DEPARTMENT OF GEOLOGY 
S3 
7. Illustrations of some of the uses to which petroleum pro- 
ducts are put, including waxed paper for wrapping purposes, 
water-proof coating for explosives, varnishes, wood stains and 
fillers, solvent for rubber cement, electric light carbons, and 
electrodes. 
A series of Russian petroleums which is exhibited here 
presents some features differing from the American. 
Hall 72. 
PLATINUM. GOLD, SILVER, AND LEAD. 
The collections in this hall comprise platinum, gold, silver, 
and lead ores. Besides the typical ores many unique occur- 
rences are represented here. In the examination of these, as well 
as ores of other metals, it should be remembered that the min- 
eral or metal is frequently present in such minute quantities 
that it cannot be seen by the naked eye or even with the aid of 
an ordinary magnifying glass. Ores of the precious metals are 
commonly, however, associated with certain mixtures of com- 
mon and otherwise valueless minerals known as gangue min- 
erals, and by a careful observation of such associated minerals 
and of the neighboring rocks, the skilful observer may frequent- 
ly recognize the presence of valuable metals. Opportunity is 
given by the numerous examples shown in this hall to study 
the slight indescribable variations in the appearance of a mix- 
ture of gangue minerals, which often indicate the presence or 
absence of the precious metals. It should be said, however, 
that all indications of this kind are often more or less deceptive 
and the only positive proof of presence or absence of gold or sil- 
ver is to be found in actual trial by assay. The above observa- 
tions do not apply, however, to the lead ores, which are readily 
recognized by one having acquaintance with the lead-bearing 
minerals. This hall also contains a collection of products from 
the metallurgical treatment of ores. 
These are so arranged that the separate steps in the treat- 
ment of the ores may be followed by the visitor. If the visitor 
enters from Hall 7 1 , and passes around Hall 7 2 , keeping to the 
right, the collections may be seen in the order in which they are 
mentioned in this guide. The general order will then be geo- 
graphical beginning in northwestern North America, passing 
south along the Cordillera to the south boundary of the United 
