Potassium Trihalides, 'with their Crystallography. 483 



Calculated 

 Analysis gave for RbBr . BrI. 



Rubidium.. 22*79 22-95 



Bromine 45*19 42*95 



Iodine 31-11 34-10 



An approximate specific gravity determination, made with 

 the mother-liquor, gave the number 3-84. An analysis of the 

 mother-liquor showed that it contained about 44 per cent of 

 RbBr . BrI. The mother-liquor of the corresponding caesium 

 compound contained only 4*45 per cent of CsBr . BrI. 



Mb CI . BrI. 



This body can be made by adding 27 g. of bromine and 42 g. 

 of iodine to a saturated aqueons solution of 40 g. of rubidium 

 chloride, warming until all is in solution and cooling. It forms 

 magnificent crystals which can be readily recrystallized from 

 water. Unlike the corresponding caesium compound, it does 

 not change its composition by recrystallization, hence it is 

 probable that it is a true chemical compound and not a mixture 

 of the isomorphous bodies RbBr. BrI and RbCl . C1L 



Analysis gave, 



Original 6th recrys- Calculated 



crystals. tallization. for RbCl . BrI. 



Rubidium 26"67 27-34 26-06 



Chlorine 10-65 10-82 



Bromine 24*89 24*39 



Iodine 38*13 38*72 



RbCl. CU. 



A convenient method for preparing this compound is to 

 pass chlorine into a warm, concentrated solution of rubidium 

 chloride, containing the calculated amount of iodine, until the 

 iodine is just dissolved. If too much chlorine is used, the 

 compound RbCl 4 I is formed, which we shall describe in a 

 future article. It is best to stop adding chlorine while the 

 solution is still colored red by iodine. On cooling the liquid 

 the compound separates, usually in large flat groups of parallel 



crystals. 



Calculated for 

 Analysis gave RbCl . C1I. 



Rubidium 29-85 30-15 



Chlorine 24*68 25*04 



Iodine ._ 44*68 44*79 



RbBr . Br 2 . 



This can be prepared by adding 49 g. of bromine to 45 c.c. 

 of an aqueous solution containing 50 g. of rubidium bromide, 

 warming gently until bromine dissolves, then cooling. It usually 

 forms a mass of large, brilliant, red crystals in parallel position. 



