77 
HALL 72. 
PLATINUn, GOLD, SILVER, AND LEAD. 
The collections in this Hall comprise the typical platinum, 
gold, silver, and lead ores, and the minerals of economic value 
that commonly enter into the composition of these. In the exami- 
nation of these, as well as ores of other metals, it should be remem- 
bered that the mineral or metal is frequently present in such min- 
ute quantities that it cannot be seen by the naked eye or even with 
the aid of an ordinary magnifying glass. The ores usually possess, 
however, characteristics of appearance or of association with other 
minerals, known as gangue minerals, which enable a skillful ob- 
server to recognize them as being metalliferous. 
There are also to be seen here products resulting from the 
milling and metallurgical treatment of the ores. 
PLATINUM. 
Case A. — Specimens illustrating modes of occurence of 
platinum in nature, from over twenty different localities, including 
the States of Washington, Oregon and California, U. S. A., New 
Granada, S. A., and the Ural Mountains. In all of these the metal 
will be seen to be present in the form of flattened grains associated 
with iridium, osmium, palladium, gold, copper and chromite. The 
grains are usually found in river beds or placer deposits. A com- 
plete series of rocks and soils bearing platinum, from the Demi- 
doff Platinum Mines, Nizhni Tagilisk, Ural Mountains is shown; 
a series of concentrates produced by washing these in order to 
separate the metal, and photographs of the mines and methods of 
working them. Some other uses of platinum are illustrated as 
follows: Russian platinum coin for a time used as money; coins 
struck in platinum and gilded, passed for gold in Portugal and 
Spain during the past century; bogus gold dust made of platinunj 
grains plated with gold. 
