LEACIIING-VATS, ETC.—The leaching-vats used in lixiviation-mills is shown, in vertical sec tion, in Fig. 6. In the center of the bottom is the discharge opening, 6 in. in diameter. The east-iron discharge-tube k of the same inside diameter, tightly fastened to the outside of the tank-bottom, corresponds with the discharge-hole. The lower end of the tube is at right angles with the upper end, and provided with flange o. The valve at. which is provided with a rubber gasket, can be pressed tightly against flange a by turning the wheel F. The flange o and valve as are made of brass. Around the discharge opening and fastened to the bottom of the tank is the wooden polygon t, in which is cut the groove p. Around the inner periphery of the tank, and high enough to give the filter bottom an inclination of at least * in. to the foot, is the groove p. The filter bottom consists of a wooden grating made in sections, to which the filter-cloth is well fastened, and kept in position by driving tightly a rope into the grooves p and p. The air-escape pipe d, which reaches to the rim of the tank, enters the latter close under the filter bottom. A piece of the hose is fastened to the upper end, and can be closed by a hose-clamp. X is the central hose, which reaches down into the discharge-tube k, where it has to remain during the process of charging. This hose ought to be very stiff. Before charging the tank the discharge-pipe is filled with water through the central hose, in order to keep the latter filled with water, which will prevent the inside of the hose from being obstructed by ore. When a tank is ready to be discharged the wheel F is turned, and thus the valve in pulled back. The water is injected through the central hose, while the latter is gently moved up and down. The stream undermines the tightly packed sand and causes a continual caving-in until a funnel-shaped opening is made through its depth to the surface. Then several streams are made to play on the top, while the general hose, with checked streams, is left in position to avoid obstruction of the discharge-pipe by a too sudden rush of sand.
Mr. C. A. Stetefeldt, in a paper entitled The Details of Construction for a Modern Lixivia tion Plant, read before the American Institute of Mining Engineers. June, 1891, gives the following specifications for the construction of leaching-vats: "Tanks should be made of clear, well-seasoned lumber. In the United States pine is the best material for this purpose. The staves, from 3 to 4 in. thick, according to size of tank, should be ordered cut to sweep of radius, and from 9 to 10 in. longer than the inside depth, but not gained' for the bottom. The gaining of the staves, 1 in. deep, is done by hand, leav ing a chine of 6 in. be low the bottom. In all tanks the staves stand perpendicular to the bottoms. The bottom pieces, 3 to 4 in. thick, are cut to a diameter of 2 in. greater than that of the finished tank ; they are grooved and joined by a tongue. All joints must be fitted with precision. White lead should never be put between the staves, but may be used in in serting the tongues be tween bottom pieces. The imderstructures, of substantial timbers, placed on a solid foundation, should be sufficiently high to allow access to the bottom in case of leakage. The bottoms rest on joists 3 to 4 in. wide and 10 to 12 in. deep. placed about 2 ft. 6 in. apart, so that the staves are left entirely free. Hoops are made of round iron, to 1 in. diameter, the threaded ends, with hexagonal nuts, passing through forged or cast iron lugs, giving preference to the former. In order to get the full strength of the rods, the threaded ends are taken I in. larger than the diameter of the rod. For tanks of large diameter, each hoop is made in two or three sections; this is necessary to effect a more uniform closing of the stare-joints by tightening the nuts in two or three places. After finishing, the tanks are painted on the outside, staves and bottoms, with three coats of white lead.