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Updated: May 10, 2025
These zigzag riffle-bars are nailed down. In all sluices, men must keep watch to see that the boxes do not choke; that is, that the dirt and stones do not collect in one place, so as to make a dam, and cause the water to run over the sides, and thus waste the gold. There are small sluices, from which all stones as large as a doubled fist are thrown out.
Sometimes the matter from the under-current box is led back to the main sluice. Rock-Sluices. Large sluices are frequently paved with stone, which makes a more durable false bottom than wood, and catches fine gold better than riffle-bars. The stone bottoms have another advantage that it is not so easy for thieves to come and clean up at night, as is often done in riffle-bar sluices.
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.
In some sluices, the "block riffle-bars" that is, bars cut across the grain of the tree are set transversely in the boxes, and about two inches apart. Another device is, to fill the pores of such riffle-bars with quicksilver. This is done by driving an iron cylinder with a sharp edge into the surface of the bar, then putting mercury into the cylinder, and pressing it into the wood.
With the water and the motion the dirt is dissolved, and carried down through the riddle, falling upon the apron which carries it to the head of the cradle-box, whence it runs downward and out, leaving its gold, black sand, and heavier particles of sand and gravel behind the riffle-bars.
The grade is so low, that transverse riffle-bars must be used; for with longitudinal riffle-bars or stones, there would be too much danger of choking. These tunnel-sluices, because of their low grades, require much more attention than any other kind of sluices. Ground Sluice.
But a fellow has to keep the cradle in constant motion, or the sand will pack and harden behind the riffle-bars and allow the gold to slide over it, instead of sinking down through it, as gold always will when sand or gravel is loose or in motion," as he spoke, he thrust his hand into the hopper and picked out a couple of stones too large to pass through the holes in the bottom of the hopper, and, after closely examining them to see that there was no gold clinging to their sides, threw them away.
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.
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.
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 a scoop or large spoon, and put into a pan. Five or six more sets of bars are taken up, and so on down.
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