264 INDIUM AND THALLIUM IN 



has described RbTlBr 4 H 2 and CsTlBr 4 as crystallising in 

 cubes. These salts were all obtained in this investigation, 

 but the crystalline form of KTlBr 4 2H 2 and NH 4 TlBr 4 2H 2 O 

 was found to be cubic, not rhombic. The crystals were tabular, 

 showing only the face of jlOOj, with depressions in the form 

 of inverted rectangular pyramids. Under the microscope the 

 crystals were perfectly isotropic in all positions. 



No corresponding indium bromides were obtained, and no 

 thallium or indium chloride of this general type was isolated. 

 From solutions, however, which contained KBr and TlBr 3 in 

 the proportion 3 : 1, a salt was obtained, which, although not 

 belonging to this series, may be described here. This salt was 

 deposited in beautiful yellowish brown crystals of high lustre 

 from solutions which had previously precipitated cubic 

 crystals of KTlBr 4 2H 2 0. 



K 3 Tl 2 Br 9 3H 2 O 



Rammelsberg (18) had obtained a salt of this composition 

 from solutions containing TIBr, Br, KBr, and water. He 

 described the crystals as yellowish and apparently regular, 

 showing the faces of jlllj, *100|, and jllOj. Meyer (13) failed 

 to obtain this salt, and considered that the salt which 

 Rammelsberg obtained was probably KTlBr 4 2H 2 O. I 

 succeeded in obtaining both salts, crystallising together from 

 various solutions of the composition K 3 Tl 2 Br 9 xH 2 O. The 

 stability conditions of the salt under consideration were not 

 fully made out. Whenever it appeared, it crystallised 

 subsequent to the precipitation of KTlBr 4 2H 2 O, and the 

 slightly reddish tinge of the crystals made them conspicuous 

 among the pale yellow plates of the other salt. But in many 

 cases usually on slight rise of room temperature the crystals 

 disappeared shortly after formation ; and from several 

 solutions no precipitation of the salt took place. Low room- 

 temperatures and fairly acid solutions were distinctly favour- 

 able conditions. 



