Thallous chloride, T1C1, is readily obtained from the solution of any thallous salt, by the addition of hydrochloric acid, as a white precipitate similar in appearance to silver chloride, like which it turns violet in the light and fuses below redness into a (yellow) liquid which freezes into a horn-like flexible mass. It is also formed when the metal is burnt in chlorine. One part of the precipitated chloride dissolves at o° C in 500 parts of water, and in 4o parts at oo° C. It is less soluble in dilute hydro chloric acid. Thallous iodide, T1I, similarly obtained as a yellow precipitate, requires 16,000 parts of cold water for its solution. The yellow crystals melt at 190°, and when cooled assume a red colour, which changes to the original yellow on standing. Thallous bromide, T1Br, is a light yellow crystalline powder; it is formed analogously to the chloride. Thallous Perchlorate, T1C104, and periodate, are interesting inasmuch as they, together with several other thallous salts, are isomorphous with the correspond ing potassium salts. • Thallous carbonate, T12CO3, more nearly resembles the lithium compound than any other ordinary carbonate. It is produced by the exposure of thallous hydrate to carbon dioxide, and therefore is obtained when the moist metal is exposed to the air. It forms resplendent monoclinic prisms, soluble in water. The bicarbonate is not known.
Thallous sulphate, T12SO4, forms rhombic prisms soluble in water, which melt at a red heat with decomposition, sulphur dioxide being evolved. It unites with aluminium, chromium and iron sulphates to form "alums" (q.v.). It also forms double salts of the type Fe or Zn)SO4.6H20. Thallous sulphide, is obtained as a black precipitate by passing sulphuretted hydrogen into a thallous solution. It is insoluble in water and in the alkalis, but readily dissolves in the mineral acids.
Thallous nitrate, is obtained as white, rhombic prisms by crystallizing a solution of the metal, oxide, carbonate, etc., in
nitric acid. Various thallous phosphates are known, e.g., T14P207, etc. ; they bear a close resemblance to the corresponding phosphates of the alkali metals.
Thallic chloride, is obtained by heating the monochloride with chlorine under pressure, or by saturating a suspension of the monochloride in water with chlorine ; when anhydrous it is a crystalline mass which melts at It forms several double salts, e.g., with hydrochloric acid and the alkaline chlorides. The chlorine is not completely precipitated by silver nitrate in nitric acid solution, the ionization apparently not proceeding to all the chlorine atoms. The mixed chlorides and are also produced by the regulated action of chlorine on the mono chloride. Thallic iodide, is interesting on account of its isomorphism with rubidium and caesium tri-iodides, a resemblance which suggests the formula for the salt, but T. M. Lowry and A. J. Berry (1928) have shown that it does not give the reactions of a thallous salt, and, when dissolved in methyl alcohol, it behaves as a binary electrolyte, i.e., as or as Tl Thallic and thallic nitrate, are obtained as colourless crystals on the evapora tion of a solution of the oxide in the corresponding acid. The sulphate decomposes into sulphuric acid and the trioxide on warming with water, and differs from aluminium sulphate in not forming alums.
Thallium salts are used in the manufacture of certain optical glasses on account of the high refractive index conferred on the glass. They are all poisonous, having an action somewhat re sembling that of lead salts, and are said to have a pronounced depilatory action, but this has also been denied.
Thallous acetylacetone, prepared from an alcoholic solution of acetylacetone and the hydroxide, is of interest. On the application of thallium compounds to organic syntheses, see R. C. Menzies, I. Chem. Soc., 1924, et seq.