MINING. 249 
so warm that the hand can scarcely bear it, the amalgam is 
softened and loosened, so that it can be scraped off readily. 
The plate is then sprinkled anew with quicksilver, and is ready 
for use again. Mercury does not amalgamate with copper so 
readily as with gold or silver. A copper plate, the sixteenth 
of an inch thick, may be used for at least five years, and. per- 
haps for ten; whereas a gold plate of equal thickness would, 
if exposed to the action of quicksilver in the same manner, fall 
to pieces in a few weeks. After a time the quicksilver per- 
vades the copper, and gives it a silvery whiteness all through 
on the under side. It is said that a solution of cyanuret or 
prussiate of potash, is used instead of nitric acid in applying 
mercury to copper plates, and that it is still better, there being 
then no trouble with the green spots of nitrate of copper. 
A good amalgamated copper plate is considered as service- 
able as a bed of quicksilver of equal size, and it is very much 
cheaper and more convenient to manage. 
The dirt and water should be admitted to the copper plate, 
by falling first through a sheet-iron plate, pierced with holes 
half an inch long and a sixteenth of an inch wide. Some 
miners place this sheet-iron plate immediately over the copper. 
Very soon after the water and dirt commence to run in the 
sluice, all the spaces between the riffle-bars are filled with 
sand, gravel, and dirt; which, however, present many little 
inequalities of surface, sufficient to catch all the particles of 
gold larger than a pin-head. The largest gold is caught near 
the head of the sluice; and the farther down the sluice, the 
finer the gold. In some sluices, where the pay-dirt contains 
much coarse gold, the quicksilver is introduced from thirty to 
sixty yards below the head, so as to catch only the fine par- 
ticles of metal. 
§ 181. Cleaning up—the separation of the gold, amalgam, 
and quicksilver, from the dirt in the bottom of the sluice, is 
called “cleaning up;” and the period between one “clean- 
ing” up and another is called a “run.” Arun in a common 
board-sluice usually lasts from six to ten days. Ordinarily the 
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