The smaller vat, Figure 2, Plate 4, is to contain a solution of iron sulphate. It is provided with a filter, and a discharge pipe which reaches to the gold precipitating tub, and which, when not in use, is turned up and fastened as in the figure. This vat is elevated so that the precipitant may be used with convenience. For silver a similar vat contains the calcium polysulphide. It does not require a filter, but the pipe is inserted a little higher, to allow room for sediment.

Apparatus   Vats.

Apparatus - Vats.

59. Troughs for conveying the lixivium from the leaching vats to the precipitating tubs, are not built, but hollowed out of timber. They are about five inches wide and four deep, and are tarred.

Well

60. Well. As the silver leaching solution, or "hypo," is not thrown away, but is used again continually, it is usual to provide a well on a lower level than that of the silver precipitating tubs. A tub or square vat sunk in the ground answers the purpose.

Pumps

61. Pumps. For elevating the leaching liquid from the well a wooden pump is used. The small quantity of metal used in its construction, for fastening the valves, etc., is not injurious. In case, however, a pump is used to raise weak lixivium from the gold leaching, it must be constructed entirely without metal, except lead, in those parts which come in contact with the lixivium. Rubber ball valves are best for this pump. A well may be dispensed with if desired, by having the discharge pipes of the silver precipitating tubs connected directly with the pump.

Filters

62. Filters. To receive the precipitate from the silver tub there is a filter vat, either round or square, in which it is drained and washed. The filter is made like those in the leaching vats, except that, instead of burlap, cotton drilling is used. Filters for the precipitated gold are simple pointed bags made of drilling, or sheets of drilling secured over the rims of water buckets which have plug holes near the bottoms, with hollow plugs through which the filtrate flows to a receptacle beneath. A large tank, in which is a filter made of sand or saw dust, is usually placed outside the works. It is used for filtering the liquid drawn from the gold tub after the precipitation of the gold.

Plate IV.

Plate IV.

Scale, 1/2 inch=1 foot.

Plate V.

Plate V.