Thallium forms two series of salts: thallous, in which the metal is monovalent; and thallic, in which it is trivalent.
In the thallous series many analogies with lead compounds are observed; in the thallic some resemblance to aluminium and gold.
Thallous hydroxide, T10H, is most conveniently prepared by decomposing the solution of the sulphate with baryta water.
769) by acting with hydrogen peroxide on an alkaline solution of thallous sulphate at low temperatures, an initial red precipitate rapidly changing into a bluish-black compound.
It melts at 720° and decomposes rapidly above 800°, giving oxygen and thallous oxide.
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.
Thallous iodide, T11, is obtained as a yellow precipitate, which requires 16,000 parts of cold water for its solution, by the addition of potassium iodide to a solution of a thallous salt, or by the direct union of its components.
Thallous bromide, TIBr, is a light yellow crystalline powder; it is formed analogously to the chloride.
Thallous fluoride, T1F, forms white glistening octahedra; it is obtained by crystallizing a solution of the carbonate in hydrofluoric acid.
Thallous chloroplatinate, T1 2 PtC1 6, readily obtainable from thallous salt solutions by addition of platinum chloride, is a yellow precipitate soluble in no less than 15,600 parts of cold water.
Thallous Perchlorate, T1C10 4, and periodate, Tl10 4, are interesting inasmuch as they are isomorphous with the corresponding potassium salts.
Other instances of the isomorphism of thallous with potassium salts are the nitrates, phosphates, hydrazoates, sulphates, chromates, selenates, and the analogously constituted double salts, and also the oxalates, racemates and picrates.
Thallous carbonate, T1 2 CO 31 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.
Thallous sulphate, T1 2 SO 4, forms rhombic prisms, soluble in water, which melt at a red heat with decomposition, sulphur dioxide being evolved.
Thallous sulphide, T1 2 S, is obtained as a black precipitate by passing sulphuretted hydrogen into a thallous solution.
Thallous nitrate, T1NO 31 is obtained as white, rhombic prisms by crystallizing a solution of the metal, oxide, carbonate, &c., in nitric acid.
Various thallous phosphates are known.
On thallous salts see W.
Thallic hydroxide, TI(OH) 31 is obtained as a brown precipitate by adding a hot solution of thallous chloride in sodium carbonate to a solution of sodium hypochlorite.
Hydrochloric acid gives thallous chloride and chlorine; sulphuric acid gives off oxygen; and on heating it first gives the trioxide and afterwards the monoxide.
By heating the metal or thallous chloride in chlorine, T1C1 T1C1 3 is obtained, which on further heating gives3TlCI.T1C13.
From solutions containing it as thallous salt the metal is easily precipitated as chloride, iodide, or chloroplatinate by the corresponding reagents.
Thallic salts are easily reduced to thallous by means of solution of sulphurous acid, and thus rendered amenable to the above reactions.
Many are readily soluble in water, the chief exceptions being silver chloride, mercurous chloride, cuprous chloride and palladious chloride which are insoluble in water, and thallous chloride and lead chloride which are only slightly soluble in cold water, but are readily soluble in hot water.