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

18 THE METALLURGY OF ANTIMONY.
counteract this effect, bisulphide of carbon is used. The solution is
then dibtilled, producing the tribromide, which can be purified by
sublimation. Obtained in this way, it is a colourless crystalline
mass, though crystals belonging to the rhombic system can be formed
from a solution of bisulphide of carbon. The specific gravity of the
solid mass is 4*148 at 23°. It melts at from 90° to 94°, forming a
liquid having a specific gravity of 3*641. Its molecular volume is
116*8 (Kopjf). The boiling-point is 275*4°, and the specific density
of its vapour is 12*57 (Worcester).
Its chemical properties are analogous to those of the trichloride.
It absorbs water from the moisture of the air, and in water it
changes into an oxybromide.
The complex salts are:—
2SbBr3.3RbBr, 10SbBrs.23RbBr (IVheel&r),
and the yellow ammonium salts are:—
3SbBr3.7NH4Br, 2SbBr3.3NH4Br [Caven).
Antimony Tri-iodide can be best obtained by putting the pulverised
metal in a solution of iodine in bisulphide of carbon with
a slight excess of the metal. The medium used is then distilled off,
and the product thus obtained is purified by sublimation (Nickles).
The reaction will be very energetic and violent if bisulphide of carbon
is not used. The powder must also be added in small quantity at a
time.
The solid tri-iodide has been observed to possess three allotropic
modifications, the relationship of which, one to another, is not yet
known. The stable form, crystallising in the hexagonal system, is
obtained by sublimation at a temperature over 114°. It can also be
obtained from a diluted solution. It is red, and its specific gravity
is 4*848 at 26°. It is isomorphic with bismuth iodide. The metastable
form, crystallising in the monoclinic system, is obtained by
allowing the carbon bisulphide solution to be evaporated in sunshine.
It is red, and its specific gravity is 4*768 at 220°. The most unstable
of the three is the greenish-yellow rhombic form, which is obtained
through sublimation at a low temperature. At higher temperatures
the two unstable forms change to the stable modification.
The melting-point of the stable form is 167°. The liquid is garnet
red and boils at 401°, forming a red vapour, the specific density of
which is 17*59, the theoretical one being 17*33.
The tri-iodide is soluble in carbon bisulphide, alcohol, and benzol
It is changed to the sulphate in sulphuric acid.