252 INDIUM AND THALLIUM IN 



account for the low value for the water of crystallisation 

 obtained by Pratt. 



K 3 InBr 6 2H 2 



From solutions containing potassium bromide and indium 

 bromide in the proportions 3:1, precipitation of KBr takes 

 place till the solutions are almost completely evaporated. 

 Very small reddish-brown crystals then begin to appear. 

 Although on varying the concentration of the solution more 

 favourable conditions for the deposition of this salt are 

 obtained, it crystallised invariably as a very fine powder, and 

 good crystals could not be isolated. The angular measure- 

 ments obtained in the goniometer showed that the crystals 

 were isomorphous with the compounds already described. 

 This salt effloresces, however, so readily on exposure to the 

 air that it was found impossible to obtain exact crystallo- 

 graphical data. The specific gravity of the crystalline powder 

 was found to be as accurately as possible under the circum- 

 stances 3*140 at 20. 



Analyses gave the following results : 



K. In. Br. 



16-89 15-24 63-97 

 Calculated 15-90 15-56 65-00. 



Owing to the very efflorescent character of the salt, no 

 attempt was made to obtain the value of the water of crystal- 

 lisation. The salt is, however, undoubtedly isomorphous 

 with compounds of the type R 3 MX 6 2H 2 0, and one is justified 

 in assuming that it also contains two molecules of water of 

 crystallisation. 



No other salt isomorphous with those already described 

 has been obtained in this investigation. It would appear that 

 the only compounds of the series R 3 MX 6 2H 2 O, where R=K, 

 (NH 4 ), Rb, Cs or Tl; M=In or Tl; X=C1 or Br, that are in 

 equilibrium with their solutions under ordinary conditions of 

 temperature and pressure are (1) K 2 T1C1 6 2H 2 ; (2) (NH 4 ) 3 



