NOV. 4, 1921 



WYCKOFF: STRUCTURE ALKALI HALIDES 



433 



Rubidium bromide 

 The structure of this crystal has already been determined^ as iden- 

 tical with that of sodium chloride; (iioo = 6.93 A. U. 



® R • X 



Fig. 2. The unit cell of the body-centered grouping. 

 Rubidium iodide 



Caesium chloride 

 Caesium chloride has been shown^" to be body-centered; Jioo = 4.12 



A. U. 



Caesium bromide 



Calculations based upon the positions of the lines in the photographs 

 and the previously determined density show that but one molecule 



3 W. p. Davey. Phys. Rev. (2) 18: 103. 1921. 



10 W. P. Davey and F. G. Wick. Phys. Rev. (2) 17: 403. 1921. 



