Precipitating Vat

57. Precipitating Vat. Figure 1, Plate 4 - This is also a wooden tub, and, if for gold, is coated inside as the leaching vat. A smooth bottom is made in it, either by means of a layer of tar and asphalt, melted together in such proportions as to harden on cooling, or by a bed of Portland cement, which can be shaped as desired, to facilitate the removal of the precipitate. A precipitating vat is made wider at the bottom than at the top, in order that the precipitate may not settle upon the staves.

58. For drawing off the waste liquor after precipitation, the most convenient, because self-acting arrangement is a piece of two inch hose, drawn water-tight through the side of the tub near the bottom, and long enough on the outside to lead to a filter, or a settling tank, on a lower level, and on the inside to reach the top of the tub, where it is secured, when not in use, by a wooden clamp. On this end is a wooden float which causes the hose, when in use, to draw always from the surface; also serving to prevent its drawing too near to the bottom so as to cause a loss of gold. The other opening, furnished with a large wooden faucet, is only used when collecting the precipitate.

The silver precipitating tubs must be larger, or more numerous, than those for gold, because the volume of silver solution is much the greater. The size represented in Plate 4, is sufficient for the gold lixivium from one vat, such as is shown in Plate 3, but both for gold and for silver, extra vats are provided for very weak solutions, drainings, etc.