282 RESOURCES OF CALIFORNIA. 
The mechanical appliances used in quartz-mills in separating 
the gold from the pulverized rock, are the blanket, the sluice, 
and the rawhide. 
The blanket is a coarse, rough, gray blanket, which is laid 
down in a trough sixteen inches wide and six feet long. The 
pulverized quartz is carried over this by a stream of water, 
and the particles of gold are caught in the wool. The blanket 
is taken up and washed, at intervals depending upon the 
amount of gold deposited. In some mills where a large 
amount of rock is crushed, and where the powder is taken 
over the blanket before trying any other process of separation, 
the washing takes place every half-hour. In mills where the 
pulverized quartz is exposed to amalgamation first, the blanket 
may be washed three or four times a day. The washing is 
done in a vat, kept for that especial purpose. 
The sluice used in quartz-mills is similar to the placer board- 
sluice, but the amount of matter to be washed is less, and there 
is no dirt to be dissolved, and there are no large stones, and 
therefore the sluice is not so large, so strong, or so steep in 
grade, as the placer-sluice, and the riffle-bars are not so deep. 
In some quartz-mill sluices there are transverse riffle-bars. If 
the quartz has much iron or copper pyrites, the sluice is used 
to collect this material and save it for separation at some future 
time. The pyrites ordinarily contains, or is accompanied by 
much gold, which it protects from amalgamation. This separa- 
tion of the pyrites from the pulverized rock is called “ concen- 
trating the tailings,” and the material collected is called * con- 
centrated tailings.” In the sluices of some quartz-mills cast-iron 
riffle-bars are used; cast in sections abont fifteen inches square, 
and abvut an inch deep. Much study has been devoted to the 
subject of making these riffle-bars in such a manner that the 
dirt will not pack in them, but will always remain loose, and 
keep in constant motion under the influence of the water run- 
ning over them; but the object has never been fully attained. 
Quicksilver is used in nearly all quartz-mill sluices. 
The rawhide used in separating gold from the pulverized 
