the dissolved
sulphates.

_Reducing the Silver Sulphate to Fine Silver._--The mother acid is
pumped from C to the reservoir, B, for this purpose an iron pipe
connecting the top of B with a recess in the bottom of C. The tank, B,
is cast as a closed vessel, with a manhole in the top, which is
ordinarily kept closed by an iron plate resting on a rubber packing.
The air is exhausted from B by a steam injector, and the acid rises
from C and enters B without coming in contact with any valves. The
volume of fresh commercial acid necessary for another dissolving
operation, say 800 pounds, more or less, for refining 800 pounds of
bullion in A A, is lifted from some other receptacle into B in the
same manner. The mixture of the two acids in B now represents the
volume of acid to be employed for dissolving and settling the next
charge of 800 pounds of bullion in A A. In this reservoir, B, the
cloud of lead sulphate mentioned above finds an opportunity for
settling.

The crystals of silver sulphate are detached from C by an iron shovel
and thrown into D. D is a lead lined tank about 4 ft. by 4 ft. and 3
ft. deep. It is divided into two compartments by means of a
horizontal, perforated false bottom made of wood. From the lower
compartment a lead pipe discharges into the lead lined reservoir, E.
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