In dry stamping there is also a considerable loss of silver
in the fine particles of rich ore which are carried away as dust and
irrevocably lost. To prevent this loss, the writer proposed while at
Huanchaca that a chamber should be constructed, into which all the fine
dust might be exhausted or blown by a powerful fan or ventilator.
_Roasting_.--From the stamps the stamped ore is taken in small ore cars to
the roasting furnaces, which are double bedded in design, one hearth being
built immediately above the other. This type of furnace has proved, after
various trials, to be that best suited for the treatment of the Bolivian
silver ores, and is stated to have been found the most economical as
regards consumption of fuel, and to give the least trouble in labor.
At the Huanchaca mines these furnaces cost about 100_l_. each, and are
capable of roasting from 2 to 21/2 tons of ore in twenty-four hours, the
quantity and cost of the fuel consumed being as follows:
Bolivian dollars at 3s. 1d.
Tola (a kind of shrub), 3 cwt., at 60 cents. 1.80
Yareta (a resinous moss), 4 cwt., at 80 cents. 3.20
Torba (turf), 10 cwt., at 40 cents. 4.
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