[Illustration: THE FRANCKE "TINA" PROCESS FOR THE AMALGAMATION OF SILVER
ORES.]
Within the vat, and working on the top of the copper plates, there is a
heavy copper stirrer or muller, B, Figs. 1 and 2, caused to revolve by the
shafting, C, at the rate of 45 revolutions per minute. At Huanchaca this
stirrer has been made with four projecting radial arms, D D, Figs. 1 and
2; but at Guadalupe it is composed of one single bell-shaped piece, Figs.
3 and 4, without any arms, but with slabs like arms fixed on its
underside; and this latter is claimed to be the most effective. The
stirrer can be lifted or depressed in the vat at will by means of a worm
and screw at the top of the driving shaft, Fig. 3.
The bevel gearing is revolved by shafting connected with pulley wheels and
belting, the wheels being 3 ft. and 11/2 ft. in diameter, and 6 in. broad.
The driving engine is placed at one end of the building. Each vat requires
from 21/2 to 3 horse-power, or in other words, an expenditure of 1
horse-power per ton of ore treated.
At the bottom of the vat, and in front of it, a large wooden stop-cock is
fitted, through which the liquid amalgam is drawn off at the end of the
process into another shallow-bottomed and smaller vat, Figs.
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