A Comprehensive Treatise on Inorganic and Theoretical Chemistry

PLATINUM 197
he assumed that the insoluble part is a chemical compound. G. Tammann's study
of the action of gold chloride, nitric acid sp. gr. 1*44, fuming hydrochloric acid,
palladium chloride, ferric chloride, cupric chloride, mercurous nitrate, ammonium
sulphide, and sodium sulphide indicated a limit with alloys having up to 32 per
cent, of platinum.
J. P. J. d'Arcet 3 prepared platinum-silver alloys by melting the component
metals together. H. Ie Chatelier observed that molten silver at its m.p. gives off
enough vapour to attack platinum. F. E. Carter said that silver rapidly hardens
platinum, and alloys used in dentistry, and in making electrical contacts are fairly
ductile. The so-called dental alloys, first and second qualities, contain, respectively,
66 and 75 per cent, of silver—the remainder being platinum. Some alloys containing
51 to 62 per cent, of tin, 3O to 46 per cent, of silver, 1 *3 to 5-8 per cent, of
gold, and 0*4 to 1*6 per cent, of platinum, are, according to E. A. Smith, used in
the preparation of dental amalgam. The silver-platinum dental alloys were
studied by E. M. Wise and co-workers.
J. Murray, H. Rossler, C. Winkler, F. Doerinckel, J. F. Thompson and
E. H. Miller, A. von der Ropp, and V. Strouhal and C. Barus obtained the alloys
by melting the constituent metals either in the blast-gas name, the oxyhydrogen
flame, or in high temp, furnaces. W. Truthe studied the effect of silver on platinum
in cupellation. W. Spring noted that when platinum electroplated with silver is
drawn into wire, the metals alloy under the severe press. E. Priwoznik obtained
the alloy by igniting silver nitritoplatinite. II. Rossler said that the two metals
form alloys in all proportions, but F. E. Carter said that the alloys do not form a
continuous series of solid soln. as in the case of platinum alloyed with gold, or
palladium with silver. The metals do not readily dissolve in one another, and they
tend to separate on cooling. J. Prinsep attempted to measure the m.p. of silverplatinum
alloys by a gold air thermometer ; and to use the alloys as pyroscopes.
C. T. Heycock and F. JH. Neville observed that adding 3*55 per cent, of platinum
to silver raised the f.p. to 990°. F. Doerinckel found that a series of solid soln.
is formed with from O to 48 per cent, of platinum ; the composition of the endmember
of the series is platinum diargentide, PtAg2, but it is not considered to be
a chemical individual. Above 1184°, it decomposes into crystals rich in platinum,
and a fused mass with about 32 per cent, of platinum. J. F. Thompson and
E. H. Miller thought it possible that a compound is formed because of some irregu-
I I 1 i !••>• i J I i 1 -J 0 I 1 1 1 1 1 1 1 1 1 1
O 20 40 60 80 100 O 20 40 6O BO WO
Per cent of platinum Atomic per cent, of platinum
Fios. 33 and 34.—Freezing-point Curves of the SiIvor-Platinum Alloys.
larities in the solvent action of nitric acid ; and for similar reasons A. von der
Ropp suggested that platinum, hemitriargentide, Pt2Ag3, is formed. G. Tammann
added that no evidence of any compound of the two elements appears on the f.p.
curve. N. S. Kurnakoff and W. A. Nemiloff's correction of F. Doerinckels curve
is shown in Fig. 33, where A represents a solid soln. of platinum in silver ; B, a