00
----
Bolivian dollars. 9.00, say 28s.
One man can attend to two furnaces, and earns 3s. per shift of twelve
hours.
Probably no revolving mechanical furnace is suited to the roasting of
these ores, as the operation requires to be carefully and intelligently
watched, for it is essential to the success of the Francke process that
the ores should not be completely or "dead" roasted, inasmuch as certain
salts, prejudicial to the ultimate proper working of the process, are
liable to be formed if the roasting be too protracted. These salts are
mainly due to the presence of antimony, zinc, lead, and arsenic, all of
which are unfavorable to amalgamation.
The ores are roasted with 8 per cent. of salt, or 400 lb. of salt for the
charge of 21/2 tons of ore; the salt costs 70 cents, or 2s. 2d. per 100 lb.
So roasted the ores are only partially chlorinized, and their complete
chlorination is effected subsequently, during the process of amalgamation;
the chlorides are thus formed progressively as required, and, in fact, it
would almost appear that the success of the process virtually consists in
obviating the formation of injurious salts.
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