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Berzelius). J. Farbaky (Zeit. angew. Chem., 1897, p. II) extracts the element from black tellurium as follows:—The ore is boiled with concentrated sulphuric acid, the See also:

SOLUTION (from Lat. solvere, to loosen, dissolve)

solution diluted, hydrochloric acid added and the tellurium (together with selenium) precipitated by See also:

SULPHUR

sulphur dioxide and the See also:

PROCESS

process repeated when a purer tellurium is obtained.

B. Brauner (See also:

MONA

Mona's., 1889, to, p. 414) recommends the following method for the See also:

PURIFICATION

purification. The crude element is treated with aqua regia and then evaporated with an excess of hydrochloric acid, the solution diluted and the tellurium precipitated by a current of sulphur dioxide. The precipitated tellurium is then fused with See also:

POTASSIUM [symbol K (from kalium), atomic weight 39.114 0=16)]

potassium See also:

CYANIDE

cyanide, the melt extracted with water and the element precipitated by See also:

DRAWING

drawing a current of air through the solution and finally distilled in a current of See also:

HYDROGEN [symbol H, atomic weight x-oo8 (0=16)]

hydrogen. Tellurium is a brittle silvery-See also:

white element of specific gravity 6.27. It melts at 452° C. and boils at 478° C. (F. See also:

KRAFFT (or KRAFT), ADAM (c. 1455-1507)

Krafft, Ber., 1903, 36, p. 4344). When heated in a current of hydrogen it sublimes in the form of brilliant prismatic crystals. An amor- phous form is obtained when tellurium is precipitated from its solutions by sulphur dioxide, this variety having a specific gravity 6•o15.

When heated in air, tellurium See also:

burns, forming the dioxide TeO2. The element is insoluble in water, but dissolves in concentrated sulphuric acid forming a deep red solution. Like sulphur and selenium, tellurium combines directly with hydrogen to form telluretted hydrogen, TeH2, an extremely objection-able smelling and highly poisonous See also:

gas, which was first prepared by See also:

Sir H. See also:

DAVY, SIR HUMPHRY

Davy in 181o. It is best obtained by decomposing metallic tellurides with See also:

MINERAL

mineral acids. It is soluble in water, the solution gradually decomposing with deposition of tellurium; it also decomposes on exposure to See also:

LIGHT

light. It burns, and also, like sulphuretted hydrogen, precipitates many metals from solutions of their salts. It may be liquefied, the liquid boiling at o° C., and on further cooling, it solidifies, the solid melting at -48° C. Many tellurides of metals have been examined by C. A. Tibbals (Jour. Amer.

Chent. See also:

Soc., 1909, 31, p. 902) who obtained the sodium and potassium tellurides by the See also:

DIRECT

direct See also:

union of their component elements and others from these by precipitation. The tellurides of the See also:

ALKALI

alkali metals immediately decompose on exposure to air, with liberation of tellurium. Two chlorides are known, the dichloride, TeC12, and the tetrachloride, TeCla. They are both obtained by passing See also:

CHLORINE (symbol Cl, atomic weight 35`46 (0=16)

chlorine over tellurium, the product being separated by See also:

DISTILLATION (from the Lat. distillare, more correctly destillare, to drop or trickle down)

distillation (the tetrachloride is the less volatile). The dichloride is an amorphous, readily fusible, almost black solid. It is decomposed by water with formation of tellurium and tellurous acid: 2TeC12+3H20=Te+H2Te03+4HCl. The tetrachloride is a white crystalline solid which is formed by the See also:

ACTION

action of chlorine on the dichloride or by sulphur chloride on the element. It melts at 224° C. and is exceedingly hygroscopic. Water deoomposes it with formation of tellurous acid and other products. It combines directly with sulphur trioxide to form a complex of See also:

composition TeCl4.2SO3.

