A N T I M O N Y : ITS HISTORY, CHEMISTRY, MINERALOGY ...

100 THE METALLURGY OF ANTIMONY.
With ores containing 18 to 20 per cent, of antimony, 4J tons per
twenty-four hours can be treated, with a consumption of 5 to 6 per
cent, gas coke or 7 to 8 per cent, charcoal.
The gold, if present in the quartz of the ore, is almost all recoverable
from the scoria.
For each apparatus four workmen are employed in the twenty-four
hours, and 3 H.P. is used for the ventilators and pump.
(6) The working conditions.—The best size of ore to be treated
is from 1 to 4 centimetres. The ore dust must be separated
out and, if in large quantity, can be moulded with 7 to 8 per
cent, of clay into balls of the proper size and charged along with
the ore.
(c) The actual working is thus:—The roasting furnace is at first
charged with old scoria up to a height of about 10 centimetres.above
the uppermost iron bar forming the bottom ; then enough wood and
charcoal are put in to a height of another 10 centimetres; as soon
as they are lighted and burn freely, another charge of 300 kgs.
of old scoria, mixed with 6 per cent, of charcoal, is put in; and,
finally, when the burning is thorough and the furnace is hot, a
charge of 50 kgs. of ore (containing about 15 to 20 per cent.
Sb) mixed with 2 kgs. of charcoal is put in, and this is continued
until the furnace is full to within 30 centimetres from the mouth.
The same charge is continued every 12 to 14 minutes, according to
the rate of revolution of the ventilators—which is from 1200 to 1400
revolutions per minute—and the scoria is discharged accordingly.
Gas coke gives better results, if it is obtainable; and, if it is used,
only 2 to 6 per cent., or 1 to 3 kgs. for every 50 kgs. of the same
class of ore, are necessary, according to the richness of the ore
roasted.
The temperature of roasting should not be more than 400° C.
Water used per day for one apparatus is 30 cubic metres.
(4) Results of the Experiments, (a) First Experiment.—The furnace
was lighted at 8.30 a.m. on the 24th of April, and it was not until
10.5 a.m. that the furnace was hot enough to admit the first charge.
The working was continued- regularly until 11 p.m. of the same
day; the total working time was therefore 12 hours 55 minutes.
The charging was as follows :—Each charge consisted of 50 kgs.
of ore, minus the ore dust, which had previously been sieved off.
The first three charges were mixed with 10 per cent, of charcoal,
the fourth-to the tenth charges with 4 per cent., the eleventh to the
nineteenth with 2 per cent., and from the nineteenth to the last
with 4 per cent. The total charges amounted to 2850 kgs. of ore.