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THORIUM (symbol Th, atomic weight ,23...

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Originally appearing in Volume V26, Page 879 of the 1911 Encyclopedia Britannica.
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THORIUM (See also:symbol Th, atomic See also:weight ,232.42 [0=16]) , a metallic chemical See also:element. It belongs to the See also:group of metals whose oxides are generally denominated " rare earths," and its See also:history is See also:bound up in the history of the group, which is especially interesting from the fact that it supplies the material for the manufacture of the mantles used in incandescent See also:gas-See also:lighting, and also that the radio-active substances are almost invariably associated with these oxides. The name thoria (after the Scandinavian See also:god See also:Thor) was first given in 1815 by See also:Berzelius to a supposed new See also:earth which he had extracted from several rare See also:Swedish minerals. This " new earth " turned out. to be nothing more nor less than a basis See also:yttrium phosphate. In 1828 he gave the name thoria to an earth which he extracted from a See also:mineral found at Leron. This mineral is the See also:modern See also:thorite. Thorium has proved to be very widely, although extremely sparingly, distributed: pyrochlor, orangite, See also:monazite, euxenite, gadolonite, orthite, and in fact most of the rare minerals of this type contain it (see B. Szilard, Le Rddium, sgog, 6, p. 233). The extraction of thorium salts from these minerals is a See also:matter of much tedium. Metallic thorium is obtained by See also:heating See also:potassium thorium chloride or the tetrachloride with See also:sodium (see W. von See also:Bolton, R. J.

See also:

Meyer and H. Karstens, Journ. Chem. See also:Soc., 1909, vol. 96). It forms microscopic hexagonal plates having a See also:silver-See also:white streak. It is very heavy; its See also:density being about II; it inflames when heated in See also:air and is not attacked by alkalis; it readily dissolves in nitric See also:acid and aqua regia, but with difficulty in hydrochloric acid. In its salts, thorium is tetravalent, and in the periodic See also:classification it occurs in the same sub-group as See also:titanium, See also:cerium and See also:zirconium. Thorium dioxide or thoria, ThO2, is the most important See also:compound, being manufactured commercially in comparatively large quantities from monazite sands, with a view to its utilization for gas mantles (see LIGHTING, GAS). It is an amorphous white See also:powder; but it may also be obtained in crystals isomorphous with cassiterite by heating the amorphous See also:form with See also:borax to a very high temperature. An See also:oxide Thi0i is formed by heating the oxalate. Thorium fluoride, ThF4, is obtained as a heavy white insoluble powder by dissolving the See also:hydrate in hydrofluoric acid and evaporating.

By precipitating a thorium See also:

salt with a fluoride, a gelatinous hydrate, ThF4.4H2O, is obtained. Acid potassium fluoride precipitates K,ThF6.4ThFeH2O from a See also:solution of thorium chloride. Potassium thorofluoride, K2ThF6.4H10, is a heavy See also:black powder formed by boiling the hydroxide with potassium fluoride apd hydrofluoric acid. Thorium chloride, ThC14, is obtained as white shining crystals by heating a mixture of See also:carbon and thoria in a current of See also:chlorine. See also:Baskerville (Journ. Amer. Chem. Soc., 1904, 26, p. 922) divided the product into three fractions according to their volatility. He concluded that the first contained the chloride of berzelium, having an atomic weight of 212, the second contained thorium chloride, and the third the chloride of caralinium, having an atomic weight of 255.6. E. Chauvenet (See also:Comet. rend., 1908, 147, p.

1046) obtains it by heating thoria in a current of carbonyl chloride. Thorium chloride readily deliquesces on exposure and forms See also:

double salts with alkaline chlorides. Thorium sulphate, Th(SO4)2, is obtained by dissolving the oxide in sulphuric acid. It forms several crystalline hydrates. Evaporation of a solution at See also:ordinary temperatures gives colourless mono-clinic prisms of Th(SO4)2v9H2O, which is isomorphous with See also:uranium sulphate, U(SO4)2.9H2O. Above 43° Th(SO4)2.4H2Q is deposited. B. Roozeboom (Zeit. phys. Chem., 1890, 5, p. 198) has described several other hydrates. Thorium sulphate forms double salts with the alkaline sulphates. Thorium nitrate, Th(NOi)4.12H2O, forms white deliquescent tables very soluble in See also:water.

It forms double salts such as MgTh(NO,)s•8H2O, which are isomorphous with the corresponding cerium compounds. Thorium sulphide, ThS2, is obtained by burning the See also:

metal in See also:sulphur. It cannot be produced by precipitation. The atomic weight has been variously given. Berzelius found 235.5 ; Delafontaine, 229.7 ; Cleve, 232.6 by analyses of the sulphate, and 232.2 by analyses of the oxalate. Kriiss and Nilson derived the value 230.7 (H=I) from analyses of the carefully purified sulphate. For the so-called " disintegration of the thorium. See also:atom " and the relation of this element to the See also:general subject of radio-active emanations, see RADIO ACTIVITY. A number of salts of thorium have been prepared for therapeutic use, including the hydroxide, nitrate, salicylate, oleate and lactate. The oleate has been used in chronic See also:eczema and See also:psoriasis and locally in See also:cancer. Inhalations of thorium emanations produced from thorium nitrate through a See also:wash-See also:bottle inhaler are said to have a bactericidal See also:action in diseases of the lungs. F. Soddy has used them in See also:phthisis, and Louisa See also:Chesney speaks favourably of the emanations in chronic and acute See also:laryngitis and in tuberculous laryngeal ulcerations.

End of Article: THORIUM (symbol Th, atomic weight ,232.42 [0=16])

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