Warm distilled water is allowed to percolate the crystals until the
usual ammonia test indicates that the copper sulphate has been
sufficiently dissolved. Then the outflow is closed, sheets of iron are
thrown on and into the crystals, the apparatus is filled with hot
distilled water, and steam is moderately admitted into the lower
compartment. Ferrous sulphate is formed, and in connection with the
iron rapidly reduces the silver sulphate to the metallic state, the
reduced silver retaining the heavy compact character of the crystals.
When the reaction is completed, as indicated by the chlorine test, the
liquid is discharged into E, the iron sheets are removed and the
silver is sweetened either in the same vessel, D, or in a special
filtering vessel which rests on wheels and may be run directly to the
hydraulic press.
The vat, E, is the great reservoir where all liquids holding silver
sulphate in solution are collected; for instance, that from sweetening
the gold and from washing the tools. Sheets of iron here precipitate
all silver and copper, and the resulting solution of ferrous sulphate
is, with the usual precautions, discharged into the sewer.
Occasionally when copper and silver have accumulated in E in
sufficient amount the mass is thrown into D, silver sulphate crystals
are added and sheet copper is thrown in, instead of sheet iron.
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