After the
bullion is fully dissolved all the acid still available is run from B
into A A. The temperature and strength are thereby reduced, the fuming
ceases, any still undissolved copper sulphate dissolves, and the gold
settles. In assuming that the settling of the gold takes place in A
itself, the author follows the practice of the United States mints. In
private refineries, where refining is carried on continuously, the
settling may take place in an intermediate vessel, and A A be at once
recharged. Owing to the large amount of free acid present, the
temperature must fall considerably before the separation of silver
sulphate commences, and sufficient time may be allowed for settling if
the intermediate vessel be judiciously arranged.
[Illustration]
_Separating the Silver Sulphate._--The clarified solution is siphoned
off the gold from A A into C, which is an open cast iron pan, say 8
ft. by 4 ft. and 1 ft. deep. It is supported by means of a flange in
another larger pan--not shown in the diagram--into which water may be
admitted for cooling. Steam is blown into the acid solution, still
very hot, as soon as C is filled. The steam is introduced about 1 in.
below the surface of the liquid, blowing perpendicularly downward from
a nozzle made of lead pipe through an aperture 1/8 in.
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