Page:The American Cyclopædia (1879) Volume VIII.djvu/90

82 mints and assay offices $1,102,264,541. (See .) Of this amount coinage to the value of $35,249,337 and bars valued at $20,495,616 were issued during the year ending June 30, 1873. The amount of gold of domestic production, exclusive of coins, deposited at the various mints and assay offices of the United States from their establishment to June 30, 1873, with the sources of production, has been as follows:

The localities given in this table are merely those from which the mint deposits were declared or inferred to come; hence they do not represent correctly the actual origin of production. A considerable amount, for example, is attributed to Kansas, which really produces no gold. The gold coinage of Great Britain and Australia for 10 years has been as follows:

The exports of domestic gold from the United States during the year ending Dec. 31, 1873, amounted to $55,178,229 in coin, and $12,754,257 in bullion.—. Gold occurs principally in metallic form, as threads, scales, spangles, films, grains, monometric crystals, nuggets, &c. Such native gold always contains from 1 to 40 per cent. silver, and often also small quantities of iron, copper, mercury, palladium, platinum, or iridium. Gold ores proper are rare; the undoubted species are tellurides. More commonly gold occurs associated with other minerals, chiefly (in decomposed ores) the oxides of iron, and (in solid ores) iron and copper pyrites, galena, blende, mispickel (all of which may be auriferous), bismuth, stibnite, magnetite, hematite, various spars, and quartz. It is believed by many that auriferous pyrites often contains its gold in chemical combination with antimony, arsenic, or sulphur; but this is probably not the case with all pyrites, or with all the gold in any variety of pyrites. Gold is classified further as quartz gold (found in veins, &c.), and wash gold (found in placers, gravel and cement deposits, &c.). The methods of extraction are mechanical, chemical or both, according to circumstances. Mechanical methods involve the agency of air or water. Air separation is the rude process of winnowing, occasionally practised in localities where water is wanting. The dry pulverized material is repeatedly thrown into the air, allowing the wind to carry off the lighter portions, the remainder being caught as it falls in a hide or blanket, or a shallow wooden basin called a batea. The process is concluded by blowing the last residuum with the mouth. Washing is the almost universal method of mechanical separation. In exploring for gold, the earth or pulverized rock suspected to contain it is washed on the blade of a shovel, or in an iron pan, wooden batea, or horn scoop. The operation is commonly called panning. It consists essentially in stirring and shaking under water the contents of the vessels employed in such a way as to suspend the finer earthy particles and allow them to escape over the edge, while the gold, with the larger stones or lumps of clay, remains behind. The stones are removed with the fingers, and the lumps of clay are rubbed between the hands and reduced to a slime, the process being skilfully continued until nothing is left except gold and heavy black sand, usually titaniferous iron, which accompanies native gold in most localities and cannot be separated by washing. When perfectly dry, a part of it can be removed by blowing and a part by the magnet. It is common to melt the finer dust with fluxes and collect it in buttons. Quicksilver may also be introduced in panning, to take up and secure the fine gold. The cradle, or rocker, is an apparatus somewhat resembling a child's cradle. The box is usually about 40 in. long and 20 wide, and from 15 in. to 2 ft. high at the upper end, upon which is set a hopper or riddle, a box 20 in. square and 6 in. deep, having a bottom of sheet iron perforated with half-inch holes. Under the riddle is placed an inclined apron of canvas, and across the bottom of the main box are nailed two bars or riffles, about three fourths of an inch high. In washing, the dirt is shovelled into the hopper, and the workman ladles water upon it with one hand, rocking the cradle with the other. The sheet-iron bottom retains the larger stones; the disintegrated earth, passing through the riddle, falls upon the apron, which carries it to the head of the cradle box, whence it flows along the bottom and escapes at the lower end, leaving behind the riffle bars the gold, black sand, and heavier particles of gravel, which are cleaned up two or three times a day. This apparatus is both slow and wasteful in operation; but it is cheap and portable, and requires little water, since the same water can be used in it over and over again. The long tom is a