72 ACIDS AND BASES.
Compt. rend. 110, 784 (1890)). Dependent preparations: Cupric
Bromide (No. 37), Ammonium Tribromide (No. 69), Hexammine
Nickelous Bromide (No. 128), Praseocobalt Bromide (No. 135).- Thallous and Thallic Hydroxides.
Thallium in thallous halides and in thallous sulphide shows unmistakable
similarity to silver and lead: in thallous hydroxide and in the thallous double
salts, it appears like an alkali metal. In the tervalent thallic compounds,
thallium is similar to aluminium quite in accordance with its position in the
periodic classification.
Mix 13.3 g. of thallous nitrate
1
(1/20 mol.) and 3 g. concentratedsulphuric acid in a platinum crucible, and drive off the volatile
acid slowly by heating the upper edge of the crucible with a
Bunsen burner which is held in the hand and moved about so as
to avoid spattering. The decomposition is complete when the
contents of the crucible no longer give off acid vapors. Dissolve
the thallous sulphate thus prepared in 50 c.c. of water, and pre-
cipitate barium sulphate from the boiling solution by adding a
hot solution of 8 g. crystallized barium hydroxide, the amount
of the latter reagent being slightly in excess of that theoretic-
ally required. After filtering, precipitate the excess of barium
hydroxide by the careful addition of very dilute sulphuric acid.
A drop of the solution should not, at the last, give a precipitate
either with barium hydroxide or with sulphuric acid. Evaporate
the solution to a volume of about 25 c.c, filter again and then
evaporate to about 5 c.c, after which, place the evaporating dish
in a desiccator over dry lime. Suck the crystals of thallous
hydroxide free from liquid in a small filter funnel and obtain a
second crop by further evaporation of the mother liquor. Neu-
tralize the last mother liquor with nitric acid, and use the resulting
solution of thallous nitrate for the reaction described below.
(^1) In order to obtain thallous nitrate from metallic thallium, cut the latter
into small pieces and dissolve them in the calculated amount of dilute nitric
acid. Introduce hydrogen sulphide into the hot, slightly acid solution to
remove lead as sulphide, and evaporate the filtrate until the nitrate crystallizes
out. Drain the crystals with suction, and evaporate the mother liquor to-
gether with the wash-water for more crystals. Yield, theoretical. F. Foerster
(Z. anorg. Chem. 15, 71 (1897)) shows how thallium can be recovered from the
flue gas of pyrite burners.