antimony - Sciencemadness.org

130 THE METALLURGY OF ANTIMONY.
into a compound of antimonious and antimonic acids, the greater part
of which would remain undissolved in the tartaric acid. A sublimate
of arsenious acid, treated in this manner, would, of course,
yield a yellow precipitate, easily distinguishable by its colour, however,
from the deep-orange antimonial sulphide. The crystalline character,
etc., of this sublimate would also effectually prevent any chance of
misconception.
"(y) Dr A. Weller proceeds as follows for the estimation of
antimony :—Antimonic acid and antimonic oxide, and in like manner
antimony penta- and tri-chloride, can be most easily distinguished
from each other by their different behaviour with potassium iodide.
The property of the former, when in hydrochloric solution, of
separating two atoms of iodine from potassium iodide for each atom of
antimony can be used for the qualitative estimation of antimony. In
order to verify this method, weighed quantities of finely pulverised
pure metallic antimony are oxidised in a flask at a gentle heat with
potassium chlorate and hydrochloric acid, and the excess of chlorine
is expelled by strong heating. The solution of antimony pentachloride
thus obtained is introduced into the flask of Bunsen's chlorine
distillation apparatus by means of hydrochloric acid, considerably
diluted and mixed with a sufficiency of perfectly pure potassium
iodide, avoiding too great an excess. The liberated iodine is distilled
into dilute 'solution of potassium iodide, observing all the precautions
laid down by Bunsen, and especially cooling the retort well in flowing
water. When cold the distillate is titrated in the usual manngr by
means of very dilute sulphurous acid and an iodine solution of known
strength. The distillation requires from five to ten minutes.
Particularly important is the fact that stannic acid and stannic
chloride in acid solutions do not decompose potassium iodide. This
behaviour renders it possible to estimate antimony in presence of
tin, as in alloys, easily and accurately. The tin is calculated as
difference."
The detection of the impurities accompanying the sulphide can be
made thus:—The mineral is pulverised and is heated with concentrated
hydrochloric acid, until all of it enters into solution. The
lead will separate out in the form of lead chloride, upon the cooling
of the liquid. Water added to the clear supernatant liquid will
cause the precipitation of antimony oxychloride (SbOCl), a white
powder, while iron and copper remain in solution. Copper may be
detected by the blue coloration when a few drops of ammonia are
added to the filtrate, while the presence of iron may be proven by
the addition of a solution of potassium ferrocyanide.