BISMUTH TRIBROMIDE. 77j
first, and should be driven off by playing a second flame over the
neck of the retort (Hood); then the bismuth tri-iodide sublimes
and condenses in the form of a shower of crystalline spangles.
Collect these in a porcelain evaporating dish which is placed so
that the neck of the retort rests in its lip. Cover the dish with a
watch-glass, and protect the space still left open with some asbestos
paper cut to the proper shape.
On standing, bismuth iodide decomposes rather easily with
liberation of iodine.
Basic Bismuth Iodide, BiOI. Triturate 10 g. of bismuth tri-
iodide in a mortar with water, and decant off the liquid together
with the finest powder into a beaker; treat the residue with
another portion of water in exactly the same way, and continue
the treatment until all of the material is obtained in a state of
finest subdivision with from 200 to 400 c.c. of water. Boil the
mixture for an hour or two, collect the product of hydrolysis on a
suction filter, wash it with water, and dry it in the hot closet.
Small, light-brown to red crystal leaflets are obtained which are
somewhat lighter colored than red phosphorus. Yield, about 7.5 g.
The hydrolysis of the iodide, which is difficultly soluble in water, takes
place more slowly than that of the more soluble chloride, an indication that
such interactions of a solid substance under a liquid do not take place with
the solid itself, but involve rather only that part of the substance which exists,
at the moment, in solution.
- Bismuth Tribromide.
A mixture of powdered bismuth and bromine reacts only slowly and in-
completely in the cold, but with almost explosive violence when heated. The
simplest way to prepare bismuth tribromide is to pass bromine vapors over
heated bismuth.
The apparatus employed is similar to that used in the prepara-
tion of ferric chloride (No. 42). The neck of a tubulated retort,
of from 100 to 150 c.c. capacity, is bent downward a little, near
the bulb, and a little farther away it is bent upward (cf. Fig. 15).
Introduce 10 to 15 g. of bismuth in the depression of the neck,
and connect the end of the latter with a wash bottle containing
bromine, through which dry carbon dioxide is to be passed in the
direction of the retort.
1
Through the tubulus of the retort in-
1
Instead of conducting bromine diluted with carbon dioxide over the
bismuth, the pure vapors may be distilled from a second smaller retort. The
reaction then takes place more rapidly, but requires more attention.