If potassium oxalate is added to a solution of the trichloride, the
antimony may be readily reduced, but the metal adheres still less firmly
to the electrode than it did in the first instance. An adherent coating
may be obtained by adding an alkaline tartrate, but in that case the
separation takes place too slowly. The precipitation of antimony may be
very readily effected from solutions of its sulpho salts.
To a liquid, which may contain free hydrochloric acid, hydrogen sulphide
is added, then neutralized with ammonium hydrate, and saturated with
ammonium sulphide in excess. The reduction may be accelerated by the
addition of some ammonium sulphate. The antimony separates out as a
fine, light gray precipitate on the electrode, and which adheres very
firmly, provided the precipitation has not been carried on too rapidly,
_i. e._, if the current employed for the reduction was not too strong.
When the reduction has been completed, the supernatant liquid is poured
off, and the residue washed in the ordinary manner.
DETERMINATION OF ARSENIC.
Arsenic cannot be completely separated from either its aqueous
hydrochloric acid, or from a solution to which ammonium oxalate has been
added in excess. From its aqueous as well as from its oxalate solution,
a portion of the metal may be separated, but if the current is passed
through its hydrochloric acid solution for a sufficient length of time,
all the arsenic will be volatilized as arsenious hydride (AsH_3).
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