Amalgam coming from battery stamps is often mixed with all sorts of rubbish. After being gathered, it is dried with a sponge, foreign matter picked off the surface and clean quicksilver added. Soft unglazed paper thrust into the mercury removes the last vestiges of water, and then a card is drawn vertically or a piece of blanket horizontally across the mercury to clean it of iron. After squeezing, the amalgam is retorted.
GOLD RETORT.
All the amalgam is placed in one large kettle and, if possible, the latter is put on a strong table having an inclined surface with a groove and hole at the lower end to catch any stray globules of quicksilver. Sodium amalgam, one ounce to each 75 pounds of mercury, is put in the amalgam kettle and the whole stirred. This sodium amalgam is not absolutely necessary, but is desirable. After some minutes, water is poured on the mercury and the whole stirred. All dirt rises to the surface and is removed with a sponge. The cleaning is continued until the mercury seems absolutely free from any impurity, when it is dried with a sponge. It is next turned into pointed bags of stout canvas and force applied until most of the quicksilver has squeezed through. The amalgam remains behind. The quicksilver still contains some gold, but it had better remain if the mercury is to be used again, as gold attracts gold; it can always be recovered by retorting.
Sodium amalgam is best made by the miner himself, enough for one clean-up at a time. Metallic sodium and quicksilver are the necessary ingredients; the former being kept in a wide-mouthed bottle covered with coal oil. A frying-pan makes a useful mixer. It must be dry and clean. Five pounds of clean mercury is poured into the pan, and dried with a sponge, and heated beyond the boiling-point of water, but not much above, or there will be a sensible loss of mercury. A piece of sodium is wiped dry, cut into ½-inch squares and placed with a long pair of tongs in the center of the warm quicksilver, which, by the way, is now off the fire and in the open air, the operator meanwhile keeping religiously to windward of it, unless he courts salivation and all its attendant ills. As soon as the sodium touches the mercury a flash and mild explosion will follow, but after a few cubes have been introduced into the frying-pan, always in the center, this will cease. As soon as a solid mass of amalgam forms in the middle of the pan, the contents must be stirred slowly, and a little more sodium added. The whole mass now crystallizes out, and if put into closely-stopped bottles it will keep without further protection for a little time. Once opened, each bottle must be used. Observe all these directions faithfully, then there will be no danger of inhaling mercurial fumes nor of being blown to atoms. After the amalgam is once made, it is safe as sugar.
In retorting amalgam never fill the flask too full, and apply the heat gradually, and always from the top of the flask downward.
The rocker is a box 40 inches long, 16 inches wide on the bottom, sloped like a cradle, and with rockers at each end.
CROSS SECTION OF ROCKER.
A hopper 20 inches square and 4 inches deep, having an iron bottom perforated with ½-inch holes, occupies the top. A light canvas-covered frame is stretched under this, forming a riffle. Riffles, and occasionally amalgamated copper plates, are placed in the bottom. The gravel is fed into the hopper, the cradle being then rocked by one hand while water is fed by a dipper with the other.