with so great difficulty that it is impossible to separate 
|t from the clay, unless the latter is brought to a liquid 218 
PRACTICAL DENTAL METALLURGY 
state, and even then the fusion of the iron, which is 
necessary for complete separation, is only effected after 
Fig. 49.—Sectional view of blast furnace. 
it has formed a more easily fusible compound with the 
small proportion of carbon derived from the fuel. The IRON 
219 
clay is even more difficult to fuse than the iron, so it is 
necessary to add with the ore to be smelted some sub- 
stance capable of forming with clay a combination 
which is fusible at the temperature of the furnace. As 
has been previously stated, limestone produces the re- 
quired result by forming the double silicate of alumina 
and lime, which becomes perfectly fluid. 
As the air passes from the tuyere (at B', Fig. 49) 
pipes into the bottom of the furnace, it parts with its 
oxygen to the carbon of the fuel which converts it into 
carbon dioxide (C02) ; this latter passing over the red- 
hot fuel as it ascends in the furnace is converted into 
carbon monoxide (CO) by combining with an addi- 
tional quantity of carbon. It is this carbon monoxide 
which reduces the calcined ore to the metallic state, 
when it comes in contact with it, at a red heat, in the 
upper part of the furnace, for this abstracts the oxygen 
at a high temperature, from the oxide of iron; itself 
becoming carbon, dioxide, the iron remaining in a free 
state. The tendency in the past has been to select the 
flux or limerock carefully, to wash the coal, or screen 
the coke and pick the iron ore and then introduce a 
blast of air containing four-fifths nitrogen which robs 
the furnace of a great deal of heat. The tendency in 
the future will be to manufacture cheap oxygen at the 
plant or employ air rich in oxygen to save heat and 
fuel. In determining the weight of gases passing out 
of the stack, it was found that they amount to twenty 
times the weight of the slag. The metal as it melts 
being the heavier sinks by its own gravity through 
the fuel into a crucible or cavity (A, Fig. 49) at the 
bottom of the furnace; as it sinks, however, it com- 
bines with small proportion of carbon to form east 220 
PRACTICAL DENTAL METALLURGY 
iron. At the same time the fluid slag, composed of the 
clay, or earth, made fluid by the addition of carbonate 
of lime as a flux, sinks also into the crucible, built at 
the bottom of the furnace, where it forms a layer of slag 
over the molten metal. When the slag so accumulates 
that no more will be contained in the crucible, it is al- 
lowed to run over its edge down the incline (E in Fig. 
49) on which the furnace is built. Thus the process is 
carried on until there is sufficient metal melted to con- 
stitute what is termed a charge, which rises almost to 
the aperture of the blast. The furnace is then tapped, 
at an opening provided for that purpose, and the metal 
run off into molds, when it is cast into rough, semi- 
cylindrical masses called pigs—crude cast iron. For 
purposes where hardness without flexibility is wanted, 
the remelted iron in this state is extensively used. 
ELECTRIC FURNACE REDUCTION.—The process 
of reduction in the electric furnace is a modification 
of the blast furnace method. The furnace is usually 
of a smaller type, the one at Iieroult, Cal., being a rec- 
tangular steel box 27 feet long, 13 feet wide, and 12 
feet high, lined with fire brick. Four graphite elec- 
trodes supply the current at from 40 to 80 volts. No 
air is allowed to enter, as in the blast furnace and the 
carbon used is only for purposes of reduction. A 
charge consisting of 500 lbs. of magnetite ore, 140 lbs. 
of charcoal, 3.5 lbs. of lime, 12.5 lbs. of quartz is fed 
into the furnace at stated intervals. The furnace is 
tapped three times a day and from six to seven tons 
of high grade pig iron is run off each time. The cost 
approximates $14 a ton. 
The electric furnace offers a particularly favorable 
means of working over steel scrap. It is possible to IRON 
221 
melt nickel, chrome, or vanadium steel, old tools, etc., 
make an assay of the product, add the necessary ele- 
ments and produce a good steel alloy. The quality of 
castings made in the electric furnace, especially for 
automobiles, is considered superior to that made by 
any other process. 
PROPERTIES.—Pure iron is a hard, malleable, duc- 
tile and tenacious metal, of a grayish-white color, and 
of fibrous texture, a slightly styptic taste, and has a 
sensible odor when rubbed. Its strength and tenacity 
are very high. In magnetic character it is superior to 
all other substances, nickel and cobalt being next. 
When it is almost pure, the magnetic influence pro- 
duced, owing to induction, by the proximity of a per- 
manent magnet or of an electric current, disappears 
entirely on removal of the magnet or current; if, on 
the other hand, carbon be present (as is usually the 
case to some small extent even in the softest mal- 
leable iron), there remains, after the removal 
of the magnet, or current, a greater or less amount 
of permanent magnetism, according to the cir- 
cumstances ; hard steel exhibiting the greatest poAver of 
becoming permanently magnetized under given con- 
ditions. In thermic and electric conductivity iron is 
16.65 and 14.6 respectively. Its specific gravity is 
7.85, its specific heat 0.1162, and its melting point is 
variously estimated from 1500°-1600° C. (Pouillet) to 
1900°-2000° C. (Deville). The presence of minute quan- 
tities of carbon, sulphur, etc., very sensibly lowers the 
fusing point, while 1 per cent of the former furnishes 
a steel melting at several hundred degrees lower than 
pure iron. Cast iron, containing more carbon, melts 
very much lower. It possesses the remarkable prop- 222 
PRACTICAL DENTAL METALLURGY 
erty of becoming plastic just before fusion, so that two 
hot masses may be pressed or squeezed together into 
one by the process of welding. So by forging, rolling, 
hammering, or other analogous operations, it can read- 
ily be fashioned into shapes which its rigidity and 
strength when cold will enable it to maintain. It is 
combustible and, when heated to whiteness, burns in 
atmospheric air, and with brilliant scintillations in 
oxygen gas. It combines with all the nonmetallic ele- 
ments, except hydrogen and nitrogen, and with most 
of the metals. 
MODIFICATIONS OF IRON.—There are three dis- 
tinct modifications of iron, viz., cast iron, wrought iron 
and steel. Other immediate varieties are recognized 
technically, but all are closely related and impercepti- 
bly shaded into each other, due to various percentages 
of carbon, etc., contained in the metal. The discovery 
that carbon in varying proportions with iron consti- 
tutes steel and other classes of iron dates from about 
1790 and probably emanates from England. 
CAST IRON is an impure carburized iron. The 
melted metal drawn off from the furnace below is con- 
ducted into a large main, called the “sow,” and thence 
into lateral molds called “pigs;” hence the term 
pig iron. This iron is found to have combined with a 
considerable quantity of carbon, about 4.5 per cent 
being the maximum; a portion of which exists as a 
chemical combination, the carbide of iron, the remain- 
der having been simply dissolved in the form of graph- 
ite. Other substances in the furnace are also found 
dissolved and combined in the iron, and have an im- 
portant bearing upon its physical properties. These IRON 
223 
are principally phosphorus, silicon, sulphur, manga- 
nese, etc. 
Pig iron may, therefore, be recognized as a crude 
form of cast iron. It is assorted and classed by the 
iron masters as Nos. 1, 2 and 3, differing in the amount 
of carbon contained. No. 1 is most highly carburized, 
No. 2 less, and No. 3 contains the least carbon. The 
first melts and runs so fluid that it is used for orna- 
mental castings of fine pattern, and furnishes cast-iron 
cutlery from which the carbon is subsequently ex- 
tracted. 
Cast iron, which contains the most carbon, is the 
most fusible variety, melting at about 1200° C. It is 
hard and brittle. Though some kinds admit of being 
made hard or soft nearly in the same manner as steel, 
and like steel, assume different degrees of hardness, 
according to the rapidity with which the pieces are 
allowed to cool; but unlike steel, when once hardened, 
will not admit of that hardness being reduced by va- 
rious gradations to any specific degree, called temper- 
ing. To soften materially it must be submitted for 
some time to a white heat, and then very gradually 
cooled. 
WROUGHT IRON is the cast, or pig iron, freed from 
carbon, and may be considered a nearly pure decar- 
burized iron; at least, it is the purest form of commer- 
cial iron, containing the least amount of carbon—less 
than 0.25 per cent. The decarburization is effected by 
first remelting the pig, or cast iron, and refining by ex- 
posing it to an intense heat and forcing a blast of air 
over its surface, in order to remove some of the im- 
purities of the metal; it is then run out into a large 
flat mold, and acquires the name of plate metal. 224 
PRACTICAL DENTAL METALLURGY 
The next process is called “puddling,” the object 
being to free the metal of its carbon. The operation is 
conducted in a reverberatory furnace, where the metal 
is again reheated and converted into wrought iron by 
keeping it in a state of fusion with a certain amount of 
black oxide of iron, Fe304, which gives up its oxygen 
after a time to the carbon and other impurities of the 
melted mass, leaving the latter nearly pure iron. As 
the process approaches termination, the fusing point of 
the mass grows higher, until it loses nearly all its fluid- 
ity. It is then divided into several parts and formed 
into balls, which are removed from the furnace and 
subjected to intense pressure through a series of pow- 
erful rollers, which squeeze out the more fusible slag 
entangled in it and convert it into bars or “blooms.” 
A number of these blooms are then raised to a welding 
heat and repeatedly passed through rollers, until all 
the remaining slag is forced out and the metal be- 
comes tough and fibrous. Thus the process is repeated, 
usually once, and sometimes—to produce a superior 
iron—twice or three times. By this process the metal 
is converted from a fusible, hard and brittle substance, 
as cast iron, into a tough, elastic bar; in fact, it has 
been rendered malleable, ductile, more closely com- 
pact, and of a fibrous texture, and is less fusible. It is 
also very tenacious, and added to its properties is a 
new and remarkable one, by virtue of which two pieces 
being heated similarly may be forged or welded to- 
gether. For purposes where lightness, strength, and 
durability ,are wanted, it is more extensively em- 
ployed than cast iron. In this state it is known in 
commerce as bar, or wrought iron. IRON 
225 
STEEL is composed of iron and carbon, and is some- 
times formed from wrought iron, by heating the latter 
in contact with carbon, and sometimes from cast iron, 
by depriving it of impurities, and all but a small per- 
centage of carbon. The proportion of carbon varies, 
of course, in the different qualities of steel; but in that 
used ordinarily the carbon rarely exceeds one and one- 
half per cent; for some purposes it is as low as one per 
cent. Good ordinary tool steel contains about one and 
one-half per cent of carbon. 
Different kinds of iron produce steel of different 
properties, and different qualities of steel are used 
for different purposes. 
To harden iron, add carbon. 
To harden steel, add tungsten, nickel, or chromium. 
For steel for magnets, add molybdenum. 
For steel with high electrical resistance, add nickel 
or chromium. 
For steel with good wearing qualities, add titanium. 
To make steel tough, add vanadium. 
There are two distinct processes employed for the 
production of steel, known as the Cementation Process 
and Bessemer’s Process.* By the latter process steel 
can be manufactured of any degree of hardness di- 
rectly from the cast iron, without the intermediate 
operation of making it malleable by puddling, etc. 
The principle of the process consists in directing a 
blast of cold air upon the molten cast iron contained 
in a “converterThe oxygen of the blast combines 
*There are many processes for the manufacture of steel, but these two 
processes are typical, and, generally speaking, all processes are but modi- 
fications of either one of these two ways—i. e., by adding a certain percent- 
age of carbon to a lightly carburized iron, such as wrought, iron; or by 
abstracting an amount of carbon from a heavily carburized iron, such as 
cast iron. 226 
PRACTICAL DENTAL METALLURGY 
with the carbon, silicon and manganese. Sulphur and 
phosphorus are difficult to remove by this process; 
hence the necessity of employing ores as free from 
these as possible. The intense combustion of the car- 
bon in the iron is attended with great elevation of tem- 
perature, so that the metal is maintained in a fluid 
state throughout the whole operation, solely by the 
energy of the reaction in the converter. Thus the 
cast or pig iron is decarburized, or converted into tool 
steel, or to mild welding steel, or to the state of mal- 
leable iron, according to the length of time the com- 
bustion is continued. It has been found, however, that 
a better quality of steel can be produced by continuing 
the decarburizing and purifying process until all, or 
as nearly all as possible, of the carbon and impurities 
are removed, and then adding to the fused wrought 
iron a certain quantity of a peculiar kind of white 
cast iron known as spiegel-eisen* ‘‘looking glass” iron, 
containing a known quantity of carbon and a little 
manganesium and silicon. 
Bessemer steel is largely used in the construction of 
railroads, bridges, armor plates for vessels, girders, 
etc., in the construction of edifices, the manufacture 
of machinery, tools, etc. 
The Cementation Process.—The furnace in which the 
iron is cemented and converted into steel, called a con- 
verting furnace, has the form of a large oven, con- 
structed so as to form in its interior two large and 
long cases commonly called troughs or pots and built 
*Spiegel-eisen is composed of the following: 
Iron 82-86 
Manganesium 10.71 
Silicon 1.00 
Carbon 4.32 IRON 
227 
of good fire-stone or fire-brick. Into each of these pots 
layers of the purest malleable iron bars, and layers of 
pulverized charcoal are packed horizontally, one upon 
the other, to a proper height and quantity, according 
to the size of the pots, leaving room every way in 
them for the expansion of the metal when it becomes 
heated. After the packing is completed, the tops are 
covered with a bed of sand or clay. This is to confine 
the carbon and exclude the atmosphere. The whole 
is then heated for eight or ten days, according to the 
degree of hardness required. Then the mass is left to 
cool for several days. 
The properties of the iron are remarkably changed 
by this process; it acquires a small addition to its 
weight, becomes much more brittle and fusible than 
originally, loses much of its ductility and malleability, 
but gains in hardness, elasticity and sonorousness. The 
texture, which was fibrous before, has now become 
granular; and its surface.is found to be covered with 
blisters, and it presents, when broken, a fracture much 
like inferior iron. Iron under this process has been 
shown to have taken up about 1 per cent of carbon. It 
is, however, far from being homogeneous in composi- 
tion, and is called blister steel. Uniformity of composi- 
tion is secured by subjecting bundles of the carburized 
iron bars to repeated blows from a steam hammer, at a 
welding heat, striking in rapid succession, until it closes 
the seams and removes the blisters. It is then termed 
shear steel. After this treatment is repeated, it is called 
double-shear steel. Homogeneity is best obtained, how- 
ever, by using the blister steel in crucibles, covering 
the mass with clay or some other substance to exclude 228 
PRACTICAL DENTAL METALLURGY 
air, and casting it into ingots. It is then designated as 
cast steel or crucible steel. 
Spring steel is blister steel simply heated and rolled. 
Case hardening is accomplished by heating such ar- 
ticles of forged, or bar iron, as it is desired to harden 
superficially in contact with some substance rich in car- 
bon and afterwards chilling them in water. Gun-locks 
are thus treated.* 
Red-short.—Sulphur when present in as small a pro- 
portion as 0.1 per cent serves to make the metal brittle 
and liable to fracture when worked or rolled at red 
heat, hence the term. 
Cold-short.—Phosphorus, when present, renders the 
steel brittle when cold. It serves, however, to neutral- 
ize the effect of sulphur; but steel containing phospho- 
rus is extremely difficult to temper. 
Harveyized steel, which is employed for armor plate 
on account of its extremely hard and resistant surface, 
is prepared by heating the steel plate to the melting 
point of cast iron and then tightly packing its surface 
with carbon; after it has taken up about 1 per cent 
of the carbon, the plate is dropped into water and 
cooled. 
Nickel Steel.—In 1889, M. Henry Schneider of Creu- 
sot, France, patented an alloy of steel and nickel. The 
alloy usually contains about 5 per cent of nickel, and 
is especially suitable for use in the construction of ord- 
nance, armor-plate, gun-barrels, and projectiles. It is 
said that ordinary steel is more readily acted upon by 
sea water than are the more impure grades of iron, but 
*The best temperature for case hardening is from 950° to 1000° C. This 
is only high enough to allow supersaturation of carbon at the surface of 
the steel. IRON 
229 
nickel steel is less liable to corrode in salt water than 
ordinary steel. 
Chrome Steel.—Chromium gives greater hardness, 
tensile strength, and elasticity to iron, but decreases 
its weldability. It is also stated that chromium steel 
is more susceptible of oxidation than ordinary steel. 
Chromium is added to iron by heating the mixed ox- 
ides of iron and chromium in a brasqued crucible with 
pulverized charcoal and fluxes. Chrome steel is then 
produced by melting chrome iron with wrought iron or 
steel in graphite crucibles. 
Manganese Steel.*—-When about 15 per cent of man- 
ganese is added to steel, it produces an alloy of great 
strength and toughness, and so hard that it is almost 
impossible to work the product by ordinary methods. 
The alloy is usually prepared by adding manganese 
iron to molten Bessemer, or open-hearth steel. From 
4 to 5 per cent of manganese gives to the alloy its ex- 
treme brittleness. Extremes of atmosphere, heat or 
cold, do not appear to affect the properties of manga- 
nese steel. When a piece of it is heated sufficiently to- 
be seen red hot in a dark room and is plunged into 
cold water, it becomes soft enough to be easily filed. 
Hardness is then restored by reheating to a bright red 
and cooling in air. The presence of manganese in 
proper proportions in nickel steel is said to very much 
improve it. Indeed, the best results are only obtained 
by the admixture. 
Copper Steel.—This alloy usually contains from 5 to 
20 per cent of copper, according to the purpose for 
which it is to be used. It possesses remarkable 
*Manganese steel is chiefly used for safes and rails. 230 
PRACTICAL DENTAL METALLURGY 
strength, tenacity, and malleability, and these proper- 
ties are still further developed by tempering. 
Aluminum Steel.—In amounts not greater than 1 per 
cent, aluminum is said to slightly increase the tensile 
strength and proportionally, the elastic limit, of rolled 
and cast steel. 
Arsenic, Antimony, Bismuth.—Arsenic in small quan- 
tities and bismuth in slightly larger quantities, im- 
proves the magnetic qualities and increases the electri- 
cal resistance of iron. The presence of antimony al- 
ways injures the mechanical strength of iron. 
Tungsten in small quantities produces an exceed- 
ingly hard steel, without the necessity of tempering. 
CARBURIZED IRON.—As has been previously 
hinted, carbon may be present in iron under two condi- 
tions. When iron is fused in contact with carbon, it is 
capable of combining with nearly 6 per cent of the lat- 
ter element, to form a white, brilliant, and brittle com- 
pound, which may be represented pretty nearly by 
Fe4C. Under certain circumstances, as this compound 
of iron and carbon cools, a portion of the carbon sepa- 
rates from the iron and remains disseminated through- 
out the mass in the form of minute crystalline particles 
very much resembling natural graphite. 
Iron containing the least possible carbon, and other- 
wise comparatively pure, is called wrought iron. 
Iron containing from 1.04 to 4.81 per cent of carbon 
is designated as cast iron. 
Iron containing from 0.15 to 1.04 (Bloxam) is con- 
sidered steel. “The portion of combined carbon within 
certain limits bears a direct relation to the tensile 
strength of the metal, variations as minute as .01 per IRON 
231 
cent, making a considerable alteration in this quality. 
The same is true of hardness, the effect of carbon up 
to a certain point being to increase tenacity and de- 
crease ductility, and also to cause the metal, when 
heated and suddenly cooled, to become more or less 
hard, the hardening being in direct proportion to the 
amount of carbon present and the rate of cooling.”* 
One and four-tenths per cent of carbon in iron pro- 
duces a highly carburized steel that must be worked 
with great care. It should not be heated above a 
cherry red, for fear of burning. Such steel is used for 
the manufacture of razors, and tools for cutting hard 
metals. 
Steel containing from 1 to 1.25 per cent of carbon is 
used for making most tools. 
Steel containing about 1 per cent of carbon can be 
welded readily, and a portion of a tool made of it can 
be made tough, so as to stand a blow from a hammer, 
without chipping, while another part can be hardened, 
as in the case of a cold chisel. 
GALVANIZED IRON.—Iron oxidizes so readily in 
the presence of moisture that some measures must be 
taken to prevent this corrosion when the metal is 
subjected to moist atmospheres. The common method 
is by galvanizing, though various pigments and 
hydrocarbon compounds are employed. A metallic 
coating to be protective must be electropositive to the 
underlying metal, and though copper, bismuth, tin, 
lead, cobalt, and nickel are such, none are so useful as 
zinc. The galvanic property becomes useful when 
the iron becomes exposed, since the current flows from 
*Kirk, American System of Dentistry, Hi, p. 900. 232 
PRACTICAL DENTAL METALLURGY 
the iron to the zinc, the latter being corroded rather 
than the former. 
There are three methods of galvanizing: (1) Hot 
galvanizing, or dipping the iron into molten zinc. (2) 
Wet galvanizing, or electroplating the zinc on the 
iron. (3) Dry galvanizing, or keeping the iron in con- 
tact with metallic zinc dust, plus “blue dust,” a by- 
product from the zinc smelter, in a drum at a certain 
temperature for a given length of time. The zinc 
alloys superficially with the iron, presenting a very 
tenacious coating, which resists corrosion well. 
HARDENING AND TEMPERING STEEL.—After 
soft steel has been shaped into the form of instrument 
desired, it may be made full hard, by first heating to 
redness and then immediately chilling by plunging into 
cool water, oil, or mercury. If, however, the hardened 
steel be heated to redness again and allowed to cool 
slowly, it returns to its soft condition. Any desired 
variation between these two extremes may be obtained 
by heating the steel to redness and quickly chilling it, 
thus obtaining the full hard state. If this be polished 
and heated gradually and carefully, it will be found to 
take on a succession of shades and colors, owing to the 
formation of a film of oxide which grows thicker and 
of deeper shade and color as the heating progresses. 
The temperature at which given degrees of temper are 
produced has been carefully determined, and the ex- 
perienced operator knows by the shade or color of the 
film of oxide the temper of the instrument operated 
upon, provided the piece is known to be steel and to 
have been full hard. IRON 
233 
The following table shows the approximate tempera- 
tures corresponding to the various shades and colors: 
Temperature 
Color 
Temper 
220° to 238° C. 
243° 
1 V'ery faint yellow 
| to pale straw.. 
Full yellow 
1 Lancets, razors, surgical in- 
| struments, enamel chisels... 
1 Excavators, very small cold 
| chisels. 
Pluggers, scissors, pen-knives. 
J Axes, plane irons, saws, cold 
| chisels. 
Table knives, large shears. 
Swords, watch springs. 
Fine saws, augers. 
Hand and pit saws. 
254° . 
265° 
1 Brown with pur- 
j pie spots 
276° 
287° 
292° 
Full blue 
315° 
Dark blue 
Since the amount of hardness which can be devel- 
oped in steel is directly in proportion to the amount 
of carbon and rate of cooling the article from the 
heated condition, and as pieces of steel vary greatly in 
their content of carbon, the temperature at which it is 
necessary to heat them before chilling must be deter- 
mined by actual experiment, in order to produce the 
greatest hardness. The piece should never be over- 
heated. It is better to err upon the side of under- 
instead of over-heating, for under the latter condition 
the steel is burned, presents a blistered, scaly appear- 
ance, and is incapable of taking a fine temper. When 
small instruments, such as burs, excavators, etc., are 
to be hardened, it is best to protect the surface of the 
steel with some substance to prevent a loss of carbon 
by oxidation in the heating. “Common soap answers 
admirably for this purpose,” says Dr. Kirk. 
The means of applying the heat to articles when they 
require hardening will, of course, depend upon the size, 
shape, and use of the article. They may be heated in 234 
PRACTICAL DENTAL METALLURGY 
the flame of a Bunsen burner, alcohol lamp, open fire, 
and sometimes it is best to enclose them in a sheet-iron 
ease with carbon, and heat in a suitable furnace; but 
for a more uniform degree of heat red-hot lead is 
probably better than any other means. 
In chilling, water is by no means essential, as the 
sole object is to extract the heat as rapidly as possible 
by good conduction; and the more suddenly the heat 
is extracted, the harder the steel will be; but if the 
hardness is not carried to an extreme, a certain amount 
of tenacity is also obtained with the hardness. 
Water with a small amount of acid or salt is some- 
times used, the former to aid in removing the oxide, 
and the latter to increase the conductivity. For ex- 
treme hardness mercury is used, which, on account of 
its superior conductivity, chills the piece immediately. 
TEMPERING.—A rod of good steel in its hardest 
state is broken almost as easily as a rod of glass of the 
same dimensions. This brittleness can only be dimin- 
ished by decreasing its hardness; and the management 
of this is called tempering. The surface of the steel is 
brightened and tried with a fine file to make sure of its 
full-hardness, and is then exposed to the heat, which, 
upon the appearance of the color desired and previously 
determined upon, is discontinued, and the article cooled 
by instantly plunging into cool water. The methods 
for applying the heat for tempering are as varied as 
those for hardening. The heat for this purpose should 
be slowly applied; indeed, it is said that the slower the 
heating, the tougher and stronger will be the steel. 
The article may be placed upon a hot iron plate, upon 
the surface of melted lead, or in a bath of a more 
fusible alloy (previously coating the instrument with ffiON 
235 
a solution of ochre in water, or liquid silex to prevent 
the adhesion of the molten metal), in hot sand, a gas 
stove, or in almost any place where sufficient tempera- 
ture may be gradually obtained, without injury to the 
steel. 
The following table of alloys of lead and tin may be 
conveniently used to secure a uniform temper: 
Composition 
Melting Points 
Degrees C. 
Lead 
Tin 
7. 
4 
210° 
7.5 
4 
221° 
8.5 
4 
232° 
10. 
4 
243° 
14. 
4 
254° 
19. 
4 
265° 
30. 
4 
276° 
48. 
4 
287° 
50. 
4 
293° 
Boilina- oil. . . 
315° 
When instruments are only partially dipped and 
afterwards tempered by the heat from the back, they 
must be cooled in water, or other substance, instantly 
on the cutting part attaining the desired color; other- 
wise the body of the instrument will continue to supply 
heat, and the cutting part may become too soft. In 
the case of excavators, enamel chisels, and cutting in- 
struments with slender, tapering shanks, terminating 
in a fine cutting edge, the edge must be protected from 
the heat while tempering the shank, the latter being 
drawn to a blue, a state much too soft for the former. 
The point or edge may be protected by placing against 
a large piece of cold iron or other substance, which, on 
account of its conduction, prevents the heating of the 
end of the instrument. 236 
PRACTICAL DENTAL METALLURGY 
Rubber-dam clamps are best tempered a blue spring 
by what is known as blazing off. This is accomplished 
by dipping them in oil, and then burning the oil off. 
COMPOUNDS WITH OXYGEN.—Iron forms three 
compounds with oxygen: 
Monoxide, Ferrous Oxide, FeO, is a very powerful 
base, but is almost unknown in the separate state on 
account of its tendency to absorb oxygen and pass into 
the sesquioxide. 
Sesquioxide, or Ferric Oxide, Fe203, is a weak base 
and occurs native in most beautiful crystals as specular 
iron ore; also as red and brown hematite. It may be 
artificially prepared by precipitating a solution of ferric 
sulphate or chloride with excess of ammonia, washing, 
drying and igniting the yellowish-brown hydrate thus 
produced. It is of a red color, the tint varying with the 
temperature at which it has been exposed. It occurs 
commercially under the name of colcothar jeweler’s 
rouge, and Venetian red, which is obtained by calcining 
the green sulphate of iron— 
2 (FeO.SOg) = Fe203 + S02 + S03. 
It is dissolved in acids with difficulty, forming a 
series of reddish salts. 
Triferro-tetroxide, Ferroso-ferric Oxide, Fe304, is also 
called black iron oxide, magnetic oxide, and loadstone. 
It occurs native, and is one of the most valuable of 
the iron ores. It is the chief product of the oxidation 
of iron at a high temperature in the air and in aqueous 
vapor. 
ACTION OF ACIDS ON IRON.—Iron dissolves in 
the acids, and the carbon which it always contains, so 
far as combined in the carbide of iron, passes off as IRON 
237 
carburetted hydrogen, and so far as uncombined will 
remain undissolved, as graphite. 
In dilute sulphuric acid iron dissolves, forming fer- 
rous sulphate, liberating hydrogen— 
Fe + H2S04 = FeS04 + H2. 
In hydrochloric acid it dissolves, to form ferrous 
chloride, with liberation of hydrogen. 
In nitric, cold and dilute, it is soluble, forming ferrous 
and ammonium nitrate— 
4Fe + IOHNO3 = 4Fe (N03) 2 + H4NN03 + 3H20, 
and in warm, dilute nitric to form ferric nitrate, liberat- 
ing nitric oxide— 
2Fe + 8HN03 = Fe2 (NOa) 6 + 2NO + 4H20. 
ALLOYS.—Iron combines with many of the metals. 
None of its alloys are of any great importance. 
With mercury, iron cannot be made to combine di- 
rectly, yet Bloxam claims that it forms a chemical 
combination with this element, having the formula 
FeHg. The combination is effected by adding a little 
amalgam of sodium to the metallic mercury. The 
amalgam may also be prepared by “rubbing together 
very finely divided iron with mercuric chloride and 
water and a few drops of metallic mercury. Pure 
amalgam of iron forms lustrous white crystals, which, 
however, soon become coated with rust. By lying in 
the air the iron contained in the amalgam is in a short 
time converted into ferric oxide, which floats upon the 
metallic mercury.”* 
*Brannt, Metallic Alloys, p. 363. 238 
PRACTICAL DENTAL METALLURGY 
It alloys somewhat with the noble metals; also with 
tungsten, titanium, chromium, and manganesium. 
An alloy of cast iron 79, tin 19.50, and lead 1.50, may 
be used as a casting metal, giving fine impressions, fill- 
ing the molds, and being malleable to a certain extent. 
Arnold’s Iron Alloy.—Crude cast iron, 100; soda, 1; 
copper, 1; tin, 5 ; antimony, 5 ; and zinc, 5. A compact 
and malleable alloy, capable of taking a fine polish, 
and resisting the corrosive action of sea water. It is 
used for ship propellors. 
Marie’s Nonoxidizable Alloy.—Iron, 10 parts; nickel, 
35; brass, 25; tin, 20, and zinc, 10. 
TESTS FOR IRON IN SOLUTION.—Ferrous salts.— 
The solutions are green, and hydrogen sulphide pro- 
duces no precipitate in an acid solution, but may give 
a slight one in a neutral solution. 
Ammonium sulphide gives a black precipitate of fer- 
rous sulphide, insoluble in excess of the precipitant. 
Potassium ferricyanide is the characteristic test; it 
throws down a deep blue precipitate (Turnbull’s blue). 
2K3FeCN6 + 3FeCl2 = 6KC1 + Fe3(Fe2CN6)2. 
Ammonia throws down hydrated ferrous oxide (the 
antidote for arsenic*). This is, at the moment of for- 
mation, white, but passes rapidly through the shades of 
light green, dark green, and ultimately brown, the lat- 
ter being an indication of its conversion into ferric 
oxide. 
*It should be the invariable rule of everv dentist to keep on hand in his 
office the materials for preparing this antidote, for an emergency, as it 
should be freshly prepared at the time of need. A very efficient antidote 
may be prepared by precipitating the tincture of the chloride of iron with 
bicarbonate of sodium. IRON 
239 
Ferric Oxide.—Potassium ferrocyanide is a charac- 
teristic test, producing a precipitate of Prussian blue. 
3[K4Fe(Cn)6] + 4FeCl3 = 12KC1 + Fe4[Fe(Cn)6]3 
Final Test: Add Hydrogen sulphide, H2S, to the 
acidified solution and filter. To the filtrate add ammo- 
nium sulphide (NH4)2S, and filter. Dissolve precipi- 
tate in hydrochloric acid, IICL, and add ammonium 
hydroxide, NH40H. Filter and dissolve precipitate in 
HCL, and add sodium hydroxide, NaOH. Brown pre- 
cipitate shows presence of iron. Add HCL to brown 
precipitate and add potassium sulpho-cyanide, KSCN. 
Red color shows iron. CHAPTER N1Y 
ALUMINUM 
Aluminum. 
Valence III. 
Atomic weight, 27. 
Melting point, 658° C. 
Ductility, 7th rank. 
Conductivity (heat), 34.35. 
Symbol, Al. 
Specific gravity, 2.583 at 4°. 
Malleability, 4th rank. 
Tenacity, good. 
Chief ore, cryolite. 
Conductivity (electricity), 63.0. 
(Silver being 100.) 
Specific heat, 0.2220. 
Color, bluish-white. 
Crystals, octahedral. 
OCCURRENCE.—With the exception of silicon and 
oxygen, aluminum is the most abundant element in 
the earth’s crust. It is never found in the free or 
metallic state, but occurs combined with silicon and 
oxygen, as marl, clay, slate, pumice stone, feldspar, 
mica, and nearly all rocks, with the exception of lime- 
stone and sandstone. As the crystallized oxide— 
alumina—it occurs as corundum, emery, ruby, sapphire, 
emerald, topaz, and amethyst, which are used as gems. 
The metal is further found in combination with nearly 
two hundred different minerals. Dana gives the form- 
ula for the principal ores as: 
Cryolite Na3AlF6 
Corundum A1203 
Gibbsite Al(OH)3 
Bauxite A120(0H)4 
Kaolin H4Al2SiO„ 
Feldspars KAlSi3Os 
NaAlSi308 
CaAl2Si203 
240 ALUMINUM 
241 
REDUCTION.—It was first isolated in 1827 by 
Wohler, who obtained it as a gray powder by decom- 
posing aluminum chloride with potassium. It re- 
mained a laboratory product until St. Claire Deville, 
about 1858, succeeded in improving the mode of pro- 
duction, so as to render the operations capable of man- 
agement on a manufacturing scale. The process con- 
sists in heating to a red heat the double chloride of 
aluminum and sodium with metallic sodium. A vigor- 
ous action takes place, chloride of sodium being formed 
and the metallic aluminum separated— 
AlCl3.NaCl + 3Na = A1 + 4NaCl. 
The chemical processes are now practically replaced 
by electrolytic methods of reduction. 
Chas. M. Hall,* an Ohio college student, conceiving it 
possible to extract aluminum from its ores by elec- 
trolysis, set to work to accomplish the task. Recogniz- 
ing the impossibility of attaining practical results from 
an aqueous solution, he sought other solvents, and 
finally discovered that a melted bath of the double 
fluorides of aluminum and metals more electropositive 
than aluminum, such as sodium or calcium, was a per- 
fect solvent for alumina, the oxide of aluminum, tak- 
ing it up as hot water dissolves sugar, and dissolving 
as much as 25 per cent of its weight. Having found an 
anhydrous solvent for alumina, the discoverer next 
sought to ascertain whether the solution would yield 
up the aluminum promptly to electrolysis. Great sue- 
*On January 20, 1911, Chas. M. Hal! received the Perkins medal, granted 
to a chemist residing in the United States for valuable work in applied chem- 
istry. His company, the Aluminum Company of America, has five large 
plants, consuming 140,000 horse power of electricity, more than any other 
single company in the world. The annual output in 1910 was 40,000,000 
tons and the price has dropped from $90.00 a pound in 1855 to 22 cents a 
pound in 1910. 242 
PRACTICAL DENTAL METALLURGY 
cess attended his experiments in this particular and by 
superior intelligence and great patience Hall worked 
out the practical application of his discovery. At 
present his company has two plants at Niagara which 
combined are capable of yielding about 10,000 pounds 
in twenty-four hours. 
PROPERTIES.—Aluminum is a bluish-white metal 
somewhat resembling silver in appearance. It ranks 
fourth in malleability, seventh in tenacity, and ranks 
next to gold in the conduction of heat and electricity. 
It is harder than tin, but softer than copper. By ham- 
mering in the cold it may be made as hard as soft iron, 
but is softened again by fusion. It is remarkably 
sonorous, and has been used for making bells. It is 
one of the lightest of metals, being approximately only 
2y2 times heavier than water, and *4 the specific grav- 
ity of silver. It fuses at 658° C., and when cold oxi- 
dizes superficially on exposure to the air. It has no 
action on water at ordinary temperatures, nor is it acted 
upon by the compounds of sulphur, thus preserving its 
luster where silver would tarnish and blacken. It is 
without odor or taste. 
Aluminum may be melted in an ordinary clay cruci- 
ble, using zinc chloride as a flux. Aluminum oxide 
forms as a thick pasty mass, is impossible to skim, and 
when it enters the castings weakens them. Dry ZnCl2 
is used in small pieces, stirring each time, until surface 
is mirrorlike, when enough has been used. The black 
dross should be skimmed before casting. 
IN THE ARTS aluminum is used in the manufacture 
of weights of small denomination, such as the milligram. 
Its low specific gravity renders it particularly well 
adapted to such use. It is further used, on account of ALUMINUM 
243 
its lightness and resistance to atmospheric action, for 
the manufacture of delicate physical', mathematical, 
and optical apparatus, as well as ornamental articles, 
such as medallions and badges of a souvenir character; 
also for parts of bicycles, tablewear, and cooking uten- 
sils.* The apex of the Washington Monument is of 
highly polished aluminum. 
IN DENTISTRY this metal is employed as a base 
for artificial dentures. Its many valuable properties, 
chiefly conductivity, lightness, malleability, cheapness, 
and unalterableness in dry or moist air, render it ap- 
plicable for such a purpose. The base is swaged be- 
tween a zinc die and a lead counterdie, but will not 
stand the rough swaging usually given to gold or plati- 
num. Caution must be used to prevent contamination 
with the lead or zinc. It being difficult to determine 
during the progress of the conformation whether or not 
any contamination has occurred, the pattern is best 
swaged betAveen sheets of thin tissue paper, removing 
the paper as it becomes broken. The metal should be 
occasionally annealed by coating with pure sweet-oil 
or talloAv and passing through the flame until the oil 
or fat is carbonized, when at the moment the last trace 
of black (carbon) disappears from the metal, it may be 
dropped into water. Before applying the oil and an- 
nealing, however, the metal should be thoroughly 
brushed Avith pumice stone, to remove any contaminat- 
ing lead or zinc which might otherwise become alloyed 
with the base, causing small holes or pits to appear on 
its surface, or perhaps the occurrence of galvanic 
action. A simpler and cleaner method of annealing is 
'Experiments to determine the effect of food upon cooking utensils 
showed that aluminum was strongly attacked by NaHCOg, MgSo* and min- 
eral waters only. 244 
PRACTICAL DENTAL METALLURGY 
to heat the metal in a Bunsen flame until it is hot 
enough to show a streak of carbon when a dry pine 
stick is rubbed across it. Then cool it slowly. 
Vulcanite is attached to such a base by spurs made 
with a sharp-pointed graver, countersunk holes, or 
loops made with a punch along the alveolar ridge. 
After waxing up the denture the base may be varnished 
to protect it from the plaster during vulcanization, 
after which the varnish is removed with alcohol, and 
the plate polished Avith pumice stone and whiting, but 
it cannot be well burnished. 
The process of making cast aluminum dentures was 
first introduced by Dr. J. B. Bean of Baltimore, who 
cast the metal through tall conduits lined with clay 
and attached to the gates of his flask, the entire appa- 
ratus being first heated to an elevated temperature. 
The pressure of the column of metal thus produced 
overcame the sluggish flow due to an inherent lack of 
fluidity and lightness of the metal, and forced it into the 
finer parts and irregularities of the mold. 
The cast bases were abandoned for a long time be- 
cause of corrosion and decomposition in the mouth, but 
with the advent of improved methods of casting the 
use of cast aluminum for dentures has been revived 
with success. 
THE COMPOUND WITH OXYGEN.—Aluminum 
oxide, Alumina, the Sesquioxide of Aluminum, A1203, 
is found crystallized in hexagonal prisms in nature, as 
ruby, sapphire, corundum,* etc., colored by admixtures. 
It may be prepared by treating a solution of alum with 
*Cbemical formulae of some of the oxides of aluminum: 
Corundum (Ruby and sapphire the same) AI2O3. 
Garnet (CaMgFeMn)3Al..S:-0.2. 
Cyanite AUSiOb. ALUMINUM 
245 
an excess of ammonia, by which an extremely bulky, 
white, gelatinous precipitate of aluminum hydrate is 
formed. This is wrnshed, dried, and ignited to white- 
ness. Thus obtained, alumina constitutes a white, taste- 
less, feebly basic coherent mass, very little acted upon 
by acids, and fusible in the oxyhydrogen flame. Emery 
is impure corundum, containing iron and aluminum 
oxides. 
Feldspar is regarded as the double silicate of po- 
tassium and aluminum, a natural glass and as having 
the formula Al203.K20.6Si02. It is much used in the 
preparation of bodies, frits and enamels for the manu- 
facture of porcelain. 
Kaolin, china clay, is known as a hydrated silicate of 
aluminum (2Al203.3Si02) + 3II20, and is the purest 
form of clay. It results from the decomposition of 
feldspar by the weathering out of the potassium hy- 
droxide (KOH). It is practically infusible and forms 
the refractory substance of fine porcelain, being much 
used in the preparation of bodies for the manufacture 
of dental porcelain. 
Porcelain.—The typical porcelain may be regarded 
as a fused mixture of the fusible feldspar, binding to- 
gether the particles of the infusible kaolin in a homo- 
geneous mass. 
ACTION OF ACIDS AND ALKALIES ON ALUMI- 
NUM.—Sulphuric acid, concentrated and boiling, dis- 
solves aluminum, but it is not soluble in the dilute acid. 
Nitric acid does not affect aluminum. 
Hydrochloric acid, hot or cold, readily dissolves it, 
forming aluminum chloride, and evolving hydrogen— 246 
practical dental METALLURGY 
2A1 + 3HC1 — A1C18 + 3H 
2A1 + 6HC1 — A12C16 + H0. 
In Potassium or sodium hydrate it is soluble, form- 
ing aluminates and liberating hydrogen— 
A1 + 3KOH = K3AIO3 + 3'H. 
ALLOYS.—Aluminum alloys with nearly all metals, 
except lead; indeed, the wonderful alloys it is capable 
of producing gives it, perhaps, its greatest value. 
Aluminum may be melted in a graphite crucible with- 
out flux, but great care must be taken not to heat it 
too hot. On account of its high specific and latent heat, 
aluminum requires a long time to melt; but, unlike some 
other metals, it soon becomes fluid after the melting 
point is reached. 
With mercury alone aluminum is said to form an un- 
stable amalgam. The experiments made by Dr. Black 
showed aluminum in the proportion of 1 to 5 per cent 
in silver-tin amalgam alloys to so increase the expan- 
sion in amalgams made of them as to exclude this metal 
as a component in dental-amalgam alloys. Mercury in 
contact with aluminum tends to expose the latter to 
the action of the air, probably by destroying the super- 
ficial oxide of aluminum which normally prevents fur- 
ther oxidation. This action will continue until the 
surface of the aluminum is deeply pitted or eroded, 
and is marked by repeated growths of aluminum oxide 
at the point of contact. 
Gold and aluminum unite, forming a hard and brit- 
tle alloy. One per cent of aluminum in gold destroys 
the ductility of the noble metal and gives it a green- 
ish cast; 5 per cent of aluminum with gold yields an 
alloy brittle as glass, and 10 per cent of aluminum ALUMINUM 
247 
produces a grayish white, crystalline and brittle alloy. 
Niirnberg gold, an alloy, for cheap goldware, very 
much resembling gold, and unchanged in air, is com- 
posed of aluminum 7.5, gold 2.5, and copper 90 parts. 
Silver and aluminum readily unite, forming alloys 
of beautiful whiteness and unchangeable on exposure 
to air. Their hardness is considerably greater than 
aluminum, but they are more easily worked. An alloy 
of 100 parts of aluminum and 5 parts of silver differs 
but little from pure aluminum, save that it is consider- 
ably harder and takes a beautiful polish. An alloy of 
aluminum 169 parts and silver 5 parts possesses con- 
siderable elasticity, and has been recommended for 
springs, dessert and fruit knives. Equal parts of the 
two metals produce an alloy equal to that of bronze in 
hardness. 
