INDIUM AND THALLIUM IN CRYSTALLO- 

 GRAPHICAL RELATIONSHIP 



INTRODUCTORY 



EXCEPT in the case of the double sulphates (1), isomorphous 

 relationships between salts of indium and thallium have not 

 been made the subject of investigation. The literature 

 dealing with the crystallography of indium salts is in fact 

 remarkably scanty. Thiel and Koelsch (2) have described an 

 oxide of indium presumably In 2 O 3 which crystallises in 

 octahedra, with spinel habit, like Fe 3 O 4 . The compound 

 In F 3 3H 2 crystallises, according to Thiel (3), in four-sided, 

 probably rhombic, prisms. No similar compound of other 

 trivalent metal has been investigated crystallographically, and 

 no compound of the type MF 3 3H 2 0, where M=A1, Tl, Ga, has 

 hitherto been isolated. Some interesting cases of isomorphism 

 among the silicotungstates of the trivalent metals, including 

 indium, have been studied by Wyrouboff (4) . Thus in the series 

 of salts R 4 (W 12 Si0 40 ) 3 60H 2 0, where R=A1, Fe, Cr, Ga, Bi, 

 the results furnished by Wyrouboff are interpreted by Groth (5) 

 to indicate isomorphism in the case of the salts of Al, Fe, Cr, 

 Ga, and similarity of axial angle, though considerable diver- 

 gence in axial constants, in the salt of Bi, and in In 4 (W 12 SiO 40 ) 3 

 63H 2 0, which differs from the other salts by three molecules 

 of water of crystallisation. The series R 4 (W 12 Si0 40 ) 3 87H 2 0, 

 where R=A1, Cr, Ga, is undoubtedly isomorphous. The 

 members of the two series R 4 (Mo 12 Si0 40 ) 3 93H 2 0, where 

 R=A1, Cr, Fe, and R 4 (W 12 SiO 40 ) 93H 2 O, where R=A1, Cr, Fe, 

 Ga, In, crystallise in octahedra. Lastly, the salt K 3 InCl 6 



2n 



