Wells and Penfield — Series of Caesium Trihalides. 25 



CsBrI a . 



Iodine dissolves in considerable quantity in a hot aqueous 

 solution of caesium .bromide, but it nearly all separates on 

 cooling. It is therefore necessary to use a mixture of alcohol 

 and water in preparing this trihalide. A good crop of crystals 

 was obtained by dissolving one-half the theoretical iodine in a 

 solution of one part of caesium bromide dissolved in two parts 

 of water and one part (by volume) of alcohol. 



The following numbers show the composition of the crys- 

 tals. 



Calculated for 

 Found. CsBrI 2 . 



Caesium 28-54 28-48 



Bromine... 18-11 17-13 



Iodine.. 52-01 54-39 



CsBrJ. 



This may be made by dissolving the theoretical amounts of 

 iodine and bromine in a solution of one part of caesium bro- 

 mide in ten parts of water. A considerable excess of bromine 

 does not interfere with its formation. 



The crystals have the following composition : 



Calculated for 

 Found. CsBr 2 I. 



Caesium 31-32 3T67 



Bromine... 37-63 38-09 



Iodine 29-57 30-24 



The solubility of this substance in water was approximately 

 determined by estimating the free halogens volumetrically in 

 the mother-liquor from a recrystallization at about 20°. The 

 amount found corresponded to 4 - 45 per cent of CsBr 2 I. 



[CsCU,] 



[Repeated attempts to make this substance, by using concen- 

 trated solutions of caesium chloride and iodine in mixtures of 

 water and alcohol and cooling to low temperatures, invariably 

 failed. 



Gs GIBrl. 



This may be made by dissolving about one- fourth of the 

 theoretical bromine and iodine in a solution of one part of 

 caesium chloride in five parts of water. If an excess of 

 caesium chloride is not taken the product will contain too little 

 chlorine and too much bromine. 



An analysis of the product, properly prepared, gave : 



