Wells and Walden — Caesium- Cupric Bromides. 95 



double chlorides of caesium and copper exist, while no corre- 

 sponding bromides were obtained indicates that the rule does 

 not apply in all cases. 



2:1 Caesium Cupric Bromide, Cs<fiuBi\ : — This compound 

 forms opaque, black crystals having a greenish tint. The 

 powder is black. In form and habit it resembles the correspond- 

 ing chloride and is evidently orthorhombic like that salt. 

 Elongated prisms, usually not over 5 to 10 mm in length, com- 

 monly occurring in groups in parallel position, were observed 

 where aD excess of caesium bromide was used. When the pro- 

 portion of cupric bromide was increased, small short crystals 

 made their appearance. 



With 50 g. of caesium bromide the compound is formed in 

 the presence of from 5 to about 70 s of cupric bromide. 

 The range of conditions under which it is formed are consider- 

 ably wider than in the case of the corresponding chloride. 



Of the analyses given below, A, B, C, D and E represent a 

 series of preparations in which copper bromide was gradually 

 increased from 5 g in A to 46 s in E, while the caesium bro- 

 mide remained constant at about 50 g and the volume increased 

 from 100 cc in A, to 150 cc in E. The sample F was obtained 

 by recrystallizing the salt from water, while G resulted from 

 recrystallizing CsCuBr 3 . 





Cs. 



Cu. 



Br. 



A 



40-80 



9-46 



49-38 = 99-64 



B 







9-68 





C_.__ 



40-75 



9-74 



48-97 = 99-46 



D 



40-88 



9-69 



48-95 = 99-52 



E 







9-78 



49-40 



F____ 



41-11 



9-66 



..... 



G 







10-00 







Calculated ) 

 forCs CuBi\ \ 



40-96 



977 



49-27 = 100-0( 



1:1 Caesium- Cupric Bromide, CsCuBr r — This salt forms 

 short, hexagonal crystals which are strung together end to end. 

 They are dark and opaque, giving a bronze-colored reflection, 

 while their powder is nearly black. When recrystallized from 

 water the compound gives the 2 : 1 salt, thus differing from the 

 chloride. It was obtained from a solution containing 50 g of 

 caesium bromide and 70 g of copper bromide with sufficient 

 water to form a volume of 200 cc , and it continued to be pro- 

 duced as cupric bromide was added until the solution became 

 saturated with that compound. 



The following analyses were made of separate preparations 

 which were obtained under wide variations of conditions. 



