Arsenic with Coesium and Rubidium. 



93 



The analyses show a considerable variation from the com- 

 position required by the formula, the products made under the 

 extreme conditions giving ratios of arsenious oxide to caesium 

 chloride of 3 : 4 and 3 : 2 instead of 1 : 1. The conditions varied 

 so widely however that it seems fair to assume the existence of 

 a 1 : 1 compound. 



When the double chloride of rubidium was recrystallized from 

 about 15 per cent HC1, a white crystalline crust was obtained 

 on slowly cooling. This gave analytical results agreeing with 

 the formula KbCl . As 2 3 . 



Calculated for 

 RbCl. As 2 3 



Rb 26-90 26-80 



As._. 47-03 



CI .- 11-41 I 1-13 



O 1504 



Under the microscope these compounds appear as irregular 

 grains or plates, of indefinite crystalline form. 



CsBr . As 2 O s and EbBr . As 2 3 . — When the double bromides 

 are recrystallized from water, or dilute HBr, they yield these 

 oxy-compounds, and these generally separate in the form of a 

 white crust on the bottom and sides of the beaker. Analysis 

 of such products gave : 



3CsBr.2ASBr 3 



3CsBr . 2 As Br 3 recrystallized. 



recrystallized from CsBr Calculated for 



from water. solution. CsBr . As 2 3 



Cs 32-42 32-36 



As 36-52 36 50 



Br ... ... 19-57 19-59 19*46 



O [1149] 11-68 



3RbBr.2AsBr 3 3RbBr. 2AsBr 3 Calculated 

 from dilute HBr. from water. for RbBr . As 2 3 



Rb___ 24-24 16-56 23*52 



As 40-06 50-74 41-27 



Br... 24-53' 15-91 22-01 



O [11-17] [16-79] 13-20 



It is to be noticed that the product obtained by recrystal- 

 lizing 3RbBr . 2AsBr 3 from water is impure, while the caesium 

 compound made in the same way corresponds to the formula. 

 This is an illustration of the greater tendency of the caesium 

 halide to form double salts than in the case of the rubidium 

 halide. Both these compounds are white, but the rubidium 

 compound turns somewhat yellow on drying. Under the 

 microscope, six sided plates were seen in the case of the caesium 

 compound when the solution was slowly cooled. There were 

 also observed hexagonal crystals with a short columnar rhom- 

 bohedral habit. They were uniaxial with weak, negative 



