75 
a heavy jet of water under pressure upon the bank, and washing 
of the gravel through sluices containing distributed mercury. The 
mercury forms an amalgam with the gold and thus holds it. 
SILVER. 
Case 7 .—Type specimens of silver bearing minerals. These 
are in the order of their richness — native or wire silver, three fine 
specimens from the Mollie Gibson mine, Colorado, also specimens 
from Mexico and Chile; argenttte, Saxony, 87 per cent, of silver; 
Cerargyrite, or horn silver, Chile, 75 per cent, of silver; pyrargy- 
rite or ruby silver, Peru, 65 per cent, of silver; proustite, Chile, 
65 per cent, of silver; stephanite, Saxony, 68 per cent, of silver. 
With these should be mentioned as silver bearing minerals, tetra- 
hedrite, which sometimes contains as high as 17 per cent, of silver 
galena, always containing some silver, and a number of rarer 
minerals. 
Kemainder of Case 7, Cases 8 and E. Silver ores from 
Colorado. 
Cases 9 and lO. — Silver ores from Mexico and South 
America. 
Cases 11, 12, 13 and 14. — Ores, chiefly from Colorado 
and New Mexico, which are worked both for the silver and lead 
which they contain. Galena is the most important mineral in 
their composition. 
Cases F andO. — Products obtained at different stages in 
the process of extraction of gold and silver from their ores, as 
treated by the Argo Smelting Co. A chart giving a complete out- 
line of the process may be seen on the wall near by. Processes 
of extraction used by other companies are also illustrated 
LEAD. 
Case 15.— Type specimens of lead-bearing minerals. These 
— Galena from Missouri, the most abundant lead mineral and 
the fundamental lead ore; it contains 86 per cent, of lead; Cerussite, 
