a
scoop or large spoon, and put into a pan. Five or six more sets of bars
are taken up, and so on down. Sometimes all the riffle-bars are taken
up at once, save one set in every thirty-six feet, and then the work of
cleaning up is dispatched much more rapidly.

The quicksilver and amalgam taken from the sluice are put into a
buckskin or cloth, and pressed, so that the liquid metal passes
through, and the amalgam is retained. The amalgam is then heated, to
drive off the mercury. This may be done either in an open pan or in a
close retort. In the former, the quicksilver is lost; in the latter, it
is saved. The pan is generally preferred. Often a shovel or plate of
iron is used. Three pounds of amalgam, from which the liquid metal has
been carefully pressed out, will yield one pound of gold. The gold
remaining after the quicksilver has been driven off by heat from the
amalgam, is a porous mass, somewhat resembling sponge-cake in
appearance.

_Riffle-Bars._--The riffle-bars are usually sawn longitudinally with
the grain of the wood, but "block riffle-bars" are considered
preferable; the latter are cut across the tree, and the grain stands
upright in the sluice-box. The block riffle-bars are three times more
durable than the longitudinal; and as the latter kind are worn out in a
week in some large sluices, there is a considerable saving in using the
former. The block riffle-bars are only two or three feet long.

In some small sluices the riffle-bars are not placed in the boxes
longitudinally, nor in sets; but one bar near the head runs downward at
an angle of forty-five degrees to the course of the box, not touching
its lower end to the side of the box, but leaving an open space of an
inch there. Just below this open space another bar starts from the side
of the box and runs downward at right angles to the course of the first
bar, and an open space is again left at the end of this bar; and so on
down to near the lower end of the sluice, where there are longitudinal
riffle-bars in sets as described in the preceding paragraphs. The
consequence of using this kind of riffle-bar is, that though much of
the water and light dirt runs straight over the bars, the heavier
material runs down from side to side in a zigzag course. Near the head
of the sluice is a vessel, from which quicksilver falls by drops into
the box; and it follows the course of riffle-bars, overtaking the gold
which takes the same route. These zigzag riffle-bars