with Potassium, Rubidium and Caesium. 271 



little hot water completely, the difference being shown on 

 cooling, when a considerable portion of the tellurium separates 

 as tellurous acid. While in the case of the caesium salt both 

 hot and cold water, in large and small amounts, fail to dissolve 

 the salt, the result being immediate decomposition. Only a 

 small part of the tellurium in this case goes into solution. 

 Most of these double salts can be conveniently recrystallized 

 from dilute solutions of the corresponding acid. The excep- 

 tions are potassium-tellurium chloride, which is decomposed by 

 this treatment, and caesium-tellurium iodide, which is practi- 

 cally insoluble in hydriodic acid. The fact, first noticed by 

 Godeffroy,* that double halides, containing the metals potas- 

 sium, rubidium and caesium, generally decrease in solubility 

 from potassium to caesium, which has frequently been noticed 

 in this laboratory, is again well illustrated by these compounds. 

 For the determination of the solubility of these salts in acids, 

 they were finely powdered, and saturated solutions were then 

 prepared by digesting a mixture of the acid and an excess of 

 the salt for about a week, at ordinary temperature. This was 

 done in a closed flask. Weighed portions of these solutions 

 were evaporated to dryness and the residues dried at 100° and 

 weighed. These solubilities were all taken at 22°, and the 

 results are the average of two or more closely agreeing deter- 

 minations. 



1 00 parts HC1 1 00 parts HC1 



Sp. gr. 1-2 dissolve Sp. gr. 1 05 dissolve 



2RbCl.TeCl 4 0-34 parts. 13-09 parts. 



2(JsCl.TeCl 4 0-05 " 0-78 " 



] 00 parts HBr 1 00 parts HBr 



Sp. gr. T49 dissolve Sp. gr. 1'08 dissolve 



2KBr.TeBr 4 6'5V parts. 62-90 parts. 



2RbBr.TeBr 4 0-25 " 3'88 <• 



2CsBr.TeBr 4 0-02 " 013 " 



The double tellurium chlorides, described in this article, are 

 more soluble than the bromides, and the bromides more soluble 

 than the iodides. The solubility of these compounds in 

 strong alcohol shows the same gradation as their solubility in 

 acids, the caesium salts being practically insoluble in this men- 

 struum, while the rubidium salts dissolve to a trifling but 

 clearly perceptible extent, and the potassium salts dissolve con- 

 siderably or are decomposed with separation of the potassium 

 halide, or both solution and decomposition take place, accord- 

 ing to the salt experimented with. 



* Ber. d. Chem. Gcs., viii, 9. 



