Caesium and Zirconium. 19 



The materials used for the preparation of the caesium salts 

 under consideration were carefully purified by ourselves. 

 Hydrofluoric acid was made from perfectly pure fluor-spar and 

 sulphuric acid, using a platinum still and redistilling the 

 product. Caesium carbonate, purified by the method described 

 by one of us 3 * was used in preparing the fluoride. Zircon was 

 used as the source of zirconium. The crude hydroxide was 

 conveniently obtained by fusing the finely pulverized mineral 

 with four parts of sodium carbonate, treating the resulting 

 mass with hydrochloric acid, evaporating with an excess of 

 sulphuric acid until the latter fumed, taking up with water, 

 filtering and precipitating with ammonia. For purifying the 

 zirconia, the method of Mitchell which has been advocated by 

 Baskervillef was found convenient. This consists in dissolving 

 the zirconium hydroxide in hydrochloric acid, nearly neutraliz- 

 ing with ammonia, adding a strong solution of sulphur dioxide 

 and boiling. The precipitate, which, from the results of 

 Tenable and Baskerville,J appears to be a basic zirconium 

 sulphite, can readily be washed free from iron. 



The double salts were prepared by mixing solutions of the 

 two fluorides in widely varying proportions, in the presence of 

 more or less hydrofluoric acid, evaporating to the proper point 

 and cooling. 



When caesium fluoride is in excess, even with very small 

 amounts of zirconium fluoride, the salt 2CsF . ZrF 4 is formed. 

 It crystallizes in rather large, simple hexagonal plates, show- 

 ing negative double refraction, and it can be recrystallized 

 unchanged from water. 



When a larger proportion of zirconium fluoride is used, the 

 salt CsF . ZrF 4 . H 2 is obtained. This forms monoclinic crys- 

 tals elongated in the direction of the h axis, and with faces 

 which are usually too rough for accurate measurement. This 

 salt also can be recrystallized unchanged from water. 



With a large excess of zirconium fluoride extremely small, 

 difficultly soluble crystals of the salt 2CsF . 3ZrF 4 . 2H,0 are 

 produced. The small crystals have a slight action upon polar- 

 ized light, but their form could not be made out. It does not 

 recrystallize from water in a pure condition, the product being 

 mixed with the 1 : 1 salt. 



To determine caesium and zirconium, the fluorides were con- 

 verted into sulphates, then zirconium was separated from 

 caesium by the use of ammonia, and zirconium oxide and 

 caesium sulphate were Anally weighed. In order to determine 

 fluorine a separate portion was dissolved in water, zirconium 

 hydroxide was precipitated with ammonia, sodium carbonate 



*This Journal, xlvi, 188. f Jour. Am. Chem. Soc, xvi, 475. 



\ Jour. Am. Chem. Soc, xvii, 448. 



