with Potassium, Rubidium and Caesium. 269 



halides of tellurium with potassium, rubidium and caesium. 

 As a result the following compounds have been prepared : 



2KC1 . TeCl 4 2RbCl . TeCl 4 2CsCl .TeCl 4 



2KBr . TeBr 4 2RbBr . TeBr 4 2CsBr . TeBr 4 



2KBr . TeBr 4 . 2H„0 2RbI . Tel 4 2CsI . Tel 4 

 2KI.2TeI 4 .2H 2 Q" 



It is to be noticed that all of these compounds conform to 

 the usual type of double halides of tetravalent metals in con- 

 taining the alkali metal and tellurium in the ratio of two atoms 

 of the former to one of the latter, and no indications of the 

 formation of salts of a different type were observed: The 

 anhydrous double halides of tellurium crystallize in the iso- 

 metric system, with an octahedral habit, and it is an interest- 

 ing fact that this form seems to be characteristic for anhydrous 

 double halides of this type. The caesium and rubidium salts 

 are new compounds, as well as the crystallized, anhydrous, 

 double potassium bromide. New formulae have been assigned 

 to the hydrous potassium double bromide and to the double 

 iodide of potassium. A considerable difference is shown in 

 the affinity of the double halides of tellurium and potassium 

 for water of crystallization. The double chloride is anhydrous 

 and no hydrous form of it was observed, the double bromide 

 was prepared in both the hydrous and the anhydrous forms, 

 while the iodide was obtained only with water of crystalliza- 

 tion. This water was more firmly held than in the case of 

 the hydrous bromide, as was shown by the fact that it formed 

 from hot solutions and did not as readily effloresce. 



The methods used in the preparation of pure material for 

 this work, and which deserve to be mentioned' on account of 

 giving satisfactory results, are given below. The tellurium 

 was obtained by purifying the commercial product by precipi- 

 tation with sulphurous acid, according to the method of Divers 

 and Shimose.* The halides of tellurium were prepared from 

 this material in the usual way. 



Caesium chloride was obtained in a pure state by the method 

 of Godeffroy.f The bromides and iodides were obtained in 

 the usual manner from the carbonate, the latter having been 

 prepared from the pure chloride by converting into nitrate, 

 then into oxalate and igniting the latter, as suggested by J. L. 

 Smith, X for the conversion of potassium chloride into carbo- 

 nate. The rubidium was purified by Allen's§ acid tartrate 

 method. In the case of the potassium salts, Kahlbaum's pure 

 material was used. 



* Jour. Chem. Soc, xlvii. 439. f Ber d. chem. Ges., vii, 375. 



{This Journal, II, xvi, 373. § Ibid., II, xxxiv, 367. 



