antimony - Sciencemadness.org

116 THE METALLURGY OF ANTIMONY.
moulds used in the previous fusion; the matte and skimmings are
added to subsequent smeltings of ore.
The metal thus obtained is known as " star bowls," and contains
99*53 per cent, antimony, 0*18 per cent, iron, 0*16 per cent,
sulphur. The presence of sulphur, due to the excess of sulphide
used, is indicated by the crystalline pattern being covered
over with small glistening patches; this appearance is known
as "flouring."
In order to remove this sulphur another fusion is necessary. The
custom of the trade is to sell antimony as " starred " or crystallised
on the upper surface, and therefore it is necessary to obtain this star
on the surface. These two results are achieved by melting the metal
with a peculiar flux known as the " antimony flux," a substance not
easily prepared, and one which is often difficult to obtain at first; but
once obtained, its subsequent production is easy. The process of
making this flux is a rule-of-thumb one, and is carried out thus:—
Three parts of ordinary American potash are melted in a crucible,
and two parts of ground liquated sulphide of antimony are mixed in.
When the mixture is complete and the fusion has become quiet, the
mass is poured out and tried on a small scale in order to find out
whether it yields a good, "star"; if it does, the ingot of metal
obtained is broken and the metal then examined, in order to judge
whether it is free from sulphur. But if not, the flux is remelted
and more of one ingredient or the other is added, as experience
dictates.
The consumption of coal per week is 22 tons, or 1 £ tons per shift
of twelve hours. About eleven crucibles are used per ton of antimony
produced. The loss amounts to 10 per cent., due to volatilisation.
The yield of such furnace, for ore containing 52 per cent, antimony,
is 14 J tons per week.
The fume given off is collected in condensing chambers. It is
whitish in colour, heavy and crystalline, appearing like arsenic, and
contains 70 to 72£ per cent, of metallic antimony.
The smelting of this fume is thus carried out:—A test experiment
is made in order to ascertain the amount of carbon,, in the form of
coke or anthracite, necessary to reduce all the antimony present in
the fume. This having been found, the fume is mixed by grinding
it under edge-runners with the proper quantity of carbonaceous
matter.; a few pounds of the mixture so produced are added to each
charge of ore and iron required in smelting for singles. As the
gases given off in the process are apt to cause the mixture in the
pots to overflow, the "boiling ore" is looked upon with disfavour