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

114 THE METALLURGY OF ANTIMONY.
been found by experiment that, with 10 per cent, of Glauber salt
and 2 to 3 per cent, of coal, 44 per cent, of iron is required;
whereas Liebig states that 42 per cent, is sufficient, while Hering
uses only 40 per cent. The following proportions are given by
Berthier: —Antimony sulphide, 100 \ forge scale, 60 ; soda, 45 to 50 ;
coal dust, 10. Iron separates out as FeS, or as Fe8Sr according to
Schweder.
In England, where the ores used are free from the impurities of lead
and arsenic, iron is generally used in excess, part being afterwards
eliminated by a subsequent fusion with more sulphide of antimony.
The loss of antimony occasioned during the process is due to
volatilisation and slagging: 64 per cent, is the yield, as given by
Karsten, when crucibles are used; but Berthier gives 65 to 67 per
cent.; whereas, theoretically, the yield should be 71*5 per cent.
This process is generally carried out in crucible furnaces, as adopted
in England, Hungary, and other places; but shaft furnaces have been
used experimentally \ reverberatory furnaces are sometimes used, in
spite of the great loss of antimony.
The English process "* of smelting is as follows :—
The ores for smelting must be free from lead and arsenic. The
ore is ground under edge runners and passed through a coarse screen,
the largest to pass through being the size of a hazel-nut. After grinding,
a sample is taken to be assayed for the amount of iron. The process
consists in reducing the sulphide by metallic iron in crucibles in
a long reverberatory furnace. The dimensions of the furnace are : 54
feet long, including the fireplaces, 7 feet 4 inches broad (inside size),
covered by a low arch which springs almost from the surface of the
ground, the bed itself being below the ground level. It is heated by
a fireplace at each end, communicating into a common flue in the
middle of the floor of the furnace. The crucibles are lowered into
their places through circular holes (14 inches in diameter) in the arch.
There are forty-two holes, twenty-one on each side. There are two
4-inch holes in the furnace roof at each end of the bed, used for the
removal of clinkers, etc. The sides and roof of the furnace are covered
with cast-iron plates. The pair of crucibles nearest the fireplaces at
each end is kept for "starring" or refining the crude metal. The
charge for each crucible is : 42 lbs. of ground ore, containing about 50
per cent, of antimony, 16 lbs. of iron, 4 lbs. of common salt, and 1 lb.
of skimmings from the next operation, or else the same weight of
impure slag from a previous melting. The iron usually consists of
* Taken from " Antimony, " by Professor Kemp, The Mineral Industry, 1892,
p. 23.