Copper and aluminum form some exceedingly im- 
portant alloys, differing according to the quantity of 
aluminum they contain. Those of a small content of 
copper cannot be used industrially. With 60 to 70 
per cent aluminum they are very brittle, glass-hard, 
and beautifully crystalline. With 50 per cent the alloy 
is quite soft; but under 30 per cent of aluminum the 
hardness returns. The usual alloys are 1, 2, 5, and 10 
per cent of aluminum. These are known as aluminum 
bronze. The 10 per cent bronze has a bright golden 
color, and retains its polish when exposed to air; it 
may be easily engraved, exhibits a great elasticity, and 
can be easily soldered with 18-carat gold solder. When 
first made, it is brittle, acquiring its best qualities after 
three or four meltings, after which it may be melted 
several times without sensible change. It casts well in 
molds, but shrinks greatly. It has a specific grav- 248 
PRACTICAL DENTAL METALLURGY 
ity of 7.68, about equal to soft iron. Its strength when 
hammered will equal that of the best steel. Annealing 
makes it soft and malleable. It does not clog a file, 
and may be drawn into a wire. It melts at about 
927° C. 
Aluminum bronze as a base for artificial dentures: 
In the proportion of aluminum 10 and copper 90 it 
oxidizes but superficially in the mouth, and is as strong 
and resistant to attrition as 18-carat gold, it may be 
swaged as easily as 20-carat gold, but it must be an- 
nealed frequently, and it is necessary to carry the 
heat almost to whiteness, for if the bronze be merely 
heated until it assumes a dark-red color, it remains as 
hard as before. 
Zinc is the cheapest known hardener of aluminum. 
It increases rigidity and strength up to 15 per cent 
zinc. Zinc chloride is the best flux for molten alumi- 
num, the metal subsequently showing a trace of zinc. 
An analysis of the alloys used in the construction of 
Zeppelins shows: aluminum, 88 to 90 parts; zinc, 7 to 
9 parts; copper, 7 to 9 parts, and a small amount of 
tin, iron, silicon, and manganese. 
Aluminum and magnesium produce an alloy with a 
specific gravity of about 1.75. It is hard, can be 
turned and drilled, is much tougher than brass and has 
a tensile strength equal to it, yet is extremely mal- 
leable. It can be drawn into wire and rolled and beaten 
like silver. 
Solders.—There is no solder which operates with 
aluminum in the same way that ordinary solders operate 
with copper, tin, etc. The reasons are because alumi- 
num does not alloy readily with other metals at low 
temperatures, and its surface becomes coated with an ALUMINUM 
249 
invisible oxide, very refractory, and insoluble in al- 
most everything except hydrofluoric acid. This oxide 
must be removed by mechanical abrasion while the 
solder is in position in a fluid state. 
A steel or brass scratch brush may be used while the 
solder is in a molten state. Zinc appears to alloy more 
readily with aluminum than any other metal. Tin, 
zinc and a very small proportion of aluminum is a very 
effective solder. It requires a blast flame and does not 
run freely. It will not flow by capillary attraction, 
and enough solder must be placed on the joint to sweat 
it together before bringing edges in contact. 
Wm. Frismuth of Philadelphia recommends the fol- 
lowing solders for aluminum, with vaseline as the flux: 
SOFT SOLDER 
Pure Block Tin from 90 to 99 parts 
Bismuth “ 10 “ 1 “ 
HARD SOLDER 
Pure Block Tin from 98 to 90 parts 
Bismuth “ 1 “ 5 “ 
Aluminum “ 1 * ‘ 5 “ 
Schlosser recommends the following for dental 
laboratory use: 
PLATINUM-ALUMINUM SOLDER 
Gold 30 parts 
Platinum 1 ‘ ‘ 
Silver 20 “ 
Aluminum 100 “ 
Gold 50 parts 
Silver 10 “ 
Copper 10 “ 
Aluminum 20 “ 
GOLD-ALUMINUM SOLDER 250 
PRACTICAL DENTAL METALLURGY 
0. M. Thowless has patented the following solder for 
aluminum and method for applying it. 
Tin 55 parts 
Zinc 23 “ 
Silver 5 “ 
Aluminum 2 “ 
First melt the silver and aluminum together, then 
add the tin and zinc in the order named. The surfaces 
to be soldered are immersed in dilute caustic alkali or 
a cyanide solution, and then washed and dried. They 
are next heated over a spirit lamp, coated with the 
solder, and clamped together, small pieces of solder 
being placed at the points of union; the whole is then 
heated to the melting point. No flux is used. The 
following are useful as solders: 
I 
II 
III 
Zinc 
85 parts 
92 parts 
Aluminum 
20 “ 
15 “ 
8 “ 
The flux used in soldering is composed of 3 parts 
balsam of copaiba, 1 part Venetian turpentine, and a 
few drops of lemon juice. The soldering iron is dipped 
into the mixture. 
Another solder for aluminum, recommended by the 
Scientific American, is composed of the following: 
Cadmium 50 parts 
Zinc 20 “ 
Tin 30 “ 
The zinc is first melted in a suitable vessel; then the 
cadmium is added, and then the tin, in small pieces. 
The proportions of the various ingredients may be 
varied, in accordance with the use to which the article 
is put. For instance, when a strong and tenacious sol- 
dering is required, a larger proportion of cadmium cq.n Aluminum 
251 
be used; where great adhesion is desired, a large pro- 
portion of zinc should be used, and where a nice and 
durable polish is desired, a greater per cent of tin 
should be used. 
An alloy of zinc, copper, and aluminum has been in- 
troduced as a dental base. It is said to be unaffected 
by the oral fluids. 
Tin and aluminum form alloys little affected by 
acids. With 100 parts aluminum and 10 parts tin an 
alloy is produced much whiter than aluminum and but 
little heavier. It can be welded and soldered like 
brass. 
Iron and aluminum unite readily. Ostberg, a Swed- 
ish inventor, discovered that an exceedingly small con- 
tent of aluminum (0.005 of 1 per cent) in wrought 
iron served to lower its fusing point about 500° F., so 
that castings may be made from it as readily as from 
the highly carburized cast iron. Iron may be coated 
with aluminum much as it is with tin. 
Zinc and aluminum unite to form alloys very useful 
for soldering the latter. They are prepared by first 
melting the aluminum and adding the zinc gradually, 
after which some fat is introduced to prevent oxida- 
tion, and the alloy is stirred rapidly with an iron rod. 
Aluminum may be frosted by immersion in a solution 
of potassa. 
TESTS FOR ALUMINUM IN SOLUTION.—Hydro- 
gen sulphide does not produce a precipitate when 
added to a solution of a salt of aluminum. 
Ammonium hydrosulphide produces a white precipi- 
tate of aluminum hydrate and evolves sulphuretted 
hydrogen. 252 
PRACTICAL DENTAL METALLURGY 
Ammonium hydroxide throws down a bulky, gelatin- 
ous aluminum hydroxide, slightly soluble in the pre- 
cipitant. 
Final Test: Add hydrogen sulphide, H2S, to the acid- 
ified solution and filter. To the filtrate add ammonium 
hydroxide, NH40H, till it becomes alkaline and add 
H2S. Filter and dissolve the precipitate in hydro- 
chloric acid and add sodium hydroxide, NaOH. Filter 
and acidify the filtrate with nitric acid, HN03, and 
add NH40H. White gelatinous precipitate indicates 
aluminum, Al(OH)3. CHAPTER XY 
MERCURY 
Hydrargyrum. 
Valence, I, II. 
Atomic weight, 200.6. 
Melting point, —38.85. 
Boiling point, 357.3° C. 
Conductivity (heat), 1.48. 
Specific heat, 0.0337 at 0° C. 
Color, silver-white. 
Symbol, Hg. 
Specific gravity, 13.595. 
Malleable at —38.85 C. 
Conductivity (electricity), 1.6. 
Chief ore, cinnabar. 
Crystals, octahedral at —39° C. 
OCCURRENCE.—Mercury occurs in nature chiefly 
as the red sulphide, HgS, cinnabar, which, as a rule, is 
accompanied by more or less of the reguline metal. The 
most important mercury mines of Europe are those of 
Almaden, Spain, and of Idria, in Illyria; it is also found 
in China, Mexico, Corsica, Peru, and California. The 
European mines, until lately, furnished the bulk of the 
mercury of commerce, but they have been eclipsed by 
the rich deposits of New Almaden, near San Jose, Cali- 
fornia. The mines of the latter have been the most 
productive in the world, yielding more than 3,000,000 
pounds annually, and large quantities are still taken 
from them. The California cinnabar is richer in mer- 
cury, because purer, than the Spanish, the former yield- 
ing about 70, the latter about 38 per cent of mercury. 
Mercury is also found free; forming an Amalgam with 
silver and in the form of protochloride (native calomel). 
REDUCTION.—The metal is obtained almost exclu- 
sively from the sulphide or native cinnabar, and is ex- 
tracted by two principal methods. By the first 
253 254 
PRACTICAL DENTAL METALLURGY 
method the mineral is picked, crushed, and mixed with 
lime. The mixture is then introduced into cast-iron 
retorts, which are placed in rows, one above the other, 
in an oblong furnace and connected with earthenware 
receivers, one-third full of water. Heat is applied, the 
lime combines with the sulphur, forming the sulphide 
and sulphate of calcium— 
4HgS + 4CaO = 3CaS + CaS04 + Hg4, 
while the mercury distills over, and is condensed in 
the receivers. In the second method the decomposition 
of the cinnabar is effected by the direct exposure of 
the ore to the oxidizing flame of the furnace, and the 
mercury vapor is recovered in more or less imperfect 
condensers. 
PURE MERCURY.—The commercial article, as a 
rule, is quite pure chemically, and only needs to he 
forced through chamois skin to be fit for ordinary pur- 
poses; but it frequently contains foreign metals, such 
as lead, tin, zinc, and bismuth. It is seldom inten- 
tionally adulterated. When impure, the metal has a 
dull appearance, leaves a trace on white paper, is 
deficient in due fluidity and mobility, which is shown by 
its inability to form perfect globules, is not totally dis- 
sipated by heat, and, when shaken in a glass bottle, 
coats the sides with a pellicle, or, if very impure, de- 
posits a black powder. If agitated with strong sul- 
phuric acid, the adulterating metals become oxidized 
and are dissolved, thus the metal may be to a limited 
extent purified. 
Detection of Lead.—Lead may be detected by shak- 
ing the suspected metal with equal parts of acetic acid 
and water, and then testing the acid with sulphate of MERCURY 
255 
sodium, or iodide of potassium. The former will pro- 
duce a white, the latter a yellow, precipitate, if lead 
be present. 
Detection of Bismuth.—Bismuth is shown by drop- 
ping a nitric acid solution of the mercury, prepared 
without heat, into a quantity of distilled water, when, 
if bismuth be present, the subnitrate of bismuth will 
be precipitated. 
I 
Detection of Tin.—Complete solubility of the metal 
in nitric acid shows the absence of tin. 
Lead is the chief impurity, and may be removed by 
exposing thin layer of the metal to the action of nitric 
acid diluted with twice the quantity of water, which 
should well cover the surface and remain a day or two, 
with frequent stirring. The lead is much more easily 
oxidized and dissolved than the mercury, though some 
of the latter also passes into solution. The mercury is 
afterwards well washed with water, and dried first 
with blotting paper, then by gentle heat. In the same 
manner most of the other metallic impurities are 
removed. Mercury for dental use should, however, be 
purified by redistillation. 
Chemically. pure mercury may be obtained by de- 
composing pure mercuric oxide by heat, and washing 
the condensed metal with dilute nitric acid. 
PROPERTIES.—Mercury or quicksilver, as it is 
often called, is of a silver-white color, liquid at ordi- 
nary temperature (above —38.85), odorless and taste- 
less. It is volatile at ordinary temperatures, but more 
rapidly volatilizes as the temperature increases. At 
357.3° C. it boils, being finally volatilized without resi- 
due. When globules are dropped upon white paper, 256 
PRACTICAL DENTAL METALLURGY 
they should roll about freely, without tailing, retaining 
their globular form. It should be perfectly dry, and 
present a bright surface. When perfectly pure it un- 
dergoes no alteration by the action of the air or of 
water, but in the ordinary state it will exhibit a slight 
tarnish. It solidifies at —38.85° with considerable con- 
traction into a compact mass of regular octahedra, 
which can be cut with a knife, or flattened under the 
hammer. 
USES.—It is constantly required in the chemical lab- 
oratory, and is greatly used in the construction of 
thermometers, barometers, and manometers, for the 
determination of the capacity of vessels, and for many 
other purposes. 
In medicine, in the uncombined state, it is inert, but 
in combination acts as a peculiar and universal stimu- 
lant. When exhibited in the finely divided state, it 
forms several preparations, producing peculiar effects; 
this fact, however, does not prove that the uncombined 
metal is active, but that in minute division it is favor- 
able to chemical action and combination. Rubbed up 
with chalk, mercury forms hydrargyrum cum creta; 
with the confection of roses and licorice, massa hydrar- 
gyri; with lard and suet, unguentum hydrargyri. 
Mercurial poisoning, ptyalism, salivation, is first ob- 
servable by a coppery taste, a slight soreness of the 
gums, and an unpleasant sensation in the alveoli of 
the teeth, when the jaws are firmly closed. 
In dentistry mercury is used to form alloys known 
as amalgams. (See chapter on Amalgams.) 
COMPOUNDS WITH OXYGEN.—Monoxide, or 
Mercuric Oxide, HgO, perhaps more commonly known as 
red oxide of mercury, or red precipitate. The compound MERCURY 
257 
may be prepared by several methods, the most promi- 
nent of which are: First, by exposing mercury in a glass 
flask with a long, narrow neck, for several weeks, at a 
temperature of about 315° C. The product of such ex- 
posure and heat is highly crystalline and of a dark red 
color. Second, as it is generally prepared, by cautiously 
and thoroughly heating any of the mercuric or mer- 
curous nitrates to complete decomposition, which lat- 
ter fact is recognized by the absence of the character- 
istic red fumes and odor of nitric oxide. By this 
means the acid is decomposed and expelled, oxidizing 
the metal to the maximum if it happens to be in the 
state of mercurous salt. The product thus obtained is 
also crystalline and very dense, but of a much paler 
color than the preceding. While hot, it is nearly black. 
Third, by adding caustic potash in excess to a solution 
of mercuric chloride, by which a bright yellow pre- 
cipitate of mercuric oxide is thrown down. This pre- 
cipitate is destitute of crystalline character, and much 
more minutely divided than the two preceding. 
The monoxide is only slightly soluble in water, com- 
municating to the latter an alkaline reaction and metal- 
lic taste; it is highly poisonous. When strongly heated, 
it is decomposed into mercury and oxygen gas. 
Mercurous Oxide, IIg20; Suboxide or Gray Oxide of 
Mercury, may be prepared by adding caustic potash to 
mercurous nitrate. It is a dark gray, nearly black, 
heavy powder, insoluble in water, slowly decomposed 
by the action of light into metallic mercury and the 
red oxide. 
ACTION OF ACIDS ON MERCURY.—Hydrochloric 
acid does not attack mercury. 258 
PRACTICAL DENTAL METALLURGY 
Sulphuric acid, boiling, converts it into mercurous 
sulphate, liberating sulphur dioxide. 
Nitric acid, is the most effective solvent for mercury. 
It dissolves readily in the dilute acid if heated, or in 
the cold, if nitrous acid is present; with the strong 
acid, heat is soon generated, and with considerable 
quantities of the material the action acquires an ex- 
plosive violence. At ordinary temperatures, dilute 
nitric acid, when applied in slight excess, produces 
chiefly normal mercurous nitrate, but when the mer- 
cury is in excess, more or less of basic mercurous 
nitrate is formed; hot dilute nitric acid, in excess, 
forms chiefly mercuric nitrate; when the mercury is in 
excess, both basic mercurous and basic mercuric ni- 
trates are formed. In all cases, chiefly nitric oxide gas 
is evolved. 
ALLOYS.—Mercury unites readily with most metals 
except iron and platinum. With the former it has been 
found to unite only indirectly; for example, by rubbing 
very finely divided iron with mercuric chloride, water, 
and a few drops of metallic mercury. The latter metal 
can only be combined in the spongy state. Yet both of 
these metallic elements combine chemically with mer- 
cury to form definite compounds, according to Bloxam 
and other authorities, and present the composition, 
FeHg and PtHg2, respectively. 
Of gold and mercury, Dr. H. H. Burchard,* in an 
exceptionally able paper, quotes: 
“A gold amalgam 1 to 1000 has all the fluid mercury 
expressed through chamois; the residue treated with 
dilute nitric acid at a moderate heat. A solid amalgam 
’Dental Cosmos, xxxvii, p. 989. MERCURY 
259 
is left, Au8Hg, which crystallizes in four-sided prisms, 
and does not melt even Avhen heated until the mercury 
volatilizes.”* And further, “A mixture of gold and 
mercury was heated to a temperature a little above the 
boiling-point of mercury, and the heat maintained 
until the weight became constant, and there resulted an 
amalgam containing 10.3 per cent of mercury, giving a 
formula of AugHg.” (Hiorns.) 
Then adds: “Guettier points out that a saturated 
solution of gold in mercury is Au2Hg, a mass of waxy 
consistence. Evidently, when the gold exceeds this 
ratio, there is not a perfect chemical compound, as, for 
instance, in the Au8Hg amalgam.” 
Silver and mercury combine very readily, and un- 
doubtedly from a definite chemical compound. Joule 
gives its formula as Ag2Hg,, Bloxam as Ag2Hg3. It 
also forms two native amalgams having the formulae 
of AgHg and Ag2Hg6. 
With copper, zinc, tin, and lead it also forms definite 
chemical compounds, and their formulae may be ex- 
pressed respectively as: CuHg, Zn2Hg, Sn2Hg, and 
Pb2Hg. The conclusion, then, is obvious that our den- 
tal amalgams are probably mostly—fundamentally, at 
least—chemical compounds, but usually with mercury, 
and, perhaps, some other constituent in excess. 
VERMILION.—Mercuric sulphide, HgS, occurs na- 
tive as cinnabar, a dull-red mineral, the most important 
ore of mercury. It may be prepared by several differ- 
ent methods, much depending upon the purity of the 
materials employed. When mercury and sulphur are 
heated together, the union is accompanied with much 
*T. H. Henry, Philos. Mag., ix, p. 468. 260 
PRACTICAL DENTAL METALLURGY 
energy, and if the product be sublimed, becomes the red 
or mercuric sulphide. The sulphur is best first melted 
and the mercury gradually added by straining through 
linen cloth, whereby it falls in a minutely divided state, 
while the mixture is constantly stirred. When the 
temperature arrives at a certain point, the combina- 
tion takes place suddenly with a slight explosion, at- 
tended with the ignition of the sulphur, which must 
be extinguished by covering the vessel. The product 
of the combination is a black mass, generally contain- 
ing an excess of sulphur, which, before the sublima- 
tion is performed, should be got rid of by gentle heat 
on a sand-bath. Sublimation is best carried on in a 
closely stoppered glass matrass, which should be placed 
in a crucible containing sand, and, thus arranged, ex- 
posed to a red heat. The resulting vermilion is re- 
duced to a fine powder by levigation, the beauty of the 
tint depending much upon the extent to which the 
division is carried. 
It is prepared in a wet way by intimately mixing 100 
parts of mercury with 38 parts flowers of sulphur, 
and the black sulphide of mercury thus obtained di- 
gested with constant agitation, in a solution of 25 
parts of caustic potash in 150 parts of water at 45° C. 
(the water lost by evaporation being constantly re- 
placed), until the preparation has come up to its maxi- 
mum of fire and brilliancy, which takes a good many 
hours. Purely sublimed vermilion has a compara- 
tively dull color, and must be manipulated with an 
alkaline (potassium) sulphide solution to give it the 
necessary fire. The action of the alkaline sulphide 
consists probably in this, that it dissolves successive MERCURY 
261 
installments of the amorphous preparation and rede- 
posits them in the crystalline form. 
Properties.—It is a fine, bright scarlet powder, perma- 
nent in air, odorless and tasteless, insoluble in water, 
alcohol, dilute nitric, concentrated hydrochloric, or sul- 
phuric acids. Nor is it acted upon by boiling potas- 
sium hydroxide, sulphide of ammonium, cyanide of 
potassium or sulphite of soda. It is slightly acted 
upon by concentrated hot nitric acid, and completely 
soluble in a solution of potassium sulphide in the pres- 
ence of free alkali or a solution of sodium sulphide. 
Nitrohydrochloric acid decomposes it into mercuric 
chloride, which is readily soluble. It may be com- 
pletely sublimed, as has been seen, without decomposi- 
tion, but if exposed to a temperature of 315.5° C. it is 
decomposed into metallic mercury and sulphur dioxide. 
It is frequently adulterated with red lead, dragon’s 
blood, chalk, ferric oxide, realgar (As2S2), and brick- 
dust. If lead be present, it will yield a yellow pre- 
cipitate when digested with acetic acid and potassium 
iodide added. Dragon’s blood may be detected by al- 
cohol, which will take up the coloring matter of that 
substance if present. Chalk is detected by an efferves- 
cence on the addition of an acid. Most other impuri- 
ties may be detected by subliming a small portion of 
the compound. The nonvolatile substances used for 
adulteration will remain behind. 
Uses.—When pure it is much used as a pigment, on 
account of its brilliancy and color. Its unalterable- 
ness and resistance to chemical action render it par- 
ticularly valuable in giving the red color to vulcaniz- 
able rubber used in the construction of artificial den- 262 
PRACTICAL DENTAL METALLURGY 
tures of red and pink vulcanite in the composition of 
which it forms, in some cases, about one-third of the 
entire weight of the compound. Notwithstanding the 
poisonous character of mercurial compounds in gen- 
eral, and the frequency of troubles of an inflammatory 
nature of the mucous membrane in mouths fitted with 
rubber dentures, it is obviously very improbable, when 
we consider the properties of pure vermilion, that 
such conditions can be in any degree attributable to 
the presence of this substance per se. It is quite possi- 
ble that impure vermilion may contain from the start 
free mercury; be contaminated with arsenic bisulphide, 
or poisonous adulterants. Again, the practice of dis- 
solving tin-foil off of the surface of plates with nitro- 
hydrochloric acid just after vulcanization may possibly 
decompose some little vermilion, forming soluble bi- 
chloride. It is highly improbable that any of these 
conditions can be found, yet it is possible. It is said 
that free mercury has been observed with the micro- 
scope in finished vulcanite. The occurrence of oral 
inflammatory conditions, under black rubber dentures, 
precisely similar to those under red rubber, practically 
relieves vermilion of the responsibility. Such inflamma- 
tory troubles are directly attributable to its rough and 
porous surface, lack of cleanliness on the part of the 
wearer, and the fact that rubber is a nonconductor of 
heat. 
TESTS FOR MERCURY IN SOLUTION.—Hydro- 
gen sulphide, gradually added to mercuric solutions, 
forms at first a white precipitate; by further additions 
of the reagent, the precipitate becomes yellow-orange, 
then brown, and finally black. Such progressive varia- MERCURY 
263 
tion of color is characteristic of mercury. With mer- 
curous compounds, hydrogen sulphide, and soluble 
sulphides precipitate mercurous sulphide, Hg2S, black, 
without change of color. 
Soluble Iodides precipitate mercuric iodide, Hgl2, 
from mercuric compounds, first reddish-yellow, then 
red. From mercurous solutions they precipitate mer- 
curous iodide, Hg2I2, greenish-yellow in color. 
Potassium hydroxide or sodium hydroxide precipi- 
tates yellow mercuric oxide from mercuric salts, and 
black mercurous oxide from mercurous salts. 
Ammonium hydroxide throws down a “ white precipi- 
tate” of mercuric chloramide (H2NHgCl) from mer- 
curic salts, but black precipitates are thrown down 
from mercurous salts. 
Final Test: The mercury may be in the mercurous 
or mercuric state, (a) Add hydrochloric acid, HC1, to 
the solution, filter and treat precipitate with ammo- 
nium hydroxide, NH40H. Black residue indicates a 
mercurous salt, HgClNH2. (b) Add hydrogen sulphide, 
II2S, to the solution and filter. Treat precipitate with 
boiling nitric acid, HNOs. Black residue soluble in 
bromine water indicates a mercuric salt. Boil to expel 
excess bromine and add SnCl2. White or gray pre- 
cipitate shows mercuric mercury Hg2Cl2. CHAPTER XVI 
SILVER 
Argentum. 
Valence I. 
Atomic weight, 107.88. 
Melting point, 961. 
Ductility, 2d rank. 
Conductivity (heat), 100. 
Specific heat, 0.0559. 
Color, white. 
Symbol, Ag. 
Specific gravity, 10.50. 
Malleability, 2d rank. 
Tenacity, 4th rank. 
Conductivity (electricity), 100 
Chief ore, silver glance. 
Crystals, isometric. 
OCCURRENCE.—Silver is widely diffused through- 
out the earth’s crust. It is found chiefly in the United 
States, Mexico, Peru, and Chile; Austria-Hungary, 
Norway, and Australia also furnish considerable 
amounts. 
Of the varieties of silver ores the following chiefly 
are metallurgically important. (1) Reguline silver, (2) 
horn silver, (3) silver glance, (4) silver-copper glance, 
(5) pyrargyrite, (6) stephanite, and (7) polyhasite. Sil- 
ver is also frequently met with in base metallic ores, 
as in lead ores and many kinds of pyrites. 
Reguline Silver, native silver. Owing to the weak af- 
finity of silver for other substances it is frequently 
found free in a metallic state, occurring in flat masses, 
and at times in arborescent form, composed of nu- 
merous isometric crystals strung together, or in twisted 
filaments. In the Lake Superior district it occurs 
with native copper, showing in specks upon the sur- 
face of the latter metal. With mercury it is found as 
a native crystalline amalgam. Native silver is usually 
264 SILVER 
265 
free from, any considerable admixture of other metals, 
but it always contains gold. 
Horn silver, native chloride, AgCl. The ore is named 
from its resemblance to horn in texture and appearance. 
It is of a pearl-gray color when freshly cut, and on 
exposure to sunlight turns brown. It contains about 
75.3 per cent silver. The corresponding bromide and 
iodide also occur native. 
Silver glance, native sulphide, Ag2S, is the most im- 
portant ore of silver. It is a soft, gray, and somewhat 
malleable mineral, may be cut with a knife, is quite 
fusible, and when pure contains 87.1 per cent silver. 
It is frequently found associated with copper, as silver- 
copper glance (AgCu)2S; with antimony, as pyrargyrite, 
Ag3SbS3, and as stephanite, Ag5SbS4, with copper, anti- 
mony and arsenic, as polybasite, 9(Ag2,Cu2)S + (Sb2, 
As2)S3 ; with lead, as argentiferous galena, and with iron. 
REDUCTION.—The method by which silver is ex- 
tracted from its ores depends chiefly on the nature of 
the admixtures, the state of the combination of the 
silver being as a rule irrelevant in the choice of proc- 
ess, because some of the noble metal is always present 
as a sulphide, and the mode of treatment for it includes 
all other forms.* 
Amalgamation.—If the ore is comparatively free from 
base metals, amalgamation is resorted to. Most ores 
contain too great a proportion of earthy matter, etc., 
to admit of any other method economically, even in 
localities where fuel is plentiful. Several methods of 
amalgamation are employed, varying with different 
localities and circumstances, but the principles involved 
*See also Cyanidation, chapter on Gold. 266 
PRACTICAL DENTAL METALLURGY 
are similar, and a general description will suffice for all. 
The ore is ground and roasted at a dull-red heat 
with common salt, which converts the sulphide of silver 
into chloride— 
Ag2S + 2NaCl + 202 (from the air) = 2AgCl + Na2S04. 
Fig. 50.—A primitive Philippine Arastra; the same type was used by 
the Spaniards and Mexicans and the process of reduction was very similar 
to the chloridizing and amalgamation process. 
The mass, along with certain proportions of water, 
scrap-iron, and mercury, is placed in barrels, which 
are made to rotate about their axis, so that the several 
ingredients are forced into constantly varying contact 
with each other. The salt solution takes up a small 
proportion of the chloride, which in this (dissolved) SILVER 
26? 
form is quickly reduced by the iron to the metallic 
state— 
2AgCl + Fe = FeCl2 + 2Ag, 
so that there is, so to say, room made in the brine for 
another installment of silver chloride, which in turn is 
reduced, and so on. The metal, as soon as freed, is 
combined with the mercury in a semifluid amalgam, 
which, on account of its specific gravity, is easily 
separated from the dross. The silver amalgam is then 
pressed in linen or some other suitable cloth bags, to 
separate the amount of comparatively free mercury, 
which is used again in the process. The remaining solid 
amalgam is subjected to distillation from iron retorts, 
the mercury recovered as a distillate, while the silver in 
a more or less impure state remains in the retort. 
The silver furnished by the amalgamating process 
is never pure, even in a commercial way. A general 
method of its purification is to fuse it with lead, and 
subject the alloy to cupellation. Cupel silver is apt to 
contain small quantities of lead (chiefly), bismuth, 
antimony, copper, and more or less gold. The first 
three can be removed by recupellation, without added 
lead, at a high temperature. The gold, if present to 
the extent of 1 per cent or more, is removed by treat- 
ing with nitric or sulphuric acid. The copper is al- 
lowed to remain, for commercial silver. 
Argentiferous Galena.—The lead extracted from ga- 
lena often contains a sufficient quantity of silver to 
allow of profitable extraction. This is accomplished 
by first concentrating the lead and silver alloy by the 
Pattinson process, which is based upon the fact that the 268 
PRACTICAL DENTAL METALLURGY 
alloy of silver and lead has a lower fusing point than 
lead alone, and therefore remains fluid after the purer 
lead crystallizes. Alloys are thus concentrated from 
lead containing not more than 3 or 4 ounces of silver 
per ton to that which contains about 300 ounces to the 
ton, when by cupellation the lead and other oxidizable 
metals are removed as oxides, leaving pure silver. 
Desilvering Lead.—The process is thus described by 
Bloxam: 
“Eight or ten cast iron pots, set in brickwork, each 
capable of holding about six tons of lead, are placed 
in a row with a fire placed underneath each of them. 
Suppose that there are ten pots numbered consecutively, 
that on the extreme left of the workmen being No. 1, 
and that on the extreme right No. 10. About 6 tons 
of the lead containing silver are melted in pot No. 5, 
the metal skimmed, and the fire raked out from beneath, 
so that the pot may gradually cool, its liquid contents 
being constantly agitated with a long iron stirrer. As 
the crystals of lead form,. they are well drained in a 
perforated ladle (about ten inches wide and five inches 
deep) and transferred to pot No. 4. When about four- 
fifths of the metal has thus been removed in the crys- 
tals, the portion still remaining liquid, which retains 
the silver, is ladled into pot No. 6, and the pot No. 5, 
which is now empty, is charged with fresh argentiferous 
lead, to be treated in the same manner. 
“When pots Nos. 4 and 6 have received, respectively, 
a sufficient quantity of the crystals of lead and of the 
liquid part rich in silver, their contents are subjected 
to a perfectly similar process, the crystals of lead being 
always passed to the left and the rich argentiferous 
alloy to the right. As a final result to these operations, SILVER 
269 
the pot No. 10, to the extreme right, becomes filled 
with a rich alloy of lead and silver, sometimes contain- 
ing three hundred ounces of silver to the ton, while 
pot No. 1, to the extreme left, contains lead in which 
there is not more than one-half an ounce of silver to 
the ton.” 
Cupellation.—The extraction of the silver from the 
rich alloy of silver and lead is accomplished by a proc- 
ess of refining or cupellation, which is based upon the 
property possessed by certain oxides of being absorbed 
Fig. si. 
by the porous cupel. The process is necessarily modi- 
fied according to the quantity of alloy to be cupellated; 
the principle, however, remains identical. 
The cupel, Fig 51, a small, shallow crucible, so named 
from the diminutive of the Latin cupa, a cup, is made 
from prepared bone-ash, moistened with sufficient warm 
water to hold it together. Sometimes a little wood- 
ashes or potassium carbonate is added to the water for 
moistening the bone-ash. After proper moistening and 
mixing the cupel is formed by packing and tamping 270 
PRACTICAL DENTAL METALLURGY 
the moistened ash into a steel mold made for the pur- 
pose, and the cupel knocked out by a gentle tap. The 
ash should not be too fine or packed too densely, or the 
cupel will lack porosity; nor should it be too coarse or 
too loosely packed, resulting in a cupel so porous as to 
cause a loss of the metal. A good cupel, well dried, 
should not crack on being heated, and should be capable 
of absorbing nearly its own weight in lead oxide. 
The furnace used in operations of a small character 
is a muffle furnace, called an assayer’s furnace, similar 
to a continuous-gum furnace. The muffle contained is 
identical with that employed for continuous-gum work, 
except that a narrow slit is provided on each side or at 
the end, for the circulation of a current of air over the 
cupel. 
The cupel is first heated in the muffle to an even tem- 
perature with the latter, which should be a full red 
heat. The weighed mass of alloy may then be gently 
placed on the cupel, the muffle closed, and the alloy 
heated to redness as soon as possible. When this degree 
is attained, the muffle is opened and air admitted. As 
the air strikes the molten mass, a film of oxide quickly 
makes its appearance upon its surface, which, waving 
over the melted alloy, is quickly absorbed by the cupel, 
only to be replaced- by other oxide, which is also ab- 
sorbed; this is continued, the metallic globule rapidly 
diminishing in size until at last all of the lead has 
been reduced to an oxide and got rid of. The operator 
must carefully watch the process during this time, for 
if the mass becomes too highly heated, silver will be 
lost by volatilization, and if insufficient heat is main- 
tained, the mass freezes, and the proper temperature 
cannot be restored without loss of noble metal. A SILVER 
271 
proper temperature is maintained by observing the 
color of the muffle and cupel, the former of which 
should be reddish-white, and the latter full red, the 
molten alloy will then appear luminous and clear, and 
fumes of oxide will be seen whirling over the mass. 
When the last of the lead has been oxidized and got 
rid of, the metallic globule remaining is observed to 
rapidly revolve on its axis, is covered with iridescent 
tints, and later assumes an exceedingly bright appear- 
ance, which is technically termed brightening or corusca- 
tion of the button. When this is observed, the tempera- 
ture should be somewhat increased to insure the expul- 
sion of the last traces of lead. When the operator is 
assured that all the lead has been expelled, the button is 
allowed to slowly cool to prevent spitting1,* sputtering1 
or vegetation of the mass, resulting in a loss of some of 
the silver. Removing the lead, however, is not the only 
action; if it were, little would be gained in the process. 
Another action goes on while the lead is being oxi- 
dized in a current of air, and other metals, except gold 
and silver, are also oxidized and carried off with the 
litharge. If the lead is therefore properly proportioned, 
the resulting button will consist of silver and gold, if 
the latter was present originally. Any gold present 
may be recovered by the parting process. (See chapter 
on Gold.) 
CHEMICALLY PURE SILVER in small quantities 
may be easily prepared in the laboratory by dissolving 
commercial or coin silver in pure dilute (50 per cent) 
nitric acid contained in a Florence flask, hastening the 
action by gently heating over a sand bath. After the 
*The O is dissolved as atomic O or as AgoO, which dissociates at about 
1000° C. into Ag and O, which escapes and causes the “spitting.” 272 
PRACTICAL DENTAL METALLURGY 
silver has been dissolved, and the solution somewhat 
cooled, add an equal bulk of distilled water, and filter 
into a second flask. To the filtrate add a saturated 
solution of sodium chloride (common salt) until no 
more white precipitate of silver chloride is formed— 
AgNOg + NaCl = AgCl + NaN03. 
The flask should then be stopped and shaken for sev- 
eral minutes, when, on being allowed to rest, the chlo- 
ride will quickly fall to the bottom, leaving a clear, 
supernatant liquid above, which, if copper be present, 
will be colored a bluish-green. If to this clear super- 
natant liquid the salt solution be added, the operator 
is enabled to determine instantly whether all of the 
silver has been thrown down as the chloride or not. If 
so, the clear liquid is decanted off and the chloride 
washed until the wash-water does not assume the 
slightest tinge of blue upon the addition of ammonia. 
The chloride is now best transferred to a beaker, or 
some other wide-mouthed vessel, and about twice its 
bulk of water, acidulated with about 10 per cent of 
sulphuric acid, added. Several small pieces of iron in 
some form, preferably lath-nails, may now be added to 
the mixture, and the whole stirred with the closed end 
of a test tube. The following reactions then take 
place, during which ferrous sulphate and hydrochloric 
acid are formed and silver liberated, thus— 
Fe + H2S04 + 2AgCl = 2IIC1 + 2Ag + H2S04. 
The completion of the reaction is recognized by the 
changing of the precipitated mass from white to a dark SILVER 
273 
gray, which is the color of the finely divided silver. The 
small pieces of iron are now removed, the precipitated 
silver washed and rewashed with dilute hydrochloric 
acid, then with distilled water, dried, mixed with about 
an equal bulk of potassium carbonate, and melted in a 
well-boraxed crucible. 
Pure Silver Nitrate Crystals* or pure Silver may be 
prepared by digesting commercial, or coin silver, in 
nitric acid, as before, and evaporating the solution over 
a sand bath. After the water and free acid is driven off, 
a greenish solid of silver and copper nitrates remains. 
By continued heat the former is fused and the latter is 
changed to black oxide of copper, CuO, by driving off 
the nitrogen tetroxide (or dioxide, at high tempera- 
tures, N02). When the evaporating dish has suffi- 
ciently cooled to be handled, a small quantity of dis- 
tilled water is added and the contents of the dish stirred 
and then filtered; the soluble nitrate of silver passes 
through as a filtrate, leaving the insoluble black cupric 
oxide on the filter paper. If the preparation of pure 
silver nitrate crystals is the object of the experiment, 
evaporate the filtrate to crystallization. If the desire 
is to recover the silver, this may be done by the addi- 
tion of sodium chloride to the nitrate solution as 
before, or by immersing a clean strip of copper in the 
solution, when the silver will be precipitated upon the 
copper. Silver obtained in this manner, however, is 
seldom entirely free from contamination with copper. 
*AgNOs, 96 parts, and HC1, 4 parts, when fused yields “lunar caustic.” 
AgN03, 1 part, and KN03, 2 parts by weight, when fused yields diluted 
silver nitrate or “mitigated caustic.” Silver nitrate in the presence of sun- 
light stains organic substances a dark brown color which is difficult to re- 
move after the color change has occurred. If silver nitrate (crystals or 
solution) come in contact with the skin, discoloration may be prevented by 
the immediate application of tincture of iodine followed by a solution of 
hyposulphite of soda. 274 
PRACTICAL DENTAL METALLURGY 
PROPERTIES.—Silver is the whitest of metals, very 
brilliant, tenacious, malleable and ductile, in the last 
two qualities being inferior only to gold; if consid- 
ered weight for weight, it is superior to gold, for while 
one grain of gold may be beaten so thin as to cover an 
area of 75 square inches, a grain of silver may be made 
to cover 98 square inches, though the foil of the former 
is much thinner than that of the latter. The extent 
of the malleability of gold and silver has never been 
absolutely determined, as the means employed have in- 
variably failed before the property in either was ex- 
hausted. In tenacity silver is superior to gold. It is 
also harder than gold, but softer than copper, and is 
the best known conductor of heat and electricity. It 
fuses at 961.5° C., far below the fusing point of either 
gold or copper. It volatilizes appreciably at full red 
heat; in the oxyhydrogen flame it boils, with the forma- 
tion of a blue vapor. The fused metal readily absorbs 
oxygen gas (when fused under potassium nitrate it 
takes up as much as twenty times its volume.) As 
the metal cools, the oxygen, escaping through the semi- 
solid crust on the surface of the fused mass, produces 
very beautiful effects. Pure silver retains a trace of 
the absorbed oxygen permanently. It is unaltered in 
the air at any temperature, but is readily acted upon 
by sulphur, phosphorous, or chlorine. 
COMPOUNDS WITH OXYGEN.—There are two 
oxides of silver, only one of which (Ag20), however, 
can be regarded as a well-defined compound. 
The Monoxide, or Argentic Oxide, Ag20, is a strong 
base, yielding salts isomorphous with those of the 
alkali metals. It is obtained as a pale-brown precipi- SILVER 
275 
tate on adding caustic potash to a solution of silver 
nitrate. Very soluble in ammonia, and slightly so in 
pure water, forming an alkaline solution. It is easily 
decomposed by heat; the sun’s rays also effect a slight 
decomposition, as is the case in most compounds of 
silver. The other oxide is Silver Peroxide, AgO. 
ACTION OF ACIDS ON SILVER.—Nitric Acid is 
the proper solvent for silver, and is most efficient when 
diluted about 50 per cent, but active whether concen- 
trated or dilute, with production of nitric oxide (NO) 
and silver nitrate (AgN03). 
Sulphuric Acid hot and concentrated, acts upon sil- 
ver, forming a sulphate which is sparingly soluble. 
Hydrochloric Acid, hot and concentrated, forms ar- 
gentic chloride, slightly soluble in the concentrated re- 
agent, but precipitated on dilution. 
Fused alkaline hydroxides or potassium nitrate is 
without action upon silver; hence, it is used for the 
manufacture of crucibles for the fusion of caustic 
alkalies, etc. 
ALLOYS.—Pure silver is too soft for coinage or com- 
mercial purposes, and for casting because it absorbs 
oxygen, which is given off on cooling, producing a 
cauliflower-like appearance, or the oxygen may be re- 
tained as bubbles. It is, therefore, alloyed variously 
for its different purposes to increase its hardness. 
Gold.—Formerly silver was much used to alloy gold. 
The metals are easily mixed together, but do not ap- 
pear to form definite compounds. With certain propor- 
tions of the metals the resulting alloys are more ductile, 
harder, more sonorous and elastic than either metal 276 
PRACTICAL DENTAL METALLURGY 
considered singly. While the tensile strength is in- 
creased, up to 50 per cent of the alloy, silver hardly 
lowers the fusing point of gold. An alloy of Au. 40, 
Ag 60, requires more than 1050° C. to fuse, whereas 
the melting point of gold is 1060° C. 
Copper.—The alloys of copper and silver are the 
most useful of the alloys of silver. In most countries 
the silver coins are made of these two metals. In the 
United States the silver for coinage is alloyed with 10 
per cent copper, the proportion of each being stated in 
the thousandths; thus, pure silver being 1000 fine, the 
coin or “standard silver” is 900 fine, with 100 parts 
of copper added. The German and French silver coins 
are of the same grade, those of Great Britain are 925 
fine, with 75 parts of copper added, being known as 
“sterling” silver. Most silverware is of “sterling” 
fineness. The presence of copper does not modify the 
color of silver so long as the proportion of the former 
does not exceed 40 or 50 per cent. Copper imparts to 
silver greater hardness, tenacity and strength, Ag 80, 
Cu 20 giving maximum degree. 
Comparison of the silver dollar of the United States 
with that of Mexico: 
U. S. Dollar 
Mexican Dollar 
Pure Silver 
. 371.25 grs. 
377.14 grs. 
‘ ‘ Copper 
41.25 “ 
40.65 “ 
Total weight... 
. 412.50 “ 
417.79 “ 
The Mexican dollar contains 5.89 grains more silver 
than the United States dollar, and .60 grains less cop- 
per. It is also 5.29 grains greater in weight than the 
United States dollar. 
The Mexican dollar is equal to 0.866 of a Troy ounce. SILVER 
277 
Zinc and silver have a great affinity for each other, 
and are consequently readily alloyed. 
Silver solder for soldering the metal is usually com- 
posed of an alloy with copper and zinc. The following 
are well adapted for the purpose: 
No. 1* 
Silver 66 parts 
Copper 30 “ 
Zinc 10 “ 
No. 2t 
Silver 6 parts 
Copper 2 “ 
Brass 1 “ 
When the material to be united is composed of pure 
silver and platinum, silver coin alloyed with one-tenth 
zinc may be used as a solder. 
So-called standard silver is also an excellent solder 
for high fusing brass and German silver. If the article 
is to be soldered twice, this may be used first and the 
silver solder afterwards.$ 
Dr. Kirk§ recommends the following compositions: 
Fine Silver 
4. 
Copper 
Brass 
3. 
Zinc 
2. 
1. 
19. 
1. 
10. 
5. 
66.7 
23.3 
.... 
10. 
50. 
33.4 
16.6 
11. 
4. 
1. 
