GOLD MINING IN COLOEADO. 



551 



splaslied against these plates, adheres to the amalgamated surfaces and is 

 retained upon them. The batteries and plates are cleaned up at stated inter- 

 vals, differing in length in various mills, in some once each day, in others only 

 once in three or four days, and the amalgam that has collected in the battery, 

 about the stamps and on the plates, is removed. From one-half to three- 

 fourths of the total product is obtained from this source, while the remainder 

 comes from the other appliances used outside the battery for the purpose 

 of catching the amalgam. These consist mainly of aprons or tables, covered 

 with amalgamated copper-plates and constructed in various ways. Usually 

 the stream of water flowing from the batteries and carrying with it the finely 

 crushed ore, some of the amalgam and quicksilver, with much still unaraal- 

 gamated gold, passes over an inclined plane or table, 5 or 6 feet wide and from 

 6 to 12 feet long, and covered with copper-plate. These tables are placed 

 in front of the batteries, so that the stream passes directly over them. 

 Generally one table of the dimensions above given is provided for each bat- 

 tery of stamps, though in some mills there is but one table for two batteries. 

 The table should be fixed at such an inclination that the stream of water may 

 run down readily over its surface, carrying with it the charge of crushed rock, 

 but with not so great a velocity as to wash away the amalgam or prevent its 

 adherence to the plate. This inclination is usually about one inch of fall to 

 six inches or one foot of length, but is variously determined by different mill- 

 men, depending chiefly on the quantity of water used, and other conditions, 

 as experience may direct. In some mills the material first passes over a short 

 copper-plated apron, only 20 or 30 inches long and thence to shaking-tables, 

 that instead of being fixed are suspended at about the same inclination as the 

 stationary table, and to which a slight forward and backward movement is 

 given, accompanied by a sudden shock or percussion. The surface of the 

 table, instead of being smooth, has a number of rifl3es or grooves, at right 

 angles to the long side of the table or the line of motion, which serve to con- 

 tain quicksilver and afford increased opportunities for contact with the ore and 

 amalgamation of the gold. Leaving these machines the stream continues to 

 flow on, in some cases immediately out of the mill into tanks or basins where the 

 residue of the material, or "tailings," is deposited; in other cases over a variety 

 of machines provided for the further saving of the gold or the concentration of 



