uice, where it is caught by its
gravity and by quicksilver. The board-sluice is the great washing
machine, and the most important instrument used in the placer mining of
California. It washes nearly all the dirt and catches nearly all the
placer gold of the country. It was invented here, although it had
previously been used elsewhere; it has been more extensively employed
here than in any other country, and it can be used here to more
advantage than elsewhere. It is not less than fifty feet long, nor less
than a foot wide, made of boards. The width is usually sixteen or
eighteen inches; and never exceeds five feet. The length is ordinarily
several hundred and sometimes several thousand feet. It is made in
sections or "boxes" twelve or fourteen feet long. The boards are an
inch and a half thick, and are sawn for that special purpose, the
bottom boards being four inches wider at one end than the other. The
narrow end of one box therefore fits in the wide end of another, and in
that way the sluice is put together, a long succession of boxes, the
lower end of each resting in the upper end of another, and not fastened
together otherwise. These boxes stand upon trestles, with a descent
varying from eight to eighteen inches in twelve feet. It is therefore
an easy matter to put up or take down a sluice after the boxes are
made, and it is not uncommon for the miners to haul their boxes from
one claim to another. The descent of a sluice is usually the same
throughout its length, and is called its "grade." If there be a fall of
eight inches in twelve feet, the sluice has an "eight-inch grade," and
if the fall be twice as great, it is a "sixteen-inch grade." The grade
depends upon the character of the pay-dirt, the length of the sluice,
and its position. The steeper the descent, the more rapidly the dirt is
dissolved, but the greater the danger also that the fine particles of
gold will be carried away by the water. The tougher the dirt, that is,
the greater its resistance to the dissolving power of the water, the
steeper, other things being equal, should be the sluice. A slow current
does not dissolve tough clay, and that is the greater part of the
pay-dirt, so rapidly as a swift one. The shorter the sluice, other
things being equal, the smaller the grade should be. There is more
danger that the fine particles of gold will be lost by a short sluice
than by a longer one, and to diminish this danger, the rapidity of the
current must b