antimony - Sciencemadness.org

THE ANALYSIS OF ANTIMONY COMPOUNDS. 183
and carbon bisulphide, (4) with alcohol alone, and (5) with ether.
Dry the precipitate by warming it slightly. Remove as much
precipitate as possible from the niter on to a watch-glass, and use
hot ammonium sulphide to dissolve the remaining portion upon the
filter-paper, which is then evaporated to dryness in a weighed crucible.
The main part of the precipitate is then added to the crucible. Pass
fuming nitric acid into the crucible covered with a watch-glass.
After the first violent action is over, the crucible is heated in a
water-bath until the evolution of gas has entirely ceased. Eemove
the watch-glass and evaporate the contents of the crucible to dryness.
In order to oxidise all the sulphur, this operation is repeated. The
H2SO4 formed is eventually driven off by carefuj heating over a free
flame. The open crucible is placed in the opening of an inclined
disc of asbestos board, and the temperature is gradually increased
until the full heat of the Teclu burner is obtained.
(y) Estimation of Antimony in Native Sulphide of Antimony, according
to Crookes.—The mineral is powdered, and 20 grains of it are
taken. They are treated with a slight excess of HC1, and the mixture
is gently heated until the H2S has completely evaporated. The
solution is then filtered, and the filter is washed with dilute HCL
The solution is then slowly evaporated in the flask until it is concentrated
enough and freed from the excess of HCL The antimonv is
now in the form of trichloride. A newly prepared solution of gallic
acid is carefully added to a slight excess. Hot water is next added,
and the precipitate of antimony bigallate is washed, dried, and
weighed. The filtrate can be tested for iron, lead, copper, silver,
arsenic, and, sometimes, zinc, cobalt and other metals remaining
in solution. As iron is difficult of complete separation in the
presence of gallic acid, other well-known methods are used for its
determination.
According to Mr L. Parry, the determination of antimony by the
gravimetric method, especially if estimated as SbOo, is quite
unreliable.
(h) VoluTnetric.—(a) Mohr's Method*—Conversion of antimonious
acid in alkaline solution into antimonic acid by iodine.
Antimonious oxide, or any of its compounds, is dissolved in tartaric
acid and water ; sodium carbonate is used to neutralise any excess of
the acid used ; then a cold saturated solution of sodium bicarbonate
is added in the proportion of 10 c.c. to about 0*1 gramme SboOs; to
the clear solution starch is added, and ^ iodine until the blue colour
appears. This operation must be done quickly, as when the bicar-
* This is a useful method "when copper is absent..