PLATINUM AND ALLIED METALS. 149
place
and at the same time be sufficiently pliable to be worked to the
desired shape; its coefficient of expansion must be low; it should
readily unite with gold, silver, and other metals and their solders;
its cost should be low as compared with platinum. Of binary alloys of
chromium, manganese, iron, cobalt, copper, silver, gold, and
palladium, only those of palladium with gold and silver have any
practical value. Palladium-silver alloys can be made which will meet
the requirements of dental foil and cost from 1 to 50 per cent less
than platinum. Palladium-gold alloys are superior to the
palladium-silver alloys but more expensive. No alloy of gold, silver,
and palladium was found which would replace platinum-iridium alloys
where hardness and strength are required.
Tests
of tungsten and molybdenum, which can not be worked by ordinary fusion
methods, were made. It was found that ordinary wires of these metals
coated with gold and palladium met most of the conditions of hardness
and strength, but were sometimes as brittle as glass. Methods of
overcoming this brittlcness and of producing uniform results are
described. Brittleness is ascribed to coarseness of crystallization,
which can be avoided by proper manipulation in pre-
p
aring briquets and in
drawing wire and can be controlled by metal-lographic studies of
material in course of production. As a result of this investigation a
substitute for platinum was practically produced, "in many ways
superior to platinum and its alloys," by coating pure ductile tungsten
with gold, palladium, or alloys of these metals.
In
the electrical industry platinum has largely been replaced by tungsten,
molybdenum, and nickel-chrome alloys. Various alloys have been
perfected to meet different conditions under which platinum was
formerly used. One of the latest, rights to whioh have been recently
acquired by the General Electric Co.,1 is a copper-jacketed
nickel-steel wire having an outside coating of platinum. This wire is
said to have a coefficient of expansion such that in sealing an
incandescent lamp a tight joint is assured. Thomas A. Edison has been
granted patents (U. S. patent No. 1163329) for producing films of
tungsten for incandescent lamps. It is noted 2 that
recently the Hoskin Manufacturing Co. was sustained in its contention
that the General Electric Co.'s alloy calorite was an infringement of
the Marsh patent (U. S. patent 811859) oovering a nickel-cnrome-alloy
for electrical use.
Platinum
dishes and utensils for chemical investigation have become essential
in accurate analytical work. That chemical platinum ware of different
makers differs in composition and life is evidenced by a recent study
by the United States Bureau of Standards.3 This article
describes and discusses experiments for the thermoelectric,
microscopic, and. chemical tests for the determination of platinum
purity and concludes:
There
has been devised a simple thermoelectric method suitable for the
determination of the purity of platinum ware. This method does not mar
the article tested and gives data for the classification of platinum in
terms of its equivalent iridium or rhodium content * * *. A method has
been developed for determination of the exact loss on treating of
platinum crucibles by means of a suitable electric furnace
1
Jour. Ind. and Eng. Chemistry, vol. 8, No. 1, p. 86, January, 1910. ' »
Metal, and Chem. Eng., vol. 13, pp. 414-15, July, 1915.
'Burgess, O. K., and Sale, P. D., A study of the quality of platinum ware: U. S. Bur. Standards Sci. Paper 254,1915.
