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

190 THE METALLURGY OF ANTIMONY.
1 litre; then 1 c.c. =0*010 grm. silver, and 108 silver = 25 arsenic.
This same treatment, somewhat modified, is used in testing the ore
qualitatively for arsenic. After fusion, the addition of acid, boiling,
and the addition of zinc oxide in excess, the whole is filtered, and the
neutral filtrate tested for arsenic as before.
Ores are divided into three classes: (1) the soluble ores, such as
stibnite; (2) the practically insoluble ores, such as cervantite; (3)
the partially soluble ores, as oxysulphides (stibnite mixed with cervantite).
Ores of the first class are thus treated:—1 grm. of the
finely ground ore is treated in a No. 3 beaker with 25 c.c. of concentrated
HC1, covered and boiled until apparently decomposed and the
solution does not occupy more than 15 c.c. in bulk. About 2 grms.
of tartaric acid are added, and as soon as these are dissolved from 4
to 6 drops of concentrated HN03 are also added, and the whole boiled
for a short period. On cooling and diluting, H2S is passed through
for about an hour, and the Sb precipitated as sulphide. After warming
slightly, it is allowed to stand in the cool for an hour or more and
then filtered. These precautions having been attended to, no more
Sb will be precipitated either on standing or passing additional H2S.
If lead or other metals of the fifth group have been found, it may be
necessary to dissolve the precipitate in excess of ammonium sulphide.
The antimony is again precipitated as before. The precipitate, in
any case, is well washed, and dried in an air-bath at 110° C. to constant
weight. As the precipitate contains a certain amount of fre#
sulphur, it is necessary to determine the amount of black anhydrous
antimonious sulphide it contains. This is done by weighing a certain
amount of the precipitate into a platinum boat, which is placed
in a combustion tube and the free sulphur driven off in a stream
of CO2.
The insoluble ores,* are best treated by fusion with a flux composed
of equal parts of flower of sulphur and sodium carbonate. One
gramme of ore is used to eight or more parts of the mixed flux. The
mixture is put in a crucible of 40 c.c. capacity, covered with a portion
•df flux, placed in the muffle, and heated cautiously to fusion, which
takes place in about ten minutes. Many precautions have to be observed,
as it is very difficult to fuse the readily volatile antimony, even
at a low heat, without loss. The mass, when fused, is dissolved in
hot water, and the solution, which contains the antimony, filtered off
* A. Chippendale (JSng. and Mln. Journal, May 12, 1900) recommends the use
of potassium-iodide, to be added occasionally to the boiling concentrated HC1 solution
containing the oxide ores. When dissolved, the antimony may be determined
by the usual methods.