Caesium alum

The high solubility of the caesium salt is interesting in view of the low solubility of ferric caesium alum (see p. 164). 

In2(SO<)j is a white solid, very hygroscopic and very readily soluble in water. The simple sulfate forms a hydrate with difficulty, but the ammonium, rubidium, and caesium alums crystallize readily double sulfates resembling the alums but of the composition M Oi In2(SO<) 5 8 H20 have also been prepared with sodium, potassium, ammonium, and thallium. 

Solubility of Caesium Alum, Rubidium Alum, and of Thallium... 

Caesium Alum. RuUdium Alum. Thallium Alum. ... 

According to J. M. Ordway, when alkali hydroxide is added to a soln. of chromic nitrate, chromic hydroxide is precipitated. The precipitate appears when more than two-thirds of the acid has been neutralized. This proves that nitric acid can dissolve more chromic hydroxide than eorresponds with the normal nitrate. C. Montemartini and L. Losana studied the e.m.f. of the soln. N. Bjerrum and C. Fourholt determined the masked hydroxide, Cr(H20)e—, by precipitation as caesium alum. With soln. of chromic nitrate they obtained the results indicated in Table V. 

Uses Of the Stassfurt salts.—The magnesium compounds in the Stassfurt salts are used for the preparation of magnesium and of its salts. The potash salts are an essential constituent of many fertilizers used in agriculture, etc. 22 and potassium chloride is the starting-point for the manufacture of the many different kinds of potassium salts used in commerce—carbonate, hydroxide, nitrate, chlorate, chromate, alum, ferrocyanide, cyanide, iodide, bromide, etc. Chlorine and bromine are extracted by electrolysis and other processes from the mother liquids obtained in the purification of the potash salts. Boric acid and borax are prepared from boracite. Caesium and rubidium are recovered from the crude carnallite and sylvite. 

Precipitate with aq. ammonia. Evaporate the soln. down to about 100 c.c., and filter the ot liquid so as to remove calcium sulphate. The cone. soln. is sat. with ammonium alum and allowed to stand for some time. The mixed crystals of potassium, rubidium, and oeesium alums and of lithium salt are dissolved in 100 c.c. of distilled water and recrystal-lized. The recrystallization is repeated until the crystals show no spectroscopic reaction for potassium or lithium. The yield naturally depends on the variety of lepidolite employed. 100. grms of an average sample gives about 10 grms. of crude crystals and about 3 grms. of the purified caesium and rubidium alums. For the purification of caesium and rubidium salts, see the chlorides. The mother-liquors are treated with an excess of barium carbonate, boiled, and filtered. The filtrate is acidified with hydrochloric acid, and evaporated to dryness. The residue is extracted with absolute alcohol in which lithium chloride is soluble, and the other alkali chlorides are sparingly soluble. 

The alkali sulphates can also be made by neutralizing, say, a soln. of 5 grms. of sulphuric acid in 30 c.c. of water with the alkali hydroxide or carbonate, and evaporating the soln. until crystals begin to form. The process is not economical except on a small scale. It is used mainly for lithium, rubidium, and caesium sulphates. H. Erdmann 20 treated a hot soln. of crude rubidium iron alum with milk of lime made from purified lime, and filtered the liquid from the excess of lime, calcium sulphate, and ferric hydroxide, by suction. The small amount of lime in soln. is precipitated by adding rubidium carbonate. The filtrate is neutralized with sulphuric acid, and evaporated to the point of crystallization. 

Caesium Rhodium Alum, Cs2S04. Rh2(S04)3.24H20, is the most readily prepared of all the rhodium alums on account of its sparing solubility in cold water. The salt crystallises in small yellow octahedra which melt at 110° to 111° C. to a yellowish red liquid. When warmed in a desiccator it loses water, remaining yellow at 100° C., becoming yellowish red at 150° to 180° C., and brown up to 250° C., when it is almost entirely anhydrous. 

This alum is of interest inasmuch as its formation renders it easy to separate rhodium from iridium. The sulphates of the metals, dissolved in acidulated water, are treated with caesium sulphate and evaporated. The rhodium alum crystallises out in a pure state, entirely free from iridium.1... 

Caesium. Iridium Alum, Cs2S04. Ira(S04)3.24H20, yields bright yellow, octahedral crystals, melting at 109 to 110° C. to a yellowish red liquid. Its aqueous solution is yellow, becoming rose-coloured on warming above 40° C. The crystals become anhydrous at 300° to 350° C. 

Preparation.—The main source of rubidium compounds is the residual mother-liquor obtained in the extraction of potassium chloride from carnallite. The solution contains rubidium-carnallite, RbCl,MgCI2, a substance transformed by addition of aluminium sulphate into rubidium-alum, RbAl(S04)8,12H20. Separation from the potassium and caesium salts also present is effected by fractional crystallization of the alum,8 of the chloroplatinate 8 Rb2PtCl8, of rubidium-iron-alum,4 and of the double chloride with stannous chloride5 or with antimony trichloride.6... 

Preparation.—The isolation of caesium compounds is facilitated by the relatively low solubility of certain double salts, such as the alums, chloroplatinates, and double chlorides with antimony, tin, and lead.3 Its separation from rubidium depends on the solubility of its carbonate in alcohol, that of rubidium being only slightly soluble. 

Ferric caesium selenium alum, Cs2Se04.Fe2(Se04)3.24H20, prepared in an analogous manner to the preceding salt,1 yields violet crystals of density 3 6176 at 15° C. These melt in their combined water at 55° to 60° C. 

M.C.M. O Brien, From her lecture on The Paramagnetism of Caesium Titanium Alum , given at the Department of Chemistry, University of Bern in 1997, shortly before her untimely death. 

Extraction.—Rubidium may he extracted from lepidolite by decomposing the finely ground mineral wilh ertlcium fluoride and sulfuric arid heat, tlirn extract with water, evaporate, and allow the caesium-ridlidiiun alums to crystallize. 

Does Eka-caesium exist — Several considerations point to the possibility of the existence of an undiscovered alkali element, with atomic number 87 and an atomic weight of approximately 224. Diligent search in caesium materials has been made1 for this missing element by fractionation of the nitrate, di-chloriodide, chloride, perchlorate, sulfate, and alums. In every case careful examination of the extreme portions of the material failed to reveal any indication of a new element. If such an element exists, it must belong very definitely to the radioactive series and it may have such a short life period that its detection becomes very difficult. 

Solubility of Caesium Chromium Alum, Caesium Iron Alum, Caesium Indium Alum, and of Caesium Vanadium Alum in Water. 

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