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

136 THE METALLURGY OF ANTIMONY.
At Banya the data are:—
Charge for the furnace, impure antimony (high grade, Sb = 9O per cent.) 990 lbs.
» (low grade, Sb = 74 „ ) 110 „
Sodium sulphate added 92-6,,
Powdered charcoal . . . . . . • • . . 11 ,,
Raw ore . . . 330 ,,
After ten hours the slag is drawn off, and the materials to form the
star slag are added :—2*2 lbs. of crude antimony, 13*2 lbs of roasted
sulphide of antimony, 7 # 5 lbs. of potash, and 5*7 lbs. of soda ash. The
following gives the analysis of the impurities found in the refined
star antimony thus obtained :—
Arsenic 0*330 per cent.
Iron 0-052 ,,
Silver 0'006 ,,
Sulphur . . . . . 0720 ,,
Total . . . 1*108
At Siena, where the unrefined metal is less impure, the following
shows the proportions in 260 charges:—
Unrefined metal . . . . 115,255 lbs.
Salt 27,229 ,,
Roasted ore . . . . ' . 767 „
Refinery slag 12,549 ,,
Refined antimony obtained, 107,697 lbs., which is equal to 93-5 per
cent.
Antimony contains small quantities of iron, lead, sulphur, arsenic,
etc., as impurities.
In order to produce an almost absolutely pure antimony, Liebig's
process may be used. Mix powdered antimony with one-eighth of its
weight of carbonate of sodium and one-sixteenth of its weight of
sulphide of antimony, and heat the mixture in a Hesse crucible. The
button thus obtained is submitted to another fusion with carbonate of
sodium only for two hours, and to a third fusion with a mixture of
carbonate of sodium to which a small quantity of potassium nitrate has
been added. In these operations the sulphur of the antimony sulphide
transforms the foreign metals present, except lead, into sulphides,
which remain in solution in the scoria; the arsenic compounds pass
in part to the sulpho-arsenate of soda and in part to the state of
arsenate. The addition of potassium nitrate removes the last trace
of arsenic by .converting it into arsenate of soda.
The Products of Kenning.-—The products of refining are refined
antimony, slag and star slag.