These may be used for soldering the surfaces of 
standard silver. 
TESTS FOR SILVER IN SOLUTION.—Hydro- 
chloric acid and the soluble chlorides precipitate silver 
chloride, AgCl. It is a white, curdy substance, quite 
insoluble in water, and nitric acid; one part of silver 
’Richardson, Mechanical Dentistry, p. 78. 
flbid. 
tProfessor C. L. Goddard. 
§Am. System of Dentistry, iii, p. 879. 278 
PRACTICAL DENTAL METALLURGY 
chloride is soluble in 200 parts of hydrochloric acid, 
when concentrated. When heated, it melts, and on 
cooling it becomes a grayish, crystalline mass, which 
cuts like horn. It is found native in this condition, con- 
stituting the mineral called horn-silver. Silver chloride 
is decomposed by light, turning violet to brown (form- 
ing argentous chloride, Ag2Cl) both in the dry and in 
the wet state, very slowly if pure, and quickly if or- 
ganic matter be present. It is reduced also when put 
in water with metallic zinc or iron. It dissolves very 
readily in ammonia and in a solution of potassium 
cyanide. This precipitation is the most delicate of the 
ordinary tests for silver, being recognized in solution 
in 250,000 parts of water. 
Potassium and sodium hydroxide precipitate from so- 
lutions of silver salts, silver oxide, Ag20, grayish brown, 
insoluble in excess of the reagents, easily soluble in 
nitric, acetic, or sulphuric acid, and in ammonia. 
Hydrogen sulphide throws down a black precipi- 
tate of silver sulphide. 
Potassium chromate gives a red precipitate of 
silver chromate, Ag2Cr04, which is soluble in ammonia, 
and concentrated nitric acid. 
Final Test: Add hydrochloric acid, HC1, to the solu- 
tion and filter. Treat precipitate with ammonium hy- 
droxide, NH40H, and filter. Acidify filtrate with IICl. 
White precipitate soluble in NTI40H shows silver chlo- 
ride, AgCl. 
ELECTRODEPOSITION OF SILVER.—Silver is the 
most important and prominent metal in electroplating 
processes. 
The solution generally used is the cyanide, and it SILVER 
279 
may be prepared by either of two methods—the bat- 
tery or the chemical process. 
The method of procedure in the former is simple, 
when thoroughly understood. First must be ascer- 
tained the percentage of actual cyanide in the salt 
used. If, say, it contains about 50 per cent, dissolve 
each ounce in about one quart of distilled water; or 
if it contains more, add more water, and vice versa 
in proportion. Suspend a large anode and a small 
cathode of silver in the liquid, and pass a strong cur- 
rent of electricity through, until the required amount 
of metal is dissolved from the anode. As this process 
produces some caustic potash in the liquid, some of the 
strongest hydrocyanic acid may now be added to form 
cyanide, and more of the anode dissolved in the mix- 
ture aided by the battery. 
Making solutions for deposits by the chemical proc- 
ess is accomplished as follows: 
Take four parts of pure grain silver, and reduce it 
by mixing with nitric acid to argentum nitrate. Dis- 
solve this in distilled water, in the proportion of one 
quart to every one-half ounce of silver used. At the 
same time make a solution of from two to three parts 
of cyanide of potassium in twenty or thirty parts of dis- 
tilled water. This is to be added gradually to the 
solution of nitrate of silver as long as it produces a 
white precipitate. If too much be added, however, it 
will cause some of the precipitate to be redissolved 
and wasted. In such a case the liquid should be stirred 
and then allowed to settle clear. A small amount of 
nitrate of silver dissolved in distilled water should be 
added as long as it produces a white cloud. This may 
be better conducted by using a glass vessel and ob- 280 
PRACTICAL DENTAL METALLURGY 
serving the precipitate as it dissolves. The liquid 
should now be left to settle until quite clear, and the 
clear portion then decanted, and the precipitate washed 
four or five times in a large quantity of water by simply 
adding the water, stirring and allowing it to settle 
again and decanting as before. Next dissolve from six 
to eight parts of cyanide of potassium in twenty parts 
of distilled water, adding it, a portion at a time, with 
free-stirring, to the wet cyanide of silver, until the 
whole is barely dissolved; then add about three parts 
more of cyanide of potassium to form free cyanide, and 
sufficient distilled water to reduce the whole to the 
proportion of about one-quarter of an ounce of silver 
to the quart; finally, when all the free cyanide is dis- 
solved, filter the solution and it is ready for use. The 
specific gravity of the solution should be maintained at 
between 1.8 and 1.15. 
Deposit solutions are very numerous, but in the 
author’s judgment, the above is best adapted for a 
good, reguline solid deposit. 
Knowledge of the management of solutions is essen- 
tial. There are varying circumstances which must be 
noted in order to keep them in good condition for a 
reguline deposit. New solutions do not work as well, 
usually, as old ones, provided the latter is not too old. 
Solutions two or three years old work probably the 
best. They change from many causes; they become 
dirty and concentrated from exposure; increase or de- 
crease in their relative proportions of cyanide and 
metal; they acquire other metals in solution, dissolved 
from the anode and corroded from the cathode; plaster 
and plumbago accumulate in them, and in consequence 
of which they should be filtered; they gradually de- SILVER 
281 
compose, become brown, discolored, and evolve am- 
monia by exposure to light, especially if they contain 
too much free cyanide; therefore, all these deviations 
from the proper condition should be corrected. The 
specific gravity should be maintained, and the proper 
amount of metal and cyanide kept in solution. To de- 
termine any disproportion in the latter, place 25 grams 
of the solution in a test tube of proper size and add to 
it, at first freely, and afterwards gradually, until at 
last, drop by drop, with constant stirring, a solution 
of one gram of crystallized nitrate of silver in ten 
grams of distilled water. If the precipitate formed is 
dissolved rapidly, with but little need of stirring, there 
is too much cyanide. If, however, it does not dissolve, 
even after much stirring, there is too little cyanide; 
but if it wholly dissolves (the latter part quite slowly) 
the proportion of silver to cyanide is about correct. 
Many other minor troubles not mentioned are en- 
countered, which must be corrected by means gath- 
ered only from experience in working the process. 
The process for making dental bases by electrodepo- 
sition on the plaster cast of the mouth was patented 
February 5, 1889, by Joseph G. Ward, of Irvington, 
N. J. 
The author has had some experience in the work; 
in fact, was engaged in perfecting a process for the 
same result when Mr. Ward secured his patent. The 
method of proceeding in the preparation of a dental 
base is as follows: 
A true impression of the mouth is secured, and from 
this a cast is obtained by filling in the usual manner. 
After the cast has become thoroughly dry it should be 
soaked in hot fluid paraffine until saturated, and be- 282 
PRACTICAL DENTAL METALLURGY 
fore cooling the surface wiped clean of all superfluous 
adhesions which might in any way destroy the exact- 
ness of the model. The cast is then coated freely where 
the deposit is desired with a mixture of equal parts of 
pure finely pulverized plumbago and the finest tin- 
bronze powder or any other conducting substance suit- 
able under the circumstance. This is applied with a 
thick, short-haired camel’s-hair pencil. The cast is now 
so wired that perfect connection is made with the pala- 
tine, buccal, and labial surfaces. From these guiding 
wires a cathode-hook suspends the cast in the solution. 
After the metal has been deposited to a sufficient thick- 
ness, the cast, with its deposit, is to be taken from the 
bath, the deposit removed from the cast, trimmed and 
polished; but if it is desired to have the plate of in- 
creased thickness at any part to give the appear- 
ance of a turned-rim, etc., the cast, with the deposit 
adhering to it, may be removed from the bath, and all 
the exposed surface of the deposit, except the portions 
to be thickened, may be covered with a coating of wax 
or some other nonconducting substance and resub- 
merged in the bath and left there until the required 
thickness of deposit is secured in the parts desired. 
It may then be taken from the bath, burnished, 
trimmed by scraping, burring and filing to the proper 
shape and thickness, then polished, and spurred. A 
thick plating of gold should now be added to the 
properly shaped plate, or the rubber for the attach- 
ment of the teeth will not harden and adhere to the 
plate during the process of vulcanization (the sulphur 
of the vulcanite combining with the silver). After the 
teeth have been attached and the vulcanite and all 
properly finished, a second coating of gold should be SILVER 
‘283 
electroplated over it all to cover portions that had 
been made bare in finishing the vulcanite. 
The denture may be made by depositing the metal 
directly on the teeth as in cheoplastic work, and, where 
necessary, clasps may be formed. Broken dentures 
have been soldered with 18-carat gold solder. 
Crowns and bridge work may also be made in various 
ways by this process. 
Electrolytic methods of refining the rare metals have 
superseded all others in the United States mints, where 
the problem is to separate the metals in a pure state 
from mixtures of all proportions of gold, silver, and 
base metals. The silver is first brought up to purity 
and then the gold. The silver rarely runs lower than 
99.9% pure. The platinum is recovered by precipita- 
tion and is a valuable by-product. CHAPTER XVII 
IRIDIUM 
Iridium. 
Valence III, IV. 
Atomic weight, 193.1. 
Melting point, 2360° C. 
Color, steel-white. 
Symbol, Ir. 
Specific gravity, 15.86 spongy. 
Specific gravity, 22.42 crystalline. 
Malleable, at red heat. 
Chief ore, iridosmine. 
Crystals, hexagonal. 
OCCURRENCE.—The metal occurs chiefly as a na- 
tive alloy of iridium and osmium, known as osmiridium 
or iridosmine, in combination with platinum. The prin- 
cipal source of supply is Russia, where the crude plati- 
num carries from one to three per cent of iridium. The 
United States produces from 100 to 200 ounces annually. 
One area in Trinity County, Cal., carries twice as much 
iridium as platinum in the gravel beds. Other sources 
of supply are Oregon, Colorado and Columbia, South 
America. 
REDUCTION.—It is obtained from its native alloy by 
mixing with an equal weight of dry sodium chloride, 
and heating to redness in a glass tube, through which a 
moist stream of chlorine gas is transmitted. The mix- 
ture of iridium and osmium sodio-chlorides thus formed 
is dissolved in water and evaporated, and distilled with 
nitric acid, removing the osmium as osmic acid; when 
its complete removal is thus effected, ammonium chlo- 
ride is added to the residual solution, which precipi- 
tates the ammonio-chloride of iridium as a dark-red- 
brown precipitate. From this spongy metallic iridium 
284 IRIDIUM 
285 
is obtained in the same manner as the production of 
spongy platinum. 
PROPERTIES.—Iridium is a steel-white metal, ex- 
ceedingly hard, brittle when cold, but somewhat mal- 
leable when at red heat, having a specific gravity in 
the spongy state of 15.86 and in the crystalline state of 
22.42, unaltered in air, and fusible only in the oxyhy- 
drogen flame. If the precipitated metal be moistened 
with a small quantity of water, pressed tightly be- 
tween filter paper, and then very forcibly in a press, 
and calcined at a white heat, it may be obtained in 
the form of a very hard compact mass, capable of taking 
a good polish, but still very porous, and having a spe- 
cific gravity not to exceed 16. 
COMPOUNDS WITH OXYGEN.—Iridium forms 
two common oxides: 
The Sesquioxide, or Iridious Oxide, lr203, may be 
formed by exposing the metal at a red heat to the 
action of the oxygen of the air. It is a black powder, 
insoluble in the acids and much used for imparting an 
intense black to porcelain. 
The Dioxide, or Iridic Oxide, Ir02, is also a black 
powder, obtained by heating the dihydroxide in a 
current of C02. It is insoluble in acids, and is said to 
be the most stable oxide of the metal. 
ACTION OF ACIDS ON IRIDIUM.—The pure metal 
itself is not acted upon by the acids, but when reduced 
by hydrogen at a low temperature, it oxidizes slowly at 
a red heat; and may be dissolved in nitrohydrochloric 
acid. It is, however, usually rendered soluble by fusing 
it with potassium nitrate and caustic potash. Its hy- 
droxides are also soluble. It forms two chlorides, 286 
PRACTICAL DENTAL METALLURGY 
IrCl3 and IrCl4, and analogous iodides, and three sul- 
phides analogous to the three oxides. 
ALLOYS.—With Mercury. Dr. Kirk relates that 
“Bottger formed an amalgam with iridium by immers- 
ing sodium amalgam in an aqueous solution of chlori- 
date of sodium; he describes the amalgam as soft and 
viscid.” 
With Gold iridium forms a malleable and ductile 
alloy, its color depending upon the proportions of the 
metals. 
Platinum and iridium form some very valuable and 
useful alloys. Jewelers find such alloys durable and 
safe for setting diamonds, pearls, and other light 
colored precious stones. Aside from these, and the use 
of the metal and its alloy with phosphorous for point- 
ing gold pens, iridium is of little value. 
With Silver it is claimed there is no alloy; and that 
after exposing a mixture of these metals to a high tem- 
perature, or attempting to pour out the contents of the 
crucible, silver alone flows out and a thick mass is left 
in the crucible. CHAPTER XVIII 
PALLADIUM—TUNGSTEN 
Palladium. 
Valence, II, IV. 
Atomic weight, 106.7. 
Melting point, 1550° C. 
Conductivity (heat), —. 
Symbol, Pd. 
Specific gravity, 11.4-11.9. 
Malleability, 11th rank. 
Chief ore, in gold and platinum. 
Conductivity (electricity), 12.1. 
Specific heat, 0.0592. 
Color, platinum-white, 
(Silver being 100.) 
Crystals, fibrous. 
OCCURRENCE.—Palladium is found native in com- 
pany with platinum from which it is distinguishable 
by its fibrous structure. It is usually found, however, 
alloyed with platinum and with some specimens of 
Brazilian gold. 
REDUCTION.—When the solution of crude plati- 
num from which the greater part of the metal has been 
precipitated by ammonium chloride, is neutralized by 
sodium carbonate, and mixed with a solution of mercuric 
cyanide, palladium cyanide separates as a whitish in- 
soluble substance, which on being washed, dried, and 
heated to redness, yields metallic palladium in a spongy 
state. The palladium may then be welded into a mass 
in the same manner as platinum.* 
PROPERTIES.—Palladium is a white metal, much 
resembling platinum, though somewhat darker in color. 
Its specific gravity differs greatly from that of plati- 
num, being only 11.4. It is also very much less ductile 
and malleable than that metal; it is the most fusible of 
"Manual of Chemistry, Physical and Inorganic, Watts. 
287 288 
PRACTICAL DENTAL METALLURGY 
the platinum group, yet it barely melts at the highest 
wind-furnace heat, or about the temperature at which 
malleable iron fuses, 1550° C., and when heated to red- 
ness and exposed to the air, especially in its spongy 
state, it acquires a blue or purple superficial film of 
oxide, but may be restored to its brightness and luster 
upon being heated to a more intense degree, the oxide 
being reduced. If heated and fused in air, it is apt to 
vegetate on cooling, similarly to silver. 
The metal is most remarkable for its property of 
“occluding” or absorbing hydrogen. According to Gra- 
ham the compact metal when immersed in cold hydrogen 
gas takes up little or none of it; but at higher temper- 
atures very considerable occlusions take place. A cer- 
tain specimen of palladium-foil at 245° C. was found 
to absorb 526 times its own volume of hydrogen; and 
at red heat will absorb nearly 1,000 volumes. The 
hydrogen, as in the case of platinum, is retained in the 
metal on cooling. Graham views hydrogenized palla- 
dium as a true alloy, containing its hydrogen in the 
form of a metal—“hydrogenium.” Palladium has not 
the power of absorbing oxygen or nitrogen. If palla- 
dium be used as the negative electrode in the electrol- 
ysis of water, the coefficient of absorption is very high; 
especially is this the case when the palladium was pro- 
duced electrolytically and hydrogenized while itself in 
the nascent state. Such metal cold was found to con- 
tain 982 volumes of hydrogen, corresponding approxi- 
mately to the formula Pd4H3. The element does not 
lose any of its metallic properties by being hydro- 
genized, but it loses nearly 10 per cent of its specific 
gravity. At the same time its bulk is increased about 
one-tenth. PALLADIUM TUNGSTEN 
289 
DENTAL APPLICATIONS.—Formerly palladium 
was used to some extent as a base for artificial den- 
tures. Its lightness (having little more than half 
the specific gravity of gold), hardness, and resistance 
to discoloring and corroding influences made it desir- 
able. Scarcity prevents its present use. 
COMPOUNDS WITH OXYGEN.—Palladious Oxide, 
the Monoxide, PdO, may be prepared by evaporating 
to dryness and cautiously heating the solution of pal- 
ladium in nitric acid. It is of black color, but slightly 
soluble in acids, and decomposed by high temperature. 
Palladic Oxide, the Dioxide, Pd02, is not known in 
the separate state. From palladic chloride solutions 
alkalies and their carbonates throw down a brown pre- 
cipitate, hydrated palladic oxide combined with the 
alkali. The hydroxide is decomposed by high heat; 
dissolves slowly in acids, forming yellow solutions. 
ACTION OF ACIDS ON PALLADIUM.—In Hydro- 
chloric or Sulphuric Acid boiling and concentrated pal- 
ladium is slightly soluble, forming palladious chloride, 
PdCl2, or palladious sulphate, PdS04. 
Nitric acid dissolves it slowly, but it is more readily 
soluble in a mixture of nitric and nitrous acids, form- 
ing palladic nitrate, Pd (N03)2. 
Nitrohydrochloric acid is a ready solvent for this 
metal, forming palladic chloride, PdCl3. The solution 
is a deep brown color, decomposed upon evaporation 
with a liberation of chlorine and becoming PdCl2. 
ALLOYS.—With Mercury, in the finely divided state, 
it readily combines to form a gray plastic amalgam. 
This union is attended with the evolution of some heat, 
and is said to result in a definite chemical compound. 
(See chapter on Amalgams.) 290 
eracticaL dental metallurgy 
Palladium renders its alloys harder and more brit- 
tle. These are chiefly used in the manufacture of fine 
watches, and the most important are those with silver 
and the so-called palladium bearing-metal. 
In the laboratories of the Research Institute of the 
National Dental Association, experiments have been 
made with many metals which might possibly serve as 
a substitute for platinum.* Of all the alloys experi- 
mented with, the palladium-gold group presented the 
best results. The authors state that “the remarkable 
property of palladium from a metallurgic point of view 
is its great solvent power for other elements, forming 
solid solutions in perhaps more cases than any single 
element. These two metals alloy readily in any pro- 
portion. The alloy is insoluble in hydrochloric acid 
and aqua regia, slightly soluble in sulphuric acid, and 
soluble with difficulty in nitric acid. It may be rolled 
into very thin sheets and used as a substitute for plati- 
num foil. One per cent of palladium changes the color 
of gold to a light yellow, two to three per cent gives 
a bronze color, and five per cent approaches the color 
of palladium. It was found that this alloy will “sol- 
der as well as pure gold.” 
Silver.—An alloy of palladium 9 parts and silver 1 
part was used for dental bases, as was also the follow- 
ing: platinum 10, palladium 8, and gold 6 parts. Mr. 
Fletcher says * * # a silver alloy poor in palla- 
dium is worthless, as a large amount of the latter is 
necessary to protect it from sulphuretted hydrogen. 
And, further, that pure palladium is the best metal 
known for plates for artificial teeth, owing to its high 
* Weston A. Price and F. A. Fahrenwald: Metallurgical, Physical, and 
Chemical Researches, Jour. N .D. A., i, No. 4, 71-109. PALLADIUM TUNGSTEN 
291 
specific heat, its extreme lightness and hardness, re- 
quiring no alloy, and also to its absolute freedom from 
tarnish. 
The same author further says: “As an alloy, the 
presence of palladium in small quantities is frequently 
objectionable, * # # almost inadmissible, even in 
so small a proportion as 1 to 2000 in silver for making 
amalgams.” 
Price and Fahrenwald found that “palladium in- 
creases the hardness of silver in the alloy without 
adding value to its tensile strength or workability.” 
“It therefore offers no special values as a substitute 
for platinum and iridium alloys.” 
With nickel it forms a malleable alloy susceptible to 
high polish. 
With antimony, bismuth, tin, zinc, iron, and lead it 
combines to form very brittle alloys. 
Palladium bearing-metal.—An uncommonly hard 
alloy used as bearings for fine watches, and is said to 
produce less friction upon arbors of hard steel than the 
jewels generally used. The composition is, palladium 
24, gold 72, silver 44, and copper 92. 
TESTS FOR PALLADIUM IN SOLUTION.—Salts 
of palladium may be discriminated by:— 
Hydrogen sulphide or ammonium sulphide, which 
throws down a black precipitate of palladious sulphide, 
insoluble in alkaline sulphides, but soluble in hydro- 
chloric acid. 
Potassium iodide gives a black precipitate of palla- 
dium iodide from palladious chloride. 
Potassium hydroxide or sodium hydroxide yields a 
red precipitate soluble in excess of alkali if heated. 292 
PRACTICAL DENTAL METALLURGY 
Mercuric cyanide, the characteristic test, gives a yel- 
lowish-white gelatinous precipitate of palladious 
cyanide from solutions of palladious chloride, which 
is soluble in hydrochloric acid. 
Nearly all the compounds of palladium are reduced 
by heat, before the blowpipe, to a “sponge.” If this 
be held in the inner flame of an alcoholic lamp it ab- 
sorbs carbon at a heat below redness; if then removed 
from the flame, it glows vividly in the air, till the car- 
bon is all burnt away—(distinction from platinum). 
TUNGSTEN, until recently a rare metal, has been 
developed into a very valuable one. It occurs gen- 
erally in the presence of manganese and tin ores and 
for a long time was considered a constituent of cas- 
siterite. It is prepared by heating pure tungstic oxide 
in an atmosphere of hydrogen, in the form of briquets, 
0.5x0.5x15. cm., sintering at about 1300° C. until the 
oxide is reduced. These briquets are then heated 
electrically to about the melting point of tungsten and 
then subjected to repeated swagings to weld into a 
solid compact mass. It is then drawn through diamond 
and ruby draw-plates, first hot and then cold, until the 
size of wire needed is obtained. 
The symbol is W., named wolfram on account of its 
causing the loss of tin in smelting in the same sense 
that antimony was called “the wolf” by the alchem- 
ists because it devoured the base metals when em- 
ployed in refining gold. It has an atomic weight of 
184.0, a specific gravity of 18.77, and a melting point 
of 3400° C. It is both brittle and ductile, depending 
on the manner of working it. The acids have only a 
slight action on it, usually forming tungstic oxide 
which prevents further action. The alkali carbonates 293 
PALLADIUM—TUNGSTEN 
and a saturated solution of hypochlorite attack it ap- 
preciably. 
It is used and most commonly known as the metallic 
filament in electric lamps. The U. S. Dept, of Mines 
has estimated that if tungsten filament lamps were sub- 
stituted for carbon filament lamps, an annual saving 
of $250,000,000 would be effected. It is also used for 
targets in roentgen tubes, for electric furnaces where an 
atmosphere of hydrogen or nitrogen can be maintained, 
for standard weights, and for filtering acid liquors. It is 
paramagnetic and very elastic and therefore suitable 
for watch springs. It is extensively used as a con- 
stituent in lathe tool-steel, since it has the property of 
retaining its temper at red heat, and is known as self- 
hardening steel. It is curious that the old Damascus 
steel has been found to contain both chromium and 
tungsten. Colorado, U. S., and Australia are the larg- 
est producers. 
F. A. Fahrenwald* in endeavoring to find a depend- 
able substitute for platinum in dentistry, has produced 
tungsten wires coated with gold and palladium. They 
are designed to serve as dowels for crowns, and for 
orthodontic appliances. As yet they have not fulfilled 
all the exacting requirements for this service in a prac- 
tical way. An effort was also made to produce an 
alloy of gold and tungsten, by mixing gold chloride 
and tungstic oxide in varying proportions, placing the 
compound in a quartz tube electric furnace, and reduc- 
ing to a metallic state in the absence of oxygen. A 
very fragile alloy was the result, no matter what com- 
bination was used. 
*F. A. Fahrenwald: A Development of Practical Substitutes for Plat- 
inum, etc., Jour. N. D. A., iii, pp. 47-84. CHAPTER XIX 
PLATINUM 
Platinum. 
Valence, II, IV. 
Atomic weight, 195.2. 
Melting point, 1755° C. 
Ductility, 3d rank. 
Conductivity (heat), 16.64. 
Symbol, Pt. 
Specific gravity, 21.48 at 17.6°. 
Malleability, 6th rank. 
Tenacity, 3d rank. 
Conductivity (electricity), 14.4. 
(Silver being 100.) 
Specific heat, 0.0323. 
Color, bluish silver-white. 
Chief ore, polyxene. 
Crystals, octahedral. 
OCCURRENCE.—Tlie ore of platinum “polyxene,” 
which is a most complex mixture of a number of heavy 
reguline species of platinum, osmiridium, iron-plati- 
num, platin-iridium, iridium, palladium, gold, and a 
number of nonmetallic species, notably chrome-iron 
ore, magnetic iron oxide, zircone, corundum, and oc- 
casionally also diamond, is found in the province of 
Choco, South America, where it was first discovered in 
1736, in New Granada, Barbacos, California, and Aus- 
tralia, but chiefly in alluvial deposits in the Ural dis- 
trict. The variable percentages of the several compo- 
nents range approximately as follows: Platinum, 60 
to 87; other polyxene metals, 3 to 7; gold, 2 and more; 
iron, 4 to 12; copper, 0 to 4; nonmetallic gangue, 1 to 
3. Gold is separated by amalgamation when it exists 
in any considerable quantities. 
Platinum is rarely found in large nuggets, but usually 
in granules, which are generally small, but occasionally 
assume considerable dimensions. The Demidoff Mu- 
294 PLATINUM 
295 
seum contains a native platinum lump weighing 21 
pounds troy. 
Within recent years platinum has been found in 
lodes, notably at the Goodspeed mine in Nevada and 
more recently near Pretoria, South Africa. The latter 
consists of a quartz impregnable fault zone with branch 
fissures. The platinum bullion contains from 20 to 40 
per cent palladium, very small quantities of iridium 
and the other metals of the group are very rare. Sam- 
ples assayed from 0.35 to 173' ounces per ton, the rich- 
est ore being in the branch lode. 
REDUCTION.—The extraction of platinum is accom- 
plished by two distinct methods. The first, devised by 
Wollaston, which produces the purest metal, is more 
of a chemical than a metallurgic process, a modification 
of the method of Herieus is as follows: The ore is di- 
gested within glass retorts in dilute aqua regia, by 
which the platinum, palladium, part of the iridium, and 
more or less of the other metals pass into solution, the 
platinum, palladium, and iridium as tetrachlorides. 
The solution is then evaporated to dryness, and the 
residue heated to 125° C., to reduce the palladic and 
iridic chlorides to the lower stages of PdCl2 and Ir2Cl6, 
which form soluble double salts with ammonium chlo- 
ride. The heated residue is dissolved in water acidu- 
lated with hydrochloric acid; the solution filtered and 
mixed with a hot concentrated solution of ammonium 
chloride, when a quite pure chloroplatinate, PtCl6 
(H4N)2, comes down in a yellow precipitate, which is 
washed first with a saturated ammonium chloride solu- 
tion, then with hydrochloric acid. This precipitate 
needs only to be exposed to a dull red heat to be eon- 296 
PRACTICAL DENTAL METALLURGY 
verted into “spongy platinum,” that is, metallic plati- 
num in the form of a gray, porous mass. Care must be 
taken that no gold chloride in combination with am- 
monia remains since it is violently explosive and the 
application of heat may do serious damage. 
The second method, known as Deville’s, is based 
upon the tendency of platinum to be dissolved in 
melted lead. The ore is fused with an equal weight 
of galena (sulphide of lead) and as much of the oxide 
of lead. The sulphur and oxygen escape as sulphur 
dioxide, the reduced lead dissolving the platinum, and 
leaving the very heavy alloy of osmium and iridium to 
sink to the bottom undissolved. The upper portion 
containing the platinum is then ladled out and cupellated, 
(see chapter on Silver), when the latter metal is left in 
a spongy mass, the lead having passed off as the oxide. 
FUSING PLATINUM.—Modern practice in the fu- 
sion of platinum does not differ materially from pre- 
vious methods. The modern method of fusing by the 
oxy-hydrogen flame was introduced by Dr. Robert 
Hare, the inventor of the blowpipe, in the first decade 
of the nineteenth century. In 1859 Debray and 
Deville in France introduced the hollowed lime 
crucible. An ordinary sand crucible, with one side 
knocked out, may be used, but a block of freshly 
calcined lime, obtained from magnesia limestone, free 
from silicon, iron, and aluminum is better than straight 
calcium limestone. It should be wrapped with wire to 
prevent cracking, and placed on a block of magnesite 
or some other refractory substance to prevent loss of 
heat. An oblong or rectangular trough is cut in the 
lime to facilitate handling the button or ingot. An 
oxyhydrogen flame, or gasoxygen flame with a specially PLATINUM 
297 
constructed burner is used, for the gas usually comes 
under a pressure of less than a pound, while the oxygen 
is under great pressure. A pressure regulator must be 
attached to the oxygen tank. The flames should not be 
sooty as the carbon may contaminate the metal. The 
scrap should not be massed but stacked up against the 
side of the crucible and the flame directed below gradu- 
ally fusing the lower portion and allowing the upper 
portion to melt in. 
When the ingot is cool enough to handle, it should 
be inverted on a soldering block and the flame directed 
against the surface to fuse the roughened surface, 
thus getting rid of the pits and siliceous substances that 
may be attached. This is called sweating. One part 
of silicon in 3000 parts of metal will render the latter 
brittle. When the mass melts in two layers and does 
not fuse in the crucible, is swaged and separates in 
two layers, or blisters, it is called “double platinum.” 
Remelting will correct this condition. In the case of 
platinum sponge the mass is introduced before heating 
up the furnace, and it is here that the furnace acts as 
a cupel; the impurities remaining in the metal are oxi- 
dized and volatilized or absorbed by the lime of t’he 
furnace. The temperature produced is supposed to be 
about 2870° C. Osmium does not melt at this point 
but if present is volatilized with palladium and gold. 
Platinum may also be fused by placing the metal 
between the carbon tips of an arc light. 
PROPERTIES.—The metal is bluish silver-white, 
about as soft as pure copper, and has a specific gravity 
of 21.48. It is tough, ductile, and malleable, and may 
be rolled or beaten into foil or drawn into wire of 298 
PRACTICAL DENTAL METALLURGY 
almost microscopic fineness. Dr. Arendt states* that a 
cylinder of platinum, one inch in diameter and five 
inches long, may be drawn into a wire sufficiently long 
to encircle the earth at the equator. The fine wire used 
in micrometer eye-piece of microscopes suggested by 
Wollaston is made by drawing a composite wire of 
platinum, coated with silver, to its greatest attenua- 
tion, and then dissolving off the silver in nitric acid. 
Platinum possesses tenacity in a high degree, being 
slightly inferior to iron and copper. The fusing point, 
according to Violle is 1753° C. When heated much 
above its fusing point, it soon begins to volatilize. 
The fused metal, like silver, absorbs oxygen, and conse- 
quently spits on freezing. At a red heat it occludes 
hydrogen gas. The volume of hydrogen absorbed by 
a unit volume of metal at a red heat, under one atmos- 
phere’s pressure, was found, in the case of the fused 
metal, to vary from 0.13 to 0.21, volumes measured 
cold; in the case of merely welded metal from 2.34 to 
3.8 volumes. Oxygen, though absorbed by the liquid, 
is not occluded by the solid metal at any temperature, 
but when brought in contact with it at moderate tem- 
peratures, suffers considerable condensation at its sur- 
face, and in such a state exhibits a high degree of 
chemical affinity. When a jet of hydrogen gas strikes 
a layer of spongy platinum it causes it to glow and 
the gas takes fire. 
The most striking example of the property of the 
metal for absorbing gases is demonstrated in the finely 
divided state known as “platinum black.” This state 
is produced by dropping platinum chloride solution 
*Dr. Kirk in American System of Dentistry, iii, p. 887, frprn 
ijolien Cliemjf. PLATINUM 
m 
into a boiling mixture of 3 parts of glycerine and 2 of 
caustic potash. Platinum black is said to absorb 800 
times its volume of oxygen from the air, and is, there- 
fore, a most active oxidizing agent, acting catalytically, 
that is, after having given up its oxygen to the oxidiz- 
able substance it takes up a fresh supply from the 
atmosphere. 
DENTAL APPLICATIONS.—About one-third of the 
world’s total production of platinum is used in dentis- 
try, and from the nature of its use it is recovered in 
only small amounts. The metal has become so valuable 
in science and industry where the recovery is large that 
the Federal Government has proposed measures looking 
toward the conservation of the supply and the substi- 
tution of other metals for jewelry and dental purposes. 
Dentists should welcome any effort made to provide 
suitable substitutes and encourage research looking to 
that end.* Platinum was introduced in France as early 
as 1820 for a base in continuous-gum work. Its low 
rate of expansibility under increased temperature, its 
coefficient being about equal to that of glass, and its 
very high fusing point make it most useful for porcelain 
work, and for pins for artificial teeth. Its compara- 
tively great resistance to chemical agents insures it 
against corrosive action, and places it on an equality 
with gold for dental bases, crowns, and bridge-work. 
Platinum and gold is used as a filling material in the 
form of platinum and gold folds, platinized gold folds, 
and platinum and gold foil. The color of this material 
inserted as a filling is not as beautiful as that of either 
gold or platinum alone. The yellow of gold having al- 
*See footnote, p. 293. 300 
PRACTICAL DENTAL METALLURGY 
most entirely disappeared leaves an ashen effect to the 
platinum, which very much detracts from its character- 
istic color and appearance. The advantage it possesses 
over gold is its tough, resistant property—making a sur- 
face that will stand the abrasive action of mastication 
much better than gold. 
Coils of platinum are much used in the construction 
of muffles for electric furnaces and in various forms of 
electric heating devices. The heat is free from products 
of combustion and can be most accurately controlled. 
A device of this nature is especially valuable in anneal- 
ing gold. 
COMPOUNDS WITH OXYGEN.—Platinum forms 
two compounds with oxygen. 
Platinous Oxide, or Monoxide, PtO, is obtained by 
digesting the platinous chloride with caustic potash as 
a black powder, soluble in excess of the alkali. It is 
not known in the separate state, is a feeble base, and is 
decomposed by heat, leaving metallic platinum. 
Platinic Oxide, or Dioxide, Pt02, also a weak base, 
occasionally acting as an acid; hence, it is sometimes 
termed platinic acid. It is best 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 plati- 
num as platinic hydroxide. The hydroxide is a bulky 
brown powder which, when gently heated, becomes 
black and anhydrous. If this oxide be dissolved in 
dilute sulphuric acid and the solution mixed with an 
excess of ammonia, a black precipitate or fulminating 
(explosive) platinum is obtained, which detonates vio- 
lently at about 190° C. PLATINUM 
301 
ACTION OF ACIDS ON PLATINUM.—The metal is 
not sensibly tarnished by sulphuretted hydrogen vapor 
or solution; and is not attacked at any temperature by 
nitric, hydrochloric or sulphuric acid; but it dissolves in 
nitrohydrochloric acid to form platinic chloride. It is, 
however, less readily soluble in this acid than gold. 
ALLOYS.—Platinum alloys with most of the metals. 
With mercury spongy platinum unites to form an ex- 
ceedingly unctious amalgam. It does not, however, 
unite readily, and its union is best accomplished by 
continuous rubbing in a warm mortar. 
Iridium from 10 to 15 per cent added to platinum 
greatly increases its hardness, elasticity, infusibility, 
electrical resistance, and resistance to chemical action. 
Platinum alloyed with iridium can be made very use- 
ful in dentistry as dowels, etc., and to strengthen weak 
parts of partial continuous-gum and partial vulcanite 
dentures and crown and bridge-work. An alloy of 78.7 
platinum and 21.3 iridium will withstand the action of 
aqua regia. An alloy of iridium 5-20 parts and plati- 
num 95-80 parts is used as a thermocouple in electrical 
pyrometers. Equal parts of the metals form a very 
brittle alloy. 
Gold and platinum form an alloy of great value for 
the construction of dental bases. Platinum gives to 
gold a greater hardness and elasticity. Two parts to 
one of gold forms a brittle alloy, while with equal 
parts the alloy is malleable. Dr. Weston A. Price rec- 
ommends an alloy of platinum, 6 parts, and gold, 94 
parts, for casting, upon which porcelain can be baked. 
Dr. George L. Bean recommends adding scrap plati- 
num foil to coin gold, in proportions to suit the opera- 
tor’s judgment, for casting plates and bridges. Gold 302 
PRACTICAL DENTAL METALLURGY 
75 parts and platinum 25 parts forms an alloy much 
used in continuous gum and porcelain crown and 
bridge-work. It is usually called 25 per cent platinum 
solder. 
Silver.—By small additions of platinum to silver its 
pure white color is changed to a gray, and its hardness 
is increased. The alloys are difficult to make, on ac- 
count of the separation of the platinum, owing to its 
greater specific gravity. 
Platine au titre, an alloy composed of from 65 to 83 
per cent of silver, has been used for dental bases in 
preference to coin silver, on account of its resistance 
to chemical action and its greater elasticity. Nitric 
acid will dissolve an alloy of silver and platinum when 
the latter is not present, to exceed 10 per cent. 
Cadmium and platinum unite, to form a definite 
compound, having the formula of PtCd2. 
Copper and platinum, equal parts, form a gold-col- 
ored alloy tarnishing in air. 
Iron; reinforced platinum protected by U. S. patents, 
is made by taking a metal of the iron group, encasing 
it in a tube of platinum, and heating it to welding heat 
when union takes place. It may be made by casting 
superheated ferrous alloys against platinum. Spun 
ware from this double faced platinum is thus produced. 
Lead and tin unite with platinum in all proportions, 
resulting in hard and brittle alloys with comparatively 
low fusing points. Pure platinum should never be 
brought in contact with these or other low fusing 
metals or their alloys at high temperatures, as alloys PLATINUM 
303 
of platinum having a low fusing point and brittle 
character are readily formed.* 
TESTS FOR PLATINUM IN SOLUTION.—Hydro- 
gen sulphide throws down, after heating, a blackish 
brown precipitate. 
Potassium or ammonium hydroxide each throws down 
a very characteristic yellow crystalline precipitate, the 
former soluble in large excess of precipitant, and the 
latter, when dried and heated, yielding metallic 
platinum. 
By the reducing blowpipe flame, the compounds of 
platinum are reduced to spongy platinum. 
’Organic or other salts of lead, bismuth and antimony should not be 
heated on platinum, for the metals may be reduced and form fusible alloys 
with the platinum. CHAPTER XX 
GOLD 
Aurum. 
Valence, I, III. 
Atomic weight, 197.2. 
Melting point, 1063° C. 
Ductility, 1st rank. 
Conductivity (heat), 70.03. 
Symbol, Au. 
Specific gravity, 19.32. 
Malleability, 1st rank. 
Tenacity, 5th rank. 
Chief ore, found native. 
Conductivity (electricity), 76.6. 
(Silver being 100.) 
Specific heat, 0.0316. 
Color, yellow. 
Crystals, octahedral. 
OCCURRENCE.—Gold is found in nature chiefly in 
the metallic state, or as native gold, and less frequently 
in combination with tellurium, lead, and silver. It is 
also found combined, or, perhaps, more strictly speak- 
ing, minutely mixed with pyrites and other sulphides, 
more commonly called “sulphurettes.” 
Native gold occurs rather frequently in crystals be- 
longing to the cubic system, the octahedron being the 
commonest form, but other and complex combinations 
have been observed. Large crystals are rarely well de- 
fined, owing to the softness of the metal, the points 
being commonly rounded. The most characteristic 
forms, however, are the nuggets or pepites. These, 
when of weight less than one-quarter to one-half an 
ounce, are known as gold dust. 
Except the larger nuggets, which are usually more 
or less angular or irregular, gold is generally found 
in a bean-shaped or somewhat flattened form, the 
smallest particles being scales of scarcely appreciable 
304 305 
GOLD 
thickness, and owing to their small bulk, as compared 
with their surface, they are frequently suspended in 
water and may be washed away by rapid current; 
hence, they are known as float gold. 
In the museum of the Mining Bureau in San Fran- 
cisco are several plaster of Paris models of famous gold 
nuggets found in the various gold regions of the world. 
The largest single piece of gold ever found was taken 
out at Ballarat, Victoria, Australia. It weighed 2166 
troy ounces, and was valued at $41,882. The second 
largest was discovered in the Ural Mountains district, 
and weighed 1200 ounces. The third largest, which 
was also found in Victoria, Australia, weighed 1121 
ounces, and was valued at $22,000. 
The physical properties of native gold are quite simi- 
lar to those of the melted metal and its alloys. The 
composition varies considerably in different localities 
as shown in table on page 298. 
The most important minerals containing gold are: 
Sylvanite, or graphic tellurium, (AgAu)Te2 contain- 
ing 24 to 26 per cent. 
Calaverite, AuTe2, containing 42 per cent. The 
calaverite, a nearly pure telluride of gold, has been 
found to some considerable extent in Calaveras County, 
California. Hence the name of the county. 
Nagyagite, or foliate tellurium, of a complex and 
rather indefinite composition, and containing from 5 
to 9 per cent only of gold. 
The minerals of the second class, called auriferous, 
are comparatively numerous, and include many of the 
metallic sulphides. The most important of these are 
iron pyrites and galena; the first of these is of great 306 
Practical dental metallurgy 
ANALYSIS OF NATIVE GOLD FROM VARIOUS LOCALITIES 
Locality 
Gold 
Silver 
Iron 
Copper 
EUROPE: 
British Isles— 
Vigra and Clogau 
90.16 
9.26 
Trace 
Trace 
Wicklow (River) 
92.32 
6.17 
.78 
.... 
Transylvania 
60.49 
38.74 
0.77 
ASIA: 
Russian Empire— 
Brezovsk 
91.88 
8.03 
Trace 
.09 
Ekaterinburg 
98.96 
0.16 
.05 
.35 
AFRICA: 
Ashantee 
90.05 
9.94 
— 
AMERICA: 
Brazil 
94.00 
5.85 
Central America 
88.05 
11.96 
Titiribi 
76.41 
23.12 
0.87 
California 
90.12 
9.01 
Mariposa 
81.00 
18.70 
Caribou 
84.25 
14.90 
.03 
AUSTRALIA: 
South Australia 
87.78 
6.07 
6.15 
Ballarat 
99.25 
0.65 
— 
.... 
practical importance, being found in many districts ex- 
ceedingly rich, and, next to the native metal, is the 
most prolific source of gold. 
A Native Amalgam of gold is found in California, 
but rarely in any considerable quantities. 
Gold is so widely distributed throughout the earth’s 
crust that few regions may be said to be destitute of 
slight traces of it; yet it has been found in compara- 
tively few localities in quantities sufficient for economic 
extraction. The principal supplies of the metal have GOLD 
307 
been derived from Africa, California, Nevada, Alaska, 
Australia, Mexico, Brazil, Ural Mountains, Transyl- 
vania, etc. 
Sutter 
Marshall 
Fig. 52.—James W. Marshall, who discovered gold in California in January, 
1848, and John A. Sutter who financed the expedition. 
Fig. 53.—The “tail race” at Sutter’s Mill, California, where gold was 
discovered by John W. Marshall. 
California was for many years chiefly known to the 
world as the region where gold was found in extra- 308 
PRACTICAL DENTAL METALLURGY 
ordinarily large quantities. Great excitement was oc- 
casioned by the discovery of the precious metal in 
January, 1848, and its subsequent extraction from the 
placers of the Sierra Nevada Mountains. The gold re- 
gions of California are the mountain counties lying be- 
tween Shasta and Lassen on the north, and Fresno on 
the south. At the time of their greatest productive- 
ness the yield reached about $65,000,000 in value a 
year, this was from 1850 to 1853. 
Fig. 54.—A California prospector in early days. 
The association and distribution of gold may be con- 
sidered under two different heads; namely, as it oc- 
curs in mineral veins, and in alluvial or other super- 
ficial deposits which are derived from the waste or dis- 
integration of the former. As regards the first, it is 
usually found in quartz veins or reefs traversing slaty 
or crystalline rocks either alone or associated with such 
metals as iron, copper, tellurium, and rarely bismuth, 
or such minerals as magnetic and arsenical pyrites, GOLP 
309 
galena, specular iron ore, and silver ore, and rarely 
with the sulphides of molybdenum, tungstate of cal- 
cium, bismuth, and tellurium minerals. 
