Thallous carbonate, Tl₂CO₃

Thallous carbonate, Tl₂CO₃, is obtained by passing carbon dioxide into thallous hydroxide solution, by exposing granulated thallium to warm air for some time and then heating it with ammonium carbonate solution, or by shaking and heating barium carbonate with thallous sulphate solution. The carbonate crystallises from water in colourless, glittering, monoclinic prisms (a:b:c = 1.3956:1:1.9586; β = 94°47') of specific gravity 7.164, melts at 273°, and at high temperatures loses carbon dioxide. The carbonate is insoluble in alcohol; 100 grams of water dissolve the following amounts of the salt (Lamy, Crookes): -

Temperature, °C.	15.5°	18°	62°	100.8°
Grams of Tl2CO3	4.02	5.23	12.9	22.4

The solution has a caustic taste and an alkaline reaction.

An acid carbonate is not known in the pure state, in spite of various attempts to prepare it. A basic carbonate has been described.