The tetrabromide similarly gives Te0Br2.2SO3 (W. Prandtl, Zeit. anorg. Chem., 1909, 62, p. 237). Iodides are also known. Two oxides of the element are definitely known, viz., the dioxide, TeO2. and the trioxide, Te03, whilst a monoxide, TeO, has also been described. The dioxide is formed by burning tellurium in air or KXvI. r',-See also:

TEMESVAR

TEMESVAR 577 by warming it with nitric acid. It is a colourless crystalline solid which readily fuses to a yellow liquid. The trioxide is an See also:

orange-coloured solid which is formed when telluric acid is strongly heated. Tellurous acid, H2TeO3, is obtained when the tetrachloride is de-composed by water, or on dissolving tellurium in nitric acid and pouring the solution into water. It is a colourless solid and behaves as a dibasic acid. The alkaline tellurites are soluble in water.

It also gives rise to super-acid salts, such as KHTeO3•H2TeO3; K2TeO3.3Te02. Telluric acid, H2TeOa, is obtained in the form of its salts when tellurium is fused with potassium carbonate and See also:

NITRE

nitre, or by the oxidizing action of chlorine on a tellurite in alkaline solution. The See also:

FREE

free acid may be obtained by decomposing the See also:

BARIUM (symbol Ba, atomic weight 137'37 [0=16])

barium See also:

salt with sulphuric acid and concentrating the solution, when a crystalline mass of composition H2TeOa•2H20 separates. It is also formed when the dioxide is oxidized by hydrogen per-See also:

OXIDE

oxide in See also:

CAUSTIC (Gr. rcavvraubs, burning)

caustic potash solution (A. Gutbier, Zest. anorg. Chem., 1904, 40, p. 260), and perhaps best of all by oxidizing tellurium with a mixture of nitric and chromic acids. It crystallizes in prisms, which lose their water of See also:

CRYSTALLIZATION

crystallization at 16o° C. The tellurates of the alkali metals are more or less soluble in water, those of the other metals being very sparingly or almost insoluble in water. Some tellurates exist in two forms, a colourless form soluble in water and acids, and a yellow form insoluble in water and acids. An oxychloride of tellurium has been described, but the investigations of V. Lenher (Jour.

Amer. Chem. Soc., 1909, 31, p. 20) seem to negative its existence. A considerable amount of See also:

WORK

work has been done on determinations of the atomic weight of tellurium, the earlier results giving the value 128. According to its position in the periodic See also:

CLASSIFICATION (Lat. classis, a class, probably from the root cal-, cla-, as in Gr. icaMce, clamor)

classification of the elements one would expect its atomic weight to be less than that of See also:

IODINE (symbol I, atomic weight '26.92)

iodine, instead of approximately equal, and on this See also:

account many efforts have been made to isolate another element from tellurium compounds, but none have as yet been successful. See also:

RECENT

Recent investigations of the atomic weight are due to G. Gallo (Atti. R. Acad. Lincei, 1905 (iv.), 14, pp. 1, 23, 104), who, by a determination of the electrochemical See also:

EQUIVALENT

equivalent of the element, arrived at the value 127'61; A.

Gutbier (See also:

Ann., 1905, 342, p. 266) by reduction of the dioxide obtained 127.6; Marckwald, by determining the ratio of telluric acid to tellurium dioxide, obtained 126.85; H. B. See also:

Baker (Jour. Chem. Soc., 1907, 91, p. 1849), by determining the ratio of tellurium dioxide to See also:

OXYGEN (symbol 0, atomic weight 16)

oxygen and by See also:

ANALYSIS (Gr. avci and Meta, to break up into parts)

analysis of tellurium tetrabromide, obtained 127.6o, and V. Lenher (Jour. Amer. Chem. Soc., 1909, 31, p. 20), by heating the See also:

double salt, TeBr4.2KBr, first in chlorine and finally in a current of hydrochloric acid to convert it into potassium chloride, obtained the value 127.55.

P. E. See also:

Browning and W. R. See also:

Flint (Amer. J. Sci., 1909 (iv.), 28, p. 347) claim to have separated two substances (of atomic weights 126.49 and 128.85 respectively) from tellurium, by fractional precipitation of tellurium chloride with water, but in the See also:

OPINION (Lat. opinio, from opinari, to think)

opinion of H. B. Baker this would seem to point to the fact that the tellurium used was insufficiently purified, since his work showed that there was no difference between the first and last fractions (see Chem. Soc. Ann.

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