EXTRACTION BY WASHING. Extraction of gold by washing alone is possible only in the case of ores carrying native gold. The process is not exten sively used in civilized countries, on account of the heavy losses of gold entailed by it, which may amount to 50 per cent. In combination with amalgamation, it is, however, the method most commonly employed. Simple washing is per formed by means of pans, cradles, long toms, and sluices, the last being the appliance most used in the United States. The operation called pan ning is the simplest of all methods of gold-wash ing and the most wasteful. Prospectors make use of it, however, in testing for gold, and it is still carried on to some extent as a commercial process. In panning, the dish, filled to about two thirds of its capacity with the pay dirt, is placed under water until the lumps can readily be broken up. The operator then grasps the dish with both hands, raises it to nearly the level of the water, and gives it a gentle oscillatory mo tion. The mud and fine sand are washed over the far edge, which is gradually lowered until little but coarse pebbles, heavy minerals. and gold remain. After removing the pebbles, the pan is lifted and shaken so as to spread out the mate rials, when the yellow specks or colors of gold are visible. The cradle is a box provided with a sieve in the upper part, the whole resting on rockers so that it can he rocked by means of a handle. The gold-bearing gravel is placed in the sieve and washed with water, the coarse par ticles remaining in the sieve and the tine with the gold passing through and falling on the in clined bottom, where the light, material runs off with the water, the heavier gold sinking to the bottom, where it is retained by transverse slats known as riffles. The long tom consists of two
troughs, of which the lower one has cross-riffles on its inclined bottom. Roughly, the upper trough is about 14 feet long, 20 inches wide at the upper end, and 30 inches wide at the lower end, which is closed by a sieve. The lower end of the upper trough discharges into the upper end of the lower trough, which is about 12 feet long and 3 feet wide. By means of a strong stream of water flowing in at the upper end of the upper trough, the material is carried through both troughs, the gold being caught in the riffles of the lower box. Sluices consist of a series of 12-foot troughs emptying into one another, and often forming a line of troughing several hundred feet long. .The bottoms of the troughs have rif fles, and at intervals the bottom of the box is replaced by a grating known as a grizzly. Under neath the grating there is a broad trough running at right angles to the main trough and opening into another trough parallel to the main direc tion and which forms the continuation of the sluice. The coarse gravel is caught by the gratings, and the gold is deposited in the riffles as previously described. Frequently mercury is sprinkled into the riffles, thus combining amalga mation with washing. The sluice is considered the best device for washing gold-bearing gravels. Among the other apparatus for washing gold are puddling tubs or boxes and pugmills. Where water is scarce separation is performed by win nowing or dry blo*ing. In America the separa tion of gold by washing is practiced chiefly by prospectors and individual placer miners.