In the second or alluvial class (placers) of deposits 
it is associated chiefly with those minerals of great 
density and hardness, such as platinum, osmiridium, 
and other metals of the platinum group, tinstone, 
chromic, magnetic, and brown iron ores, diamond, sap- 
phire, ruby, topaz, etc., which represent the more dur- 
Fig. 55.—Ancient gold mining in the Sudan. The milling or crushing 
of the. ore was done in stone grists, the nether stone being hard and about 
20 inches in diameter. The mullers were of a softer, coarse-grained granite. 
The quartz was fed through the hole in the top and the rocking or grinding 
effected by means of a short stick in the smaller hole on the side. The 
washing table in the lower picture is much like the modern sluice. 
able original constituents of the rocks whose disinte- 
gration has furnished the detritus. 
MINING AND EXTRACTION.—It is believed that 
gold has reached the maximum of production. There 
are very few localities in Siberia, South America and 
Africa which have not been fully explored. In the 
future the increase in production must come from more 310 
PRACTICAL DENTAL METALLURGY 
intensive working and a closer saving. The simplest 
and oldest form of mining and extracting the precious 
metal is known as— 
Placer mining, which consists of washing the alluvial 
deposits, sands of rivers, and other earthy matter, by 
which the lighter particles of earth and sand are 
Fig. 56.-—Panning gold. 
washed away, while the gold in irregular and flattened 
grains by its gravity remains. 
In the early days of California, when rich alluvial 
deposits were common at the surface, the simplest ap- 
pliances sufficed, the most characteristic of which 
was— 
The pan, a circular dish of sheet-iron, with sloping 
sides about 13 or 14 inches in diameter. The pan, about GOLD 
311 
two-thirds filled with pay dirt to be washed, is held in 
a stream or in a pool of water. The large stones sepa- 
rated by hand; the pan is given a twisting lateral mo- 
tion, keeping the contents suspended in the stream to 
remove the lighter substances, the heavier gold remain- 
ing on the bottom. This process is termed panning out. 
The cradle is a simple contrivance based upon the 
Fig. S 7.—Tlie ‘‘cradle” in use in the Alaskan gold fields. 
same principle for treating somewhat larger quantities. 
The tom is a sort of cradle with an extended sluice 
placed on an incline. Under certain circumstances mer- 
cury is used in the sluice to amalgamate the gold. 
The sluice, a Californian invention, is used in 
working on a larger scale, where the supply of water is 
abundant. The simplest form of this consists of a rec- 
tangular trough of boards set up on trestles at an ip- 312 
PRACTICAL DENTAL METALLURGY 
clination that the stream of water may carry off all but 
the largest stones, which are kept back by a grating, 
and removed by hand as they accumulate. The floor 
of the sluice is provided with riffles made of strips of 
wood laid parallel with the current, and at other points 
with boards having transverse notches filled with mer- 
Fig. 58.—Sluicing gold in Alaska. Water is oftentimes very difficult to 
obtain in some fields and then it is used over and over again. 
cury for the accumulation of the gold. The length of 
the sluice depends, of course, upon the volume and 
flow of water, the ordinary ones ranging from 100 to 
500, and even to 1000 feet in length, while the sluices 
leading from hydraulic operations are sometimes a 
mile in length. 
Hydraulic Mining.—This method is also a Californian GOLD 
313 
Figs. 59 and 60.—Two views of hydraulic operations; the first shows 
the mortar at work tearing down the soil, while the second shows the big 
sluices into which all the detritus flows. 314 
PRACTICAL DENTAL METALLURGY 
invention, and has for the most part been confined to 
the placer mining of this State. The method is em- 
ployed where an abundance of water is available, and 
where thick hanks of auriferous gravel are to be re- 
moved ; it consists in loosening and washing away 
banks of gravel, sand, and soil with powerful streams 
of water discharged from nozzles resembling those of 
a fire hose. It is supplemented by the use of gunpowder 
for breaking up and removing “bed rock,” immense 
boulders, etc., and arrangements must be made for 
saving the gold without interrupting the flow of water, 
and for disposing of the vast masses of impoverished 
gravel. The stream from the site of operation laden 
with stones and gravel passes into sluices where the 
gold is recovered in the manner already described. 
Quartz mining does not greatly differ from the 
methods employed in the extraction of similar deposits 
of other metals. The quartz is first reduced to a very 
fine powder; this is accomplished in the most produc- 
tive regions, such as California and Australia, by means 
of the stamp mill. In this operation cylindrical iron 
pestles, weighing from 600 to 800 pounds, are lifted 
by means of cams, and allowed to fall some 8 or 10 
inches at the rate of from 30 to 90 blows per minute 
upon the quartz. A stream of water carries the com- 
minuted material into contact with mercury, which, on 
account of its great affinity for the gold, absorbs and 
separates it from the earthy gangue. To prevent 1he 
“sickening” and “flouring” of the mercury, which is 
produced by certain associated minerals in the ere, and 
which occasions much annoyance and some consider- 
able loss of both gold and mercury, by greatly dimin- GOLD 
315 
ishing the solvent powers of the latter metal, a small 
quantity of the amalgam of sodium is added to the 
mercury. 
Before the mercury becomes saturated it is removed 
and subjected to powerful pressure in leather bags, 
Fig. 61.—A primitive Philippine dredger operated by hand on the 
interior rivers. 
when the excess is squeezed out through the pores of 
the leather leaving the more or less coherent mass of 
rich amalgam inside. The mass is then heated in a 
proper vessel, when the mercury is distilled over and 
recondensed in iron retorts. The gold is left in a 316 
PRACTICAL DENTAL METALLURGY 
spongy state usually quite free from other metals, ex- 
cept silver, which is separated by the “parting 
process,” to be subsequently described. The spongy 
gold with its silver content is then melted in plumbago 
crucibles with the addition of a small quantity of suit- 
able fluxes and shipped as bullion. 
In some cases it has been found advantageous to 
smelt the ore by fusing it with lead, which latter in the 
fused state has a very great affinity for gold. In such 
Fig. 62.—A huge dredger operating in one of the rivers in the Alaskan 
fields. During the summer months the machinery is in operation twenty- 
four hours in the day with no need for electricity for illumination. 
operations the crushed ore is mixed with suitable pro- 
portions of metallic lead or litharge and charcoal, to- 
gether with some lime or clay as a flux for the silica 
and fused on the hearth of a reverberatory furnace. 
The melted lead dissolves the particles of gold, just as 
mercury does, and sinking beneath the lighter slag, is 
drawn off and afterward separated from the gold by 
cupellation. GOLD 
317 
DREDGER MINING.—Dredger mining differs from 
other methods only with respect to the manner of ob- 
taining the ore. Usually a mining claim is selected in 
a valley where the debris from the surrounding moun- 
tainous country has been accumulating for countless 
centuries, and where the hard pan or bed rock is not 
more than forty feet below the surface of the soil. 
It makes no difference whether the claim is on an 
arid portion of the land or in a river bed if water to 
float the dredger can be obtained. A large excavation 
is made and filled with water; the dredger is launched 
and operations begin. The earth is removed by a 
series of buckets on an endless chain, each bucket hav- 
ing a capacity of 1000 pounds or more. The lips of 
the buckets are constructed of manganese steel and are 
thus capable of withstanding heavy stresses in scoop- 
ing up the earth. Usually they engage about six inches 
of the hard pan or bed rock for most of the gold is 
found there, and then every bit of earth is taken up to 
the surface. The water in the excavation tends to 
soften the earth and is also used on the washing tables. 
The earth is carried to a large revolving separator 
which separates the large rock from the clay and finer 
earth, the latter passing over the jig table if no pulver- 
izing is necessary. From there the ore is washed over 
the amalgamators where the gold is collected for fur- 
ther refining. 
Chlorination Process.—Under some circumstances it 
is found best to separate the gold from the quartz in a 
wet way by means of chlorine. The process depends 
upon the fact that chlorine acts rapidly upon gold, but 
does not attack ferric oxide, and is now adopted in 
Grass Valley, California, where the waste minerals prin- 318 
PRACTICAL DENTAL METALLURGY 
cipally pyrites, have been worked for a considerable 
time by amalgamation. 
The ore is roasted at a low temperature in a rever- 
beratory furnace, during which salt is added to convert 
all the metals present, except iron, into chlorides. The 
auric chloride is, however, decomposed, at the elevated 
temperature, and the finely divided particles are readily 
attacked by the chlorine gas. The roasted mineral, 
slightly moistened, is then introduced into a wooden vat 
which is provided with a double bottom. Chlorine gas 
is led from a generator beneath the false bottom, and 
rises through the moistened ore, converting the gold 
into a soluble chloride which is afterwards removed by 
washing with water. The noble metal is then precipi- 
tated by the sulphate of iron. The method is very ac- 
curate and yields metal of great purity. 
FLOTATION PROCESS.—See chapter on compounds 
of metals and nonmetals, p. 55. 
CYANIDE PROCESS.—This process has been de- 
veloped to increase the production of precious metals, 
gold and silver, by a greater recovery, and is based 
upon the solubility of these metals and some of their 
mineral compounds in an alkaline cyanide solution. 
Eisner’s theory of the action of oxygen in the dissolu- 
tion of precious metals first showed the possibilities of 
this method of reduction. The equation showing the 
reaction is as follows: 
2Au + 4KCN + 0 + H20 = 2KAu(CN) 2 + 2KOH. 
The ore is first crushed to free the native metal, if 
gold, or the gold and silver compounds from the gangue, 
and is mixed with water to form a slime. In certain GOLt) 
319 
instances where the ore requires a long contact with the 
cyanide solution to dissolve it, the crushing is not car- 
ried to so great a degree of fineness, merely producing 
a coarse sand, and the minerals or metals are leached 
out. 
Formerly potassium cyanide was used, but now cyan- 
ides of sodium and calcium are used, chiefly for econ- 
omy. The calcium cyanide is converted into calcium 
hydroxide which is sufficiently soluble to keep the so- 
lution alkaline, while the suspended particles are car- 
ried away with the tailings. The essential difference 
between gold and silver cyaniding is that gold usually 
occurs native while silver is found principally as the 
sulphide, chloride, or bromide. The concentration of 
the cyanide solution as well as the time of treatment 
and the comminution of the ore are important factors 
which must be determined at the plant. 
Certain minerals or portions of the gangue may act 
as cyanicides and destroy the value of the solution as a 
metal solvent. These ores may require some prelimi- 
nary or accessory treatment, though all gold and silver 
ores are capable of recovery by this process. Usually 
the slimes are allowed to stand in contact with the 
solvent for twenty-four hours, when the solution is 
drawn off and the metal precipitated electrolytically, 
or by zinc shavings. The recovery is so complete in 
some instances that the loss does not exceed one and 
one-half grains per ton. 
The strength of the cyanide solution varies from 0.5 
to 0.3 per cent, or from 0.1 lb. to 5-6 lbs. per ton of ore. 
On such a basis the cost is less expensive than smelting. 
At Cerro de Pasco, Peru, there is a bed of tailings esti- 320 
PRACTICAL DENTAL METALLURGY 
mated at 15,000,000 tons, which is being worked by the 
cyanide process for the recovery of silver at a profit, 
and ultimate returns are estimated at $30,000,000. 
REFINING GOLD.—Unless it can be utilized, the ac- 
cumulation of gold in the form of scraps, filings, etc., 
in the dental laboratory and operating-room frequently 
becomes a source of considerable loss to the dentist, be- 
cause he is unfamiliar with the methods of refining, or 
lacks the necessary apparatus. 
Some forms of scrap gold, such as old fillings, need 
only to be melted with the proportion of silver, copper, 
or both, to produce the desired alloy. Others, as scrap 
plate of known carat, may be utilized for casting bridge 
pontics, cusps for crowns, etc. 
Old crowns, plates, bridges, mixed fillings containing 
more or less iron from the file, zinc, lead, antimony, 
and other base metals, may be converted into malleable 
gold by simply roasting with such fluxes as will com- 
bine chemically with the base metals and remove them. 
Sweepings may be washed and then carried through 
the same process, which is known as 
THE ROASTING PROCESS.—A method for roughly 
refining and rendering brittle gold malleable. This 
process may be most satisfactorily employed where the 
approximate carat of the bulk of the scraps is known 
and the gold is suspected to be unworkable, owing to 
the admixture of base metals. 
The larger pieces should be removed from the ac- 
cumulation and the smaller ones with the filings freed 
from as much iron and steel as possible by a good mag- 
net. All should then be placed in a previously well- 
boraxed and tried graphite crucible, with the addition GOLD 
321 
of sufficient potassium carbonate to well cover the 
charge; the object of this addition being to form, when 
heated, a thin flux, permitting the small particles and 
filings to sink and accumulate in one mass. 
The furnace should be placed beneath a fume-chim- 
ney or by a window with an outward draught, that the 
fumes escaping from it during' the roasting may not 
fill the laboratory, thereby endangering the health of 
the students or operator: and damaging such instru- 
ments and tools as may be unprotected. The most con- 
venient place to avoid such results is the fire-place. 
The furnace may be placed beneath its chimney in such 
a manner that all fumes will be readily carried off. 
When the metal has become thoroughly fused, the 
refining process may be begun, by first adding small 
quantities of the oxidizing agent, potassium nitrate, 
(KN03), accompanied with borax as needed to prop- 
erly protect the mass and further the process. The 
object of the potassium nitrate is to furnish sufficient 
oxygen to oxidize the contaminating base metals be- 
neath the flux, thus separating them from the gold. As 
most base metals are easily oxidized under these cir- 
cumstances, a continuation of this process from ten 
minutes to one hour and a half, according to the quan- 
tity of material, and the proportion of base metals con- 
tained, adding the nitrate and borax as required, and 
maintaining a state of perfect fusion of the metal, the 
ingot, when made by pouring into a previously warmed 
and oiled mold, will be found to be quite malleable. 
If, however, upon examination it is found to be still 
brittle, it should be placed in a clean, boraxed, and 
tried crucible, heated, and brought to a perfect state 
of fusion. A mixture of equal parts of finely pulver- 322 
PRACTICAL DENTAL METALLURGY 
ized vegetable charcoal and ammonium chloride should 
then be added; at first sufficient to properly cover and 
protect the molten mass, and afterwards a small quan- 
tity at a time as it is needed. When the metal has 
been sufficiently treated, which may be determined by 
removing small quantities and subjecting them to the 
physical tests for malleability, the crucible is to be re- 
moved from the furnace and the metal cast into an 
ingot or allowed to cool in the crucible as a button. 
The rationale of such a process is that the heat of the 
crucible breaks up the chloride compound, liberating 
the chlorine in the nascent state; which in turn com- 
bines with the metals lead, tin, and silver, contained in 
the gold to form their respective chlorides. These are 
either volatilized or taken up by the flux, and the gold 
remains free of them. 
Mercuric chloride is sometimes used when the con- 
tamination of the gold with lead or tin is extensive, or 
where it is desired to remove a quantity of silver. But 
its use is so dangerous on account of the fumes evolved 
that it is rarely employed. 
Sulphur or antimonic sulphide is used to abstract 
large quantities of silver from gold, by combining 
with the former to form fusible sulphide of silver, leav- 
ing the gold free, or if the antimonic sulphide has been 
used, contaminated with antimony, which may be re- 
moved by fusing with borax and potassium nitrate, as 
previously described. 
In the process of refining by fluxes, the first step 
should be to determine, as far as possible, the nature 
of the debasing elements; this being known or reason- 
ably approximated, the process may be confined to the 
particular flux most likely to free the gold from its con- GOLD 
323 
tamination. Iron, steel, zinc, copper, antimony, and bis- 
muth are, perhaps, best removed by oxidation, through 
the agency of potassium nitrate. Lead, tin, and silver 
are removed by chlorine. 
If, after such treatment, the alloy is found to be mal- 
leable, but stiff or elastic, or dull in color, it very prob- 
ably contains some platinum which cannot be removed 
by this means, but which may be got rid of by a wet 
method. When desired, such an alloy may be made 
direct use of as clasp gold. 
When the object is to produce pure gold from which 
to subsequently prepare desired carats by alloying the 
results, it is best and most conveniently attained by 
the process known as 
PARTING GOLD.—A wet method for refining gold 
by inquartation, or “quartation,” as it is more com- 
monly called. This is accomplished by digesting the 
thinly rolled or granulated alloy of silver and gold in 
either nitric or sulphuric acid. 
The student, in his choice of metal for this operation, 
may endeavor to obtain gold containing as much silver 
as possible, and, as this will require an additional quan- 
tity of the latter metal fused with it in order to carry 
out the operation, it is of course an object, if possible, to 
employ silver which contains small quantities of gold, 
and thus, as it may be said, to carry on a double re- 
fining process at once. 
As the actual separation of the two is effected by di- 
gesting the mixture in hot nitric acid, which, while it 
is a ready solvent for other metals, is inactive upon 
gold, it may be asked: Why not at once treat the alloy 
with acid without such alloying? Such would be quite 
useless, for, the foreign metals being in so small a 324 
PRACTICAL DENTAL METALLURGY 
relative proportion, the acid would only remove the 
alloy at or near the surface, the metal being sufficiently 
close in texture to mask all the rest from the action ot 
the acid. 
The sulphuric acid process is doubly recommended, 
especially when large quantities of the alloy are to be 
digested, as it is less expensive, and the gold is obtained 
of a greater degree of fineness. The oxidizing action of 
the nitric acid is of especial value, however, when tin or 
antimony is present in the batch of metal. 
Preparation of the alloy.—The impure gold is first 
weighed and the approximate weight of the silver, if it 
contains any, subtracted; silver is then added in the 
proportion of three to one, less the amount already 
contained in the alloy, thus when melted forming an 
alloy of three parts silver and one part impure gold. 
Hence the term “ quartation. ’ ’ These proportions are 
then fused together in a clean and boraxed crucible, 
well mixed, and either poured into warmed and oiled 
ingot molds, to be subsequently rolled, or dropped while 
molten from the crucible into a wooden tub or tank of 
cold water for the purpose of granulation. The latter is 
unquestionably the simplest method of preparing it for 
digesting process, for, if poured into the ingot molds, 
the alloy will require rolling to a very thin ribbon (No. 
35 gauge), after which it must be cut into small pieces. 
The rolling many times is impossible, because of the 
gold that it is desired to refine being exceedingly brit- 
tle. The alloy being thus prepared, is ready for the 
acid. 
Nitric Acid Process.—For this process the prepared 
alloy is placed in a Florence flask and nitric acid to the 
amount of about one and one-half times the weight of GOLD 
325 
the alloy poured on. The acid should always be tested 
for chlorine by adding a drop of the solution of silver 
nitrate (AgN03) to it, which, if chlorine be present, will 
instantly be rendered milky from the precipitated chlor- 
ide of silver. Heat the flask gently in a sand-bath over 
a Bunsen or alcohol flame. Copious red futnes of the 
oxides of nitrogen and ammonium yill be given off, 
showing vigorous action on the alloy, and the silver and 
other metals will be dissolved, leaving the gold in a 
spongy mass of a blackish-brown color. When this 
evolution has entirely ceased and the flask is clear, care- 
fully decant the solution of the nitrates of silver, etc., 
thus formed and preserve it, adding a fresh portion of 
nitric acid and boil until all fumes cease to rise, which 
marks the termination of the digesting process. The 
acid is now replaced by distilled water two or three 
times, for the purpose of washing the gold remaining. 
At length filter the contents of the flask, catching the 
gold on the filter paper, add a sufficient quantity of 
potassium carbonate, fold the paper over the whole, and 
place in a previously boraxed crucible, melt and pour 
into warmed and oiled ingot molds. 
Gold thus refined may reach .998 fineness, and is 
ready for any desirable alloying. 
For the recovery of the silver, see chapter on that 
subject. 
Sulphuric Acid Process.—The use of sulphuric acid 
for the operation is preferred by many. For, as was 
stated, it is more economical; and the gold so refined is 
more thoroughly freed from silver; indeed, it is said 
that gold having been previously refined by the means 
of nitric acid may be freed of still more silver by this 
acid. In operating the metals are so mixed that the 326 
PRACTICAL DENTAL METALLURGY 
gold amounts, at most, to not quite half the weight of 
the silver; and if copper is contained, (which in small 
proportions facilitates the operation), it should be un- 
der 10 per cent, for, if too much be present, a large 
quantity of sulphate of copper will be formed, which 
latter is insoluble in the strong acid liquors. The proc- 
ess may be employed for silver containing very small 
quantities of gold. Thus, in France, it was found very 
profitable to separate the gold from old five-franc 
pieces, which contained only .001 to .002 of gold. 
The alloy having been granulated, as before described 
is introduced into a digester (Florence flask) with about 
two and one-half times its weight of concentrated sul- 
phuric acid. This is allowed to boil, during which 
strong action is evidenced by copious evolution of sul- 
phur dioxide, while the silver and copper are simul- 
taneously converted into sulphates. This first boiling 
is continued as long as sulphur dioxide is evolved, 
which in large quantities of metal will commonly go on 
about four hours. The liquid is then removed and a 
smaller quantity of acid added, the boiling being fur- 
ther carried on for a short time, after which the diges- 
ter is allowed to remain at rest, in order that the gold 
may subside. Sometimes it may be requisite to use 
even a third acid. 
Repeated washing of the gold with boiling water is 
now necessary, as the sulphate of silver is a very 
insoluble salt, and sulphate of copper, when contained 
in so acid a menstruum, is also somewhat so. The 
gold is then dried, melted, and poured, as described 
before. 
This process affords gold as pure as .9985. GOLD 
327 
THE PREPARATION OF CHEMICALLY PURE 
GOLD.—The metal, either in the form of powders, 
granulations, thin plate, or “ cornets ” from the purest 
gold that can be obtained, is dissolved in chemically 
pure nitrohydrochloric acid. The best material to 
operate on is gold which has been refined in the ordi- 
nary way; this may be used in the form of a powder, 
as it is precipitated in the last process, as granulations 
or as plate. The acid for small quantities is best con- 
tained in an evaporating dish placed in a sand-bath 
upon a tripod, over the flame of a Bunsen burner, be- 
neath a chimney or near an open window. The action 
will be tolerably energetic when the metal is first intro- 
duced; hence, it is not necessary to ignite the burner 
at the start, but as the action slackens a moderate heat 
may be applied. 
Normal aqua regia consists of HN03 + 4HC1, but for 
dissolving gold the acid should be prepared by mixing 
200 c.c. HC1 (density 1.19), 45 c.c. HN03 (density 1.4), 
and 245 c.c. H20, which are the proportions recom- 
mended by Prat in 1870. Gold dissolves in aqua regia 
in accordance with the equation Au + HNOs + 4HC1 = 
2 H20 and NO + TIAuCl4, and any excess of either acid 
is unnecessary. 
Each ounce of gold will require about three and 
one-half ounces of mixed acid for its solution. During 
the process of solution a sediment will be noticed in 
the bottom of the evaporating dish, which will be recog- 
nized by the operator as a silver chloride, formed by 
the union of the silver contained in the gold and the 
liberated chlorine. It must not be expected that all the 
silver will be directly precipitated to the bottom as a 
chloride, for the liquor is strongly acid, and some may 328 
PRACTICAL DENTAL METALLURGY 
be held in solution. Therefore, this must be taken into 
consideration, and subsequent pains taken to throw it 
down by the thorough evaporation of the nitric acid. 
The gold having been dissolved, the solution is now 
best transferred to a clean dish by decantation, leaving 
the chloride of silver in the first and the solution con- 
tained in the second dish heated to further evaporate. 
When about one-third is evaporated more chloride of 
silver will be found to have been separated from the 
solution and precipitated. It is well, therefore, to 
again transfer the solution to a third dish by decanta- 
tion and evaporate as before, care always being main- 
tained during the heating not to apply so great a tem- 
perature as to decompose the auric salt which adheres 
to the side of the dish above the fluid. 
As the bulk is reduced over the gentle heat by evap- 
oration, small quantities of hydrochloric acid are to be 
added from time to time, which has the effect of liberat- 
ing nitrous anhydride by decomposing the remaining 
nitric acid in the liquor; these additions must, however, 
be made very cautiously, for the action produced is 
very energetic, and without due precaution, consider- 
able portions of the now rich liquor will be spurted out 
of the dish and lost. When the liquor has become of a 
deep red color, and of the consistency of syrup, it is to 
be withdrawn from the heat and permitted to rest for 
a time, when the whole of the auric chloride will crys- 
tallize, forming a mass of prismatic crystals. 
The bottom of the dish is now carefully wiped off to 
remove any sand or dirt that may have collected there 
from the sand-bath, and the dish and its contents im- 
mersed in about a half pint of distilled water, acidu- 
lated slightly with hydrochloric acid. It is better now GOLD 
329 
to let this solution stand a week, for chloride of silver, 
although slightly soluble in a very strong and hot acid 
solution, is separated by dilution, and, by allowing this 
rest, it will completely subside in the vessel. At the 
end of this time the solution must be filtered to re- 
move any foreign substance, together with the silver 
chloride. The filtrate will then be seen to be a rich 
straw-yellow, and the gold it contains is ready for 
precipitation. 
Precipitating the Gold.—The solution is now best 
contained in a large glass flask, and the precipitating 
reagent added. As gold is one of those metals which, 
as a base, combines with very feeble affinities, it is con- 
sequently not only very easily separated, but the phys- 
ical conditions of the precipitate may be much modified 
and controlled by the nature of the precipitant, as also 
by the mode of operating. Thus the gold may be 
thrown down in a powder, in scales, in more or less of a 
crystalline state, in a tolerably compact sheet or foil, 
or lastly, in a spongy condition much resembling so- 
called “solila” or “moss fiber.” And these states may 
be attained with some degree of certainty, although the 
circumstances determining the more compact forms are 
hardly yet well understood. 
Spontaneous precipitation may take place to some 
extent in a vessel of trichloride of gold when exposed 
to the air; and thus the sides of the vessel containing it 
will slowly become covered with the deposit. This is 
probably due to the action of the nitrogen of the air. 
Many elementary substances will precipitate gold from 
the trichloride. Most of the lower metals will reduce 
it, some metallic salts throw it down, and many organic 
bodies readily precipitate it. Thus sugar when boiled 330 
PRACTICAL DENTAL METALLURGY 
in it gives at first a light red precipitate, which after- 
wards darkens in color. 
Practically, however, ferrous sulphate or oxalic acid 
are the only precipitants used. The oxalic acid is pre- 
ferred, and is an excellent precipitant. 
The gold salt, being in solution, is broken up by the 
addition of a strong solution of oxalic acid, and the 
gold is precipitated to the bottom as either a crystal- 
line mass or a leafy foil. It is necessary to add a slight 
excess, and the whole should be kept at a gentle heat 
in a sand-bath over a flame. Soon after the applica- 
tion of heat some slight bubbling is noticed, a copious 
evolution of gas takes place, and at the same time the 
body of the liquid appears filled with most delicate 
spangles of metallic gold, which become coherent as 
they descend, and in consequence assume most any one 
of the forms above mentioned. The gas noticed to 
escape is C02, from the compound, oxalic acid. The 
reaction is of the simplest—an acid on a binary salt— 
2AuC13 + 3C2H204 = 6HC1 + 6C02 + 2Au. 
The action of this precipitant being gradual, and 
capable of much regulation, by the amount and nature 
of heat employed, while it is also peculiar in being at- 
tended throughout by this evolution of gas which rises 
quickly through the solution, there is produced from 
the former cause a tendency in the metal to deposit in 
a crystalline or crystallo-granular state; while from 
the latter a more or less spongy character is given to it; 
hence it will be readily seen that inasmuch as we are 
able to modify these conditions, so we can in the same 
degree influence the molecular nature of the result. 
Where ferrous sulphate is used, about four times GOLD 
331 
the weight of the gold will be necessary for precipita- 
tion. This may be dissolved quickly in hot distilled 
water and added to the gold solution. The precipitate 
thrown down is of a brown color, and will, on being 
gently burnished with the finger-nail, assume that 
metallic golden luster characteristic of the metal. The 
following is the reaction— 
AuC13 + 3FeS04 = FeCl3 + Fe2(S04)3 + Au. 
After the solution has fully subsided from the dis- 
turbance caused by addition and precipitation a quan- 
tity of hot hydrochloric acid may be added, and much 
of the supernatant liquor removed, either with a siphon 
or by decantation, and the remainder of the solution 
and precipitate poured upon the filter paper. The pre- 
cipitate is afterwards washed with hydrochloric acid, 
distilled water, aqua ammonia, and again Avith distilled 
water. The necessity of this is apparent, especially in 
the use of ferrous sulphate as the precipitate will be- 
come more or less contaminated Avith the iron, and in 
the use of oxalic acid this is to remove the copper, as 
gold precipitated by oxalic acid from an acid solution 
containing copper is ahvays contaminated with cupric 
oxalate. It is then also advisable to heat the solution 
with a slight addition of potassium carbonate, a soluble 
double oxalate of copper and potassium is formed, and 
the gold is left in the pure state. Gold may also be 
precipitated from its acid solution in a state of purity 
in the form of brilliant spangles by means of hydrogen 
dioxide,* thus— 
*The precipitation of gold is very slow in an acid solution. In the pres- 
ence of L1CO3 it is complete in a few hours, and more rapid with K2COs. 
Wash well with dilute HC1 after precipitating. 332 
PRACTICAL DENTAL METALLURGY 
2AuC13 + 3H202 = 6HC1 + 60 + 2Au. 
When the precipitated gold has been carefully washed 
and rewashed with distilled water, and the above- 
mentioned reagents, it may be dried and placed in a 
new crucible, previously boraxed, with some potassium 
carbonate and potassium nitrate melted and cast into 
an ingot. If iron ingot molds are used the gold 
should be washed after molding in hot hydrochloric 
acid to remove any trace of metallic or oxide of iron 
that may by chance have adhered to its surface during 
the process of casting the ingot. 
PROPERTIES.—Pure gold is a rich, beautiful yellow 
color, of strong metallic luster, unalterable in air. It 
is the most ductile of all metals, but ranks only fifth 
in point of tenacity. One grain, however, if covered 
with a more tenacious metal, like silver, forming a com- 
posite wire, may be drawn into a wire 550 feet in length, 
and only 1/5000 of an inch in diameter. It is also the 
most malleable of all metals. One grain of it may be 
beaten into leaves so thin as to cover an area of 75 
square inches, being of but 1/370,000 of an inch in 
thickness. 
Very thin leaves of gold appear green in color by 
transmitted light, but when heated, the light transmit- 
ted is ruby-red. 
Gold possesses the property of welding cold. Thus, 
thin leaves, foil, and other forms of gold are more 
especially adapted to the use of the dentist as a filling 
material. The small particles are welded together in 
one perfectly homogeneous mass as the filling is in- 
serted. The finely divided metal, such as that thrown 
down in the preparation of pure gold from the chloride GOLD 
333 
solution, may be compressed between dies in the form 
of disks or medals. 
The pure metal fuses at 1060° C. and its alloys at 
much lower temperatures. When heated much above 
its melting point it slowly volatilizes and is readily 
dissipated in vapor by the oxyhydrogen flame. 
Pure gold is nearly as soft as lead, in consequence of 
which articles of jewelry, coin, etc., made from it are 
alloyed with copper, silver, platinum, etc., to give them 
the requisite hardness, durability, and elasticity. 
The specific gravity of gold cast in an ingot is 19.265; 
when stamped, 19.31; and that of the precipitated metal 
from 19.55 to 19.72. 
Graham has shown that gold is capable of occluding 
0.48 of its volume of hydrogen, and 0.2 of its volume 
of nitrogen. 
GOLD BEATING.—After the gold is precipitated 
from the chloride solution, it is thoroughly washed, 
dried, and melted in a clean crucible at a temperature 
higher than necessary to simply fuse it, by which its 
malleability is said to be improved. It is then poured 
into ingot molds previously heated and oiled, and cast 
into ingots, each one inch wide, one-fourth of an inch 
thick, and from four to eight inches in length. These 
are removed from the mold, cleaned in dilute sulphuric 
acid, washed and annealed. The ingot is next lami- 
nated by being repeatedly passed through heavy steam 
rollers, and annealed after each lamination, until it is 
formed into a ribbon one inch wide, about the thickness 
of tissue paper, and its length depending upon the 
original weight of the ingot. 
The ribbons are then cut into pieces an inch square, 334 
PRACTICAL DENTAL METALLURGY 
their thickness depending upon the number of the foil, 
2, 4, 6, 10, etc., it is designed to prepare from them; 
some allowance being made for subsequent trimming, 
and the necessity for leaving the sheet of correct 
weight. These little squares are again cleansed, taken 
up by wooden pliers and placed between the leaves of a 
“ditch” made from vellum or ground parchment 
which holds about two hundred pieces. The cutch is 
then enclosed in parchment bands and beaten on a 
granite or marble block, securely and firmly set, with a 
hammer weighing from seventeen to twenty pounds. 
The hammer is short-handled, and is wielded by the 
beater with one hand, while with the other hand he 
holds and rotates the packet of gold. 
Every few moments the cutch is opened and the gold 
examined; then split in half and the position of the 
pieces reversed, so as to bring the middle ones to the 
outside and those on the outside to the middle of the 
packet. During the beating the packet is continually 
rotated and turned, to distribute the force of the blows 
equally throughout the packet; at intervals it is taken 
up and rolled between the hands to overcome any ad- 
hesion that may have taken place between the leaves of 
metal and interposed parchment. 
Considerable skill is required to produce a good qual- 
ity of foil, the physical properties of the metal being 
capable of alteration by the too great rapidity of the 
process. 
When the gold is beaten into sheets about three or 
three and a half inches square, or about the size of the 
leaves of the cutch, which requires from fifteen to 
twenty minutes, they are removed from the cutch by 
means of the wooden pliers, and placed piece by piece GOLD 
335 
ill a second packet of larger size made of the same 
material and called a “shoder. ” If, however, the 
pieces are too thick to produce the required number 
they are cut into four pieces, and the process repeated 
in the cutch. The shoder is then placed in the parch- 
ment bands, and the beating continued until the gold 
again equals the size of the skins, which requires about 
twice the length of time as before. 
After the last beating the pieces are carefully laid 
out one at a time on a calf-skin cushion lined with soft 
flannel; the blemished, broken and torn ones are laid 
to one side, and the perfect ones are cut into uniformly 
square sheets so familiar to the dentist, by means of 
an instrument carrying four edges of malacca reed 
called a wagon. The gold does not adhere to this as it 
does to the metal. The sheets are then accurately 
weighed and are ready for annealing 
The annealing’ is an important and delicate process, 
and may be accomplished in several ways: in the muffle 
of a furnace, on heated platinum, or on platinum-wire 
gauze with a spirit-lamp beneath it. Whatever may be 
the means by which it is accomplished, it must be 
properly done, i. e., the temperature must be sufficient 
to thoroughly heat and soften it uniformly in every 
part of the sheet, without melting and thickening the 
edges. 
From the first to the last step the most important 
consideration is absolute purity and cleanliness. 
Each book of gold foil contains i/g of an ounce, 2y2 
pennyweight, or 60 grains. Each full sheet is 4 inches 
square, and the number of the foil indicates the weight 
of each full sheet. Thus, a book of No. 2 would con- 
tain 30 sheets 4 inches square of 2 grains each; No. 336 
PRACTICAL DENTAL METALLURGY 
10, 6 sheets of 10 grains each; No. 30, 2 sheets (4 
inches square) of 30 grains each, and so on. 
Corrugated foil is supposed to have been an outcome 
of the great Chicago fire. When the safes of one of 
the depots were opened, it was found that the paper 
had burned to a crisp, and the foil was found in 
the form now known as corrugated foil. It was tried 
by some, and found many friends. In making the cor- 
rugated foil today a miniature Chicago fire is used to 
burn the paper. The gold is beaten as described before 
to No. 4 foil. It is then placed, sheet by sheet, between 
paper and enclosed in an iron box, with weights on the 
gold. The box is placed on a slow fire and the contents 
allowed to smolder, care being taken not to ignite the 
paper. After smoldering, the heat is gradually let on 
until the paper becomes carbonized. As the paper 
shrinks, the gold shrinks with it. The carbon is then 
blown off, sheet by sheet, and we have what is called 
corrugated or crystalline gold. 
Cylinders.—These sheets are then rolled upon them- 
selves in a cylindrical form of desired thickness, and 
cut into the size and style of cylinders required. 
The numbering of pellets or cylinders is so variable 
with the different manufacturers that it really means 
little, if anything. Some number them as follows: No. 
one-fourth, of a sheet of No. 4 foil, rolled and cut 
into pellets of varying length; No. y2, one-half of a 
sheet of No. 4 foil, rolled and cut into pellets; No. 1, a 
whole sheet of No. 4, and so on. The length of the 
pellets is also variable, and is designated as style A, B, 
C, etc., by some manufacturers.* 
*Hood and Reynolds. 337 
GOLD 
Cylinders are, in accordance with the manner in 
which they are rolled, known as loose and compact. 
The former can only be made by the manufacturers, 
and are composed of several sheets of No. 4 corrugated 
cohesive foil laid loosely upon one another and rolled 
lightly around a smooth needle-like piece of steel. The 
needle is then removed and the cylinders are cut by 
a peculiar sharp tool into assorted sizes or styles. 
The compact variety may be made by the operator in 
a similar manner except that the ends of the cylinder 
will necessarily be more compact, on account of the 
manner in which it is cut. 
There are other forms of gold used, such as mat, block, 
rope, tape, ribbon, etc. 
Rolled Gold.—The heavier foil, as Nos. 20, 30, 60, 
160, etc., is usually prepared by rolling, instead of 
beating. Flattening by rolling elongates the fiber, 
instead of increasing its surface in all directions, and 
it is thought produces a foil of greater density and 
toughness, and, when annealed, greater softness. Such 
foil is exceedingly cohesive and tenacious. It is also 
made in the noncohesive variety. 
Gold and Platinum Foils.—These are prepared in a 
variety of ways by several manufacturers of dental 
foils. Some by electrodepositing a surface of pure 
gold upon platinum foil. As a rule such combinations 
produce a filling more able to stand the stress and 
abrasive force of mastication. 
Crystal Gold .—This form of gold was first introduced 
by A. J. Watts, who prepared it by precipitating gold 
from a chloride solution by means of oxalic acid, treat- 
ing the precipitate with nitric acid and neutralizing 338 
PRACTICAL DENTAL METALLURGY 
the acid by washing with ammonia. The crystalline 
substance was then thoroughly dried in a muffle, when 
it was ready for use. The preparation fell into disuse 
on account of its unreliable quality, frequently being 
contaminated with nitric acid and other foreign sub- 
stances. It is now prepared by electrolysis from the 
chloride solution. Plates of pure gold are suspended 
in the solution which replace the metal as fast as it is 
deposited upon the platinum cathode. When prepared 
properly it is an unobjectionable material, but certain 
precautions must be observed in its use, as its manipu- 
lation is very deceptive. 
ANNEALING GOLD.—This process has a two-fold 
purpose: (1) To remove any deleterious substances 
which may have accumulated on the gold through ex- 
posure, and (2) to soften and more perfectly restore 
its cohesive quality. 
After gold has been exposed for some time to the 
action of the air and extraneous influences, it loses to a 
great extent, the qualities it possessed when first pre- 
pared, i. e., it loses its softness, cohesiveness, etc., but 
is partially, if not wholly, restored to its original con- 
dition by annealing. 
This is accomplished by a variety of methods. The 
main consideration, however, is the employment of a 
flame of as great purity as possible, free from the evolu- 
tion of such substances as sulphur, chlorine, phospho- 
rus, carbon, and their compounds. Ethyl alcohol 
(C2H5OH) is considered to be one of the most con- 
venient and desirable liquid fuels. 
The gas flame from a small Bunsen burner is one of 
almost perfect combustion; has become quite popular, 
and may be conveniently used where the gold is not GOLD 
339 
annealed by passing through the flame. The most de- 
sirable means, perhaps, is found in the pure platinum 
coils which are heated to incandescence by the electric 
current. 
It has been observed that more even and uniform 
results may be attained by annealing the gold in small 
quantities on heated mica, or platinum, since the por- 
tion of the pellet or foil held by the carriers is only 
slightly heated when passed through the flame. Gold 
is best annealed after cutting, as the action of the 
shears in cutting annealed foil tends to give it a “wire” 
edge by slightly condensing it. 
PROPERTIES OF GOLD FOIL.—These are various 
and variable with the products of different manufac- 
turers. The most prominent and important for the 
consideration of the dentist is that known as cohesive- 
ness. 
Most metals which possess the analogous property 
called weldability are weldable in proportion to the 
length of time they will remain in a plastic condition 
under heat without melting, but pure gold is weldable 
cold. It is not to be inferred that gold is the only 
metal which is weldable cold; on the contrary, the 
clean, pure surfaces of many metals, such as lead and 
copper, are quite coherent, but much difficulty is en- 
countered in obtaining and keeping them in the neces- 
sarily pure state. 
Gold prepared by the manufacturers is unfortunately 
given a variety of names, such as cohesive, semicohesive, 
noncohesive, hard, soft, etc., all of which relate to its 
property of cohesiveness, and are perplexing and mis- 
leading to the older practitioners, not to say students. 
Gold is either cohesive or noncohesive. 340 
PRACTICAL DENTAL METALLURGY 
Cohesive Gold is simply pure gold. The greater its 
purity, the more perfect its cohesiveness. It is an- 
nealed and soft when it leaves the makers, and sheets 
of it laid upon each other will cohere by mere contact. 
As stated previously, after it is exposed to air and to 
extraneous influences, handled and jostled about, it 
loses, from contact with impurities, some of its co- 
hesiveness, and from pressure, some of its softness. 
These two properties are, however, partially or fully 
restored by proper annealing. 
Noncohesive Gold.—Since pure gold is cohesive by 
virtue of its purity, it is obviously conversely true 
that wowcohesive gold is as it is from impurity. The 
process of preparing noncohesive gold is a trade secret 
which every manufacturer possesses as part of his 
stock in trade. The natural cohesiveness of gold may 
be overcome by slightly alloying with iridium or iron, 
but it is probable this property is generally destroyed 
by some surface treatment the foil receives. Nonco- 
hesive foil cannot be made cohesive by annealing, 
because the impurity cannot be removed by that 
means. 
Semicohesive foil is noncohesive before and cohesive 
after annealing. It is evident that the process of an- 
nealing purifies it, thereby restoring its natural 
property. 
The terms “hard” and “soft” are used by the makers 
and many practitioners to designate the cohesive and 
noncohesive varieties, respectively. These terms are, 
however, erroneous, and should not be used. 
“The feeling of softness,’’ says Dr. Kirk, “exhibited 
by noncohesive foil under the instrument is due largely 
to the fact of its noncohesiveness, whereby the several GOLD 
341 
laminae slip or slide one upon another, thus conveying 
a yielding or soft sensation to the tactile sense, and 
making it possible to condense large masses at a time, 
the pressure being conveyed continuously throughout 
the mass and the condensation or consolidation being 
uniform. A similar mass of cohesive foil, treated in the 
same manner and under like conditions, presents a 
greater resistance to the instrument, and conveys the 
idea of hardness, from the fact that as pressure is ap- 
plied the successive lamina; unite or weld together 
from the surface downward into a homogeneous stratum 
of metal, which offers greater resistance and becomes 
more impenetrable by constant additions to its thick- 
ness, until the condensing instrument fails to make 
any further impression; but upon removing the mass of 
gold it will be found that that portion of it which oc- 
cupied the bottom of the cavity is still in the form of 
foil and not homogeneously condensed.” 
Purity.—The physical properties of gold are more 
apt to be influenced by lack of purity than by any 
other factor. Impurity may be occasioned by several 
means: first, by admixture of other metals, especially 
those easily oxidized. Second, by surface contamina- 
tion caused by handling or exposure to vaporous gases. 
Third, by the absorption or occlusion of gases. 
