192 R. W. G. Wyckoff — Zinc Br ornate Hexahydrate. 



for the ammonia groups in the hexammonate nickel 

 halides s and in nickel nitrate hexammonate. 9 



Summary. 



From a study of the Laue photographs to which 

 crystals of zinc bromate hexahydrate give rise, it is 

 shown that they must have the symmetry of the space 

 group T h 6 . Though it is impossible to determine the 

 positions of the atoms in this crystal, such knowledge of 

 the underlying space group defines uniquely the manner 

 of arrangement of its atoms. The length of the side of 

 the unit cube which contains four chemical molecules is 

 found to be 10.31 A.U. 



Pasadena, California, 

 May, 1922. 



8 Kalph W. G. Wyckoff, Jour. Am. Chem. Soc, June, 1922. 



9 Idem. ibid. 



