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PLATINUM. 223

llic j^iini C()l(ir. and in the nianufaclure of certain porcelain
and glass to give tbcm a red color.
Purple-of-Cassins is a compound of gold, tin, and oxygen,
grouped according" to the following formula :*
Aii.O, SnO., SnO, SnO. + 4I-LO.

It is obtained by mixing a solution of stannous chlorid,
SnCls, stannic chlorid, SnCl4, and a dilute neutral solution
of gold chlorid. The result is a fine purple precipitate,
which is collected, washed and dried, when it is ready to
be incorporated with the sillous material.
Purple-of-Cassius is claimed by many to be merely a
mechanical mixture, a combination of stannic oxid, colored
with finely divided gold or one of its oxids.

PLATINUM.

Symbol; Pt. Atomic zveight, 197.
General Properties.—Platinum is a grayish-wdiite metal,
resembling, in some measure, polished steel. It is harder
than silver, and has a density greater than any known metal,
its specific gravity being 21.25. ^ white heat does not
tarnish it, nor is it any way afifected by exposure, either
in the air or water. It is insoluble in any of the simple
acids, nitro-miiriatic acid (aqua regia) being the only one
that dissolves it. It expands less by heat than any other
metal, and is much inferior to gold, silver, and copper as a
conductor of electricit3^
Platinum is soft and flexible, and when rolled into thin
sheets, say 28 or 30 of the gauge-plate, and well-annealed
at a strong zuliite heat for eight or ten mimites,' it may be
readily forced into all the inecjualities of a zinc die without
producing any appreciable change in the face of the latter.
* Bloxam's Chemistry.