C—3

One or more endless chains, preferably of cast-iron, and having ploughs or conveyors attached, pass along the hearth from end to end. One such chain is shown at D. At each end where the chain emerges from the furnace it passes over a chain-wheel D l , one of which is caused to rotate and drag the chain in a direction from the hopper end to the delivery end of the hearth. A return-way for the chain is provided in the brickwork at C l , during passage through which it becomes well cooled. The chain has attached to it at various points ploughs or conveyors adapted to thoroughly stir and " turn " the charge without carrying it too rapidly through the furnace. The ploughs are shown at D 2, in Figs. 1 and 2, and one is shown to a larger scale in Pigs. 5 and 6. In these two figures d 1 are " wings " of the plough, which are the most effective part of the device in bringing fresh portions of the charge to the surface. The speed at which the ploughs move through the charge may be varied to suit different kinds of ores requiring roasting for different periods, the usual time required when the ore has been prepared as hereinbefore described being eight to ten hours. Provision is made in this furnace for the copious admission of wet steam through nozzles or holes placed as near to the hearth as conveniently possible, so that the steam can play upon the charge during the process of roasting, the steam being required for the formation of sulphates. One form of nozzle is shown in the drawings Figs. 1 and 2, at A 4, being connected to a steam-pipe A 5 extending along both sides of the shell on the outside. Provision for the admission of air or oxygen is shown at A 7. The ore should not be heated to a higher temperature than is necessary for the formation of sulphates. When the roasted ore has been discharged into the wagons or other receptacles it may be ground and again roasted, or may be at once treated with alkali, if requiring such treatment, and transferred direct to an extractor. A special form of extractor, constructed according to this invention, is shown in Figs. 3 and 4of the accompanying drawings. Eis a cylindrical vessel, closed at each end, to the inside of whose walls B 1 is attached a lining of, say, copper E 2 , which is not subject to corrosion or the attacks of any chemicals likely to be present in the ore, and capable, in conjunction with the walls E l , of withstanding a steam-pressure of several atmospheres within the vessel E. The ore is mixed with water to a cream-like consistency, and the whole introduced into the extractor through a door E 3 . A steam inlet is provided either by using hollow trunnions or as shown by the steam-pipe E 4 , Figs. 3 and 4, and the charge is " boiled " under a high steam-pressure. I frequently find two to four atmospheres sufficient, though I do not confine myself to this or any particular pressure, but it should not be less than that of the atmosphere. This operation I term "boiling," and " boiling " under high pressure thus has been found by me to effect the extraction far more thoroughly than at ordinary pressure. A steam-gauge and safety-valve may be fitted to the extractor, and are shown at E 7 and E' respectively, E 9 being a blow-off cock. The whole vessel Eis capable of rotation about an axis transverse to that of the cylinder of which it is formed, and means for oscillating or rocking it about such an axis are provided, as shown in the drawings, F being a crank receiving rotation from a pulley F l , driven by any suitable source of power, F 2 being a connecting-rod hinged by one end to the extractor at E 7 , and connected by its other end to the crank. The extractor is mounted in bearings E 5 , which permit of oscillation about the axis F 6 . The charge is thus thrown to and fro from end to end of the cylinder E, and kept in violent agitation under steam-pressure, the result being to get all the sulphates and other soluble salts thoroughly into solution, the precious metals being subsequently thoroughly separated from the sulphates or " cleaned "by washing in vats in the usual manner. The concentrator G, illustrated in Figs. 7, 8, and 9, comprises a frame G 1 supported upon a stationary frame G 2 by means of flat springs g l , so as to be capable of receiving an oscillating motion. Neither the method of supporting the oscillating table nor the means adopted to impart the motion form, however, part of the subject-matter of the present application for patent, any suitable construction or mechanism being used as may be desired. In Figs. 8 and 9is shown in chain lines a crank-shaft X, with pulley Xl,K l , mounted on bearings K 2 , by which the desired motion may be imparted to the table through connecting-rods such as K 3 . Above the table is a device which will hereinafter be termed a "douche," and which comprises a water or compressed-air supply-pipe L, communicating with several rows of nozzles L l , each of which rows is provided with a valve L 2 to control its supply. This " douche " may be supported in any convenient way, either from one of the frames G l , G 2 , or independently of the concentrator itself. If supported from the frame G 1 a flexible coupling-pipe must be provided to unite the pipe L with the source of supply, in order at the same time to allow of the motion of the frame G l . The frame G 1 carries the table G 3 of the concentrator. This table slopes slightly from one end to the other, as is usual in such apparatus, and is provided with side walls G 4 to prevent the material from being carried over the sides. The table is faced with an amalgamated plate Hat its upper end. At the lower end of this plate is a well H 1 containing quicksilver, and below this is preferably a second amalgamated plate H 2 . Below these are several wells M, M l , M 2, M 3, the number in the example illustrated being four. These are termed "pyrites wells," as they are intended to retain the pyrites, and each well is preferably somewhat deeper than that just above it. The wells are also preferably constructed with their sides nearest the higher end of the table vertical, but with their opposite sides sloping. Each well, including the well H l , is provided with a draw-off plug, as shown at h l , to, to 1 , to' 2 , m B , respectively. The surface of the table between any two wells is shod with iron or other durable material; the second amalgamated plate H 2 may be replaced by such a plain iron plate, if desired. The walls are advantageously made sloping from end to end, so that the material settling in them is deeper at one end than the other. The amalgamated plate H 1 may have a plain surface, but it is found very advantageous to employ a plate of the construction shown at H 3 in Fig. 10, in which are depressions h arranged in rows, and alternated so that a depression in one row comes below the interval between the two depressions in the preceding row. The operation of the concentrator is as follows : The crushed, or crushed and amalgamated, ore is fed on to the plate H together with a stream of water, the table being maintained in oscillation. The globules of mercury, or of amalgam, and the particles of gold contained in the material are retained by the plate H,

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