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CAESIUM (symbol Cs, atomic weight 132.9)

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Originally appearing in Volume V04, Page 944 of the 1911 Encyclopedia Britannica.
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CAESIUM (See also:symbol Cs, atomic See also:weight 132.9) , one of the See also:alkali metals. Its name is derived from the See also:Lat. caesius, See also:sky-See also:blue, from two See also:bright blue lines of its spectrum. It is of See also:historical importance, since it was the first See also:metal to be discovered by the aid of the spectroscope (R. See also:Bunsen, See also:Berlin Acad. Ber., 1860), although caesium salts had undoubtedly been examined before, but had been mistaken for See also:potassium salts (see C. F. See also:Plattner, Pog. See also:Ann., 1846, p. 443, on the See also:analysis of See also:pollux and the subsequent See also:work of F. See also:Pisani, Comptes Rendus, 1864, 58, p. 714). Caesium is found in the See also:mineral springs of See also:Frankenhausen, See also:Montecatini, di Val di Nievole, See also:Tuscany, and Wheal See also:Clifford near See also:Redruth, See also:Cornwall (W.

A. See also:

Miller, Chem. See also:News, 1864, 10, p. 181), and, associated with See also:rubidium, at See also:Durkheim; it is also found in See also:lepidolite, ieucite, See also:petalite, triphylline and in the carnallite from See also:Stassfurt. The separation of caesium from the minerals which contain it is an exceedingly difficult and laborious See also:process. According to R. Bunsen, the best source of rubidium and caesium salts is the See also:residue See also:left after extraction of See also:lithium salts from lepidolite. This residue consists of See also:sodium, potassium and lithium chlorides, with small quantities of caesium and rubidium chlorides. The caesium and rubidium are separated from this by repeated fractional See also:crystallization of their See also:double See also:platinum chlorides, which are much less soluble in See also:water than those of the other alkali metals (R. Bunsen, Ann., 1862, 122, p. 347; 1863, 125, p. 367).

The platino-chlorides are reduced by See also:

hydrogen, and the caesium and rubidium chlorides extracted by water. See also A. Schrotter (Jour. prak. Chem., 1864, 93, p. 2075) and W. Heintz (Journ. prak. Chem., 1862, 87, p. 310). W. Feit and K. Kubierschky (Chem. Zeit., 1892, 16, p.

335) See also:

separate rubidium and caesium from the other alkali metals by converting them into double chlorides with stannic chloride; whilst J. Redtenbacher (Jour. prak. Chem., 1865, 94, p. 442) separates them from potassium by See also:conversion into alums, which C. Setterberg (Ann., 1882, 211, p. 100) has shown are very slightly soluble in a See also:solution of potash See also:alum. In See also:order to separate caesium from rubidium, use is made of the different solubilities of their various salts. The bitartrates RbHC4H4O6 and CsHC4H4O6 have been employed, as have also the alums (see above). The double chloride of caesium and See also:antimony 3CsCl • 2SbC13 (R. Godeffroy, Ber., 1874, 7, p. 375; Ann., 1876, 181, p. 176) has been used, the corresponding See also:compound not being formed by rubidium.

The metal has been obtained by See also:

electrolysis of a mixture of caesium and See also:barium cyanides (C. Setterberg, Ann., 1882, 211, p. 100) and by See also:heating the hydroxide with See also:magnesium or See also:aluminium (N. Beketoff, Chem. Centralblatt, 1889, 2, p. 245). L. Hackspill (Comptes Rendus, 1905, 141, p. 101) finds that metallic caesium can be obtained more readily by heating the chloride with metallic See also:calcium. A See also:special V-shaped See also:tube is used in the operation, and the reaction commences between 400° C. and 5o0° C. It is a silvery See also:white metal which See also:burns on heating in See also:air. It melts at 26° to 27° C. and has a specific gravity of 1.88 (15°C.).

The atomic weight of caesium has been determined by the analysis of its chloride and bromide. See also:

Richards and See also:Archibald (Zeit. anorg. Chem., 1903, 34, p. 353) obtained 132.879 (0-16). Caesium hydroxide, Cs(OH)2, obtained by the decomposition of the sulphate with baryta water,is a greyish-white deliquescent solid,which melts at a red See also:heat and absorbs See also:carbon dioxide rapidly. It readily dissolves in water, with See also:evolution of much heat. Caesium chloride, CsCl, is obtained by the See also:direct See also:action of See also:chlorine on caesium, or by solution of the hydroxide in hydrochloric See also:acid. It forms small cubes which melt at a red heat and volatilize readily. It deliquesces in moist air. Many double chlorides are known, and may be prepared by mixing solutions of the two components in the requisite See also:pro-portions. The bromide, CsBr, and iodide, CsI, resemble the corresponding potassium salts. Many trihaloid salts of caesium are also known, such as CsBr3i CsClBr2, CsI,, CsBrl2, CsBr21, &c.

(H. L. See also:

Wells and S. L. Penfield, Zeit. See also:fur anorg. Chem., 1892, 1, p. 85). Caesium sulphate, Cs2SO4, may be prepared by dissolving the, hydroxide or carbonate in sulphuric acid. It crystallizes in See also:short hard prisms, which are readily soluble in water but insoluble in See also:alcohol. It combines with many metallic sulphates (See also:silver, See also:zinc, See also:cobalt, See also:nickel, &c.) to See also:form double sulphates of the type Cs2SOg•RSO4 6H2O. It also forms a caesium-alum Cs2SO4•Al2(SO4)3•24H2O. Caesium nitrate, CsNO3, is obtained by dissolving the carbonate in nitric acid, and crystallizes in glittering prisms, which melt readily, and on heating evolve See also:oxygen and leave a residue of caesium nitrite.

The carbonate, Cs2CO3, silicofluoride, Cs2SiFs, borate, Cs2O.3B2O3, and the sulphides Cs2S•4H2O, Cs2S2•H10, Cs2S3•H2O, Cs2S4 and Cs2Ss•H2O, are also known. Caesium compounds can be readily recognized by the two bright blue lines (of See also:

wave length 4555 and 4593) in their See also:flame spectrum, but these are not See also:present in the spark spectrum. The other lines include three in the See also:green, two in the yellow, and two in the See also:orange.

End of Article: CAESIUM (symbol Cs, atomic weight 132.9)

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