The following assays were made for Dr. Kirk by 
Messrs. Dubois and Eckfeldt, assayers of the United 
States Mint, Philadelphia. The table exhibits in thou- 
sandths the relative fineness of some of the foils in 
general use.* 
‘American System of Dentistry, iii, p. 842. 342 
PRACTICAL DENTAL METALLURGY 
Each assay was duplicated: 
No. 1. Abbey’s Non Cohesive 998.8 998.7 
No. 2. Wolrab’s, from C. A. Timme..999.2 999.3 
No. 3. Quarter-Century, S. S. White 
Dental Mfg. Co 999.1 999.1 
No. 4. Bowan’s Decimal Foil from 
Gideon Sibley 999.9 999.8 
Discoloration.—The unfortunate discoloration of 
some gold fillings is in all probability due to a slight 
admixture of iron obtained during the precipitation 
from the chloride solution when ferrous sulphate is 
used, or from the iron ingot mold, or from the surface 
of the plugger point during the insertion of the filling. 
COMPOUNDS OF GOLD WITH OXYGEN.—Gold 
forms two oxides: 
Aurous Oxide, or Monoxide, Au20, is prepared by 
adding a solution of caustic potassa to the monochlo- 
ride. It is a green, unstable powder, being easily de- 
composed into metallic gold and auric oxide. 
Auric Oxide, or Trioxide, Au203, is prepared by add- 
ing magnesia to auric chloride; when the sparingly 
soluble aurate of magnesium thus formed is well washed 
and digested with nitric acid, auric oxide is left as an 
insoluble, reddish-yellow powder. It is easily reduced 
by heat or mere exposure to light; soluble in nitric, 
hydrochloric, and hydrobromic, and insoluble in hydro- 
fluoric acid. Its acid properties are marked: it dis- 
solves freely in alkalies. When digested with ammonia, 
it yields— 
Fulminating Gold.—This compound is usually pre- 
pared, however, by the addition of ammonia to tri- 
chloride of gold. It is a buff precipitate, and explodes GOLD 
343 
violently when gently heated. Its formula is probably— 
Au203(NH4)3,H20. 
ACTION OF ACIDS ON GOLD.—Gold is not tar- 
nished or affected by air or water at any temperature, 
nor by sulphuretted hydrogen. 
Neither is it soluble in sulphuric, nitric nor hydro- 
chloric acid. 
In nitrohydrochloric acid, however, it speedily dis- 
solves, forming the trichloride of gold, AuC13. 
It is also attacked by a vapor or solution of chlorine; 
By bromine, dissolving in bromine-water to form auric 
bromide, AuBr3; and 
By iodine, dissolving when finely divided in hydriodic 
acid by aid of the air and potassium iodide, forming 
potassium auric iodide— 
2Au + 6HI + 2KI + 30 = 2KIAuI3 + 3H20. 
Potassium cyanide solution dissolves precipitated 
gold with the aid of air, forming potassium auro- 
cyanide— 
2Au+ 4KCN + 0 = 2KAu(CN)2 + K20. 
Purple of Cassius.—So named from its color and 
from the name of its discoverer. It is much employed 
for imparting a rich red or reddish purple to glass and 
porcelain, and is of especial interest in dentistry, be- 
cause it is used by the manufacturers of artificial teeth 
to produce the gum tint of dental porcelain. It is a 
verifiable material composed of gold, tin and oxygen. 
The proportion, however, is thought to be variable. 
It is generally given the formula— 344 
PRACTICAL DENTAL METALLURGY 
Au20 . Sn02,SnO. Sn02.4H20. 
It is prepared by a variety of methods. Pelletier’s 
is as follows: 20 grains of gold are dissolved in 100 
grains of aqua regia containing 20 parts nitric to 80 
parts hydrochloric acid; the solution is evaporated to 
dryness over a water-bath; the residue dissolved in 
water; the filtered solution diluted with seven or eight 
deciliters of water and tin filings introduced into it. 
In a few minutes the solution becomes brown and tur- 
bid and deposits a purple precipitate, which merely 
requires to be washed and dried at a gentle heat. The 
purple thus prepared contains, in 100 parts, 32.746 
parts of stannic acid, 14.618 of protoxide of tin, 44.772 
of aurous oxide, and 7.864 of water. The precipitate 
obtained by the addition of stannous chloride to auric 
chloride is always brown. To obtain a fine purple pre- 
cipitate the auric chloride should be treated with a mix- 
ture of stannous and stannic chlorides. 
The purple is now produced by a dry method, by the 
manufacturers of gum enamel. It consists of digesting 
an alloy of gold, tin, and silver in nitric acid. The 
method was discovered by the late Professor Elias 
Wildman. The proportions are as follows: 
Pure silver 240 grains 
“ gold 24 tl 
“ tin 17.5 “ 
In preparing the alloy it should be melted and granu- 
lated four times to insure intimate admixture of the 
metals. It is afterwards placed in a flask and digested 
by the aid of gentle heat in chemically pure nitric acid 
in the proportion of 2 parts acid to I of water. After GOLD 
345 
the silver has all been dissolved the precipitate is al- 
lowed to settle, the supernatant liquid poured off and 
the precipitate washed several times with warm dis- 
tilled water. It is then again subjected to the action 
of dilute nitric acid, aided by heat and continual stir- 
ring to dissolve any of the remaining silver. When 
all action subsides, pour the contents of the flask on a 
filter paper and wash all the nitrate of silver out with 
pure water. The filtrate should be frequently tested 
with sodium chloride. When the latter reagent will 
no longer throw down the white precipitate of chloride 
of silver, the precipitated purple of Cassius on the 
filter paper is dried and is ready for use in the manu- 
facture of gum frit. 
Purple of Cassius is completely soluble in ammonia, 
upon ignition, however, it becomes insoluble. “That 
ignition,” says Dr. Kirk, “does effect such decomposi- 
tion is proved by the fact that the ignited powder can 
have all of its gold extracted by aqua regia, leaving 
pure stannic oxide, or the gold may be extracted from 
it by amalgamation with mercury, which is impossible 
before ignition.” 
ALLOYS.—Gold very readily unites with most of 
the metals, forming alloys of varied qualities. When 
in the pure state gold is too soft for any great use 
other than for filling teeth; consequently the greater 
quantity of gold is alloyed with some metal that will 
increase its hardness and durability, without greatly 
impairing its more valuable qualities. The metals 
usually employed for this purpose are silver, platinum 
and copper, 346 
PRACTICAL DENTAL METALLURGY 
Silver and gold are easily mixed together forming a 
solid solution, but do not seem to form definite com- 
pounds. Such alloys are more fusible, more ductile, 
harder, more sonorous and elastic than gold, and are 
generally of a greenish-white color. One-twentieth of 
silver is sufficient to modify the color of gold. The 
alloys of gold and silver are known to jewelers as 
yellow, green and pale gold, according to the content 
of silver. 
Copper and gold unite much more readily than silver 
and gold; indeed it is reasonable to believe from then- 
behavior that a chemical combination is formed with 
76 per cent of gold and 24 per cent of copper. Alloys 
of copper and gold are much harder, tougher, and 
more easily fused; less malleable and ductile, and 
greatly changed in color, being of a decidedly reddish 
tint, depending upon the proportion of copper with 
which the gold is debased. An alloy of gold 76, and 
copper 24, as referred to heretofore, is distinctly crys- 
talline and quite brittle; but a larger proportion of 
either gold or copper restores the malleability of the 
alloy. 
Standard Gold.—The standard alloy of most nations 
is one of copper and gold. Some contain small quan- 
tities of silver, but this is due to imperfect parting of 
silver and gold, or it may be contained in the copper 
used for the alloy. The proportion of copper to gold 
varies slightly in different countries, and such propor- 
tions are stated in thousandths; thus, pure gold is one 
thousand (1000) fine. The table on page 347 gives the 
composition of standard gold, as fixed by the nations 
mentioned. 347 
GOLD 
Nation 
Gold 
Copper 
United States 
France 
Germany 
Belgium 
Italy 
900 
100 
Switzerland 
(Carat 
21.6—) 
Spain 
Greece 
China 
Austrian Crowns 
Great Britain 
916 
84 
Ducats, Hungarian 
989 
11 
Ducats, Austrian 
986 
14 
Ducats, Dutch 
982 
18 
The first United States gold coins were ten-dollar 
pieces, coined in 1795; they weighed 270 grains each, 
and were of 916.666 (22-carat) fineness. Their weight 
was reduced in 1834 to 258 grains, with 899.225 (21.581- 
carat) fineness; and in 1837 the present standard of 
900 (21.599-carat) fineness was established. 
Alloys of gold with copper, or with silver, or with 
both, are much used in the manufacture of jewelry. 
When the gold contains copper only, it is termed red 
gold when silver only, white gold; if the gold contains 
both metals, the caratation is termed mixed. In many 
countries a legal standard of fineness is fixed for gold 
ornaments and jewelry. In England gold is stamped, 
or Hall Marked, 16, 18, and 22-carat; in France, 18, 20, 
and 22-carat; in Germany, 8, 14, and 18-carat, and, 
also, under the term joujou gold, a 6-carat gold used for 
electroplated jewelry. The purpose of the stamping is 
to protect the purchaser, who is enabled to know the 
carat of the gold he is buying. 
The following alloys used by jewelers are also of 
much interest to the dentist: 348 
PRACTICAL DENTAL METALLURGY 
TABLE OF MIXED CARATATION—Brannt 
Carats 
Parts 
Gold 
Silver 
Copper 
23 
23 
% 
% 
22 
22 
1 
1 
20 
20 
2 
2 
18 
18 
3 
3 
15 
15 
3 
6 
13 
13 
3 
8 
12 
12 
3% 
8% 
10 
10 
4 
10 
9 
9 
4% 
10% 
8 
8 
5% 
10% 
7 
7 
8 
9 
COLORED GOLDS—Brannt 
Parts 
Color 
Gold 
Silver 
Copper 
Steel 
Cadmium 
2 to 6 
1.0 
• • • • 
• • • • 
• • • • 
Green 
75.0 
16.6 
• • . • 
.... 
8.4 
l i 
74.6 
11.4 
9.7 
• • • • 
4.3 
i ( 
75.0 
12.5 
• • • • 
• • • • 
12.5 
( i 
1.0 
2.0 
.... 
.... 
Pale yellow 
4.0 
3.0 
1.0 
.... 
.... 
Dark yellow 
14.7 
7.0 
6.0 
• • • • 
• • • • 
i i a 
3.0 
1.0 
1.0 
.... 
• • • • 
Pale red 
10.0 
1.0 
4.0 
• • • • 
(( a 
1.0 
1.0 
Dark red 
30.0 
3.6 
.... 
2.6 
Gray 
1 to 3 
— 
— 
1.0 
— 
Blue 
Parts 
Color 
Carat 
Gold 
Silver 
Copper 
2 dwt. 18 grs. 
1 “ 18 “ 
2 dwt. 6 grs. 
3 “ 6 “ 
18 K 
15 “ 
Red “ 
18 K 
1 oz. 16 dwt. 
6 “ 
12 “ 
Reddish Spring gold 
16 K 
7 “ 
5 “ 
16 K 
1 oz 
2 “ 
8 ** 
Red tint 
16 K 
HIGHER CARAT COLORED GOLDS GOLD 
349 
Jewelers usually make their solders from the gold 
upon which they are to be used by the addition of 
small quantities of copper, silver or brass, the latter 
greatly increasing the fusibility and fluidity. The fol- 
lowing are: 
For 18-Carat Gold. 
18-carat gold 1 dwt. 
Silver 2 grs. 
Copper 1 gr. 
JEWELERS' SOLDERS 
For 16-Carat Gold. 
16-carat gold 1 dwt. 
Silver 10 grs. 
Copper. 8 grs. 
Carat.—The fineness of gold is also expressed in 
carats, a twenty-fourth part, formerly the twenty- 
fourth part in weight of a gold marc. It is now as- 
sumed that here are 24 carats in unity; whether the 
unit be one pound, one ounce, or one pennyweight, it 
is divisible into 24 equal parts, and each of these parts 
is called a carat to express fineness. If a quantity of 
gold is chemically pure, in other words contains no 
alloying elements, it is, as we have previously explained, 
1000 fine; or, in other words, each 24th part is gold, 
and it is, therefore, said to be of 24-carat fineness. If, 
however, 2 carats, or %4ths of the unit quantity are 
composed of one or more alloying metals, the gold is 
said to be 22 carats fine, or if 6 carats or %4ths of the 
alloy is debasing metal, the carat is 18 fine, etc. The 
table on page 342 shows the equivalent of each carat 
in thousandths. 
GOLD PLATE.—Pure gold is rarely employed in 
the dental laboratory, except for soldering continuous- 
gum cases and in some parts of crown and bridgework. 
Its extreme softness and flexibility make alloying ab- 
solutely necessary. The latter must be accomplished, 350 
PRACTICAL DENTAL METALLURGY 
Carats 
Thousandths 
Carats 
Thousandths 
1 
41.667 
13 
541.667 
2 
83.334 
14 
583.333 
3 
125.001 
15 
624.555 
4 
166.667 
16 
666.667 
5 
208.333 
17 
707.333 
6 
250.000 
18 
750.000 
7 
291.666 
19 
791.666 
8 
333.333 
20 
833.333 
9 
374.999 
21 
874.999 
10 
416.667 
22 
916.666 
11 
458.630 
23 
958.333 
12 
500.000 
24 
1000.000 
however, without practically impairing either its mal- 
leability, or pliancy, and at the same time endow it 
with that degree of hardness, elasticity and strength 
necessary to resist the stress and wear to which an 
artificial denture is exposed in the mouth. 
Copper and Silver are much used to debase or alloy, 
pure gold. It is questionable, however, whether cop- 
per should be used as almost universally as it is, in- 
deed, some regard it as exceedingly objectionable. A 
plate made from a gold alloy containing a large per- 
centage of copper is more easily tarnished, and has a 
disagreeable metallic taste, and may become a source 
of injury to the soft tissues of the mouth. 
Silver exercises a very benign influence over copper 
contained in gold plate, controlling the tendency to 
that disagreeable redness. Equal parts of silver and 
copper have little or no effect upon the color of gold. 
Silver assists in imparting hardness, elasticity and dur- 
ability to the alloy, without so far debasing it as cop- 
per alone. 
Platinum and silver are sometimes used to endow 
pure gold with the qualities necessary for a dental GOLD 
351 
base; but the labor of swaging is very greatly in- 
creased when platinum is contained in the plate. 
In order to secure the best results, alloys intended 
for plate should not be less than 18 carat fineness; 
and the alloy should contain as little copper as pos- 
sible. It may even be unsafe to use a loAver carat 
than 18. 
The folloAving are some of the formulas in use for 
the preparation of alloys for dental bases: 
Number 
of 
Formula 
Carat 
Parts Pure 
Gold 
Silver 
Copper 
Platinum 
* 1 
2 
3 
* 4 
5 
* 6 
* 7 
* 8 
t 9 
*10 
tn 
*12 
*13 
*14 
*15 
*16 
18 
18 
18 
19 
19 
20 
21 
22 
18 
18 
18 
19 
20 
20 
21 
21 
18 dwts. 
18 “ 
18 “ 
19 “ 
19 “ 
20 “ 
21 “ 
22 “ 
f 64 dwts. \ 
\ ($60.00) / 
20 dwts. 
/ 516 grs. 
\ ($20.00) 
20 dwts. 
20 “ 
/ 516 grs. ) 
\ ($20.00) / 
20 dwts. 
20 “ 
2 dwts. 
3 “ 
4 “ 
2 “ 
3 “ 
2 “ 
1 dwt. 
18 grs. 
13 dwts. 
2 dwts. 
96.45 grs. 1 
25c. coin / 
40 + grs. 
20 + grs. 
10c. coin 
13 + grs. 
4 dwts. 
3 “ 
1 dwt. 
3 dwts. 
1 dwt. 
2 dwts. 
2 “ 
1 dwt. 
1 dwt. 
1 dwt. 
6 grs. 
2 dwts. 
25 grs. 
18 grs. 
6 grs. 
75A grs. 
CLASP GOLD.—Gold for clasps, elastic wires, back- 
ings, stays, posts, dowels, etc., usually contains a small 
amount of platinum to give it greater strength and 
elasticity. The following formulas are recommended by 
Professor Chapin A. Harris: 
No. 1—20-Carat 
Pure gold 20 dwts. 
‘ ‘ copper 2 ‘ * ■ 
‘1 silver ...... 1 dwt. 
‘ ‘ platinum ... 1 “ 
No. 2—20-Carat 
Coin gold 20 dwts. 
Pure copper 8 grs. 
“ silver 10 “ 
“ platinum ... .20 “ 
*Richardson’s Mechanical Dentistry, p. 56. 
fJohnson Bros. 
tProf. C. L. Goddard. 352 
PRACTICAL DENTAL METALLURGY 
A content of platinum in gold renders the alloy more 
liable to oxidation, and, says Professor Harris, “This 
effect is so marked that such an alloy is readily acted 
upon by nitric acid. ” It is not probable, however, that 
the small amount contained in clasp gold would affect 
its integrity. 
CROWN GOLD.—Gold for crowns should combine 
strength with good color. Those alloys of a large cop- 
per content make exceedingly unsightly crowns, on 
account of their deep red color. Professor C. L. God- 
dard recommends the following for alloys the color of 
pure gold: 
No. 1—21.6-Carat 
Pure gold 90 parts 
“ silver 5 “ 
“ copper 5 “ 
No. 2—21.6-Carat 
Coin gold 50 parts 
Pure gold 45 “ 
“ silver 5 ‘ ‘ 
INLAY GOLD.—The development of gold casting in 
dentistry has increased the number and variety of al- 
loys used for such purpose. Whether a few standard 
alloys will serve the general needs of the dentist or 
whether a different alloy for each type of work is nec- 
essary remains to be proved. Most of the experimental 
work thus far done has been either empirical by the 
profession with little data available for comparison or 
by manufacturers who maintain the customary indus- 
trial secrecy regarding procedure. 
The ideal properties of a casting gold are compar- 
able to those of all other casting metals; viz., a perfect 
reproduction of the pattern. These include homogene- 
ous structure, no change in form through distortion, 
shrinkage or expansion, durability, a minimum of oxi- 
dation and gas occlusion, and such special properties GOLD 
353 
as certain alloys require, as elasticity for clasps, hard- 
ness and toughness for veneer crowns and inlays for 
bridge abutments, and a slight degree of flow for inlay 
restorations to permit of burnishing margins. 
Twenty-two carat gold alloyed with equal parts of 
copper and silver seems to give the most desirable re- 
sults for inlay restorations. The addition of platinum 
in quantities ranging from 3 per cent for veneer crowns 
and bridge abutments to 12 per cent for certain types 
of clasps has been recommended by experienced 
dentists. 
The variables prevailing in casting technic, types of 
casting apparatus, and investment materials, make it 
difficult to establish a definite procedure that will meet 
the requirements of individual practitioners. The most 
important thing to consider is the prevention of oxida- 
tion of the base metals and gas occlusion during the 
process of fusion. Defects in casting may be attributed 
to the formation of oxides and the occlusion of gases 
as in the instance of silver and oxygen which may 
cause such defects when the oxygen is liberated on 
cooling. 
Pits and marginal defects in inlays caused by these 
factors can readily be observed by microscopic exam- 
ination. Such defects must not be confused with the 
action of etching reagents which tend to act more 
readily on an amorphous or finely divided material 
than on the larger crystals or with polishing defects. 
Coarse grits used in polishing may produce scratches 
which can be burnished out, giving a mirror-like 
though irregular surface. These can be quickly ex- 
posed by etching reagents. 354 
PRACTICAL DENTAL METALLURGY 
Fig. 63-A. (See p. 356.) 
Fig. 63.-C. (See p. 356.) GOLD 
355 
Fig. 63-B. (See p. 356.) 
Fig. 63-D. (See p. 356.) 356 
PRACTICAL DENTAL METALLURGY 
Experimental work done in the metallurgy labora- 
tory, University of California, College of Dentistry, 
indicates that the fused metal when forced into con- 
tact with the investment, chills at the extreme end first 
and as it gradually congeals it forces the impurities 
into that portion of the alloy which remains liquid for 
the longest period of time. Standard methods are used 
by Mr. Shell in casting. The evidence invariably shows 
that the larger quantity of impurities is to be found in 
the last portion to solidify. 
Fig. 63 shows a comparison between two different 
castings. Figs. 63-C and 63-Z> show the quantity and 
size of the pits in each. 
A is a section of a casting close to the extreme end. 
C shows a section of the same casting on the sprue 
end. This is a 22 carat gold-silver-copper alloy. 
B shows a section of a proprietary alloy correspond- 
ing to section A of the 22 carat alloy above mentioned. 
Z> shows the section of the same proprietary alloy 
corresponding to a similar section of the 22 carat alloy 
indicated in C. 
The number of pits is much greater in C and D (indi- 
cated by arrows), although the number of pits in the 
corresponding sections is about equal. The large im- 
perfection in the center of T> may occur in any casting, 
and may be attributed to the shrinkage of the last 
portion of metal to solidify which is encased in solid 
peripheral mass. 
The same technic was used in each instance by the 
same operator. The illustrations are magnified 100 
diameters and the specimens were etched with aqua 
regia. GOLD 
357 
GOLD SOLDERS.—These are usually alloys of gold, 
silver, copper and zinc, and are designed to be a trifle 
more fusible than the parts to be soldered; this property 
is conferred upon them principally by the content of 
zinc (or brass). They should also possess considerable 
strength; too much base metal, therefore, should not be 
added, as it will, by oxidizing, tend to very materially 
weaken the alloys. Their carat should be as high or 
nearly as high as that of the plate, and color as nearly 
as possible the same. 
4^ 
Parts 
t-. 
c3 
o 
U.S.Coin 
Gold 
Pure 
Gold 
Pure 
Silver 
Pure 
Copper 
Pure 
Zinc 
Brass 
Spelter 
Solder 
1 
14 
810.00 
2 dwts. 
2 
14 
16 dwts 
5 “ 
J 3 dwts. \ 
\18 grs. J 
20 grs. 
/ 2 dwts. \ 
\ 6 grs. / 
/ 1 dwt. \ 
\ 12 grs. / 
1 part 
4 parts 
3 
15 
6 “ 
30 grs. 
/ 3 dwts. \ 
\ 6 grs. / 
10 fers. 
4 
16 
11 dwts. 
5 
16+ 
18 
Ill dwts. 1 
\12 grs. / 
12 grs. 
6 
7 
30 parts 
4 parts 
4 
1 part 
1 “ 
18 
27 parts 
f20 64\ 
\ grs. / 
6 grs. 
8 
20 
810.00 
9 
20 
—5 dwts. 
12 grs. 
6 grs. 
10 
14 
[ (18 K. gold plate) 
J formula No. 9) 1 
) 20 dwts. f 
l Johnson Bros. J 
2.5 dwts. 
20 grs. 
35 grs. 
The above formulas have yielded satisfactory results 
as gold solders. 
A simple method for making a good solder suitable 
for the plate upon which it is to be used is: 5 parts of 
the plate and one of brass or of silver solder. In the 
case of coin gold, or the crown alloy given on page 351, 
a solder thus made will be exactly 18 carat.* 
•Prof. C. L. Goddard. 358 
PRACTICAL DENTAL METALLURGY 
Zinc is best added to the alloys in the form of brass. 
The latter should be of a known formula, so that the 
desired amount of zinc may be accurately calculated; it 
should also be malleable and ductile; or the solder is apt 
to be very brittle. RULES FOR COMPUTING AND COMPOUNDING 
GOLD ALLOYS* AND EXAMPLESf 
PART I 
To ascertain the carat of any given alloy, the propor- 
tion may be expressed as follows: 
As the weight of the alloyed mass is to the weight of gold it 
contains, so is 24 to the standard sought. 
EXAMPLE—Gold 6 parts, silver 2 parts, copper 1 part, total, 
9 parts. 
9:6::24:? 
6 
9)144 
16 Answer. 
Another method when alloyed gold is used in form- 
ing the mass, instead of pure gold, is to express the 
proportion as follows— 
As the weight of the alloyed mass is to the weight of the gold 
alloy used in its composition, so is the carat of the latter, to the 
carat of the former. 
EXAMPLE—Harris No. 1 solder: 
22-carat Gold 48 parts 
Copper 16 “ 
Silver 12 “ 
Total 76 ‘ ‘ 
76:48:: 22: x carat. Ans. 13.9 carat. 
*Rules by Prof. Geo. Watt. 
tExamples by Prof. C. L. Goddard. 
359 360 
PRACTICAL DENTAL METALLURGY 
EXAMPLES UNDER RULE 1 
1. Find the carat of 36 pennyweights of gold, 8 pennyweights 
of copper, 4 pennyweights of silver. Ans. 18 carat. 
2. Find the carat of 9 pennyweights of gold, 2 pennyweights 
of copper, 1 pennyweight of silver. Ans. 18 carat. 
3. Find the carat of 38 pennyweights of gold, 6 pennyweights 
of copper, 4 pennyweights of silver. Ans. 19 carat. 
4. Find the carat of 22 pennyweights of gold, 1 pennyweight 
of copper, 18 grains of silver, 6 grains of platinum. Ans. 22 carat. 
5. Find the carat of 22 pennyweights of gold, 2 pennyweights 
of copper, 1 pennyweight of silver, 1 pennyweight of platinum. 
6. Find the carat of 6 pennyweights of gold, 3 pennyweights 
of copper, 1 pennyweight of silver. 
7. Find the carat of 48 parts of 22-earat gold, 16 parts of 
silver, 12 parts of copper. Ans. 13.9 carat. 
8. Find the carat of 20 pennyweights of gold coin, 2 penny- 
weights of copper, 2 pennyweights of silver. Ans. 18 carat. 
9. Find the carat of 20 pennyweights of gold coin, 25 grains 
of copper, 40 4 grains of silver. 
10. Find the carat of 20 pennyweights of gold coin, 18 grains 
of copper, 20 + grains of silver. 
11. Find the carat of 464.4 grains of gold, 5.16 grains of silver, 
46.44 grains of copper. 
PART II 
To reduce pure gold to any required carat, the pro- 
portion may be expressed as follows: 
As the required carat is to 24, so is the weight of gold used to 
the weight of the alloyed mass when reduced. The weight of 
gold subtracted from this gives the quantity of alloy to be added. 
Example.—Reduce 6 ounces of pure gold to 16 carat, 16:24: :6 
ounces: 9 ounces. 9—6=3 ounces alloy to be added. 
To reduce gold from a higher carat to a lower carat, 
the proportion may be expressed as follows: 361 
GOLD 
As the required carat is to the carat used so is the weight of the 
mass used to the weight of the alloyed mass when reduced. 
The weight of the mass used, subtracted from this, gives the 
quantity of alloy to be added. 
Example.—Reduce 4 ounces of 20-carat gold to 16 carat. 
16:20::4 ounces: ? 
4 
16)80 
5 ounces. 
5 ounces — 4 ounces = 1 ounce alloy to be added. 
EXAMPLES UNDER RULE 2 
1. Reduce 6 ounces gold to 16 carat. Ans. Add 3 ounces alloy. 
2. Reduce 25 pennyweights gold to 18 carat. Ans. Add 8 
pennyweights, 8 grains alloy. 
3. Reduce 4 ounces of 20-carat gold to 16 carat. Ans. Add 1 
ounce alloy. 
4. Reduce 6 ounces of 18-carat gold to 15 carat. 
5. Reduce 15 pennyweights of gold coin to 20 carat. Ans. 
Add 1.2 pennyweights. 
6. Reduce 12 pennyweights of gold coin to 15 carat. 
7. Reduce 4 pennyweights of 22-carat gold to 20 carat. Ans. 
Add 9.6 grains alloy. 
8. Reduce 48 grains 20-carat gold to 16 carat. 
9. Reduce 2 pennyweights 20-carat gold to 18 carat. 
10. Reduce 1 pennyweight, 8 grains 18-carat gold to 16 carat. 
PART III 
To change gold from a lower to a higher carat, add 
pure gold or a finer alloy. 
As the alloy in the required carat is to the alloy in the given 
carat, so is the weight of the alloyed gold used to the weight of 
the changed alloy required. 
The weight of the alloyed gold used subtracted from this gives 
■he amount of pure gold to be added. 362 
PRACTICAL DENTAL METALLURGY 
Example.—Change 1 pennyweight of 16-carat gold to 18 carat. 
First subtract 16 and 18 from 24 to find the amount of alloy in 
each carat. 
24 24 
18 16 
6 : 8 :: 1 pennyweight : ? 
1 
6) 8 
114 pennyweight. 
114 — 1 —14 pennyweight of pure gold to be added. 
To change gold from a lower carat to a higher carat, 
by adding gold of a still higher carat. 
Subtract the lower carat and the required carat each from the 
highest carat (instead of from 24) and proceed as before. 
Example.—Change 2 pennyweights of 16-carat gold to 18 carat 
by adding 22-carat gold. 
First subtract 16 and 18 from 22. 
22 22 
18 16 
4 : 6 :: 2 pennyweights : 3 pennyweights. 
3 — 2 — 1 pennyweight of 22-carat gold to be added. 
EXAMPLES UNDER RULE 3 
1. Change 1 pennyweight of 16-carat gold to 18 carat. Ans. 
Add 8 grains of gold. 
* 2. Change 2 ounces of 16-carat gold to 20 carat. Ans. Add 2 
ounces of gold. 
3. Change 11 pennyweights, 8 grains of 18-carat gold to 20 
carat. 
4. Change 9 pennyweights of 16-carat gold to 18 carat. Ans. 
Add 3 pennyweights of gold. 
5. Change 2 ounces of 18-carat gold to 22 carat. 363 
GOLD 
6. Change 18 pennyweights of 16-carat gold to 18 carat by 
adding 22-carat gold. Ans. Add 9 pennyweights of 22-carat gold. 
7. Change 3 pennyweights of 18-carat gold to 20 carat by 
adding gold coin. Ans. Add 3 pennyweights, 18 grains. 
8. Change 12 pennyweights, 10 grains of 16-carat gold to 20 
carat by adding gold coin. 
9. Change 20 grains of 16-carat gold to 18 carat by adding 
20-carat gold. 
MISCELLANEOUS EXAMPLES 
1. Find the carat of 19 pennyweights of gold, 3 pennyweights 
of copper, 2 pennyweights of silver. Ans. 19 carat. 
2. Reduce 6 pennyweights, 8 grains of gold to 20 carat. 
3. Reduce 2- ounces, 4 pennyweights, 8 grains of 22-carat gold 
to 18 carat. 
4. Reduce 12 pennyweights of 18-carat gold to 20 carat. Ans. 
Add 6 pennyweights of gold. 
5. Find the carat of 20 parts of gold coin, 3 parts of copper, 
3 parts of silver (gold plate). 
6. Find the carat of 30 parts of gold coin, 1 part copper, 4 
parts of silver, 1 part of brass (solder). 
7. Reduce 258 grains of gold coin to 20-carat gold. 
8. Reduce 516 grains of gold coin to 18-carat gold. 
9. Reduce 5 pennyweights of 16-carat gold to 18 carat by 
adding gold coin. 
10. Reduce 4 pennyweights, 6 grains of 16-carat gold to 18 
carat by adding 20-carat gold. 
($10 gold coin weighs 258 grains—$0.10 silver coin 38.58 grains.) 
11. Add 10 cents silver to $20 gold—find weight and carat. 
12. Add 25 cents silver to $20 gold—find weight and carat. 
Gold coin 20 pennyweights 
Copper 2 “ 
Silver 2 “ 
to formula for 
pure gold, and 
find carat. 
13. Change 
14. Change 
Gold coin 20 pennyweights 
Copper 25 grains 
Silver 40+ “ 
do 
Gold coin 20 pennyweights 
Copper 18 grains 
Silver 20+ “ 
15. Change 
do 364 
PRACTICAL DENTAL METALLURGY 
16. Change 
Gold 18 pennyweights 
Copper 4 11 
Silver 2 “ 
to formula for 
l gold coin, and 
find carat. 
17. A watch chain, 14 carats fine, weighs 2 ounces, 4 penny- 
weights, 16 grains. How much pure gold must be added to raise it 
to 20-carat gold. 
18. A piece of jewelry, 12 carats fine, weighs 4 pennyweights. 
How much U. S. gold coin must be added to make it 18-carat fine. 
19. Add 4 ounces, 16 pennyweights, 5 grains of 14-carat gold to 
2 ounces, 4 pennyweights, 16 grains of 16-carat gold and find the 
carat of the mixture. Ans. 7 ounces, 21 grains of 14.64-carat gold. 
20. How much pure gold must be added to the above mixture 
to make it 18 carat fine. 
21. How much U. S. silver coin and how much copper must be 
added to 3 ounces U. S. gold coin to reduce it to 18-carat gold 
containing equal parts of silver and copper. 
The alloys of gold and most of the metals have been 
discussed under the heads of the various metals. 
TESTS FOR GOLD IN SOLUTION.—Hydrogen Sul- 
phide or Ammonium Sulphide throws down a brown 
precipitate of auric sulphide (Au2S3). The second pre- 
cipitant is not used, however, as the precipitate is solu- 
ble in it. Auric sulphide is insoluble in nitric or hydro- 
chloric acid taken, separately, but soluble in aqua regia. 
Ferrous Sulphate and Oxalic Acid precipitate the 
gold in the metallic state; it is a brown powder, darker 
in the instance of the former than in the latter, but 
develops the color and luster of gold by being bur- 
nished with the finger-nail or instrument. 
Stannous and Stannic Chloride.—The most delicate 
test for gold is probably the formation of the purple 
of Cassius. GOLD 
365 
Heat and Light.—Gold is reduced from many of its 
compounds by sunlight, and from all of them by more 
or less heat. 
Touchstone Tests.—The touchstone used by assayers, 
gold bullion brokers and jewelers is a piece of smooth, 
fine grained black basalt. The metal to be tested is 
rubbed on the touchstone until it leaves a streak. Then 
various acids are added by a dropper and the effect 
noted. For instance, a supposed platinum alloy is 
rubbed on the stone, and dilute nitric acid is added. 
Platinum is insoluble in HNOs: If silver, lead, or mer- 
cury be present, they will be converted into soluble 
nitrates. HC1. will precipitate white chloride of any 
of these metals. On adding ammonia, silver chloride 
if present will be redissolved. If it is lead chloride it 
will retain its white color and remain undissolved, and 
if it is mercury, the salt will turn black. Touchstone 
tests are merely test tube tests on a minute scale. Ex- 
perts are capable of approximating the carat of a gold 
alloy by the color streak on a touchstone. 
ELECTRODEPOSITION OF GOLD.—By simple im- 
mersion.—From an acid solution of gold chloride, the 
base metals, and silver, platinum, and palladium, de- 
posit gold in the metallic state. In the double cyanide 
of gold and potassium, zinc will quickly become gilded, 
copper, brass, and German silver, slowly, and antimony, 
bismuth, tin, lead, iron, nickel, silver, gold, and plati- 
num not at all. 
Deposition by a Separate Current.—The Solution.— 
There are many solutions prepared for electrogilding, 
some being formed by chemical means, others by a sep- 
arate current from the battery; but whether they are 366 
PRACTICAL DENTAL METALLURGY 
made by chemical or electrical process, the best for a 
thick reguline deposit is the pure double cyanide of 
gold and potassium. 
A cyanide solution may be prepared as follows: 
Dissolve 120 grains of pure gold in one ounce of 
chemically pure aqua regia, thus preparing the 
chloride of gold, as described previously.* Dissolve 
the chloride obtained in 32 ounces of warm distilled 
water, and add to it 1 y2 ounces of magnesia; the gold 
is precipitated. Filter and wash with pure distilled 
water, digest the precipitate in 10 parts of distilled 
water mixed with .75 part of nitric acid to remove mag- 
nesia ; then wash the remaining oxide of gold with dis- 
tilled water, until the wash-water exhibits no acid 
reaction with test-paper. Next dissolve 3 ounces of 
ferrocyanide of potassium and 6 drams of caustic 
potash in 34 ounces of distilled water, add the oxide 
of gold prepared, and boil the solution about twenty 
minutes. When the gold is dissolved there remains a 
small amount of iron precipitated, which may be re- 
moved by filtering the solution. The liquid, a fine, 
clear, golden color, is then ready for use, to be em- 
ployed either hot or cold, but a better and quicker 
deposit is nearly always obtained from the warm 
solution. 
In electroplating objects the first essential is a fin- 
ished surface, which must be made just as it is desired 
to be when completed. The next is cleanliness. If it 
be a silver denture or any other metallic object it 
should first be cleaned of all surface combinations, as 
oxides, sulphides, etc., by polishing in the ordinary 
way; then scrubbed with a solution of hot water and 
‘Preparation of Chemically Pure Gold, p. 319. GOLD 
367 
soap by means of a brass or steel scratch brush on the 
lathe; then washed or boiled in a strong solution of 
caustic potash, afterwards washing in distilled water, 
and finally in an acidulated water to remove all traces 
of the alkali. 
The apparatus is exceedingly simple, consisting of a 
single battery cell and a glass bowl (preferably of per- 
pendicular sides) to contain the solution. The latter 
may or may not be adjusted in a water-bath, according 
to whether the operator desires to work his solution 
hot or cold. Aside from these connecting and guiding 
wires cathode and anode hooks, together with an anode, 
a thermometer, a scratch brush, etc., are all that will 
be needed. The article to be plated is suspended by a 
hook in the solution from the cathode while a piece of 
pure gold is hung from the anode to keep up the 
strength of the solution, the latter electrode being 
easily determined by the fact that gas is liberated there 
by the passage of the current through the solution. 
When a sufficient coating has been formed, the ob- 
ject is to be removed from the bath and burnished by 
the scratch brush or agate burnisher, moistened with 
a solution of warm water and soap, until the surface 
is finished as desired. CHAPTER XXI 
AMALGAMS 
An Amalgam is an alloy of two or more metals, one 
of which is mercury. 
The name is probably derived from the Greek 
malagma meaning a soft mass, and was applied to alloys 
of mercury on account of the increased plasticity and 
fusibility which it confers upon them. 
Most metals, even hydrogen and the hypothetical 
metal, ammonium, unite directly with mercury to form 
a very interesting series of alloys which are termed 
amalgams. Many are extensively used in the arts and 
industries; but to no art or profession can they be of 
more interest or importance than to dentistry. 
It must not be inferred that amalgams are to be 
given different chemical and physical theoretical con- 
sideration because they are studied thus distinctly. On 
the contrary, they are to be considered in every respect 
alloys, differing from the usual in no general way, ex- 
cept that all contain mercury and are endowed with 
some properties peculiar and dependent upon that 
metal. They are, therefore, subject to the same clas- 
sification quoted from Matthiessen in the chapter on 
Alloys.*5 They offer an excellent opportunity for study- 
ing the behavior of metals towards each other, the 
examination being facilitated by the low temperature 
at which their combinations are effected.f 
*The student should carefully review this classification. 
tMercury, it must be remembered, is simply a metal fused at ordinary 
temperatures. 
368 AMALGAMS 
369 
The affinities affording the union of mercury with its 
constituents in the formation of amalgams are not as a 
rule, strong, for many of them are decomposable by 
pressure, and all by considerable heat; yet, like all 
other metals, mercury tends to form definite chemical 
compounds with certain metals. The following have 
been formed by combining the metals named with mer- 
cury and squeezing out the excess by means of hydrau- 
lic pressure to the amount of 60 tons to the square 
inch: 
Amalgam of lead, Pb2Hg.* 
“ silver, AgHg. 
“ iron, PeHg. 
“ zinc, Zn2Hg. 
“ copper, CuHg. 
“ platinum, PtHg2. 
“ gold, Au4Hg. 
“ “ tin, Sn2Hg. 
A native compound of mercury and silver, known as 
Arguerite, Ag6Hg, is found crystallized in the form of 
the regular system. 
Beautiful crystallizations of silver amalgam (Arbor 
Diance) may be formed in long prisms having the com- 
position Ag2Hg3, by dissolving 400 grains of silver ni- 
trate in 40 ounces of water, adding 160 minims of con- 
centrated nitric acid, and 1840 grains of mercury; in a 
few hours beautiful crystals of considerable length will 
be deposited. 
The union of mercury and other metals may be said 
to take place by four different means: 
(1st.) Some by direct contact, accompanied in some 
*Bloxam’s Chemistry, Inorganic and Organic, p. 400. 370 
PRACTICAL DENTAL METALLURGY 
instances by a considerable evolution of beat. Thus, if 
a piece of clean sodium be thrown upon a clean, dry 
surface of warmed mercury, union takes place with ex- 
plosiveness, accompanied by incandescence, and the 
evolution of an amount of heat sufficient to volatilize 
portions of each metal. 
(2d.) Some by the action of mercury on a salt of the 
metal, as the introduction of metallic mercury into a 
solution of a salt of the metal. 
(3d.) Others by the action of the metal on a salt of 
mercury, as, the introduction of the metal into a solu- 
tion of a salt of mercury. 
(4th.) By voltaic action as when a metal is placed in 
contact with mercury in some acidulated solution. 
IN THE ARTS.—“Silvering’.”—The process known 
as “silvering on glass” was until recently a misnomer, 
as tin amalgam was alone employed in the manufacture 
of mirrors. 
The attraction of mercury for gold and silver is taken 
advantage of for the extraction of these metals from 
their ores. The addition of a little amalgam of sodium 
to mercury increases its combining power, and it more 
readily unites with other metals, even iron. This is 
especially recommended in the employment of mercury 
in the extraction of silver or gold from their ores. 
An amalgam of equal parts of tin and zinc with six 
parts of mercury is much used for rubbers on electrical 
machines. 
DENTAL-AMALGAM ALLOYS.—The term compre- 
hends those alloys composed principally of silver and 
tin, with the addition of small percentages of one or AMALGAMS 
371 
more other metals (which, when comminuted and mixed 
with mercury, form a coherent mass).* 
A DENTAL AMALGAM may, therefore, be under- 
stood to be a comminuted metal or dental-amalgam alloy 
mixed with sufficient mercury to form a coherent mass. 
There are alloys which contain small percentages of 
mercury, added usually to lower their fusing points. 
Within the strict reading of the definition of amalgam 
these might be considered amalgams, but in the dental 
acceptation of the term they cannot be regarded as 
such. 
FORMATION OF DENTAL-AMALGAM ALLOYS.— 
The directions for the preparation of alloys in general 
are equally applicable to the preparation of these 
special ones. The same precautions should be observed 
to avoid loss by oxidation, volatilization, etc. The 
manner of melting and pouring differs in no essential. 
It will, therefore, suffice to briefly illustrate the 
process by detailing the manner of preparing one from 
the metals usually employed, such as tin, silver, and 
gold or copper. 
The source of heat may be an open-grate, coke or 
coal fire, the forge, or what is best adapted to the 
purpose, the small injector gas furnace devised by Mr. 
Fletcher for melting metals. The crucible may be the 
ordinary refractory sand or Hessian, a clay and plum- 
bago, or the plumbago crucible alone, the latter being 
preferable after it has been tested by heat. The cru- 
cible selected should be placed in the furnace and 
*Such a distinction precludes the confusion of the terms “Dental Alloy” 
and “Dental Amalgam,” the former of which we may understand as ap- 
plicable to any of the numerous alloys used by dentists, for whatever pur- 
pose, and which do not contain, nor are designed to be mixed with, mer- 
cury ; the latter being accepted as the Dental-Amalgam Alloy mixed with 
mercury.—Author. 372 
PRACTICAL DENTAL METALLURGY 
heated to a bright red heat; then a sufficient quantity 
of borax should be added to properly cover the inner 
sides when the crucible is tipped and rotated with the 
tongs. 
The silver and gold or copper may now be added, 
preferably in small pieces of thinly rolled plate, and 
thoroughly heated until. fused. Being sure that the 
borax is melted as thin as possible, the tin may be added 
in as large pieces as convenient, that they may readily 
sink and unite with the fused metals before oxidation 
can take place. The crucible should then be removed 
with tongs, the contents well shaken or stirred with a 
stick of soft wood, and quickly poured into the pre- 
viously warmed and oiled ingot molds, after which 
it is ready for comminution. 
Borax is used as the flux, because it more perfectly 
protects the metals from oxidation and volatilization, 
absorbing the oxides that may have been previously 
formed or developed during the fusing; protects the 
molten metals from the rough and porous sides of the 
crucible, and facilitates the pouring. 
