216 MINING INDUSTRY. 



reducing tlie quartz of the Comstock lode by wet crushing, discharging through 

 a No. 5 or No. 6 screen, the average duty is about two tons in twenty -four 

 hours. In some mills it is said to reach three tons per day. Much of the 

 effectiveness of the stamps depends on the degree of care devoted to keeping 

 the working parts in good condition and with the regularity with which they 

 are supplied with ore. This is commonly done by hand labor, the rock being 

 shovelled in at such rate as it is crushed and discharged. In some mills, 

 however, automatic feeders are employed, which give satisfaction. These 

 consist of a hopper, filled with ore, from which a trough or chute leads to the 

 feed-opening of the battery, so inclined that the ore will slide down from the 

 hopper to the battery, if the chute, which is hung on a pivot, be agitated. A 

 rod is attached to the chute, and so placed that the tappet of the stamp, when 

 the latter gets so low as to require an additional supply of rock, will strike its 

 upper end, thus giving a shock which causes the ore to move down and fall 

 into the battery. 



Quantity of watee used. — The quantity of water consumed in the bat- 

 teries varies with the character of the ore and the degree of fineness to which 

 it is crushed. Usually, in the mills of the Washoe district, the consumption 

 is between 250 and 300 cubic feet per ton of rock treated, or from one-third 

 to one-half of a cubic foot of water per stamp, per minute ; but this includes 

 the water used in the pans which does not pass through the batteries. 



At the Petaluma mill the supply tank contains 4,400 cubic feet of water, 

 which is sufficient for eight hours' work of full duty. The mill has 24 stamps, 

 which crush 55 tons of rock per day, discharging at only one side of the mor- 

 tar, through a No. 6 punched screen. The consumption, in this instance, is 

 equal to 240 cubic feet of water per ton of rock, or yVo of ^ cubic foot ot 

 water per stamp, per minute. Maldng a due allowance for a portion of the 

 water used in amalgamation, without having passed through the batteries, the 

 quantity actually used in crushing, in this mill, does not exceed one-fourth, 

 or possibly three-tenths, of one cubic foot per stamp, per minute. 



The method of measurement, in the delivery of water, is by '^ miners 

 inches." A "miners' inch" is the quantity of water that will pass through an 

 orifice one inch square in the side of the measuring box, under a head, usuallj'-, 

 of six inches. The measurement is not uniform throughout the country, as 



