tri-iodide.

The atomic weight of antimony has been determined by the analysis of the
chloride, bromide and iodide. J.P. Cooke (_Proc. Amer. Acad._, 1878,
xiii. i) and J. Bongartz (_Berichte_, 1883, 16, p. 1942) obtained the
value 120, whilst F. Pfeiffer (_Ann. Chim. et Phys._ ccix. 173) obtained
the value 121 from the electrolysis of the chloride.

Pure antimony is quite permanent in air at ordinary temperatures, but
when heated in air or oxygen it burns, forming the trioxide. It
decomposes steam at a red heat, and burns (especially when finely
powdered) in chlorine. Dilute hydrochloric acid is without action on it,
but on warming with the concentrated acid, antimony trichloride is
formed; it dissolves in warm concentrated sulphuric acid, the sulphate
Sb2(SO4)3 being formed. Nitric acid oxidizes antimony either to the
trioxide Sb4O6 or the pentoxide Sb2O5, the product obtained depending on
the temperature and concentration of the acid. It combines directly with
sulphur and phosphorus, and is readily oxidized when heated with
metallic oxides (such as litharge, mercuric oxide, manganese dioxide,
&c.). Antimony and its salts may be readily detected by the orange
precipitate of antimony sulphide which is produced when sulphuretted
hydrogen is passed through their acid solutions, and also by the Marsh
test (see ARSENIC); in this latter case the black stain produced is not
soluble in bleaching powder solution. Antimony compounds when heated on
charcoal with sodium carbonate in the reducing flame give brittle beads
of metallic antimony, and a white incrustation of the oxide. The
antimonious compounds are decomposed on addition of water, with
formation of basic salts.

Antimony may be estimated quantitatively by conversion into the
sulphide; the precipitate obtained is dried at 100 deg. C. and heated in
a current of carbon dioxide, or it may be converted into the tetroxide
by nitric acid.

Antimony, like phosphorus and arsenic, combines directly with hydrogen.
The compound formed, antimoniuretted hydrogen or stibine, SbH3, may also
be prepared by the action of hydrochloric acid on an alloy of antimony
and zinc, or by the action of nascent hydrogen on antimony compounds. As
prepared by these methods it contains a relatively large amount of
hydrogen, from which it can be freed by passing through a tube immersed
in liquid air, when it condenses to a white solid. It is a poisonous
colourless gas, with a characteristic offensiv