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

THE METALLURGY OF ANTIMONY. 135
obtained in the form of crusts, formed in the hottest part of the
chimney.
According to Helmhacker, the refining process is as follows :—
Twelve hundred to 1500 lbs. of impure antimony are charged into
the furnace, previously heated to a red heat. As soon as the metal
is melted, generally in less than half an hour, 3 to 7 per cent,
of soda, with which is mixed a little coke-dust or fine charcoal, is
added, according to the purity of the metal. After this the heat is
raised to bright redness in order to fuse the soda. During the
charging and the fusion, vapour of antimonious and arsenious oxides
is given off.
The slag gradually becomes thicker and thicker, and consequently,
after about three hours, the bubbles, which at first were numerous,
rise very slowly through the slag. The slag is then very carefully
skimmed off through the working door.
Up to this point the iron and sulphur persist as impurities in
the metal. They are removed by adding ingredients capable of
forming antimony glass, such as oxysulphide of antimony. For each
100 lbs. of antimony in the charge, 3 lbs. of liquated sulphide of
antimony and 1^ lbs. of antimony tetroxide are thrown in, and, as
soon as these are fused, 4^ lbs. more of potash or white flux are added.
Care must be taken that the bath of metal is completely covered
with the fluxes.
The metal can be ladled out at the end of a quarter of an hour,
but this must be done cautiously, in order to secure the starred
appearance of the ingots. When cold, the slag covering the ingots
can be broken off by means of a hammer.
Three charges of 1300 to 1500 lbs. each can be refined in one of
these furnaces in twenty-four hours, with a consumption of 1300 lbs.
of coal.
The slag obtained in the final process of refining is called star slag,
which consists principally of antimony glass, and contains from 20
to 60 per cent, of antimony; it is generally used over again for
refining. When it becomes too impure for this purpose, it is charged
along with the ore for the first smelting. The other slags obtained
in the course of refining are also added to the charges of ore for
smelting. The impurities found in the star slag are sulphides of iron
and nickel, iron oxides and silica.
The loss due to volatilisation amounts to 20-30 per cent. Tho
flue dust consists principally of the trioxide and tetroxide. , The cost
of refining is said to be 2£ to 3 marks per 100 kilos, (i.e. Is. 3d.
to Is. 7d. per cwt.).