CAESIUM (symbol Cs, atomic weight 132.9)

This article appears in Volume V04, Page 944 of the Encyclopedia Britannica.

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CAESIUM (symbol Cs, atomic weight 132.9) , one of the alkali metals. Its name is derived from the Lat. caesius, sky-blue, from two

bright

BRIGHT, JOHN (1811-188g)
BRIGHT, SIR CHARLES TILSTON

blue lines of its spectrum. It is of historical importance, since it was the first metal to be discovered by the aid of the spectroscope (R. Bunsen, Berlin Acad. Ber., 1860), although caesium salts had undoubtedly been examined before, but had been mistaken for potassium salts (see C. F. Plattner, Pog. Ann., 1846, p. 443, on the analysis of pollux and the subsequent

work

WORK

of F. Pisani, Comptes Rendus, 1864, 58, p. 714). Caesium is found in the

mineral

MINERAL

springs of

Frankenhausen

FRANKENHAUSEN

, Montecatini, di Val di Nievole, Tuscany, and Wheal Clifford near Redruth,

Cornwall

CORNWALL

(W. A. Miller, Chem. News, 1864, 10, p. 181), and, associated with rubidium, at Durkheim; it is also found in

lepidolite

LEPIDOLITE

, ieucite, petalite, triphylline and in the carnallite from

Stassfurt

STASSFURT

. The separation of caesium from the minerals which contain it is an exceedingly difficult and laborious process. According to R. Bunsen, the best source of rubidium and caesium salts is the residue left after extraction of lithium salts from

lepidolite

LEPIDOLITE

. This residue consists of sodium, potassium and lithium chlorides, with small quantities of caesium and rubidium chlorides. The caesium and rubidium are separated from this by repeated fractional crystallization of their

double

platinum chlorides, which are much less soluble in 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 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) 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 conversion into alums, which C. Setterberg (Ann., 1882, 211, p. 100) has shown are very slightly soluble in a solution of potash alum. In 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 antimony 3CsCl 2SbC13 (R. Godeffroy, Ber.,
1874, 7, p. 375; Ann., 1876, 181, p. 176) has been used, the corresponding compound not being formed by rubidium. The metal has been obtained by electrolysis of a mixture of caesium and barium cyanides (C. Setterberg, Ann., 1882, 211, p. 100) and by heating the hydroxide with magnesium or 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 calcium. A

special

SPECIAL

V-shaped tube is used in the operation, and the reaction commences between 400 C. and 5o0 C.
It is a silvery white metal which burns on heating in air. It
melts at 26 to 27 C. and has a specific gravity of 1.88 (15C.).
The atomic weight of caesium has been determined by the
analysis of its chloride and bromide. Richards and 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 heat and absorbs carbon dioxide rapidly. It readily dissolves in water, with evolution of much heat. Caesium chloride, CsCl, is obtained by the direct action of chlorine on caesium, or by solution of the hydroxide in hydrochloric 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 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. Wells and S. L. Penfield, Zeit. 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 short hard prisms, which are readily soluble in water but insoluble in alcohol. It combines with many metallic sulphates (silver, zinc,

cobalt

COBALT (symbol Co, atomic weight 59)

, nickel, &c.) to form double sulphates of the type Cs2SOgRSO4 6H2O. It also forms a caesium-alum Cs2SO4Al2(SO4)324H2O. Caesium nitrate, CsNO3, is obtained by dissolving the carbonate in nitric acid, and crystallizes in glittering prisms, which melt readily, and on heating evolve oxygen and leave a residue of caesium nitrite. The carbonate, Cs2CO3, silicofluoride, Cs2SiFs, borate, Cs2O.3B2O3, and the sulphides Cs2S4H2O, Cs2S2H10, Cs2S3H2O, Cs2S4 and Cs2SsH2O, are also known.
Caesium compounds can be readily recognized by the two

bright

BRIGHT, JOHN (1811-188g)
BRIGHT, SIR CHARLES TILSTON

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

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