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

132 THE METALLURGY OF ANTIMONY.
The crucibles were made of fire-clay, and could stand five or six
charges each, each charge being 48*5 lbs. of impure antimony.
To each charge were added 13 to 17 lbs. of flux, which was a
mixture of sulphate and carbonate of soda, with a little salt
and pure oxidised antimony ores. The fusion lasted six hours,
with a consumption of 450 to 550 lbs. of coal. A low red heat
is necessary.
In England the process of refining and restarring the star-bowls
is as follows : —The lumps of metal, when cold, are removed from the
mould and are thoroughly cleaned from the adhering skin of slag by
chipping with sharp hammers, this part of the work being sometimes
done by women. Unless this cleaning process is carefully done, it is
well-nigh impossible to obtain good stars on the finished metal. The
chippings are returned to the second smelting. Having been cleaned,
the star-bowls are broken small. The charge made is about 84 lbs.,
together with enough flux to surround the ingots completely; the
quantity is generally 8 lbs. for ingots of the ordinary shape. The
melting takes place in the crucibles standing close to the fireplaces,
where the fusion is most rapid. The metal is charged first and is
closely watched; as soon as it begins to melt, the flux is added;
and as soon as the fusion appears to be complete the furnace-man
stirs the mixture once round only with an iron rod, and the charge
is then poured out. The flux is used over and over again, being
regenerated by the addition of carbonate of potash. The ingots
must be completely surrounded by the flux; there must be a thin
layer of it between the mould and the metal, and also the whole
surface of the ingot must be covered by the flux to a depth of
a quarter of an inch. Any traces of the flux still adhering to the
ingot are removed by washing in warm water, with the assistance
of a little sharp sand.
For a charge of 60 to 70 lba. of bowl-metal, with 1 to 2 lbs.
American potash and 10 lbs. of slag, obtained from a previous
charge of French metal, the time required is three-quarters of
an hour.
The slag obtained shows whether the operation is complete or not.
It should be smooth and of a deep black colour.
The process of refining as practised in Tuscany is as follows :—The
broken-up impure metal is mixed with one-eighth by weight of carbonate
of soda, and one-sixth by weight of sulphide of antimony.
This mixture is placed in a Hesse crucible. The metallic button
thus obtained is again fused with carbonate of soda and a little
nitrate of potash.