The difficulty in adding tin is to avoid volatilizing 
any portion of it. It has been, therefore, melted sepa- 
rately, and the molten silver and gold or copper poured 
into it. This plan very thoroughly protects the tin, 
but it is questionable if the less fusible metals are not 
so chilled that their proper alloying is prevented. In 
such a case the ingot should be broken up and remelted 
under plenty of borax. An exceedingly good plan to 
avoid volatilization is to wrap the volatile metal in soft 
paper that will conform readily to the sides of the 
piece of metal and quickly dash it beneath the surface AMALGAMS 
373 
of molten borax. The paper quickly chars and serves 
both as a covering and reducing material. 
The addition of zinc is probably the most difficult 
to accomplish without loss, as it so easily oxidizes. It 
is, therefore, sometimes united with a small amount of 
gold previously by wrapping the small grains of zinc 
in gold foil and thrusting them beneath the molten 
borax. 
Bismuth, antimony, and the other more fusible met- 
als, are alloyed with the mass similarly to tin. Plati- 
num, palladium, and such, with the silver, or silver and 
gold melted as recounted above. The table of Dr. J. 0. 
Keller (see pp. 374 and 375) gives the composition of 
some of the principal dental-amalgam alloys in use. 
Arthur W. Gray* has contributed much to our knowl- 
edge of amalgams. Pointing out certain sources of 
error and inaccuracies in the work of former experi- 
menters, he has formulated standardized procedures 
for determining the physical properties of amalgams of 
great value to the dental profession. 
Utilizing a 9000-kg. Olsen testing machine (see Fig. 
64) modified by the addition of an electric motor to 
regulate carefully the application of force, and with 
electric thermo-elements to control the temperatures 
during the tests, accurate results were obtained from 
which relative deductions can be drawn in dental 
practice. 
In preparing the cylinders for the series of experi- 
ments to determine the crushing strength, Dr. Gray 
states, “These cylinders were prepared by molding the 
* Arthur W. Gray, Ph.D., Director, Dept, of Physical Research, The 
L. D. Caulk Co., Transactions of the A. I. M. D. Supplement to Bulletin 
No. 144, December 1918. 374 
PRACTICAL DENTAL METALLURGY 
Fig. 64.—A 9000-KG Olsen Machine adapted to the testing strength of 
materials at any temperature and provided with power drive for apply- 
ing testing load with regularity. 
Fig. 65.—A comparison of cylinders packed by the testing machine (D) 
and by other methods (A, B, C.) AMALGAMS 
375 
freshly mixed amalgam in a thick-walled steel tube, 
the interior of which was highly polished. 
A measured force, applied by the testing machine 
and maintained for a measured time, was used in pack- 
ing the amalgam between an accurately fitting piston 
and the removable bottom of the mold. This packing 
squeezed out the excess of mercury and condensed the 
plastic mass into a firm, smooth cylinder with parallel 
ends. The procedure secured both uniformity of cross 
section and uniformity of packing conditions. 
Other methods of packing amalgam such as are 
commonly used in dental practice are illustrated com- 
paratively (see Fig. 65). 
Many factors enter into the mixing and placing of 
an amalgam in a tooth cavity that are probably as 
varied as there are individuals performing this opera- 
tion and it might seem because of these variables that 
standardized technic in experimental work is unneces- 
sary because it cannot be duplicated in practice. 
On the other hand such factors as proportion of 
mercury to alloy, time devoted to triturating the mix, 
the temperature of trituration, the pressure and time 
of packing the cylinders, the time that elapses between 
the making and testing of the cylinder, the tempera- 
ture at which it is stored during the interval, and the 
rate at which the crushing load was applied, were 
shown by Dr. Gray to influence the crushing strength 
of amalgams. 
Many of these factors have their counterpart in 
everyday practice and of necessity a technic that 
would give the best results which are indirectly appli- 
cable to office procedure has been established. 376 
PRACTICAL DENTAL METALLURGY 
Tin 
Silver 
Gold 
Plati- 
num 
Copper 
Zinc 
Cad- 
mium 
Anti- 
mony 
Pal- 
ladium 
Arrington’s (S. S. White’s) 
57.5 
42.5 
56.85 
42. 
.5 
.15 
.5 
61.5 
34.5 
.5 
3.5 
Chicago Refining Co’s (Old) 
56. 
37. 
5. 
2. 
(New) 
58.37 
37.55 
4. 
.1 
50. 
50. 
10. 
.5 
50. 
50. 
7. 
40. 
50. 
10. 
“ Stannous Gold 
40. 
40. 
20. 
40. 
50. 
10. 
55. 
43.65 
1 35 
“ Par-Excellence 
61.75 
27.25 
.15 
.25 
10.6 
Crown Gold Alloy 
52.85 
47. 
.15 
49 27 
48.24 
05 
2.41 
Trace 
“ Superior Amalgam 
63.55 
31.85 
.65 
.15 
2.35 
1.45 
49.65 
49.75 
.2 
.4 
53.8 
44.35 
9 
1.05 
Fletcher’s Gold Ailoy (Old) 
56. 
40. 
4. 
“ Platinum and Gold Alloy 
50.35 
43.35 
3.35 
1.3 
1.65 
35. 
60. 
5. 
35. 
37. 
5 
.3 
“ Contour Alloy 
37. 
58. 
5. 
Globe (S. S. White’s) 
53.36 
44.74 
1.5 
4. 
44. 
10. 
46. 
Hood’s Amalgam (Old) 
60.25 
37. 
2.75 
Hood & Reynold’s Gold and Platinum Alloy... 
50.4 
44.3 
3.8 
.3 
1.2 
High Grade Alloy (Tl/2 per cent Gold) 
41.5 
49. 
7.5 
2. 
Harris’ (Prof. J. H.) Amalgam 
48.1 
40. 
4.9 
7. 
Johnson & Rund’s Extra (Old) 
60. 
38. 
1.5 
.5 
61.15 
36.75 
.15 
5 
1.45 
61.65 
37.75 
.6 
61.9 
36.85 
.35 
.9 
“ “ Extra Tough Alloy 
51.25 
47. 
.3 
.2 
.25 
Justi’s Superior Gold and Platinum Alloy.... 
59.1 
35.2 
.32 
.08 
3.5 
1.8 
King’s Occidental 
54.75 
42.75 
2.5 
COMPOSITION OF SOME DENTAL-AMALGAM ALLOYS AMALGAMS 
377 
Tin 
Silver 
Gold 
Plati- 
num 
Copper 
Zinc 
Cad- 
mium 
Anti- 
mony 
Pal- 
ladium 
47. 
47. 
1. 
5. 
50.43 
44.06 
5.51 
Moffitt’s (Old) 
62. 
36. 
2. 
The Dentist’s Amalgam 
59.5 
37.9 
2.6 
Oliver’s Amalgam (Old) 
50.8 
46.1 
1.7 
1.4 
“ White Amalgam (New) 
55.25 
44.74 
40. 
55. 
4. 
1. 
Prof. Essig’s (Old) 
55. 
45. 
2.5 
2.5 
40. 
55. 
3. 
2. 
Sterling Amalgam (Old) 
62. 
31. 
1. 
6. 
67 7,7 
3i2 
.14 
4.33 
Standard Amalgam (Davis & Co.) 
55.4 
44!6 
“ Dental Alloy (Eckfeldt) 
40.6 
52. 
4.4 
3. 
Shattuck’s Standard Gold Alloy 
51.74 
46.98 
1.2 
.08 
Sibley’s Gold and Platinum Alloy 
54.65 
43.15 
.2 
2. 
88. 
1 0 
2. 
Townsend’s (Old) 
58. 
42. 
(Improved) 
54.5 
44.5 
1. 
Walker’s (Old) 
69 
TO s 
.5 
“ Excelsior Gold and Platinum Alloy.. 
51.5 
42. 
.3 
.2 
6. 
Welch’s Gold and Platinum Alloy (Old) 
54. 
44. 
1.3 
.7 
“ “ “ “ “ (New) 
51.9 
40. 
1.7 
.4 
“ Amalgam 
51.52 
48.48 
27 13 
67 OT 
4 87 
1 10 
27 13 
6S Q1 
5 21 
1.52 
3S 03 
ST SS 
8.82 
2.76 
S 7T 
*5. Odontographic Alloy 
26.48 
66.87 
0.28 
6.21 
trace 
*6. C. Ash Sons Co. (C. A. S.) Alloy 
27.16 
66.54 
5.02 
0.90 
University of California Dental Amalgam Al-'| 
loy (White) Hodgen 
4 7 
Made from Mexican Dollar 47 parts, Tin 53 f 
parts J 
‘Analysis of these popular proprietary alloys was made for the New York Institute of Stomatology by Dr. P. S. 
Burns, of the Massachusetts Institute of Technology. 
COMPOSITION OF SOME DENTAL-AMALGAM ALLOYS—Continued 378 
PRACTICAL DENTAL METALLURGY 
Liquation, or the separation of the constituents of 
the alloy, while molten or when being poured, on 
account of their differences in specific gravity and lack 
of affinity, may be best prevented by raising the alloy 
to a very high heat, stirring it with a stick of green 
wood, and pouring quickly. If it be suspected after 
pouring, the alloy should be remelted and again poured. 
Remelting is very apt to change the composition, and 
should be avoided where possible. 
COMMINUTION.—Alloys are generally comminuted 
or broken up into small particles by rasping or filing 
into grains, or turned into shavings on the lathe. 
An alloy rich in tin should be cut with a very coarse 
file, or, better, turned on the lathe, as it is frequently 
so soft that, clogging the file, it hinders further cut- 
ting. One rich in silver, however, presents a harder 
quality, and may be best comminuted with an ordinary 
coarse file. 
Mechanical devices for comminuting such alloys pre- 
vent the introduction of contaminating materials that 
might find their way into cut alloy by careless inexpe- 
rienced hand methods. After comminuting the alloy, 
if by filing, the particles should be passed through a 
sieve with not less than 100 meshes per inch to remove 
the coarser particles which do not amalgamate so 
readily. 
Dr. Gray’s experiments in passing cut alloys through 
five different sieves, ranging in mesh from 100 meshes 
to 200 meshes per inch, showed that a greater mercury- 
alloy ratio or a longer period of trituration was re- 
quired in mixing a coarse grained alloy in order to 
obtain the same degree of plasticity. A fine grained 
alloy gave the most satisfactory results. AMALGAMS 
379 
AGEING.—This term has been used to vaguely 
imply that the time factor elapsing between the com- 
minuting of the alloy and its amalgamation influenced 
its crystallization and expansion reactions. Dr. Black’s 
early experiments uncontrolled thermometrically, as 
they were, would indicate that temperature was a more 
important factor since alloys placed in bottles in the 
sun and those from the same batch of alloy placed in a 
refrigerator gave different results. 
Possibly annealing changes may result through an 
Crushing Strength in kg per circm at 37 5*C. 
Date of Manufacture 
Fig. 66. 
interval of time, yet even this is difficult to determine 
in a comminuted alloy and these may have modified the 
result. 
The resistance to crushing strength offered by al- 
loys of varying ages after comminution shown in the 
graph by Dr. Gray (Fig. 66) indicates that a standard 
alloy, hermetically sealed and stored at normal room 
temperatures for six years, will compare favorably 
with an alloy but a few days old, when the same manip- 
ulative procedures are applied. 
MERCURY.—The percentage of mercury required 380 
PRACTICAL DENTAL METALLURGY 
for the amalgamation of these different alloys varies 
greatly. If too much be added in mixing, the resulting 
solution becomes so liquid that it is worked with diffi- 
culty, if at all; if too little, the mass of alloy lacks 
coherence and homogeneity, and the result of its at- 
tempted working is unsatisfactory. The mercury, of 
course, should be pure. Any admixture or chemical 
combination with a foreign substance necessarily serves 
to weaken the affinities of the mercury, resulting in 
less mass strength. Even the moisture in a room may 
oxidize the alloy superficially and materially interfere 
with its amalgamation and resultant strength. Pack- 
ages of alloys should be kept sealed when not in use. 
AMALGAMATION.—The union of one or more met- 
als or an alloy with mercury. 
This is accomplished usually by adding the mercury 
to the comminuted alloy in a Wedgewood or ground 
glass mortar, working the metals together and then 
kneading them into a plastic mass in the palm of the 
hand or in a rubber finger cot and squeezing out the 
excess of mercury through chamois or cloth. 
Some operators take a great deal of pains to deter- 
mine exactly the amount of mercury necessary for a 
given alloy, weighing each part separately and then 
mixing and kneading. A variety of instruments and 
apparatus have been introduced for weighing and mix- 
ing though most practitioners adhere to the empirical 
method first described. While the influences which in- 
crease and diminish the ratio of mercury to alloy are 
difficult to anticipate, it is desirable that the ratio 
recommended by the manufacturers be used as exactly 
as is possible. Some manufacturers supply a measur- 381 
AMALGAMS 
ing device that meets the requirements of their alloy 
satisfactorily but it may be wholly unsuited to another 
alloy. It is particularly important in the mixing and 
working of amalgam that the mercury be evenly dis- 
tributed throughout the mass and that violent grinding 
in a mortar or squeezing in a vise be avoided. 
While such variables as differences in the content of 
two melts of the same alloy or even of a single ingot or 
CRUSHING STRENGTH IN KILOS PER CIRCULAR CENTIMETER 
MERCURY-ALLOY RATIO 
PACKED UNDER 141 KILOS 
Fig. 67. 
the degree of comminution may require a slight change 
in manipulation, experience generally assists the oper- 
ator in determining the required plasticity. 
In discussing amalgamation variables Dr. Gray* says, 
“The fact that both the strength and the mercury 
content change regularly with the packing pressure 
*Metallographic Phenomena Observed in Amalgrams, Arthur W. Gray, 
Ph.D., Trans. Am. Inst. Mining Fng., Sup. to Bull. No. 144, December, 
1918. 382 
PRACTICAL DENTAL METALLURGY 
suggests at once a close connection between the former 
and the latter. Long ago, Black found that the more 
mercury he squeezed out during the packing of a given 
amalgam, the stronger was the filling he obtained; but 
his methods of experimenting were not sufficiently pre- 
cise to bring out any quantitative relationships. That 
the suggested connection is not of the nature of cause 
CRUSHING STRENGTH IN KILOS PER CIRCULAR CENTIMETER 
MERCURY-ALLOY RATIO 
PACKED UNDER 400 KILOS 
Fig. 68. 
and effect, but is rather a coincidence resulting from 
a common cause, becomes apparent as we notice how 
strength and mercury content are affected by varying 
such factors as the mercury-alloy ratio and the tritura- 
tion time. 
Figs. 67, 68, 69 exhibit the results of varying the 
mercury-alloy ratio from 0.5 to 2.5, while the tritura- 
tion time was maintained uniformly at 1.5 min. This 
varied the mix from a very stiff to a very pasty one. AMALGAMS 
383 
The cylinders packed under the lowest pressure (141 
kg. per cir. cm.) show the phenomenon most clearly, 
both mercury content and crushing strength increasing 
rapidly in the same general way to maximum values, 
which remain constant as the mercury-alloy ratio is 
still further increased. The illustrations show how 
the increases of packing pressure progressively wipe 
out the effects and cause the maxima to be reached 
CRUSHING STRENGTH IN KILOS PER CIRCULAR CENTIMETER 
r.i L. 
MERCURY-ALLOY RATIO 
PACKED UNDER 1131 KILOS 
Fig. 69. 
sooner; also, that constant mercury content is reached 
before constant strength. 
Figs. 70, 71 exhibit the results of varying the tritu- 
ration time from 1 to 8 min. while a constant mercury 
ratio of 1.40 was used. The curves of Fig. 70 show 
that, in general, more mercury is retained in a test 
cylinder by prolonging the trituration; but it is in- 
teresting to note that when the packing pressure is 
low less mercury seems to be left in the cylinder by 384 
PRACTICAL DENTAL METALLURGY 
PACKING PRESSURES IN KILOS 
PER CIRCULAR CENTIMETER 
MERCURY CONTENT IN PER CENT. 
TRITURATION TIME IN MINUTES 
Fig. 70. 
CRUSHING STRENGTH IN KILOS PER CIRCULAR CENTIMETER 
— o — 
PACKING PRESSURES IN KILOS 
TRITURATION TIME IN MINUTES 
Fig. 71. AMALGAMS 
385 
increasing the trituration time from 1 to 2 min. Ap- 
parently this is because the shorter trituration leaves 
many of the alloy granules so large that a low packing 
pressure is insufficient to squeeze out the free mercury 
from the spaces among the solid particles. The curves 
also show that for a given trituration time the mercury 
content changes almost inversely as the logarithm of 
the packing pressure. 
Fig. 72.—Dr. G. V. Black’s amalgam micrometer. 
Increasing the trituration time while the packing- 
pressure is kept constant is accompanied by a pro- 
gressive increase in strength (Fig. 71) until the latter 
reaches a maximum when the trituration is maintained 
for about 6 min. Prolonging the time beyond this 
brings about a very gradual falling off in strength on 
account of the incipient setting of the amalgam during 
the mixing. The results also indicate that the logarith- 
mic law connecting crushing strength and packing- 
pressure is applicable for any given trituration time 
within the range investigated. 386 
PRACTICAL DENTAL METALLURGY 
The reason excessive amalgamation produces so 
little effect upon the mercury content would appear to 
be simply that the metals entering into a dental alloy 
are only very slightly soluble in mercury. 
EXPANSION REACTIONS.—This term has been 
coined by Dr. Gray who presents his views as follows:* 
“The dimensional changes that occur during the hard- 
ening of a dental amalgam are of such importance in 
connection with the tooth-restoring proporties of this 
valuable filling material that determinations of these 
changes are nearly always included in tests of amal- 
gam alloys. A contracting amalgam may shrink suffi- 
ciently to admit oral fluids and bacteria between the 
filling and the cavity walls; an expanding amalgam 
may swell sufficiently to extend above the margins of 
the cavity, or even to split the tooth. The ideal 
amalgam expands just enough to make sure that a 
properly inserted filling will remain firmly in contact 
with the tooth. 
“No theory yet advanced gives a satisfactory reason 
for the existence of these dimensional changes, which 
I call reaction expansions to differentiate them from 
thermal expansions. The prevailing belief is that silver 
causes expansion and tin contraction. Adjusting the 
composition of a dental alloy so that its amalgam will 
show a desirable reaction expansion is, therefore, re- 
garded as “balancing” the opposing tendencies of the 
component metals. 
“A study of the modifications produced by system- 
atically varying the conditions that affect reaction 
expansion has finally led me to formulate a simple 
‘Physical Review, N. S., Vol. XVIII, No. 2, August, 1921. AMALGAMS 
387 
theory that seems consistent with all facts at present 
known. I shall not enter into a consideration of this 
theory here, but shall merely present some of the ex- 
perimental evidence upon which it is based. 
“ Black had observed that some amalgams contracted 
a little before they expanded.* In a paper before the 
American Institute of Mining Engineers! I pointed out 
that the typical reaction expansion of a dental amal- 
gam is characterized by four consecutive stages: 
“1. Rapid contraction to a minimum. 
“2. Somewhat slower expansion to a maximum. 
“3. Considerably slower contraction to a second 
minimum. 
“4. Very much slower expansion to a second maxi- 
mum. 
“One or more of these stages can be masked by suit- 
able mechanical treatment of the amalgam.’’ 
“The control of the reaction expansion produced by 
this blending of various sized particles is evident on 
comparing the curve of specimen R464 with the other 
curves on the same chart, especially when the compari- 
son is extended to include observations made at inter- 
vals during a period of several months. For example, 
specimen R467 expanded 0.18 per cent beyond its first 
minimum, or 0.11 per cent beyond its diameter when 
observations began a few minutes after molding, before 
it attained its first maximum a month and a half later. 
The other amalgams from the sorted particles of alloy 
behaved very much like this, although gradual changes 
*G. V. Black, The Physical Properties of the Silver-Tin Amalgams, 
Dental Cosmos, 38, 982, 1896. 
fA. W. Gray, Metallographic Phenomena Observed in Amalgams, Am. 
Inst. Min, and Met. Eng. Trans., 60, 684 and 693, 1919; Jour. Nat. 
Dent. Assn., 6, 913 and 918, 1910. 388 
PRACTICAL DENTAL METALLURGY 
in the expansion curve are noticeable as the alloy 
becomes progressively coarser. (See Fig. 73.) 
‘ ‘ In contrast with the specimens from sorted particles, 
R464 attains its first maximum in a few hours, with an 
expansion of less than 0.05 per cent beyond its first 
PACKED UNDER 25 KG PER CIR CM 
MIXED 
LINEAR REACTION EXPANSION 
SIEVE MESHES PER INCH 
AGE OF AMALGAM IN HOURS 
Fig. 73. 
minimum, or about 0.03 per cent beyond its initial 
diameter. Contraction of about 0.02 per cent to the 
second minimum, and final expansion too small for 
reliable measurement, leave the amalgam about 0.02 
per cent larger than when first measured. The same 
amalgam when packed under 50 kg. gives an expansion AMALGAMS 
389 
curve that is practically the same in all respects as 
the curve of R464. 
“The limitation of dimensional changes exhibited by 
the curve of R464 is not an accident of experimental 
procedure. It is a direct consequence of blending- 
alloy particles that differ in size; this is shown by 
many almost identical curves obtained during routine 
tests of different lots of similarly made alloy. 
“The charts not reproduced in this paper show that, 
as the packing pressure is increased, the effect of varia- 
tion in size of alloy particles becomes progressively 
less. 
“The contraction found when amalgam from a prop- 
erly adjusted dental alloy is packed under a very 
high pressure does not in any way prevent the making 
of a tight tooth filling, because packing hard enough 
to cause contraction in such an amalgam will stretch 
the resilient dentin more than enough to make it follow 
the slight shrinkage of the filling. In fact, moderate 
contraction after very tight packing is an advantage, 
in that it relieves to some extent the straining of the 
tooth. The tighter the packing', the better the filling, 
because heavy packing pressure not only adds to the 
strength of the amalgam, but also shortens consider- 
ably the time required for it to complete all its dimen- 
sional changes and become stable. Moreover, it secures 
much better adaptation of the filling to the cavity 
walls and, consequently, reduces liability to leakage. 
The packing pressures used in this investigation ex- 
tend from well within the dental range to considerably 
beyond it. The mean effective packing pressure em- 
ployed by different individuals, in condensing amal- 
gam fillings with dental instruments, vary widely. I 390 
PRACTICAL DENTAL METALLURGY 
found the average for four individuals to be 68 kg. 
per cir. cm. The average deviation from this was 
64 per cent; the difference between the highest (234 
kg.) and the lowest (17 kg.) was 321 per cent. Such 
deviations taken in conjunction with the pressure ef- 
PASSED SIEVE OF 200 MESHES PER INCH 
PACKING PRESSURES IN KILOS PER CIRCULAR CENTIMETER 
LINEAR REACTION EXPANSION 
AGE OF AMALGAM IN HOURS 
Fig. 74. 
fects shown in Fig. 74 indicate that, regardless of the 
accuracy of the particular device employed for measur- 
ing the dimensional changes, too much reliance must 
not be placed on comparisons of dental alloys that are 
based on expansion tests of amalgams packed by hand 
pressure or by mallet blows.” AMALGAMS 
391 
“The reaction expansions of over five hundred amal- 
gam specimens have been measured under accurately 
controlled conditions that have been systematically 
varied. Some specimens have been observed at regu- 
Fig. 75. 
lar intervals for about two years. In every case the 
expansion curve was found to conform to the behavior 
outlined above. Many examples were obtained of all 
four stages showing in the same curve. 392 
PRACTICAL DENTAL METALLURGY 
“From among the many interesting cases that might 
be cited as examples, only two will now be mentioned 
to illustrate long continued dimensional changes of 
considerable magnitude. Both specimens were prepared 
from commercial dental alloys by amalgamating accord- 
ing to the directions furnished by the manufacturers and 
packing under 50 kg. per cir. cm. One specimen, made 
from a coarse-grained non-zinc alloy, took more than a 
year to reach its first maximum. During this period it 
expanded as much as 0.48 per cent. The other, from an 
alloy containing zinc, reached its first minimum in half 
Fig. 76.—Three views of amalgam cylinders used in measuring reaction ex 
pansions to an accuracy of 0.05 micron. Natural size. 
an hour, after contracting about 0.04 per cent. It then 
expanded 0.01 per cent to its first maximum, which was 
reached within three hours after molding. The second 
minimum was reached in about a day, after a contrac- 
tion of 0.02 per cent below the first minimum, or 0.06 
per cent below the diameter when observations began. 
After this, the amalgam steadily expanded towards its 
second maximum, which was not reached in eight 
months, when observations had to be discontinued be- 
cause the cylinder had grown so large that readjust- 
ment of the dilatometer would have been necessary for 
further measurement. The diameter of the specimen AMALGAMS 
393 
had increased 1.28 per cent and was still expanding. 
This abnormal expansion is not attributable to the zinc 
contained in the alloy. 
“The phenomena described in this paper are just 
what ought to be expected from a consideration of 
conditions that influence diffusion, solution and crys- 
tallization. Accurate measurements of the dimen- 
sional changes that I have termed reaction expansions 
ought to throw light on other problems of metal- 
lography and physical chemistry.” 
Fig. 77.—Individual observations made with the dilatometer every 
minute while determining the dimensional changes that occur during the 
hardening of a dental amalgam. This instrument is reliable to 0.05 micron 
= 1/500,000 inch, which is one-fiftieth the least count of Dr. Black’s 
amalgam micrometer. During measurements with the dilatometer the 
amalgam is maintained at any desired temperature by means of a thermo- 
stated stirred oil-bath. 
Of necessity absolute control of these experiments 
necessitated a special type of apparatus. The dilatom- 
eter (Pig. 75) is an illustration of one of these in- 
struments used. 
FLOW.—The property which causes a substance to 
continue to yield under stress without breach of con- 
tinuity as long as the stress is maintained. 
Closely correlated with crushing strength, this prop- 394 
PRACTICAL DENTAL METALLURGY 
erty may be alluded to in amalgams where change in 
form due to constant or intermittent pressure results 
in distortion without fracture. The amount and rate 
of force applied influences this change, as does the 
time of setting and the temperature for any given alloy. 
When flow occurs in an amalgam filling (in situ) the 
change in form is usually manifested by its being 
forced from the cavity proximally and no matter how 
slight the change may be it is detrimental to the suc- 
cess of the operation. 
The influence of temperature on the mass is clearly 
shown by crushing strength tests performed by Arthur 
W. Gray, where a marked deviation of between 70 and 
80 degrees from the normal curve is shown.* 
“Fig. 78 represents the results of crushing 63 
cylinders of a high-grade dental amalgam at tempera- 
tures fairly uniformly distributed over the entire range 
from below 25° C. to over 95° C. Each cylinder was 
prepared by incorporating the same mass of alloy 
filings with 1.60 times this mass of mercury. After 
triturating for 4 minutes, the resulting smooth plastic 
amalgam was packed under a load of 400 kg. main- 
tained for 8 minutes. This produced a cylinder 10.04 
mm. in diameter by 11.5 mm. high, 40 per cent of its 
mass being mercury.” 
“All the cylinders prepared in this way were imme- 
diately placed in an incubator kept at 37.5° C. (body 
temperature) where they remained for several days be- 
fore crushing, thus insuring practical completion of 
the hardening process. The alloy used contained ap- 
*Trans. A. I. M- E., Supplement to Bulletin Ng, 144, December, 1918. AMALGAMS 
395 
proximately 68 per cent silver, 26 per cent tin, 5 per 
cent copper and 1 per cent zinc.” 
‘‘The curve indicates that with a rising temperature 
the crushing strength of a particular amalgam repre- 
sented decreases somewhat faster than linearly from 
5300 kg. per sq. cm. at 25 degrees to 4050 kg. at 45 de- 
CRUSHING STRENGTH IN KILOS PER CIRCULAR CENTIMETER 
TEMPERATURE CENTIGRADE 
Fig. 78. 
grees and 2550 kg. at 65 degrees. At 37.5 degrees the 
strength was fonnd to be 4550 kg. per sq. cm. or nearly 
65000 pounds per square inch. ’ ’ 
Since some of our food is taken into the mouth at 
70° C. and retained for a brief time, it is not unlikely 
that heat may be absorbed by amalgam fillings and 
under the influence of masticatory force result in a 
change of form through flow. 396 
PRACTICAL DENTAL METALLURGY 
EDGE STRENGTH in an amalgam is the degree of 
resistance an edge or angle of an amalgam mass offers 
to force which tends to fracture it. 
“Amalgams have heretofore been regarded as rigid 
crystalline masses, utterly devoid of malleability. The 
discovery of the existence of flow at once modifies all 
previous conceptions and data regarding edge strength, 
for it is evident that a corner or angle might not frac- 
ture, and yet flow under the stress of the impact of 
mastication, whereupon edge strength might be said to 
be great, and in reality be but slight. In view of the 
existence of the property of flow, edge strength must 
Fig. 79.—Test cylinders of amalgam prepared by amalgamating 6 GM. 
alloy. Cylinders A and B from low-silver alloy compress and crack. 
Cylinders C, D, E, and F from high-silver alloy burst explosively. 
Cylinders B and D, both packed under 400 KG., show difference in size 
of amalgam from same weight of alloy. D is 25 per cent larger and 75 
per cent stronger than B. C, D, and E are packed under 141, 400, and 
1131 KG. per cir. CM., respectively. Natural size: 10.0 M.M. in 
diameter. 
A 
B 
C 
D 
E 
F 
be measured as rigidity, the antithesis of flow, and a 
high crushing stress.”* 
DISCOLORATION.—The discoloration of amalgam 
fillings is for the most part due to the action of hy- 
drogen sulphide. Silver and copper are readily at- 
tacked by this gas, forming the black, insoluble sul- 
phides of silver and copper. Amalgams containing a 
larger proportion of either are blackened from this 
*Burchard: The American Textbook of Operative Dentistry, p. 224. AMALGAMS 
397 
cause, nor will those metals (such as gold or platinum) 
which are themselves untarnished by this agency, se- 
cure the same immunity to amalgams containing them. 
The sulphide of cadmium is lemon-yellow; hence amal- 
gams containing this metal are discolored (as is the 
tooth structure) a light yellow. 
CONDUCTIVITY.—As a conductor of thermal influ- 
ence, says Dr. Burchard,* amalgam is midway between 
gold and the basic zinc cements. 
WASHING-.—Dental amalgams are frequently 
washed in alcohol, ether, or chloroform to remove ox- 
ides and oily matter attracted from the hand. It is, 
however, doubtful if such procedure gives any bene- 
ficial result. It has, however, been claimed that washed 
amalgams retain their color better. 
*The American Textbook of Operative Dentistry, p. 226. CHAPTER XXII 
CLASSIFIED AMALGAMS 
Dental-amalgam alloys may be classified as BINARY, 
TERNARY, QUARTERNARY, QUINARY, Etc., ac- 
cording to the number of elementary constituents. 
A BINARY DENTAL AMALGAM may be composed 
of mercury alloyed with any ONE of the various met- 
als used as constituents of dental-amalgam alloys or 
dental amalgams, such as silver, tin, gold, copper, plat- 
inum, zinc, palladium, cadmium, bismuth, or antimony. 
COPPER and PALLADIUM, however, are the only 
ones which have thus far found any place of apparent 
usefulness. 
SILVER formed the prototype of binary dental 
amalgams, as it did of dental amalgams in general. 
When finely divided, such as the precipitate, it read- 
ily and rapidly combines with mercury, evolving con- 
siderable heat, and forming a hard mass in a few sec- 
onds. In the state of larger particles, such as filings, 
it combines more slowly. According to Mr. Fletcher,* 
“The rapidity of combination is reduced by the use of 
a mixture of precipitated silver and filings. If the 
precipitate is in excess, and the mass is inserted before 
the hardening commences, there is a risk of bursting 
the tooth by the gradual expansion of the mass— 
[which Mr. Kirby claims amounts to 1/40 of the diam- 
eter of the plug] if a great excess of mercury is used 
*Dental Metallurgy, p. 33. 
398 CLASSIFIED AMALGAMS 
399 
the mass only partially hardens and the results are 
uncertain.” 
Silver, is, however, the most important and essential 
component of dental-amalgam alloys, and is usually 
the largest component of their composition. It unites 
chemically with mercury to form definite chemical com- 
pounds* having the varying formulas of Ag6Hg, Ag2 
Hg3, and AgHg. It is readily discolored by sulphur 
compounds. 
TIN very readily combines with mercury, forming a 
friable, very slowly and imperfectly hardening amal- 
gam. It is very probable that the action of tin and 
mercury when combined is a decided contraction of the 
mass. It has been stated by some that the mass ex- 
panded, and by others that it contracted, but accurate 
data are wanting. The author bases his opinion en- 
tirely upon the data furnished by Dr. G. V. Black.f 
In arriving at this conclusion, however, it is necessary 
to eliminate so many factors of influence, such as 
chemical affinities, fineness of cut of the alloy, manner 
of mix, manipulation, etc., that the opinion after all 
may seem of little value. The following notes of Dr. 
Black, rearranged, formed the data: 
Fillings, 
how 
Inserted 
Formulae 
Fresh-cut 
Per 
cent 
of 
Mer- 
cury 
How 
Mixed 
Contraction = 
(—) 
Expansion = 
(+) 
Unit of 
Measurement 
1 Thousandth 
of an inch 
Amount of 
Contraction or 
Expansion 
if any 
Silver 
Tin 
Hand pressure 
70 
30 
46.36 
Hand 
+.1— .1 
Equalized 
“ “ 
65 
35 
44.6 
a 
Neither 
Neutral 
“ it 
60 
40 
37.85 
—.05.+.1,—.05 
Equalized 
a tt 
42.45 
57.55 
37.27 
ii 
—.8, +.2,—.2 
—.0008 max’m 
Burnished . .. 
42.45 
57.55 
45.31 
Mortar 
—.9, +.1 
—.0008 “ 
*See p. 259. 
fContraction and Expansion of Silver-Tin Amalgams, Dental Cosmos, 
xxxvii, p. 648. 400 
PRACTICAL DENTAL METALLURGY 
Tin and mercury show a disposition to unite—form- 
ing a definite chemical compound of a weak crystalline 
nature said to have the formula Sn2PIg. It is second to 
silver in importance as a constituent of dental-amalgam 
alloys. 
GOLD combines with mercury at any temperature, 
but more readily if either or both be heated slightly. 
Finely divided it combines even more rapidly. “Gme- 
lin states that an amalgam of 6 of mercury to 1 of 
gold crystallizes in four-sided prisms, and that the mer- 
cury may be distilled off from this leaving the gold in 
the arborescent form.”* 
COPPER possesses the property of combining with 
mercury to form an amalgam which, on hardening or 
setting, may be softened by heat, kneaded, and inserted 
as a filling, and again becoming hard may be polished. 
It retains its metallic luster for some time when ex- 
posed to air, but blackens quickly when in contact with 
air or moisture containing hydrogen sulphide. Its 
peculiar properties have led to its introduction as a 
dental amalgam, first known as Sullivan’s Amalgam or 
Cement. Its preparation and properties Mr. Fletcher 
describes as follows:f “Precipitate from a weak solu- 
tion of sulphate of copper by rods of pure zinc. 
Wash the precipitated copper with strong sulphuric 
acid (the addition of a small quantity of nitrate of mer- 
cury assists greatly), and add mercury in the propor- 
tion of 3 copper to 6 or 7 mercury. This alloy has the 
property of softening with heat and again hardening 
after a few hours. ’ ’ 
This amalgam has been thoroughly tried as a dental 
*Makins’ Metallurgy, p. 268. 
fDental Metallurgy, p. 60. CLASSIFIED AMALGAMS 
401 
filling-material, and its use practically discontinued on 
account of the intense blue-black discoloration of its 
surface and the teeth containing it, and its undeniable 
surface disintegration. It has been thought to possess 
therapeutic value; indeed, Dr. Kirk says: “Its preserv- 
ative qualities render it a valuable constituent in 
alloys for use in teeth of a low grade of structure.” Of 
it Dr. Black says:* “This amalgam has so many good 
qualities that many abandon it with much regret. I 
think it generally acknowledged that copper amalgam 
fillings retain good margins, when they are once made 
good, better or more perfectly than any other filling- 
material.” He shows that frequent reheating deterio- 
rates the amalgam very materially; claims that it will 
not flow under stress and “within the limits of its 
strength it is as rigid as hardened steel;” that it does 
not contract, but exhibits very slight expansion on set- 
ting, and attributes the properties heretofore assigned 
to its therapeutic qualities to the fact that it simply 
seals the cavity more perfectly. 
A variety of methods of preparing copper amalgam 
has been taught in the classrooms and described in our 
literature, some of which are as follows: 
Dr. T. H. Chandler’s method for making his “No. 
1” and “No. 2” is as follows :f 
No. 1. To a hot solution of sulphate of copper add a 
little hydrochloric acid, and a few sticks of zinc, and 
boil for about a minute. The copper will be precipi- 
tated in a spongy mass. Take out zinc, pour off liquor, 
and wash the copper thoroughly with hot water. Pour 
on the mass a little dilute nitrate of mercury, which will 
*Copper Amalgam, Dental Cosmos, xxxvii, p. 737. 
fDental Chemistry and Metallurgy, Mitchell, p. 141. 402 
PRACTICAL DENTAL METALLURGY 
instantly cover every particle of the copper with a coat- 
ing of the mercury. Add mercury 2 or 3 times the 
weight of the copper, triturate slightly in a mortar, 
and finish by heating the mixture a few moments in a 
crucible. 
No. 2. Take finely divided copper (copper dust) ob- 
tained by shaking a solution of sulphate of copper with 
granulated tin; the solution becomes hot, and a fine 
brown powder is thrown down. Of this powder take 
20, 30 or 36 parts by weight and mix in a mortar with 
sulphuric acid, 1.85 specific gravity, to a paste, and add 
70 parts of mercury, with constant stirring. When 
well mixed wash out all traces of acid and cool off. 
When used heat to 705° C. It can be kneaded like 
wax in a mortar. 
PLATINUM.—“Worked platinum,” says Mr. Ma- 
kins,# “cannot be amalgamated with mercury, and the 
only method of forming platinum amalgam consists in 
rubbing finely divided platinum (such as that reduced 
from the ammonio-chloride) and mercury together in a 
warm mortar; the combination of the two will be ac- 
celerated by moistening the two metals with water, 
acidulated with acetic acid.” 
ZINC readily amalgamates with mercury to form a 
very brittle amalgam, whatever may be the relative pro- 
portion. With large amounts of mercury it forms an 
amalgam similar to that of copper, but too brittle for 
dental use. 
PALLADIUM may be precipitated from its solution 
by metallic iron or zinc. It should then be washed 
with weak nitric acid, and dried. This character com- 
‘Metallurgy, p. 304. CLASSIFIED AMALGAMS 
403 
bines quite readily with mercury, attended by evolution 
of heat. It hardens quickly as it cools, but may be com- 
bined so as to set quickly or slowly, depending upon 
the proportion of its constituents. It turns very dark, 
but does not greatly discolor the tooth structure. On 
account of its quickly setting property it is difficult to 
work, and if inserted imperfectly it may harden so soon 
that it is almost impossible to remove it. Tombes says 
it shrinks less than any of the binary amalgams. The 
expensiveness of palladium has caused the use of this 
amalgam to be almost, if not entirely, discontinued. 
Mr. Fletcher says:# 
“It may be prepared to combine with mercury so as 
to set quickly or slowly by varying the strength of the 
solution; but it must be borne in mind that unless 
precipitated palladium sets very rapidly when mixed 
■with mercury, it is totally useless for dental purposes; 
the plugs fail, unless fully hard, in so short a time, that 
the amalgam is difficult to insert whilst it remains 
plastic. Plugs of palladium amalgam generally con- 
tain about 70 to 80 per cent of mercury. ’’f 
CADMIUM forms a silver-white, somewhat brittle 
amalgam of a crystallo-granular texture, which under 
•Dental Metallurgy, Fletcher, p. 41. 
tMr. Coleman in the subjoined gives his preparation of palladium amal- 
gam: “About as much mercury as would fill the cavity to be treated is 
placed in the palm of the hand, and the palladium powder very gradually 
added. It reouires some careful rubbing with the forefinger before the two 
become incorporated, when it should be divided into small pellets, and 
these rapidly carried one after another to the cavity, each piece being well 
compressed and rubbed into the inequalities of its walls by a burnishing or 
compressing instrument and with a rotary movement of the hand. This is 
continued until the cavity is quite filled, or even, if to some slight 
extent built out, the surface being rendered smooth and polished with a bur- 
nisher until it is quite set, which is generally in a very little (too short) a 
time.”—Dental Surgery and Pathology. 
He also states, according to Kirk, that it is probably the most durable of 
all amalgams, but the most difficult to manipulate. Its surface changes to 
a black color, but as a rule does not stain the structure of the tooth.— 
Am. System of Dentistry. 404 
PRACTICAL DENTAL METALLURGY 
certain circumstances is said to be malleable, imparting 
that quality to its alloys. 
ANTIMONY AND BISMUTH.—(See chapters on 
these subjects.) 
TERNARY DENTAL AMALGAMS.—These are 
generally alloys composed of SILVER and TIN, com- 
minuted by filing or turning in a lathe, and amalgamated 
into a coherent mass with mercury. The components 
are, as a matter of course, subject to considerable varia- 
tion, the proportions of silver and tin ranging from 75 
parts of the silver to 25 of the tin, to 40 of the silver 
and 60 of the tin. The proportions of mercury range 
from equal parts by weight, to 1.4 or even 1.6 of mer- 
cury. The comminuted alloy is amalgamated with the 
mercury by rubbing them together in the palm of the 
hand or in a Wedgwood or ground-glass mortar until a 
more or less smooth and coherent mass is formed. When 
a considerable amount of mercury is used in the mixing, 
the excess is generally squeezed out through a muslin 
cloth or chamois skin. The mass, when packed to- 
gether, acquires a metallic hardness within a few hours, 
and arrives at its full degree of hardness usually in 
twenty-four to forty-eight hours. It is then a hard, 
brittle mass that may be dressed with a file and pol- 
ished as other metallic bodies. 
REQUISITE PROPERTIES OF A DENTAL AMALGAM 
1. Permanency of Form (exhibiting as little tendency to con- 
tract, expand or assume a spheroidal form as possible). 
2. Sufficient Density, Hardness, and Toughness to Resist Attri- 
tion. 
3. Strength and Sharpness of Edge. 
4. Complete resistance to the action of the Oral Secretions and 
Food. CLASSIFIED AMALGAMS 
405 
5. Freedom from Admixture with any Metal Favorable to the 
Formation in the Mouth of Soluble Salts of an Injurious Char- 
acter. 
6. Good Color. 
The first ternary dental-amalgam was that formulated 
by Dr. Townsend consisting of silver 42 and tin 58 
parts. His formula has since been changed, how- 
ever, to silver 44.5, tin 54.5, and gold 1. Investiga- 
tions and experiments then seem to demonstrate that 
those alloys containing more than 50 per cent of silver 
gave better results. 
By the table of dental-amalgam alloys submitted on 
page 374 it may easily be seen that silver and tin form 
the basis of all amalgams used in dentistry. With a 
view to overcoming the imperfections in and disad- 
vantages of this simple ternary amalgam, and increas- 
ing its tooth-conserving qualities, and, therefore, its 
usefulness, a vast amount of experimentation has been 
carried on by the profession and the manufacturers. 
Papers after papers have been written, published, and 
discussed, all of which have had a tendency to prove 
that there is good reason to believe that the addition of 
small proportions of one or more other metals will, in 
a measure, overcome the objections inherent in an amal- 
gam made of an alloy of silver and tin alone. 
QUARTERNARY, QUINARY, ETC., DENTAL- 
AMALGAMS represent the basal alloy of silver and tin 
modified by the addition of one or more of the follow- 
ing metals in small proportions: Gold, platinum, irid- 
ium, copper, zinc, cadmium, bismuth, antimony, and 
aluminum. 406 
PRACTICAL DENTAL METALLURGY 
GOLD is usually added to silver-tin dental-amalgam 
alloys to the extent of from 2 to 7 per cent. Dr. Bon- 
will regards a greater quantity very undesirable.* 
COPPER.—A very large percentage of the alloys 
found upon the market contains small proportions of 
copper, ranging usually from 3 to 8 per cent. 
