DEPARTMENT OF GEOLOGY 
49 
3. General heavy oils, including miners’ oil, leather oil, and 
various engine oils. 
4. A collection of the by-products of petroleum, including 
paraffin wax, crude, semi-refined and refined, with illustrations 
of its use for candles, matches, tapers, etc. ; axle grease, lantern 
oil, harness oil, miners sunshine,’^ for miners^ lamps vaseline 
products, such as cerates, pomades, soap and face paints. 
5. Special grades of illuminating oils. These oils are 
designed to give the best light obtainable from kerosene. 
6. High test illuminating oils. 
7. Illustrations of some of the uses to which petroleum 
products 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 mixture 
of gangue minerals, which often indicate the presence or absence 
of the precious metals. It should be said, however, that all indi- 
cations of this kind are often more or less deceptive and the 
only positive proof of presence or absence of gold or silver is 
