Thallothallic cyanide, TlCN.Tl(CN)₃

Thallothallic cyanide, TlCN.Tl(CN)₃, is prepared by dissolving thallic oxide in aqueous prussic acid, and crystallises from the solution in colourless, orthorhombic crystals. One hundred grams of water dissolve 9.75, 15.29, and 27.31 of the salt at 0°, 12°, and 30° respectively, giving a neutral solution in which the salt is probably dissociated into the ions Tl^• and Tl(CN)₄'. From the cold, aqueous solution, alkalies precipitate thallic hydroxide, but no precipitate is produced by ammonia. At 125° to 130° the salt melts and decomposes.