With tin, copper yields a very white amalgam, by 
proper manipulation. There is, however, a tendency 
to soon discolor, which may be controlled, it is said, by 
a small proportion of gold. 
ZINC.—The fact that zinc is electro-positive to most 
of the metals used in the mouth has led to a contro- 
versy in recent years over its use in dental amalgams. 
Observations by Gray in 1917 indicated that the quan- 
tity of zinc present in dental amalgam alloys “pro- 
duced but little effect on the electromotive force de- 
veloped between gold and amalgam, either in the 
mouth or in various electrolytes.” 
Souder and Petersf in discussing this question state: 
“Those familiar with the amalgam problems know 
that practically all discussions on the effect of zinc 
have hinged in the question of the electromotive forces 
of zinc and nonzinc amalgams. In the light of this, 
we include the table of values that summarizes the 
work on electromotive forces. From this table we may 
conclude that no effect need be expected due to differ- 
ences of electromotive force between zinc and nonzinc 
alloys. The question of what takes place between gold 
and amalgam is far more important. ’ ’ 
*Dental Cosmos, xxiv, p. 422. 
tW. H. Souder and C. G. Peters, Bureau of Standards. Dept, of Com- 
merce; A discussion of a paper, Transition Phenomena in Amalgams, by 
A. W. Gray, American Institute of Min. & Met. Eng., 1920. CLASSIFIED AMALGAMS 
407 
ELECTROMOTIVE FORCE OF ZINC ALLOYS 
ALLOY 
E.M.F. 
ALLOY 
E.M.F. 
0 °/o zinc 
-0.54 
-0.52 
-0.52 
0 % zinc (duplicate) ... 
-0.55 
2 % zinc 
0 % zinc, 16 % copper .. 
-0.52 
5 % zinc 
-0.51 
0 % zinc, 16 % copper . . 
(duplicate) 
-0.52 
Gold (metallic) .. 
+0.002 
In discussing the influence of zinc on amalgams Gray- 
further states,* “That zinc exerts very little influence 
upon the expansivity until the transition region is ap- 
proached, is evident from both my own curves and 
those of Souder and Peters. That zinc may, however, 
exert an enormous influence in the critical region is 
clearly seen upon comparing the expansion-tempera- 
ture curves yielded by an amalgam cylinder from an 
alloy containing 70 silver, 27 tin, and 3 copper with 
the curve yielded by a cylinder prepared in exactly the 
same way from an alloy that differed from this only 
in that one per cent of zinc was added.” 
ANALYSIS OF DENTAL AMALGAMS.—A perfect 
familiarity with the composition of the alloys used in 
individual practice is indispensable, and it is also im- 
portant, and, at times, exceedingly desirable, to be able 
to determine the composition of other alloys or old 
amalgam plugs. 
Analysis is accomplished by two means, known re- 
spectively as the dry and wet methods. 
The Dry Method consists principally of two parts: 
1. A 'physical examination, noting weight, color of 
alloy, and discoloration, if any, and hardness. 
2. Subjection to the heat of the blowpipe either alone 
or in the presence of certain reagents. 
*Jour. Nat. Dent. Assn., 6, p. 526, 408 
PRACTICAL DENTAL METALLURGY 
The Wet Method generally consists of dissolving the 
solid in some solvent, and precipitating the dissolved 
constituents separately as the simpler compounds of 
oxygen, sulphur, chlorine, etc. 
Before proceeding with the analysis of an old amal- 
gam plug by the wet method, a careful study should be 
made of its weight, color, discoloration, hardness, etc. 
MERCURY.—It may then be weighed and placed in 
a hard glass tube or porcelain crucible and heated to a 
red heat, to drive off the mercury, the amount of which 
is determined by the difference in the first weight and 
that obtained after heating. 
This method is somewhat inaccurate, on account of 
the oxidation or volatilization of some of the con- 
stituents. 
The plug deprived of its mercury is placed in a mor- 
tar and finely divided; then a weighed quantity (usually 
10 or 20 grains) is transferred to a glass flask and suf- 
ficient chemically pure nitric acid added to more than 
dissolve it, by the aid of gentle heat. 
The powdered condition of the alloy is necessary, 
otherwise the metastannic acid formed by the action 
of nitric acid upon the tin, after a few moments, so 
protects the surface of the alloy, that it greatly retards, 
if not in a measure prevents, its complete solution. 
Much can be discerned qualitatively by the appear- 
ance of the solution. After the action of the acid is 
completed, there will appear a residue in the bottom of 
the flask, with a clear supernatant liquid. If this liquid 
is colored a greenish-blue, copper is present. If the pre- 
cipitated metastannic acid is white, or nearly so, gold 
and platinum in any considerable quantity need not be 
expected, as the presence of a very small amount of gold CLASSIFIED AMALGAMS 
409 
is sufficient to tint the metastannic acid purple, due to the 
formation of the purple of Cassius; and the presence of 
platinum is determined by a black powder, small par- 
ticles of metallic platinum mixed with the metastannic 
acid. Very small quantities of this metal are, however, 
dissolved in nitric acid, in the presence of a large excess 
of silver. 
TIN.—The contents of the flask should then be fil- 
tered, the filtrate preserved, and the precipitate thor- 
oughly washed with distilled water, dried, the metas- 
tannic acid (H10Sn5O15) rendered anhydrous (Sn02) 
by calcining at a red heat, and then weighed,—78.66 
per cent of the mass representing the amount of tin in 
the alloy. 
ANTIMONY.—If there be any reason to suspect the 
presence of antimony in the alloy, the dioxide of tin 
(Sn02) should be fused in a silver crucible with sodium 
hydrate (NaOH) by which the antimonate (NaSb02) 
and stannate (Na2Sn03) of sodium are formed. The 
fused mass is now digested and disintegrated in cold 
Avater, and filtered. If antimony be present, it Avill be 
caught on the filter paper as the antimonate of sodium. 
Avhile the soluble stannate of sodium passes through 
Avith the filtrate. The antimonate should now be 
Avashed with distilled water, dried and weighed—68.92 
per cent of the mass representing the amount of anti- 
mony in the alloy. 
SILVER.—The filtrate Avhich was originally the su- 
pernatant liquid in the flask, should now be diluted 
someAvhat, and hydrochloric acid added until no more 
precipitate (silver chloride) is formed, Avhen the whole 
should be filtered, the precipitated silver chloride re- 410 
PRACTICAL DENTAL METALLURGY 
maining on the filter paper, washed with distilled 
water, dried and weighed—75.26 per cent of the mass 
representing the amount of silver present in the alloy. 
COPPER.—The original supernatant liquid in the 
flask is now treated to sulphuretted hydrogen. The 
copper and cadmium are thrown down as sulphides. 
The copper sulphide is black, while that of cadmium is 
lemon yellow. The contents of the flask are again fil- 
tered, and the copper and cadmium sulphides caught 
upon the filter paper; these are washed with distilled 
water and treated with dilute sulphuric acid, the cad- 
mium sulphide being dissolved. All is again filtered; 
the dissolved cadmium sulphide passing through, and 
the copper sulphide remaining upon the filter, should 
be washed, dried, and weighed—66.49 per cent of the 
mass representing the amount of copper present in 
the alloy. 
CADMIUM.—The cadmium sulphide may be thrown 
down now with potassium hydrate as cadmium hydrox- 
ide (Cd(OH)2) dehydrated by heating, and weighed as 
cadmium oxide, CdO—87.49 per cent of the mass repre- 
senting the amount of cadmium in the alloy. 
ZINC.—From the original solution the zinc may be 
separated as the carbonate (ZnC03) by adding one of 
the alkaline carbonates. It is then washed, heated to 
redness, and weighed as the pure oxide of zinc, ZnO— 
80.24 per cent of the mass representing the amount of 
zinc in the alloy. 
GOLD.—Probably the most practical manner of de- 
termining the amount of gold in a dental-amalgam alloy 
of approximately unknown composition is as follows: 
After drying and accurately weighing the insoluble CLASSIFIED AMALGAMS 
411 
residue of metallic platinum and precipitated com- 
pounds of gold and tin, obtained upon dissolving the 
original alloy or plug in pure nitric acid, it should be 
fused with potassium carbonate and cyanide; the tin 
oxide is dissolved by the flux, and the resulting but- 
ton is composed of gold and platinum. This should 
now be rolled to a very thin ribbon, cut up and di- 
gested in aqua regia (see chapter on gold), forming the 
soluble chlorides of gold and platinum. The chlorides 
thus formed are then dissolved in a sufficient quantity 
of distilled water, from Avhich the gold is precipitated 
in the metallic state by the addition of a solution of 
oxalic acid or the sulphate of iron. It is then collected 
by filtration, fused, and weighed. 
PLATINUM.—The platinum in the remaining solu- 
tion is thrown down as ammonio-platinic chloride 
(H4NC1)2 PtCl4, by the addition of ammonium chloride, 
washed, dried, and weighed as such—44.17 per cent of 
the mass representing the amount of platinum in the 
alloy. TABLE OF WEIGHTS AND MEASURES 
1 millimeter = 0.001 meter = 0.03937 inch. 
1 centimeter = 0.01 meter = 0.3937 inch. 
1 decimeter = 0.1 meter = 3.937 inches. 
1 meter = 39.37 inches. 
1 decameter = 10 meters = 32.8083 feet. 
1 hectometer = 100 meters = 328.083 feet. 
1 kilometer = 1000 meters = 0.62137 mile. 
1 yard or 36 inches = 0.9144 meter. 
1 inch = 25.4 millimeters. 
Meas%ires of length 
Measures of capacity 
1 milliliter = 1 c.c. = 0.001 liter = 0.0021 U. S. pint. 
1 centiliter = 10 c.c. = 0.01 liter = 0.0211 U. S. pint. 
1 deciliter — 100 c.c. — 0.1 liter — 0.2113 U. S. pint. 
1 liter = 1000 c.c. = 1.0567 U. S. quart. 
1 decaliter = 10 liters = 2.6417 U. S. gallons. 
1 hectoliter = 100 liters = 26.417 U. S. gallons. 
1 kiloliter — 1000 liters = 264.17 U. S. gallons. 
1 U. S. gallon == 3785.43 c.c. 
1 imperial gallon = 4543.5 c.c. 
1 minim = 0.06 c.c. 
1 fluidrachm = 3.70 c.c. 
1 fluidounce = 29.57 c.c. 
1 liter — 33.81 fluidounces. 
Weights 
1 milligram = 0.001 gramme = 0.015 grain. 
1 centigram — 0.01 gramme = 0.154 grain. 
1 decigram = 0.1 gramme = 1.543 grains. 
1 gramme = 15.432 grains. 
1 decagram — 10 grammes = 154.324 grains. 
1 hectogram = 100 grammes — 0.268 pound Troy. 
1 kilogram — 1000 grammes = 2.679 pounds Troy. 
1 kilogram = 2.2046 pounds avoirdupois. 
1 grain Troy = 0.0648 gramme. 
1 drachm Troy — 3.888 grammes. 
1 ounce Troy = 31.103 grammes. 
1 ounce avoirdupois = 28.350 grammes. 
1 pound avoirdupois = 453.592 grammes. 
412 WEIGHTS AND MEASURES 
413 
Commercial weights and measures of the U. S. A. 
1 pound avoirdupois — 16 ounces. 
1 ounce = 437.5 grains. 
1 gallon = 231 cubic inches 
1 gallon — 4 quarts — 8 pints. 
1 pint of water weighs 7291.2 grains at a temperature of 15.68 C. 
Apothecaries’ weights 
The apothecaries’ ounce is of the same value as the now ob- 
solete English Troy ounce. 
1 ounce = 8 drachms = 480 grains. 
1 drachm = 3 scruples ~ 60 grains. 
1 scruple = 20 grains. 
1 ounce = 31.103 grammes. 
1 grain = 64.799 milligrams. 
Apothecaries’ fluid measures 
These are derived from the U. S. gallon; the liquid pint of this 
gallon is identical in value with the apothecaries’ pint. 
1 pint = 16 fluidounces = 7680 minims. . 
1 fluidounce = 8 fluidrachms = 480 minims. 
1 fluidrachm = 60 minims. 
Jewelers’ weight 
1 carat = 0.205 gramme = 3.163 grains. 
The above tables quoted from Simon’s Chemistry. 
Troy weight 
This is still used by some dental gold manufacturers who re- 
tail their product under this system. 
24 grains = 1 pennyweight (dwt.). 
20 pennyweight = 1 ounce. 
12 ounces = 1 pound Troy. 414 
PRACTICAL DENTAL METALLURGY 
GRAIN 
TROY 
PENNYWEIGHT 
TROY 
OUNCE 
TROY 
POUND 
AVOIRDUPOIS 
OUNCE 
AVOIRDUPOIS 
POUND 
GRAM 
1. 
.041666 
.0020833 
.000173611 
.00228571 
.00014285 
.06479897 
24. 
1. 
.05 
.0041666 
.0548571 
.0034285 
1.5551754 
480. 
20. 
1. 
.08333333 
1.0971428 
.0685714 
31.103495 
5760. 
240. 
12. 
1. 
13.165714 
.822857 
373.2419478 
437.5 
18.22917 
.911458 
.07595485 
1. 
.06250 
28.3495403 
7000. 
291.66666 
14.58333 
1.215217 
16. 
1. 
453.5926449 
15.432349 
.6430145 
.03215072 
.0026792272 
.03527394 
.00220462 
1. 
Comparative Table of Troy, Avoirdupois and Metric Weights WEIGHTS AND MEASURES 
415 
Area 
SQUARE 
INCHES 
SQUARE 
FEET 
SQUARE 
MILLIMETERS 
SQUARE 
CENTIMETERS 
SQUARE 
METERS 
1. 
0.00(394 
645.11 
6.4511 
0.000645 
144. 
1. 
92,985. 
928.95 
0.0929 
1550. 
10.75 
1,000,000. 
100. 
1. 
Volumes 
CUBIC 
INCHES 
CUBIC 
FEET 
CUBIC 
MILLIMETERS 
CUBIC 
CENTIMETERS 
CUBIC 
METERS 
1. 
0.000578 
16,385. 
16.385 
0.00001638 
1728. 
1. 
28,311,000. 
28',311. 
0.028311 
61023. 
35.316 
1,000,000,000. 
1,000,000. 
1. 
3785.4 c.c. =z 128 fl. oz. = 1 gal. = 231 eu. in. = 8% lbs. avoir- 
dupois. 
1. c.c. of distilled water at 4° C. weighs 1 gm. 
Specific Resistances of Metallic Wires 
(From Smithsonian Tables) 
MICROHMS 
PER CU. CM. 
SUBSTANCE AT 0 DEG. 
CENT. 
OHMS PER MIL. 
FOOT AT 0 DEG. 
CENT. 
TEMP. CO-EF- 
FICIENT AT 20 
DEG. CENT. 
Silver (annealed) 
1.460 
8.781 
0.00377 
Silver (hard drawn) 
1.585 
9.538 
Copper (annealed) 
1.584 
9.529 
0.00388 
Copper (hard drawn) 
1.619 
9.741 
0.00365 
Gold (annealed) 
2.088 
12.56 
Gold (hard drawn) 
2.125 
12.78 
Aluminum (annealed) 
2.906 
17.48 
0.00365 
Zinc (pressed) 
5.613 
33.76 
Platinum (annealed) 
9.035 
54.35 
Iron (annealed) 
9.693 
58.31 
Nickel (annealed) 
12.43 
74.78 
0.00365 
Tin (pressed) 
13.18 
79.29 
Lead (pressed) 
19.14 
115.1 
0.00387 
Antimony (pressed) 
35.42 
213.1 
0.00389 
Bismuth (pressed) 
130.9 
787.5 
0.00354 
Mercury (pressed) 
94.07 
565.9 
0.00072 
Platinum-silver (2 Ag. 
+ 1 Pt. by weight) 
24.33 
146.4 
0.00031 
German silver 
20.89 
125.7 
0.00044 
Gold-silver (2 Au. 1 
Ag. by weight) 
10.84 
65.21 
0.00065 416 
PRACTICAL DENTAL METALLURGY 
Resistance Units 
The resistivity or the specific resistance of a conductor ma- 
terial is the resistance in ohms of a sample of the material of 
unit length and unit section. Thus, if 1 represents the length 
of the conductor, a its sectional area, r its resistance,. and p its 
specific resistance, then r = pl/a and p = ra/1. For purposes 
of comparison, 1 and a are usually taken in centimeters and 
square centimeters, respectively, and p thus expresses the re- 
sistance in ohms between opposite faces of a centimeter cube. 
Table gives value of specific resistance for various materials. 
Since most conductors are drawn wires of circular section, it is 
customary in engineering work to express the resistivity of a ma- 
terial in ohms per (circular) mil-foot, where the mil-foot rep- 
resents a cylinder of the material 1 mil or 0.001 inch in diameter 
and 1 foot in length. A mil-foot of copper has a resistance of 
10.4 ohms at 20 degrees Centigrade. 
Scale of Hardness 
1. Talc. 
2. Rocksalt. 
3. Calcite 
4. Fluorite 
5. Apatite 
6. Feldspar 
7. Quartz 
8. Topaz 
9. Corundum 
10. Diamond 
Hardness of Some Metals 
(From Smithsonian Tables) 
Aluminum 2-2.5 
Antimony 3.3 
Bismuth 2.5 
Copper 2.5-3 
Gold 2.5-3 
Iridium 6 
Iridosmium 7 
Iron 4-5 
Lead 1.5 
Palladium 4.8 
Platinum 4.3 
Platinum-Iridium 6.5 
Silver • 2.5-3 
Steel 5-8.5 
Tin 1.5 
Zinc 2.5 WEIGHTS AND MEASURES 
417 
Conversion of Thermometer Scales 
Degrees C. x 1.8 + 32° = Degrees F. 
F. - 32° 
Degrees—j-g — Degrees C. 
or 
Temperature Fahrenheit == (9/5 Temperature Centigrade) + 32° 
Temperature Centigrade = 5/9 (Temperature Fahrenheit - 32°) 
Fixed Points in Thermometry 
Boiling point of water at atmospheric pressure 100° 0 212° F 
Melting point of ice 0° C 32° F 
Absolute Zero (theoretical) -273° C -461° F 
Fahrenheit and Centigrade Scales meet at -40° C -40° F LABORATORY PROCEDURE 
FOR STUDENTS 
IN 
DENTAL METALLURGY 
BY 
J. D. HODGEN, D.D.S. 
Revised by 
J. S. Shell, B.S., 
Instructor in Chemistry and Metallurgy, 
University of California, 
College of Dentistry. RULES AND SUGGESTIONS TO STUDENTS 
I. Begin your work by placing on the bench in front 
of you, your towel, such apparatus as you need for 
the experiments, and your notebook. Prepare for 
doing the first experiment of the day, and read it 
entirely through before attempting to perform any 
part of it. 
II. Before every laboratory exercise you should make 
a thorough preparation for the experiments by study- 
ing several textbooks on the subject. 
III. Each student must be provided with a cloth to 
heap the bench clean and something to protect the cloth- 
ing, preferably a laboratory coat or apron, from injury 
while at work. 
IV. The bench at which you work must be left clean 
and dry after every laboratory exercise. Carefully wipe 
off a ring stand, burner, or other apparatus on which a 
reagent has fallen, wipe out a pneumatic tub after 
using it, and keep reagent bottles, apparatus, boohs and 
lockers clean. Iron and steel objects must not be put 
away wet, or they will rust. Any substance dropped 
on the floor must be brushed or wiped up. 
V. In experimenting, follow the directions as closely 
as possible, and ask an explanation of anything not un- 
derstood. Have your apparatus neatly arranged with- 
out artificial props, wedges, or uncouth-looking materials. 
All apparatus and chemicals must be clean and pure. 
VI. Have every delivery tube and stopper a close 
fit, to prevent leakage of gas. If a gas generates well 
421 422 
PRACTICAL DENTAL METALLURGY 
but does not pass into the receiver, there is some leak- 
age, due probably to loose bearings. Old stoppers will 
scarcely ever do to use. Rubber stoppers may be used 
for a long time, but should be detached after every ex- 
ercise. Before any tube is put into a stopper, make 
sure that it has been properly rounded. To put a tube 
into a rubber stopper, moisten both the tube and the 
hole in the stopper. To put a stopper into a test tube, 
clasp the latter near its mouth with the left hand and 
gently press in the stopper with the right, keeping it 
perfectly straight, so as not to break the glass. 
VII. In heating a test tube on a ring stand, hold the 
burner in the hand, move it slowly, and now and then 
take it away from the tube for a few seconds after 
the action has become vigorous, or the tube may melt 
or break. 
VIII. In heating a substance in an evaporating' dish 
or a flask, have the latter usually not more than 5 or 
10 cm. above the top of the burner, unless it is desired 
to heat slowly. If the ring which holds the plate can 
not be easily lowered to that distance, put a small 
ring below on which to rest the burner, but do not raise 
the burner with books placed underneath. 
IX. Mixtures of solids should be made on paper, and 
thence carefully poured into the receptacle. You should 
have in your locker old newspapers, etc., neatly cut about 
the size of the leaves of this book. Use filter papers for 
nothing but filtering. Small splints should be used for 
testing combustion. Be careful not to mix chemicals or 
reagents, ivhether solids or liquids, except as directed. 
X. Never put down a glass stopper, when using a re- 
agent bottle, if you can avoid it, but hold it between the LABORATORY PROCEDURE 
423 
first and second fingers, and replace it when yon put 
down the bottle. Do not pour back any excess of a re- 
agent from a test tube, or receiver into a reagent bot- 
tle, and do not dip a stirring rod or pipette into a reag- 
ent bottle. In reddening litmus paper for use, never 
dip it into an acid, but hold it in the fumes of HC1. 
To turn it blue, use the fumes of NII3. 
XI. In pouring a liquid into a test tube or graduate, 
hold the latter on a level with the eye, towards the 
light, and in such a way as not to conceal the sub- 
stance already therein, but so as to see any phenomena. 
XII. Pour only liquids, fine solids, or soluble salts 
into the sinks, always opening the faucet first to let the 
water run, other solids should be thrown into the jars. 
Great care must be taken not to clog the discharge pipes 
with glass, matches or other solids. 
XIII. Wipe your flask, evaporating dish, or tube per- 
fectly dry on the outside before applying heat. Tubes 
of thick glass, if they contain no liquid, should be 
heated gradually by moving them rapidly into and out 
of the flame. When once heated, they may be held 
steadily in the flame. If a hot flask or tube holds a 
liquid, it is not injured by pouring water on the out- 
side, but if it contains only a solid, or is empty, it 
should be cooled till it can be handled, or water will 
break it. 
XIV. The hottest part of a Bunsen flame is about 
half way up, just above the inner cone. Substances 
to be strongly heated should be held there. 
XV. On leaving the laboratory be sure that everything 
is put back in place, the part of the bench you have oc- 
cupied wiped clean and dry, and the locker locked. Re- 424 
PRACTICAL DENTAL METALLURGY 
agents for general use must not be taken to the indi- 
vidual’s bench, but left where they belong, and nothing 
must be put into your locker except what belongs there. 
XVI. Endeavor to carry away from each experiment 
a mental picture of the apparatus as it is set up, of the 
colors and appearance of the substances used, and of 
the products obtained—whether they are solids, liquids 
or gases, in solution or not, crystalline or amorphous, 
etc. In recalling and describing experiments state all 
of these, together with the names and symbols of the 
factors and products, but do not try to recall quantities 
of substances used. By noting and comparing the colors 
and odors of gases, many substances can be recognized. 
To take the odor of a noxious gas, waft some of the gas 
with the hand from the mouth of the tube or receiver 
to the nose, thus diluting it. 
XVII. Write your name and locker number distinctly 
across the front of your notebook, also write your 
name, locker number, subject of the experiment, and 
date, at the head of each perforated page. Be sure 
the carbon sheet is properly placed to copy it on the 
page beneath. When the page is filled, number it, 
tear it out carefully, and at the finish of the work, 
place all removed pages in drop-box provided. No 
notes should be made outside of the laboratory without 
special permission. Take your notebook with you at 
the end of the hour, and study the experiments for 
recitation. Leave the carbon sheet in your locker. 
XVIII. It is of the greatest importance that you 
should see all there is in an experiment, and the order 
in which changes take place, and state your observations 
briefly and in correct English. Your notes should em- LABORATORY PROCEDURE 
425 
body the following points—(1) Chemicals (names and 
symbols'), apparatus and adjustment (very briefly and 
not copied from the directions). (2) Observations and 
residts (such as whether solid, liquid, or gaseous, the 
color, odor, increase of temperature or of volume, effer- 
vescent action, precipitation, sublimation, etc. (3) Ex- 
planation of each change (i. e., what it indicates to you, 
or how chemists account for the phenomena, together 
with a reaction where this is possible). Put the main 
stress on (2) and (3). Try to distinguish in an experi- 
ment what you see that is important from what is not so, 
and whenever you give an explanation think whether the 
experiment teaches it, or whether you have gotten it 
from some outside source. Write each reaction on a 
line by itself immediately following the explanation it 
ABBREVIATIONS. 
app. apparatus. 
b. beaker. 
c. cubic centimeters, 
cm. centimeters. 
cpd. compound, 
dil. dilute, 
dis. dissolve. 
d. t. delivery tube. 
e. d. evaporating dish. 
Exp. experiment. 
f. f. Florence flask. 
Gm. grams. 
gen. generator, 
insol. insoluble, 
i. t. ignition tube, 
m. s. metric system. 
N. T. P. normal temperature 
and pressure (0°, 
760 mm.) 
ppt. precipitate, 
p. t. pneumatic tub. 
qcm. square centimeters, 
reagt. reagent, 
ree. receiver (wide-mouth 
bottle.) 
r. s. ring stand, 
sat. saturate, 
soln. solution. 
sp. gr. specific gravity. 
s. r. stirring rod. 
t. t. test tube, 
vol. volume. 426 
PRACTICAL DENTAL METALLURGY 
is intended to complete. Indicate gases in a reaction 
by an arrow, above and to the right of the symbol, as 
NHg/’' and precipitates by a brace underneath, as 
PbS04. Record of an experiment must be made on 
the spot, either as soon as the experiment is completed, 
or often before it is done, at a convenient place for a 
pause. For valences, symbols, names, solubilities, etc., 
of substances, refer to charts; if they are not there, 
consult the instructor. 
APPARATUS REQUIRED BY EACH STUDENT 
1. Beaker, 600 c.c. 
2. 1 Beaker, 250 c.c. 
3. 1 Florence flask, 500 c.c. 
4. 1 Funnel, 10 cm. 
5. 12 Test tubes, 17 mm. 
6. 1 Flint bottle, 150 c.c. 
7. 1 Flint bottle, 250 c.c. 
8. 1 Graduate, 120 c.c. (double graduation). 
9. 1 Piece G'ass stirring rod. 
10. 1 Porcelain evaporating disk, 150 c.c. 
11. 1 Test tube rack. 
12. 1 Test tube brush. 
13. 1 Crucible-tongs, 25 cm. 
14. 1 Sand bath, 15 cm. 
15. 1 Test tube holder. 
16. 1 Iron ladle. 
17. 1 Bunsen burner. 
18. 1 Ring-stand, 2 rings. 
19. 1 Tripod. 
20. 6 Crucibles. 
21. 1 ft. rubber tubing. 
22. 1 Cork for Florence flask. 
23. 1 Cork for flint bottle. 
24- 1 Cork for 17 mm. test tube, LABORATORY PROCEDURE 
427 
25. 50 Filter papers 15 cm., % pkg. 
26. 1 Rule (double graduation). 
27. 1 Blowpipe, 25 cm. 
28. 1 Small towel. 
29. 50 Pieces paper about 20 cm. square. 
30. 1 Notebook. 
31. 1 Small padlock. 
ASSIGNMENT OF LOCKERS 
Students may be admitted in the laboratory, for the selection 
of lockers, in accordance with any plan adopted by the college 
for the assignment of lockers and equipment. It is customary 
to defer such assignments until the instructor is advised by the 
Dean or other responsible officer that the student is entitled to 
enroll in the laboratory course. 
Place articles “furnished by student” on bench for inspection 
by Instructor. After inspection, take all articles out of locker 
and place on bench and place all articles “ furnished by stu- 
dent” in locker. 
Instructor will read “Requirements” for each student, re- 
serving the articles to be washed until the last, and as he reads, 
each student will replace the article called in the locker, thereby 
seeing that every article is present and in good condition. If 
any are missing, they must be supplied before the close of the 
period. 
All glass apparatus must be thoroughly washed and wiped be- 
fore replacing in the locker, and when invoice is completed 
student will place his own lock on the locker and retire from the 
laboratory after handing to the Instructor his Roll Number and 
Locker Number. 
The following laboratory experiments are designed to illustrate 
the subject matter of the text. Whether the instructor prefers 
to conduct the experiments prior to the specific lecture or reci- 
tation period relating thereto or following it, depends on his 
pedagogical viewpoint. It is the custom of the revisor to follow 
the latter procedure. For purposes of stimulating interest among 428 
PRACTICAL DENTAL METALLURGY 
the thinking students and to check the delinquent ones who are 
prone to evade laboratory work a number of experiments called 
“unknown’’ are introduced at occasional unannounced intervals 
by the instructor as a part of the laboratory requirement. 
PERIOD I 
COMPOUNDS OF METALS AND NONMETALS 
APPARATUS—Bunsen burner, iron ladle, ring stand, funnel, 
filter paper, evaporating dish, beaker, litmus paper. 
REAGENTS—Lead, Copper, Nitric Acid, Potassium, Potas- 
sium Hydroxide, Zinc Sulphate, Ammonium Hydroxide, Ferric 
Chloride, Magnesium Hydroxide, Ferrous Sulphate. 
EXPERIMENT No. 1: OXIDATION OF SODIUM. With 
a knife cut off a small piece of metallic sodium; observe it ex- 
hibits a brilliant luster but speedily tarnishes by combining with 
the oxygen of the air, forming the oxide (NaO) of sodium. 
Plunge the sodium into a jar of oxygen: it takes fire and burns 
with a brilliant yellow flame. 
EXPERIMENT No. 2: OXIDATION OF ZINC. With a 
piece of zinc foil form a tassel, gently warm the end, dip into 
flowers of sulphur, kindle, and let down into a jar of oxygen, 
when the flame of the burning sulphur will ignite the zinc, which 
burns with great brilliancy, forming oxide of zinc (ZnO). 
(Performed by Instructor.) 
(Performed by Instructor.) 
EXPERIMENT No. 3: ACID FORMING OXIDE. Place 
two grams of sulphur in a deflagration spoon, ignite and hold 
in a flint bottle containing 50 c.c. of water; when sulphur is 
burned, remove deflagration spoon, cork the bottle, shake well 
and test with litmus. 
EXPERIMENT No. 4: BASIC OXIDE. Oxidize five grams 
metallic lead in an iron ladle, over Bunsen flame; dissolve in 
water and test with litmus. LABORATORY PROCEDURE 
429 
EXPERIMENT No. 5: HYDROXIDE. Place a small piece 
of potassium on 100 c.c. of water in a beaker; note liberated 
hydrogen is ignited. Test with litmus. 
EXPERIMENT No. 6: FRESH HYDRATED OXIDE OF 
IRON. (Antidote for arsenic.) 
(a) Add ammonium hydroxide to 10 c.c. of ferric chloride in a 
beaker; wash ppt. until entirely freed from the odor of ammonia. 
(b) Add magnesium hydroxide to ferric sulphate. (To be used 
immediately without washing.) 
EXPERIMENT No. 7: OXIDES BY ACTION OF AL- 
KALIES OR ACIDS. Produce zinc oxide from soluble zinc sul- 
phate (ZnSOJ by action of potassium hydroxide (KOH) and dry 
precipitate by heating. 
Produce cupric oxide by digesting metallic copper in nitric acid 
and then strongly heating the copper nitrate thus formed. 
EXPERIMENT No. 8: TESTS FOR METALLIC SALTS 
IN SOLUTION. To the following salt solutions in several test 
tubes add a few drops of hydrogen sulphide. 
Pb(C2H302)2 + H2S= PbS + 2HC2H302 
Lead acetate Lead sulphide 
2AsC13 + 3H2S = As2S3 + 6HC1 
Arsenous Arsenous 
Chloride Sulphide 
Cd(N03)2+ ILS = CdS + 2HN03 
Cadmium Cadmium 
Nitrate Sulphide 
2SbCl6 + 5H2S = Sb2S5 + 10HC1 
Antimonic Antimonic 
Chloride Sulphide 
Zn(C2H302)2 + H2S= ZnS + 2HC2H302 
Zinc acetate Zinc sulphide 
HgCL, + H2S = HgS + 2HC1 
Mercuric chloride Mercuric sulphide 430 
PRACTICAL DENTAL METALLURGY 
PERIOD II 
LINING FIRE BOXES: HANDLING CRUCIBLES 
APPARATUS: Mixing basins, large bottles, crucibles, 
small flat stick 12 inches long, Asbestos, Silex, Fire Clay 
Fire Clay—% Silex—Asbestos ad lib.) 
STUDENTS INSTRUCTED how to use furnaces. 
REFRACTORY FURNACE BOX LINING. A place at the 
furnace will be assigned to two or three students in common, and 
they will make for their use, under the direction of the Instructor, 
a refractory fire box lining of clay and asbestos. This will be 
under the care of the students assigned during the year, who will 
see that no fluxes are spilled or dropped therein. 
Remove blowpipe and see that all parts are in perfect working 
order. 
Remove all debris from fire box. 
Moisten the bottom and sides of fire box thoroughly. 
Place bottle in center of fire box, place tip of blowpipe 
against the bottle firmly, then pack lining material all around 
the bottle allowing it to extend V2 inch above top of furnace box. 
Remove bottle carefully; place layer of lining material *4 inch 
thick in bottom of fire box, then place in center an inverted 
base of a crucible so that top of the base of the crucible will be 
level with the top of blowpipe. 
Smooth sides, top and bottom perfectly and then dry with 
slow fire. 
Make cover of same lining material and let stand without heat- 
ing until next period. 
PERIOD III 
ELECTRIC FURNACES 
Instructor will give a clinical demonstration of method of 
making muffle for electric furnace and method of wiring same.* 
*See Electric Furnace, p. 104. LABORATORY PROCEDURE 
431 
PERIOD IV 
METALLURGY OF LEAD 
APPARATUS: Mouth blowpipe, willow charcoal block, 
test tubes, asbestos board, tripod, ring stand, funnel, filter 
paper. 
REAGENTS: Lead monoxide, red lead, nitric acid, sulphuric 
acid, hydrochloric acid, lead foil. 
EXPERIMENT No. 9: REDUCTION. Heat on charcoal 
block under the R. P. about 1 gm. of lead monoxide (litharge) 
and obtain a metallic globule of lead. Afterwards scrape 
charcoal block clean with as little injury to it as possible. 
EXPERIMENT No. 10: LEAD DIOXIDE. To about 1 gm. 
of red lead placed in a t. t. add 10 c. c. of dilute nitric acid. 
The lead monoxide is dissolved and the lead dioxide (chocolate 
colored) remains. Dilute and filter and test filtrate for lead. 
EXPERIMENT No. 11: On asbestos board placed on tripod, 
heat 1 gm. of lead monoxide in the presence of air—red lead. 
(Note—The product soon loses its additional oxygen when 
heated but for a short time, returning to the lead monoxide.) 
EXPERIMENT No. 12: ACTION OF SULPHURIC ACID 
ON LEAD, (a) To a small piece of lead foil in a t. t. add 
dilute sulphuric acid, note action, if any. 
(b) Pour out the dilute sulphuric acid, and add concen- 
trated sulphuric acid to same foil. Note action. What is 
formed? Write reaction. 
EXPERIMENT No. 13: ACTION OF NITRIC ACID ON 
LEAD. To a small piece of lead foil in a t. t. add a small 
quantity of dilute nitric acid and warm. Note action. What 
is formed? Write reaction. 
EXPERIMENT No. 14: ACTION OF HYDROCHLORIC 
ACID ON LEAD. To a small piece of lead foil in a t. t. add 
a small quantity of strong hydrochloric acid and boil. Note 
action. What is formed? Write reaction. 
EXPERIMENT No. 15: TESTS OF LEAD IN SOLUTION. 
To a small amount of lead salt solution add the following 432 
PRACTICAL DENTAL METALLURGY 
reagents: Hydr.ogen sulphide, potassium hydroxide, ammonium 
carbonate, sulphuric acid, hydrochloric acid. Note action, char- 
acter, color and solubility of ppt. 
EXPERIMENT No. 16: To the suspected solution add, drop 
by drop, the saturated solution of hydrogen sulphide; a black 
precipitate is quickly formed, which is insoluble in an excess of 
the reagent. Adding ammonium hydrosulphide to the same sus- 
pected solution produces the same result. This is a characteristic 
test for lead in solution. 
EXPERIMENT No. 17: LEAD-TREE EXPERIMENT. 
Dissolve 4 grams of the nitrate or acetate of lead in about 
240 c. c. of distilled water and put the solution in a bottle. 
Suspend a piece of sheet zinc or a spiral of zinc wire in the 
center of the solution and let it stand. The lead will be 
deposited slowly in a crystalline form, known as arbor pVumbi. 
At the same time the zinc will pass into solution, the lead 
simply replacing the zinc. Next period after the tree has 
been formed, filter off some of the solution and see whether 
or not zinc is contained in it. There will probably be some 
lead left. In order to detect the zinc, the lead will have to 
be removed. This may be done by adding sulphuric acid 
(forming the sulphate) and alcohol (to prevent its being 
redissolved). Filter off the lead sulphate, and to the filtrate 
add just enough ammonium hydroxide to neutralize the sulphuric 
acid, and then test with ammonium hydro sulphide; white zinc 
sulphide is precipitated. 
NOTE—First part of this experiment is to be performed 
during this period. The last part during Period XI, on zinc. 
PERIOD V 
METALLURGY OF LEAD—CONT’D 
APPARATUS: Ingot molds, balances, iron ladle, evaporat 
mg dish. 
REAGENTS: Lead, tin. LABORATORY PROCEDURE 
433 
EXPERIMENT No. 18: ALLOYS. Make an ingot model 
of lead and tin, (parts and sizes as dictated to each student by 
Instructor) all alloys must be prepared with ends parallel to 
allow surface to be examined under the microscope, and approx- 
imately 7x5x5 mm. in size. 
When cold, clean, polish, and scratch neatly on one surface: 
formula and weight, before and after melting. Student pre- 
serve until end of term. 
EXPERIMENT No. 19: Polish one end of the above alloy, 
first with pumice and then with powdered chalk, being careful 
not to allow it to become dry while polishing. Finally eliminate 
all possible irregularities on this polished surface by rubbing on 
a silk cloth without allowing the metal to become overheated. 
EXPERIMENT No. 20: Etch the polished surface of this 
alloy with dilute ammonium hydroxide and hydrogen peroxide by 
placing with a glass rod a single drop of the first reagent fol- 
lowed immediately by a single drop of the second reagent and 
then removing both by blotting with filter or absorbent paper. 
EXPERIMENT No. 21: Examine the etched surface of the 
alloy under the microscope,* using a medium power objective 
1.4 mm. and draw a diagram of the appearance of this etched 
surface. 
PERIOD VI 
METALLURGY OF TIN 
APPARATUS: Funnel, filter paper, ring-stand, test tubes, 
labels, evaporating dish. 
REAGENTS: Hydrochloric acid, sulphuric acid, nitric acid, 
sodium hydroxide, ammonium hydroxide, hydrogen sulphide, stan- 
nous chloride, stannic chloride, tin foil. 
EXPERIMENT No. 22: ACTION OF SULPHURIC ACID 
ON TIN. (a) To a small piece of tin foil in a t. t. add con- 
*Any microscope can be used for this purpose by attaching a vertical 
illuminator and using a small arc for illumination; See Chemical Micros- 
copy by Chamot, and Metallography by Desch. 434 
PRACTICAL DENTAL METALLURGY 
centrated sulphuric acid. Note action carefully, (b) To a 
small piece of tin foil in a t. t. add dilute sulphuric acid. Note 
action. What is formed? Write reaction. 
EXPERIMENT No. 23: ACTION OF NITRIC ACID ON 
TIN. (a) To a small piece of tin foil in a t. t. add concen- 
trated nitric acid and heat. What is formed? Write reaction, 
(b) To a small piece of tin foil in a t. t. add dilute nitric 
acid. What is formed? Write reaction. 
EXPERIMENT No. 24: ACTION OF HYDROCHLORIC 
ACID ON TIN. To several small pieces of tin foil in a t. t. 
add a little concentrated hydrochloric acid and boil carefully. 
(Let there be more tin than will dissolve.) What is formed? 
Write reaction. Label and preserve. 
EXPERIMENT No. 25: ACTION OF AQUA REGIA ON 
TIN. To a small piece of tin foil in a t. t. add a little hydro- 
chloric acid and less of nitric acid. What is formed? Write 
reaction. Label and preserve. Be careful of the fumes. 
EXPERIMENT No. 26: ACTION OF CAUSTIC ALKA- 
LIES ON TIN. To a small piece of tin foil in a t. t. add sol. 
of sodium hydroxide (or potassium hydroxide) and boil. What is 
formed? Write reaction. 
EXPERIMENT No. 27: TESTS FOR TIN IN SOLUTION. 
To small amounts of tin salt in solution (stannous chloride 
preserved) add the following reagents: sodium hydroxide, (or 
potassium hydroxide), ammonium hydroxide, hydrogen sulphide. 
Note action, character, color, solubility, etc., of the ppt. 
EXPERIMENT No. 28: To a dilute solution of the chlorides 
of tin add gold chloride. The characteristic purple precipitate 
known as purple of cassius is thrown down. 
PERIOD YII 
METALLURGY OF TIN—CONT 'D 
APPARATUS: Ingot molds, balances, ladle, test tube. 
REAGENTS: Potassium bitartrate, stannous chloride, sheet 
copper, tin foil, tin, lead, copper, antimony, bismuth. LABORATORY PROCEDURE 
435 
EXPERIMENT No. 29: ALLOYS. Make an alloy as- 
signed by instructor. All alloys to be hereafter made, must 
be 7x5x5 mm., well polished, and on one surface the formula 
and weight before and after melting, neatly scratched. 
EXPERIMENT No. 30: Etch the alloy in the same manner 
as described in Experiment No. 20, with dilute ammonium hy- 
droxide and hydrogen peroxide being careful not to scratch the 
surface with either the glass rod or the filter paper. Examine 
as in Experiment No. 21 and draw a diagram of the etched 
surface. 
EXPERIMENT No. 31: DEPOSITION OF TIN. Place in 
a t. t. a small piece of clean sheet copper, or any brass or 
copper article, such as crown or bridge, between tin foil, and 
add a saturated solution of acid potassium bitartrate, adding 
a little stannous chloride, and boil for several minutes. 
PERIOD VIII 
METALLURGY OF BISMUTH 
APPARATUS: Bunsen burner, charcoal, blowpipe, ladle, 
ingot molds, test tubes, balances. 
REAGENTS: Sodium carbonate, solutions of hydrogen sul- 
phide, sodium hydroxide, potassium carbonate, water, tartaric 
acid, bismuth, bismuth subnitrate, lead, tin, antimony, cadmium. 
EXPERIMENT No. 32: REDUCTION OF BISMUTH. 
Heat with blowpipe 5 gm. of bismuth subnitrate with an equal 
amount of sodium carbonate, on a charcoal block. Examine 
carefully the metallic globule as to appearance, malleability, 
hardness, etc. 
EXPERIMENT No. 33: TESTS FOR BISMUTH SALT IN 
SOLUTION. To small amounts of bismuth nitrate solution in 
a t. t. add the following reagents, and note the changes, if any: 
hydrogen sulphide, sodium hydroxide, potassium carbonate. 
EXPERIMENT No. 34: To a solution of bismuth nitrate add 
distilled water and note results. To the ppt. formed by water 436 
PRACTICAL DENTAL METALLURGY 
add tartaric acid; this will distinguish bismuth from antimony. 
