ew weeks. After a
time the quicksilver pervades 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 serviceable 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
particles of metal.

_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 "cleaning up" and another is called a "run." A
run in a common board-sluice usually lasts from six to ten days.
Ordinarily the sluice runs only during daylight, but in some claims the
work continues night and day. Cleaning up occupies from half a day to a
day, and therefore must not be repeated too often, because it consumes
too much time. In some sluices the cleaning up does not occur until the
riffle-bars have been worn out or much bruised by the wear of the
stones and gravel. Cleaning up is considered light and pleasant work as
compared with other sluicing, and is often reserved for Sunday. At the
time fixed, the throwing in of dirt ceases, and the water runs until it
becomes clear. Five or six sets of riffle-bars, a distance of thirty or
thirty-five feet, are taken up at the head of the sluice, and the dirt
between the bars is washed down, while the gold and amalgam lodge above
the first remaining set of riffle-bars, whence it is taken out with