METHODS OF GOLD WASHING. 59 
the heavy metallic portion remains behind. The next most simple instru- 
ment used in gold washing is the “rocker” or “cradle,” a wooden trough 
about forty inches long and twenty wide, having at one end a hopper or 
box about twenty inches square, the bottom of which is a piece of sheet-iron 
pierced with holes half an inch in diameter. This is for the purpose of 
keeping back the coarser part of the material washed, which is thrown out 
of the hopper with the hand. The finer portion, aided by the rocking motion 
and the water, passes through the holes, and the gold is caught on the bottom 
of the cradle by projecting cleats, or “ riffles,” as they are universally called 
by the miners. The rapidity of the current through the machine depends 
on the angle at which it is placed and on the amount of water used. It is a 
very rough instrument, losing much of the gold except when this is very 
coarse ; but cheap, portable, and not requiring much water for its operation. 
The “tom”’ is a sort of enlarged cradle, although without the rocking motion, 
having a longer trough and more riffles, and requiring several men to work 
it. The “cradle” and “tom” were largely used during the early days of 
gold washing in California; but they are now seldom seen. The so-called 
“sluice” is almost universally employed, whether the operations carried 
on be on a large or a small scale. The object of the sluice is to imitate na- 
ture as closely as possible, by allowing the auriferous sands and gravels to be 
carried by water over the bottom of a box provided with riffles which detain 
the gold as it settles to the bottom. A great quantity of material can thus 
be washed, because the sluice can be made very wide and the current 
allowed to flow rapidly. The loss of gold to which this rapidity of motion 
would otherwise give rise is prevented by making the sluice very long, 
that in the North Bloomfield Tunnel, for instance, being 1,800 feet in length. 
The size of the sluice and its length are regulated by various considerations, 
such as the character of the gravel to be washed, the grade, and the volume 
of water used. The riffles which serve to detain the gold are made of vari- 
ous materials and arranged in different ways. Square blocks of pine wood, 
laid side by side, so as to have spaces of from an inch to an inch and a half 
between them, are much in use; in some districts longitudinal riffles, made 
by placing pieces of scantling lengthwise in the sluice, are preferred. In 
other localities round stones are used instead of blocks; and sometimes 
stones and blocks alternate with each other at regular distances. A very 
important, and almost essential, aid to saving the gold in the sluice is the 
quicksilver with which the riffles are charged. ‘The method and implements 