(See text, p. 152). 
EXPERIMENT No. 35: ALLOYS OF BISMUTH. Stu- 
dents will make one of the following alloys, as assigned by the 
Instructor. Calculate accurately the amount of metal needed 
to make the required size ingot, that none be wasted. Prepare 
sectional mold from natural tooth, with plaster of Paris, and pour 
bismuth alloy into same to show accuracy in copying fine lines. 
8 grams gross weight is sufficient of this alloy. 
ALLOY 
Bismuth 
Lead 
Tin 
Antimony 
Cadmium 
Newton’s 
. . 8 
5 
3 
.. 
. • 
Rose’s F. A. 1... 
. . 2 
1 
1 
Rose’s P. A, 2... 
. . 8 
8 
3 
.. 
. • 
Wood’s 
.. 6 
4 
2 
.. 
2 
Onion’s 
. . 5 
3 
2 
• • 
‘ * La Nation ’ ’ . 
.. 48 
19 
26 
. . 
13 
Hodgen’s 
. . 8 
5 
3 
2 
Mathew’s 
.. 48 
19 
13 
Darcet’si 
.. 7 
2 
4 
. • 
Darcet’s 2 . ... 
. . 16 
4 
7 
.. 
Darcet’s 3 . ... 
. . 8 
6 
2 
.. 
PERIOD IX 
METALLURGY OF ZINC 
APPARATUS: Bunsen burner, test tubes, ring stand, filter 
paper, funnel, evaporating dish, sand bath, tripod. 
REAGENTS. Zinc, zinc oxide, arsenous oxide, sulphuric 
acid, hydrochloric acid, sodium hydroxide, sodium carbonate, 
ammonium sulphide, hydrogen sulphide, sodium phosphate, 
meta-phosphoric acid, nitric acid. 
EXPERIMENT No. 36: ACTION OF HYDROCHLORIC 
ACID ON ZINC. To a small piece of zinc in a test tube add 
about 5 c. c. of dilute hydrochloric acid. Write reaction. Save 
for experiment No. 38. LABORATORY PROCEDURE 
437 
EXPERIMENT No. 37: PREPARATION OP ZINC OX- 
IDE BY ACTION OF NITRIC ACID ON ZINC. To about 
20 grams of zinc in an evaporating dish add sufficient nitric 
acid in small quantities (50% sol.) to dissolve. 
(Perform this exp. in fume chamber.) 
When zinc is in solution, place evaporating dish on sand 
bath and evaporate to dryness. Save oxide till next period. 
EXPERIMENT No. 38: TEST FOR ZINC SALT IN SO- 
LUTION: To a zinc salt in solution add the following re- 
agents and note results: ammonium sulphide, hydrogen sulphide 
in presence of sodium acetate. Compare with tests for aluminum. 
EXPERIMENT No. 39: To a zinc salt in solution add either 
sodium hydroxide or potassium hydroxide; sodium carbonate or 
potassium carbonate. Note results. 
EXPERIMENT No. 40: Filter about 15 c.c. of the solu- 
tion saved from experiment 17, ‘‘Metallurgy of Lead,” Period 
IV. To the filtrate add, drop by drop, sulphuric acid till no 
more lead sulphate is thrown down. Filter again to remove 
the sulphate of lead and test the filtrate for zinc in solution. 
NOTE: If all the lead is not removed, its presence will inter- 
fere with the test for zinc. 
EXPERIMENT No. 41: TEST FOR ARSENIC IN ZINC 
OXIDE, (a) Into a t. t. containing 5 c. c. of water place 5 
dgm. of zinc oxide and a very small quantity of arsenous oxide 
(about as much as is used in pulp devitalization). Now add 
a few drops of hydrochloric acid and boil. A little hydrogen 
sulphide will throw down a lemon-yellow ppt., the sulphide 
of arsenic. 
(b) Into a t. t. containing 5 c. c. of water, place 5 dgm. of 
zinc oxide and a few drops of hydrochloric acid, and boil. 
Test for the presence of arsenic. 43-8 
PRACTICAL DENTAL METALLURGY 
PERIOD X 
METALLURGY OF ZINC—CONT’D 
APPARATUS: Crucibles, ingot mold, mortars, bolting 
cloth, evaporating dish, sand bath, tripod, stirring rod, mixing 
.'lab, spatula, balances. 
REAGENTS: Old oxidized zinc, pulverized charcoal, stick 
of wood, zinc oxide, metallic zinc, pigments, metaphosphoric 
acid, zinc chloride. 
EXPERIMENT No. 42: BASIC ZINC CEMENT POWDER. 
Calcine in a crucible, at white heat (or as near as possible) 
for two hours, a small quantity of zinc oxide. Powder in a 
mortar, bolt through cloth, color with pigments, and preserve. 
EXPERIMENT No. 43: Calcine in a separate crucible, as 
above the zinc oxide prepared at last period by action of nitric 
acid (HN03) on zinc. 
Powder in a mortar, bolt through cloth and preserve. 
EXPERIMENT No. 44: DEOXIDIZING ZINC. Melt old 
partially oxidized zinc in a crucible, and when molten, cover 
the surface with pulverized charcoal: heat at a strong tem- 
perature, and stir with a stick of wood. After a few minutes 
the zinc may be poured, and will be found to be quite free 
of the oxide. 
EXPERIMENT No. 45: ZINC OXIDE. Prepare a small 
quantity of zinc oxide by heating metallic zinc to about 918° 
C. in an open crucible. 
EXPERIMENT No. 46: PHOSPHORIC ACID FOR 
CEMENT. Place 10 c.c. of orthophosphoric acid in an 
evaporating dish, then add aluminum phosphate to the point 
of saturation. 
NOTE: On cooling, the liquid thickens—the flame should, 
therefore, be removed a little before the desired consistence 
is attained. Mix with powder of experiment 42 as in mixing 
cement. 
' EXPERIMENT No. 47: ZINC CHLORIDE FOR CEMENT. 
Deliquesce 10 grams of zinc chloride with a very small quail- LABORATORY PROCEDURE 
439 
tity of distilled water. Warm slightly and cool. Mix with 
powder to form oxychloride of zinc—ZnClHO. 
EXPERIMENT No. 48: Make a mix of the calcined zinc 
oxide (commercial) and the cement liquid prepared from 
modified phosphoric acid (experiment 46). Preserve. 
EXPERIMENT No. 49: Make a mix of the calcined zinc 
oxide (obtained through precipitation, experiment 37) and the 
cement liquid prepared from modified phosphoric acid (experi- 
ment 46). Preserve. 
Make a comparative test of above mixes, noting solubility 
and permeability. 
PERIOD XI 
METALLURGY OF COPPER 
APPARATUS: Crucibles, ingot molds, stirring sticks, test 
tubes, knife. 
REAGENTS: Copper, zinc, tin, aluminum, nickel, borax, 
sodium hydroxide, potassium hydroxide, ammonium hydroxide, 
potassium ferrocyanide, potassium ferricyanide, zinc plate strip. 
EXPERIMENT No. 50: The student will prepare some one 
of the following alloys, as directed by the Instructor: 
ALLOYS 
Sheet brass... 
Copper Zinc 
. 68 32 
Tin 
Nickel 
Wire brass.... 
. (must be drawn). 
71 
29 
.. 
Oreide 
68 
13.5 
0.5 
Dutch Metal . 
11 
2 
• • 
Pinchbeck . .. 
88 
12 
.. 
Mosaic gold . . 
5 
5 
.. 
German silver 
50 
19 
• • 
13 
NOTE: Great care must be exercised in adding the zinc 
and tin to the molten copper, to avoid oxidation of the two 
former, as much as possible. 440 
PRACTICAL DENTAL METALLURGY 
EXPEEIMENT No. 51: Polish and etch one end of the alloy 
with ammonium hydroxide and hydrogen peroxide and examine 
under the microscope using both medium and low power objectives. 
Draw diagrams of the etched surfaces. 
EXPEEIMENT No. 52: TESTS FOE COPPEE IN SO- 
LUTION. (a) To a small amount of copper sulphate solution 
in a t. t. add sodium or potassium hydroxide—note change. 
Write reaction. 
(b) To another add ammonia, or its carbonate—note 
change. 
(c) To another add potassium ferrocyanide—note change. 
(d) To another add potassium ferricyanide—note change. 
EXPEEIMENT No. 53: DEPOSITION OF COPPEE. 
Clean your knife blade thoroughly with fine sand paper, or 
otherwise, and immerse in a solution of copper sulphate—note 
changes. 
EXPEEIMENT No. 54: In a test tube containing a small 
amount of copper sulphate in solution, place a small piece of 
zinc. Note changes. 
PERIOD XII 
METALLURGY OF COPPER—CONT’D 
APPAEATUS: Tumbler, zinc plate, copper plate, copper 
wire, crystallization dish, plaster cast wired, etc. 
EEAGENTS: Solution copper sulphate, tin foil, potassium 
bitartrate. 
EXPEEIMENT No. 55: DEPOSITION OF COPPEE: THE 
CELL. Make a voltaic cell or battery by submerging in a glass 
tumbler sufficiently full of copper sulphate solution, a piece of 
copper plate with conductor passing from it, and over it a piece 
of zinc, with conductor passing from it. 
EXPEEIMENT No. 56: DEPOSITION OF COPPEE: THE 
BATH. Make a deposition bath of glass crystallizing dish (or 
other apparatus) and fill with strong solution of copper sulphate. LABORATORY PROCEDURE 
441 
EXPERIMENT No. 57: DEPOSITION OF COPPER: 
BASE. Attach to the negative conductor, which passes to the 
positive element zinc, the plaster east properly prepared and 
wired. Then hang from the positive conductor, which arises 
from the negative element copper, the properly shaped anode of 
copper—submerge in the bath and set aside. On the cast will 
be slowly deposited a copper base, which remove, tin as directed 
in experiment 31; under Period VII on “Tin”, and use as base 
for vulcanization. 
PERIOD XIII 
METALLURGY OF IRON 
APPARATUS: Tripod, sand bath, soldering pliers, sand- 
paper, Bunsen burner, tumbler, test tube, old burs. 
REAGENTS: Ferrous sulphate, ferric chloride, ammonium 
sulphide, ammonium hydroxide, potassium ferricyanide, potassium 
ferrocyanide, potassium sulphocyanate. 
EXPERIMENT No. 58: HARDENING AND TEMPERING. 
Take eight old burs and heat to cherry red and plunge quickly 
into cold water, thus making them full hard. Polish with fine 
sandpaper, and heat again, one at a time, on sand bath which 
should be inverted and placed on tripod over the flame. (Use 
great care not to burn bench). As soon as the desired color is 
reached, roll the bur off into a glass of cool water. Prepare the 
eight different degrees of hardness as per table, page 233, text. 
NOTE: If they are made too soft in tempering, or desired 
color is not obtained polish and again temper until proper color 
is reached. 
EXPERIMENT No. 59: TEST FOR IRON IN SOLUTION. 
To small amounts of ferrous sulphate in a t.t. add ammonium 
hydrosulphide, potassium ferricyanide, ammonium hydroxide. 
Note action, if any. 
To small amounts of ferric chloride in a t. t. add potassium 
ferrocyanide, potassium sulphocyanate. Note action, if any. 442 
PRACTICAL DENTAL METALLURGY 
PERIOD XIY 
METALLURGY OF ALUMINUM 
APPARATUS: Test tubes. 
REAGENTS: Sulphuric acid, nitric acid, hydrochloric acid, 
hydrogen sulphide, ammonium sulphide, ammonium hydroxide, 
ammonium chloride, aluminum chloride, aluminum, zinc. 
EXPERIMENT No. 60: ACTION OF THE ACIDS ON ALU- 
MINUM. To small pieces of aluminum in separate t. ts., 
add the following: To the first, 1 c. c. of sulphuric acid; to the 
second, 1 c. c. of nitric acid; to the third, 1 c. c. of hydrochloric 
acid. Save for experiment No. 64. 
EXPERIMENT No. 61: TEST FOR ALUMINUM SALT 
IN SOLUTION. To small amounts of aluminum salt (pref- 
erably the chloride) solution in t. ts., add the following reagent 
drop by drop: Hydrogen sulphide, ammonium sulphide, am- 
monium hydroxide, of the latter add a slight excess. Compare 
with your notes on zinc tests. 
EXPERIMENT No. 62: Prepare a little zinc chloride by 
adding a small amount of dilute hydrochloric acid to a piece 
of zinc in a test tube. 
EXPERIMENT No. 63: To a c.c. of the zinc chloride solu- 
tion in a t. t. and to a c. c. of aluminum chloride solution in a 
t. t., add to each, first a small quantity of ammonium chloride 
solution, and then about 2 c. c. of ammonium hydrate. 
EXPERIMENT No. 64: Test the solutions made from acids 
in experiment No. 60 for presence of aluminum in solution. 
(See experiment No. 61.) 
EXPERIMENT No. 65: Students will prepare one of the 
following alloys, as directed by the Instructor. -This alloy must 
be 14x5x5 mm. in size for further experiments. 
ALLOY 
Aluminum Copper Gold Silver 
Niirnberg gold 
7.5 
90 2.5 
Aluminum silver 
7.5 
2.5 
gronze 
10 
90 LABORATORY PROCEDURE 
443 
EXPERIMENT No. 66: Polish and etch one end of the above 
alloy with ammonium hydroxide and hydrogen peroxide and ex- 
amine under the microscope using the medium power objective. 
Draw a design of the etched surface. 
EXPERIMENT No. 67: Forge the above alloy on an anvil 
until its form has been visibly altered. Cut the alloy in two 
equal sections, approximately 7x5x5 mm. Anneal one section by 
heating to redness and cooling slowly ten times. Polish and 
etch the ends of each section at the dividing line. Examine under 
the microscope as before. Draw diagrams showing the effect of 
forging and heat treatment as compared with the original alloy. 
NOTE: Each student must provide about 1 gm. of vulcanite 
filings for next period. 
PERIOD XV 
METALLURGY OF MERCURY 
APPARATUS: Test tubes. 
REAGENTS: Acetic acid, hydrochloric acid, sulphuric acid, 
nitric acid, hydrogen sulphide, potassium hydroxide, ammonium 
hydroxide, potassium iodide, mercuric chloride, mercurows nitrate, 
mercury, copper, lead, bismuth, tin, vulcanite filings. 
EXPERIMENT No. 68: TEST FOR THE PRESENCE OF 
OTHER METALS IN MERCURY. To a t. t. containing a glob- 
ule of mercury, add a small piece of lead foil and gently warm 
to readily amalgamate the two metals, then add equal parts of 
acetic acid and water, shake thoroughly and add a few drops 
of potassium iodide. Note change, if any. 
EXPERIMENT No. 69: To a globule of mercury containing 
a little bismuth, add strong nitric acid, shake thoroughly, and 
add distilled water in excess. Note action, if any. 
EXPERIMENT No. 70: To a globule of mercury containing 
a small piece of tin foil, add dilute nitric acid. Note change, 
if any. 444 
PRACTICAL DENTAL METALLURGY 
EXPERIMENT No. 71: To small amounts of red vulcanite 
filings in separate t. ts. add the following: Dilute nitric acid, 
sulphuric acid, hydrochloric acid. Save for experiment No. 73. 
EXPERIMENT No. 72: To a small amount of mercuric 
salt solution in a t. t. add the following: Hydrogen sulphide, 
potassium hydroxide, ammonium hydroxide, potassium iodide. To 
a small amount of mercurous salt solution in a t. t. add the 
following: Hydrogen sulphide, hydrochloric acid, potassium 
iodide, potassium hydroxide, ammonium hydroxide. 
EXPERIMENT No. 73: Test the solutions from experiment 
No. 71 for mercury in solution. 
EXPERIMENT No. 74: DEPOSITION OF MERCURY. 
Into a test tube containing a little mercuric chloride, slightly 
acidulated with hydrochloric acid, introduce a small strip of 
clean copper foil. 
NOTE: Each student will provide himself with a silver 
dime for next period or the equivalent amount of silver and copper. 
PERIOD XVI 
METALLURGY OF SILVER 
APPARATUS: Florence flask, sand bath, tripod, Bunsen 
burner, evaporating dish, funnel, filter paper, beaker, test tube3, 
silver dime or silver and copper alloy. 
REAGENTS: Nitric acid, sodium hydroxide, sodium chloride, 
hydrochloric acid, potassium chromate, hydrogen sulphide, potas- 
sium cyanide. 
EXPERIMENT No. 75: REFINING SILVER. Place a 
silver dime in a Florence flask, add about 20 c. c. of nitric acid, 
and dilute the acid with the same amount (20 c. c.) of distilled 
water. Gently warm the whole on a sand bath to hasten action. 
Care should be taken to avoid having silver nitrate solution or 
crystals come in contact with the skin since it stains badly when 
exposed to light. 
EXPERIMENT No. 76: PREPARATION OF SILVER 
NITRATE CRYSTALS. When the dime or alloy of silver and LABORATORY PROCEDURE 
445 
copper has dissolved, place 4 or 5 c. c. of the solution in an 
evaporating dish and evaporate at a gentle heat. (The solution 
remaining in the flask should be tightly stopped and placed in a 
locker in Metallurgic Laboratory for next period.) After the 
water of solution and free acid is driven off, the evaporating dish 
will contain a greenish solid of silver and copper nitrates. By 
continued heat and stirring the silver nitrate is fused and the 
copper nitrate changed to copper oxide by the disengagement of 
nitrogen dioxide. When all the green copper nitrate has been 
changed to the black oxide of copper and the dish has cooled 
sufficiently to be handled, add a small quantity of distilled water, 
about 20 c. c., stir well and filter. Silver nitrate is soluble in 
water and therefore passes through, while the black insoluble 
cupric oxide is left on the filter paper. Save about 5 c. e. for 
experiment No. 77. Cleanse the evaporating dish thoroughly, 
rinsing with distilled water, place the remaining silver nitrate 
solution in it, and evaporate to crystals, at a low heat. 
EXPERIMENT No. 77: TEST FOR SILVER SALTS IN 
SOLUTION. To a small quantity of silver nitrate in a t. t. 
diluted with an equal amount of distilled water add the follow- 
ing reagents, noting action, if any; sodium chloride, hydro- 
chloric acid, sodium hydroxide, potassium chromate, hydrogen 
sulphide. (Save a little silver sulphide for experiment No. 78.) 
EXPERIMENT No. 78: Divide silver sulphide prepared in 
the above experiment, into two parts. To one, add moderately 
concentrated nitric acid (distinction from mercury), to the other 
add potassium cyanide (distinction from copper.) 
PERIOD XVII 
METALLURGY OF SILVER—CONT’D 
APPARATUS: Florence flask, flint bottle, beaker, stirring 
rod, crucible, nails. 
REAGENTS: Sulphuric acid, sodium chloride, ammonium 
hydroxide, potassium carbonate, borax. 
EXPERIMENT No. 79: Pour the silver nitrate and copper 
nitrate solutions contained in the Florence flask, used at last 446 
PRACTICAL DENTAL METALLURGY 
period, into a large beaker, and add a saturated solution of 
sodium chloride until no more silver chloride is formed. Trans- 
fer to clean flask and shake for several minutes, then allow the 
ppt. to settle. A little more sodium chloride added will deter- 
mine whether all the silver has been thrown down. Decant the 
supernatant liquor. The chloride must now be washed several 
times, the water decanted off each time after the white ppt. has 
settled. By repeated washings the copper nitrate is removed, 
being soluble the presence of merest trace is indicated by a 
blue tinge on the addition of ammonium hydroxide. When en- 
tirely free from copper, the silver chloride should be placed in 
a large flint bottle, with twice its bulk of water added, to 
which a sufficient amount of sulphuric acid is then added to 
warm the whole, slightly. Twenty small nails or pieces of iron 
are now added to contents of bottle; stir the mixture with a 
glass rod until every particle of the mass becomes dark gray, 
showing that the chlorine has been disengaged and the silver 
is free. The failure to break up any portion of the chloride, 
will result in a loss of silver. Eemove all of the nails, counting 
them to be sure, wash several times, with water, dry, mix with 
an equal amount of potassium carbonate, and melt in a well 
boraxed crucible. 
EXPEEIMENT No. 80: Cast the button of pure silver ob- 
tained from the above experiment in an ingot 7x5x5 mm. Polish 
and etch one end with 50 per cent nitric acid until it appears 
tarnished, then remove excess by washing in ammonium hydroxide. 
Examine under the microscope using the low power objective. 
Draw a diagram of the etched surface. 
NOTE: Students will provide for the next period old gold 
scraps, fillings, crowns, or jewelry of any kind in sufficient quan- 
tity to produce when refined about 2% dwts. of pure gold. 
PERIOD XVIII 
GOLD 
APPAKATUS: Balances, crucible. 
EEAGENTS: Borax, potassium carbonate, potassium ni- 
trate, ammonium chloride, charcoal gold scraps. LABORATORY PROCEDURE 
447 
The Instructor must see all gold or alloy scraps before it is 
melted. 
EXPERIMENT No. 81: Weigh the gold or alloy scraps very 
accurately before proceeding, and make a note of the weight 
and character of the scraps. 
ROASTING PROCESS: Roast the alloy scraps (which should 
be brittle if simply melted, on account of a base metal content), 
for twenty minutes to half an hour, in a well-boraxed crucible 
with potassium nitrate. If the metal is in small pieces or filings, 
it should be covered with potassium carbonate. During the 
roasting, potassium nitrate in small pieces should be added from 
time to time to the molten metal, or the metal may be lost in 
the ebullient overflow of flux from the crucible. A little borax 
should also be added from time to time, as it, too, unites with 
oxides of the base metals and assists in their removal. Pour 
the contents of the crucible, after roasting, into a well-oiled 
and warm ingot mold and compare with first weight. If mal- 
leable, roll to ribbon, 30-gauge. 
If the alloy is brittle and cannot be rolled, it should be 
roasted a second time, with ammonium chloride and powdered 
charcoal. Such roasting must be continued until the gold is 
malleable. 
NOTE: Be sure and weigh the metals before and after each 
roasting, noting loss, if any, and account for any loss that may 
have occurred, also state the flux used during the roasting. 
PERIOD XIX 
GOLD—CONT’D 
APPARATUS: Balances, flask, Bunsen burner, crucible. 
REAGENTS: Nitric acid, sulphuric acid, gold alloy, silver 
borax. 
EXPERIMENT No. 82: PARTING GOLD: Alloy not less 
than two and a half pennyweights (2dwts.) of gold alloy, made 
malleable during Period XX with three times its weight of coin 
or fine silver, roll the alloy into a thin ribbon, about number 
35-gauge; cut the ribbon in very small pieces and carefully 448 
PRACTICAL DENTAL METALLURGY 
place in a Florence flask, then add about one and a half ounces 
of nitric acid or two and one-half ounces of sulphuric acid. Heat 
until no more fumes are given off. Decant off the liquid and 
save; add about an ounce of the same fresh acid and continue 
the process. Decant the acid. Wash the contents of the flask 
thoroughly in hot water, to remove the nitrates or sulphates of 
the contaminating metals. The silver of the decanted liquor 
can be saved as per experiment 79. 
PERIOD XX 
GOLD—CONT’D 
APPARATUS: Evaporating dish, Florence flask, sand bath, 
Bunsen burner, filter, funnel, ring stand. 
REAGENTS: Gold, nitric acid, hydrochloric acid, ferrous 
sulphate, oxalic acid. 
EXPERIMENT No. 83: CHEMICALLY PURE GOLD. 
After the gold resulting from the parting process is thoroughly 
washed, place it in an evaporating dish, pour on about 40 c. c. 
of hydrochloric acid and about 10 c. c. of nitric acid. Warm 
gently on sand bath. If this quantity is not sufficient to dissolve 
the gold, add more aqua regia in above proportions. The solu- 
tion must now be evaporated down at a very gentle heat (lest 
gold chloride be reduced) to about two-thirds its original bulk. 
A white ppt. will be noticed in the dish, which is the chloride 
of silver. Decant off the gold chloride solution to second evap- 
orating dish, leaving the chloride of silver in the first. Add 
hydrochloric acid to decompose the last of the nitric acid and 
further evaporate the gold chloride solution, to the consistence of 
syrup, and of a deep orange-red color. 
The solution may now be allowed to cool, the dish filled with 
distilled water and pffieed with contents in a funnel and filtered. 
Wash all the gold chloride through the filter, by the use of a 
wash bottle, into a Florence flask. 
The gold may now be precipitated by adding a saturated solu- 
tion of either ferrous sulphate or oxalic acid, slightly warming 
on a sand bath for ten or fifteen minutes. It should then be 
placed in the locker in the Metallurgic Laboratory until next 
period. LABORATORY PROCEDURE 
449 
PERIOD XXI 
GOLD—CONT’D 
APPARATUS: Funnel, filter, ring stand, tripod, evaporating 
dish, crucible, beaker. 
REAGENTS: Hydrochloric acid, ferrous sulphate, potassium 
bicarbonate, potassium carbonate, potassium nitrate. 
EXPERIMENT No. 84: CHEMICALLY PURE GOLD. 
A small amount of the precipitant may now be added to de- 
termine if all the gold has been thrown down. If so, care- 
fully decant off the supernatant liquid, wash the ppt. with 
dilute hydrochloric acid, then distilled water, then dilute 
ammonia, and again with distilled water. In case oxalic acid 
has been used as a precipitant, heat the gold in the flask over 
a sand bath with a weak solution of potassium carbonate. If 
ferrous sulphate has been used as the precipitant, warm the 
hydrochloric acid solution used above, to get rid of any iron. 
Wash the gold into an evaporating dish. In the form precipi- 
tated, of powder scales, or foil, the gold is to be dried and 
placed in a well-boraxed crucible, covered with a little potassium 
carbonate and fused with a little potassium nitrate, cooled in 
the crucible, or poured into a clean and well-oiled ingot mold, 
then washed with hydrochloric acid, rolled, and finally part of 
it further rolled out between pure filter papers, to a number 30 
foil for filling, and used in the infirmary for at least one gold 
filling.* 
EXPERIMENT No. 85: Cast the remainder of the gold into 
an ingot of standard size. Polish one end and etch with aqua 
regia. Examine under the microscope using the low power ob- 
jective and oblique illuminator. Draw a diagram of the etched 
surface. 
EXPERIMENT No. 86: Alloy the pure gold from experiment 
number 85 with sufficient copper or silver to make it 22 karat. 
Cast this alloy into an ingot of standard size. Polish and etch 
*By covering the surface of gold or platinum foil with oil, it can be 
folded upon itself and rolled much thinner than the usual way. Boil in a 
solution of KOH, and wash with dilute HC1 and water after rolling. 450 
PRACTICAL DENTAL METALLURGY 
one end with aqua regia. If a silver alloy is used the etched 
surface must be washed with a drop of ammonium hydroxide to 
remove the silver chloride formed. Examine under the micro- 
scope as above and draw a diagram of the etched surface. 
EXPERIMENT No. 87: Cast the alloy by some other method 
than that used in experiment number 86. Polish and etch one 
end and examine under the microscope as above and draw a 
diagram of the etched surface. Compare the diagrams in the 
above three experiments. 
PERIOD. XXII 
AMALGAM ALLOYS 
APPARATUS: Crucible, balances, ingot molds, glass-tubing. 
REAGENTS: Borax, silver, gold, platinum, tin, copper, zinc, 
antimony, cadmium. 
EXPERIMENT No. 88: Each student will select one of the 
alloys on pages 374 and 375 of the text, and prepare it as accu- 
rately as possible according to the formula there given. It will 
not be necessary to make more than ten pennyweights of the 
alloy. Inasmuch as the formulas are all given in hundredths, 
the preparation of ten pennyweights will express the formula 
in tenths. 
The student will carefully write the formula he desires to 
make, at the top of the page of his note book, being very careful 
to state the exact proportions and the sum of the weights of 
the various metals entering into the formula. Great care must 
be exercised in accurately weighing each metal, and in melting 
them together, so as to avoid any loss, if possible. Use only 
clean, well-boraxed crucibles; warm, well-oiled and clean ingot 
molds. After melting and pouring into ingot molds, clean up 
the ingot thoroughly, accurately weigh and note the comparison 
of the weight before and after melting. 
Before the next period the ingot of dental-amalgam alloy 
must be comminuted and presented to the Instructor for in- 
spection and tests for its various properties. LABORATORY PROCEDURE 
451 
PERIOD XXIII 
APPAEATUS: Bunsen burner, funnel, filter paper, test tube, 
beaker, evaporating dish. 
EEAGENTS: Hydrogen sulphide, hydrochloric acid, nitric 
acid, sulphuric acid. 
Follow closely “Analysis of Dental-Amalgams’> on page 407 
text. 
EXPEBIMENT No. 89: Make a qualitative analysis of 2 
grams of old amalgam fillings. 
EXPEBIMENT No. 90: While carrying on Experiment No. 
89, make a quantitative analysis of the silver in the amalgam 
filling which is being examined. 
All work must be passed in to the Instructor before the end of 
the term. 
OEIGINAL and unrequired work will be deservedly credited. 
WORK TO BE HANDED IN 
LABORATORY REAGENTS 
Left-hand End. 
Ammonium Hydroxide 
Sulphuric Acid 
Nitric Acid 
Hydrochloric Acid 
Acetic Acid 
Oxalic Acid 
Calcium Chloride 
Ammonium Chloride 
Barium Chloride 
Platinie Chloride 
Ferric Chloride 
Potassium Iodide 
Calcium Sulphate 
Eight-hand End. 
Sulphuric Acid 
Nitric Acid 
Hydrochloric Acid 
Acetic Acid 
Oxalic Acid 
Calcium Chloride 
Ammonium Chloride 
Barium Chloride 
Platinie Chloride 
Ferric Chloride 
Potassium Iodide 
Calcium Sulphate 
Potassium Sulphate 452 
PRACTICAL DENTAL METALLURGY 
LABORATORY REAGENTS 
Left-hand End 
Potassium Sulphate 
Ferrous Sulphate 
Magnesium Sulphate 
Copper Sulphate 
Lead Acetate 
Potassium Ferrocyanide 
Potassium Sulphocyanide 
Potassium Ferricyanide 
Alcohol 
Hydrogen Sulphide 
Ammonium Sulphide 
Disodium Hydric Phosphate 
Ammonium Oxalate 
Silver Nitrate 
Sodium Carbonate 
Ammonium Carbonate 
Calcium Hydroxide 
Sodium Hydroxide 
Potassium Hydroxide 
Ammonium Hydroxide 
Blank 
Blank 
Ammonium Sulphocyanide 
Space 
Bight-hand End 
Ferrous Sulphate 
Magnesium Sulphate 
Copper Sulphate 
Lead Acetate 
Potassium Ferrocyanide 
Potassium Sulphocyanide 
Potassium Ferricyanide 
Alcohol 
Hydrogen Sulphide 
Ammonium Sulphide 
Disodium Hydric Phosphate 
Ammonium Oxalate 
Silver Nitrate 
Sodium Carbonate 
Ammonium Carbonate 
Calcium Hydroxide 
Sodium Hydroxide 
Potassium Hydroxide 
Ammonium Hydroxide 
Blank 
Blank 
Sulphuric Acid 
Nitric Acid 
Hydrochloric Acid INDEX 
A 
Abbreviations, 425 
Acetylene, 75 
Acid: 
acid forming oxide, 50 
acids on metals (see sepa- 
rate metals) 
glacial phosphoric, 182 
metastannic, 157 
orthophosphoric, 181 
Alcohol, 74 
Alkali, 50 
Alloys, 117 
aluminum, 246 
annealing, 127 
antimony, 151 
cadmium, 194 
chemical combinations of, 119 
color of, 124 
conductivity of, 127 
copper, 206 
eutectic, 134 
fusibility of, 126 
gold, 345 
iridium, 286 
iron, 237 
lead, 142 
malleability, ductility and 
tenacity of, 125 
mechanical mixture, 121 
mercury, 258 
oxidation of, 128 
palladium, 289 
physical properties of, 123 
platinum, 301 
preparation of, 132 
silver, 275 
solution of one metal in an- 
other, 118 
specific gravity of, 123 
tenacity of, 125 
tin, 158 
zinc, 188 
Aluminum, 240 
acids ou aluminum, 245 
alkalis on aluminum, 246 
alloys, 246 
compounds with oxygen, 244 
dental applications, 243 
in the arts, 242 
occurrence of, 240 
properties of, 242 
reduction of, 241 
tests for, 251 
Amalgam, 117, 368 
a dental amalgam, 212, 371 
aging of, 379 
amalgamation (see mer- 
cury), 380 
antimony, 404 
binary, 398 
bismuth, 404 
cadmium, 403, 410 
comminution, 378 
conductivity, 397 
contraction of, 386 
copper, 400, 410 
dental amalgam alloys, 370 
discoloration of, 396 
edge strength, 396 
expansion reactions, 386 
flow of, 393 
formation of, 371 
gold, 400, 406, 410 
in the arts, 370 
mercury, 408 
palladium, 402 
platinum, 402, 411 
properties of, 404 
quaternary, 405 
silver, 398, 409 
Sullivan’s amalgam, 400 
table of well-known dental 
amalgam alloys, 376 
ternary, 398, 404 
tin as a component, 158, 399, 
409 
453 454 
INDEX 
Amalgam—Cont’d. 
washing, 397 
zinc, 402, 406, 410 
Annealing, 33 
gold, 338 
of alloys, 127 
Antimony, 148 
acids on antimony, 150 
alloys, 151 
compounds with oxygen, 149 
occurrence of, 148 
properties of, 149 
reduction of, 148 
tests for, 152 
Apparatus required for stu- 
dents in the labora- 
tory, 426 
Autogenous soldering, 132 
B 
Babbitt metal, 152, 160 
Bessemer process, 225 
Bismuth, 163 
acids on bismuth, 165 
alloys, 165 
compounds with oxygen, 164 
occurrence, 163 
properties of, 164 
reduction of, 163 
tests for, 170 
Blow pipes, 85 
compound, 96 
Borax, 69 
Brass, 208 
Bromides, metallic, 60 
Bronze, 161 
C 
Cadmium, 192 
acids on cadmium, 194 
alloys, 194 
compounds with oxygen, 193 
occurrence, 192 
properties of, 193 
reduction of, 192 
tests for, 196 
Calcination, 22 
Calorific energy, 71 
Cementation, 23 
carburizing, 23 
Cementation process, 226 
Cements: 
color modifications, 181 
copper, 186 
mixing, 184 
reactions, zinc oxide and 
phosphoric acid, 183 
see copper oxides, 204 
silieious, 186 
zinc, 179 
Chemistry, 17 
Chlorides: 
metallic, 58 
reduction of, 59 
Clasp gold, 351 
Coal gas, 75 
Coins, 210 
copper, 210 
gold, 347 
nickel, 210 
silver, 276 
Conductors: 
conductivity of metals, 41 
table of conductivity, 41 
Copper, 197 
acids on copper, 205 
alloys, 206 
compounds with oxygen, 204 
dental applications, 203 
electrodeposition of, 213 
occurrence, 197 
poisoning, 204 
properties of, 202 
reduction of, 199 
solders, 212 
tests for, 212 
Cradle, The, 311 
Crown gold, 352 
Crucibles, 66 
for fusing platinum, 67, 296 
graphite, 66 
metal, 67 
Cuppelation process, 269 
Cutch, 334 
Cyanides, metallic, 61 
Cyanide process, 31S 
D 
Deoxidizing agents, 48 
Dies: 
Babbitt metal, 160 INDEX 
455 
Dies—Cont’d. 
Haskell’s Babbitt metal, 160 
Haskell’s counterdies, 144 
lead counterdies, 140 
of bismuth, 166 
of zinc, 175, 189 
Distillation, 22 
Dredger mining, 317 
Dry process, 23 
E 
Electric furnaces (see fur- 
naces), 102 
Elements, 17 
gases, 26 
liquid, 26 
metallic, 20 
solids (nonmetallic), 26 
table of, 18 
Eutectic alloys, 134 
Expansion Reactions, 386 
F 
Flame, 87 
Bunsen, 90 
candle, 88 
oxidizing, 91 
reducing, 90 
Flashing point (foot-note), 74 
Flotation process, 55, 318 
Fluorides, metallic, 61 
Fluxes, 68 
acid, neutral and basic, 68 
black, 70 
borax, 69 
Fuel, 70, 73 
calorific energy of, 71 
calorific intensity of, 72 
Furnaces, 77 
blast, 77, 216 
chimney draught, 77 
Dental laboratory, 80 
electric, 62, 102 
for fusing zinc, 172 
muffle furnaces, 79, 110 
reverberatory, 77 
Fusibility of metals, 36 
G 
Galvanized iron, 189, 231 
Gangue, 20 
Gasoline, 74 
Gold, 304 
acids on gold, 343 
alloys, 345 
annealing, 335, 338 
beating, 333 
carat, 349 
chlorination process, 317 
clasp gold, 351 
cohesive gold, 340 
compounds with oxygen, 342 
corrugated foil, 336 
erown gold, 352 
crystal gold, 337 
cyanide process, 318 
cylinders, 336 
discovery in California, 308 
dredger mining, 317 
electrodeposition of, 365 
examples, 359 
flotation process, 55 
foil, 335, 337, 339 
hydraulic mining, 312 
inlay, 352 
mining and extraction, 309 
nitric acid process, 324 
noncohesive gold, 340 
occurrence, 304 
parting gold, 323 
placer mining, 310 
plate, 349 
precipitating gold, 329 
preparation of chemically 
pure gold, 327 
properties of gold foil, 339 
properties of, 332 
quartz mining, 314 
refining gold, 320 
roasting process, 320 
rolled gold, 337 
rules for computing and 
compounding alloys, 
359 
solders, 349, 357 
sulphuric acid process, 325 
tests for, 364, 365 456 
INDEX 
H 
Heat (see fuels), 86 
Hydraulic mining, 312 
Hydroxides, 50 
I 
Ingot molds, 100 
Iodides, metallic, 61 
Iridium, 284 
acids on iridium, 285 
alloys, 286 
compounds with oxygen, 285 
occurrence, 284 
properties of, 285 
reduction of, 284 
Iron, 214 
acids on iron, 236 
alloys, 228, 237 
Bessemer process, 225 
carburized iron, 230 
cast, 222 
cementation process, 226 
compounds with oxygen, 236 
electric furnaces reduction, 
220 
galvanized iron, 231 
modifications of, 222 
occurrence, 214 
pig iron, 222 
properties of, 221 
reduction of, 216 
steel, 225 
tests for, 238 
wrought iron, 223 
K 
Kaolin (see footnote), 62, 245 
L 
Laboratory reagents, 451 
Lamps, 93 
gas, 95 
oil, 94 
spirit, 94 
Lead, 138 
acids on lead, 141 
alloys, 142 
blow pipe analysis of, 146 
compounds with oxygen, 140 
Lead—Cont’d. 
dental applications, 140 
desilvering lead, 268 
electrodeposition of, 147 
occurrence, 138 
properties of, 139 
reduction of, 138 
tests for, 145 
Lime, silica and aluminum as 
fluxes, 70 
Lunar caustic (see footnote), 
273 
M 
Malacca tin, 154 
Matthiessen’s rules for alloys, 
117 
Melotte’s metal, 167 
Mercury, 253, 
acids on mercury, 257 
alloys, 258 
compounds with oxygen, 256 
method of detecting impu- 
rities, 254 
occurrence, 253 
poisoning, 256 
properties of, 255 
pure, 254 
reduction of, 253 
sulphides, 259 
tests for, 262 
uses of, 256 
Metal, 27 
annealing, 33 
Babbitt, 152, 160 
base, 24 
color of, 28 
conductivity of, 41 
crystalline form of, 30 
ductility and tenacity, 31 
elasticity of, 35 
electro-motive force, 42 
expansibility of, 39 
forging, 35 
fusibility and volatility of, 
36 
luster of, 28 
malleability, 30 
noble, 24 
nontransparency of, 28 INDEX 
457 
Metal—Cont’d. 
odor and taste of, 29 
properties of, 36 
purity of, 32 
specific gravity of, 44 
specific heat of, 38 
sonorousness of, 35 
temperature effect of, 32 
type, 143, 152 
welding, 34 
Metallic oxides, 46 
Metallography, 29 
Metallurgy, 20 
Muffles,‘80, 110 
O 
Occlusion, 22, 271, 298 
Ores, 20 
an ore, 20 
argentiferous galena, 267 
calamine, 171 
cassiterite, 153 
chalcopyrite, 198 
cinnabar, 253 
galenite, 138 
greenockite, 192 
iridosmine, 284 
magnetite, 214 
native gold, 304 
osmiridium, 284 
polyxene, 294 
reduction of, 76 
silver glance, 264 
stibnite, 148 
zinc blende, 171 
Oxides, 44 
acid forming, 50 
basic, 49 
calcination of zinc, 178 
hydroxides, 50 
metallic, 46 
of lead, 138 
reduction of, 50 
zinc, 177 
Oxidizing agents, 48 
P 
Palladium, 287 
acids on, 289 
alloys, 289 
Palladium—Cont’d. 
compounds with oxygen, 289 
dental applications, 289 
occurrence, 287 
properties of, 287 
reduction of, 287 
tests for, 291 
Panning gold, 310 
Pattinson process, 267 
Petroleum, 73 
Plate gold, 341 
Platinum, 294 
acids on, 301 
alloys, 301 
compounds with oxygen, 300 
dental applications, 299 
foil, 299 
fusing, 296 
occurrence, 294 
platinum black, 298 
platinum for muffles, 111, 
300 
properties of, 297 
reduction of, 295 
substitutes for, 290, 293 
tests for, 303 
Plumbic, cupric and ferric ox- 
ides as fluxes, 70 
Potassium carbonate, 69 
Potassium nitrate, 69 
Porcelain, 245 
Porcelain furnaces (see page 
104) 
Purple of eassius, 162, 343 
Pyrometry, 72, 114 
E 
Red lead, 140 
Reduction, 21, 76 
by electricity, 62 
cyanide process, 61, 318 
dry process, 23 
flotation process, 55 
of metallic oxides, 50 
on charcoal, 92 
wet process, 23 
with hydrogen, 52, 57 
with sulphur, 53 
Refractory materials, 64, 112 
Regulus, 21 458 
INDEX 
Rheostats, 104 
Roasting, 22 
Rouge, 236 
Rules and suggestions for stu- 
dents, 421 
S 
Scorification, 22 
Silver, 264 
acids on, 275 
alloys, 275 
argentiferous galena, 267 
chemically pure, 271 
compounds with oxygen, 274 
cupellation, 269 
eleetrodeposition of, 278 
nitrate crystals, 273 
occurrence, 264 
properties of, 274 
reduction of, 265 
tests for, 277 
Slag, 20 
Sluice, The, 311 
Smelting (see Reduction), 21 
Sodium carbonate, 69 
Sodium chloride, 69 
Solders, 129 
autogenous soldering, 132 
braziers, 130, 212 
for aluminum, 248 
gold, 344 
hard, 130, 207 
process of, 130 
silver, 277 
soft solders, 130, 157 
Specific gravity, 43 
table of, 44 
Speiss, 21 
Stannic acid, 156 
Stannic oxide, 156 
Steel, 225 
color of tempering, 233 
hardening and tempering, 
232, 234 
Sublimation, 22 
Sulphides: 
experiments for, 54 
metallic, 53 
reduction of, 55 
Supports, 98 
T 
Tempering, 128, 232, 234 
Thermite Welding, 34 
Tin, 153 
acids on tin, 157 
alloys, 158 
compounds with oxygen, 156 
dental applications, 155 
electrodeposition of, 162 
foil, 155 
occurrence, 153 
properties of, 155 
pure, 154 
reduction of, 153 
tests for, 161 
Tom, The, 311 
Touchstone test, 365 
Tungsten, 292 
Type metal, 143, 152 
y 
Vermilion, 259 
properties of, 261 
uses of, 261 
W 
Welding, 34 
Wet Process, 23 
Wolfram (see Tungsten), 292 
Z 
Zinc, 171 
acids on zinc, 187 
alloys, 188 
cements, 179 
dental applications, 175 
dies, 175 
ions, 173 
occurrence, 171 
oxides, 174 
phosphate, 184 
properties of, 172 
reduction of, 171 
test for, 190 
zinc in the arts, 174