Wyckoff — Crystal Structure of Silver Oxide. 187 



ing in the photograph fit about equally well. The agree- 

 ment is as good as could be expected in view of the uncer- 

 tainties involved in these calculations. 



Indices 



Table 2. 



Intensity (arbitrary units) 

 Estimated Calculated for arrangement ( a ) 



HI (1) 

 100 (2) 

 110 (2) 

 113 (1) 



10 77,800 

 7 34,900 

 7 43,200 

 6 50,500 



Arrangements (b), (c) and (d). — Because of its iden- 

 tity with (a), grouping (c) requires no further treatment. 

 Because of lack of knowledge of the laws of scattering, 

 an entirely satisfying elimination of (b) and (d) can 

 scarcely be made with these data. It can, however, be 

 shown that they are both improbable. 



These observations then have shown that there is but 

 one simple structure, (a), the "cuprous oxide structure," 

 which is in agreement with powder measurements 

 obtained from silver oxide. Furthermore they have 

 shown that neither of the two more complicated group- 

 ings which are possible structures from the determination 

 of the value of the ratio m/n 3 are probable. In all likeli- 

 hood, then, the atoms of silver oxide are arranged as 

 defined by (a). 



It is of interest that silver as oxide agrees with its 

 analogue, monovalent copper, in departing from the per- 

 haps more common cubic arrangement of two atoms of 

 one kind and one of another, the "calcium fluoride struc- 

 ture. ' ' Since arrangement (a) can be deduced from space 

 groups possessing either paramorphic or enantiomorphic 

 hemihedry, or holohedry, this determination of the struc- 

 ture of silver oxide has not succeeded in defining uniquely 

 its crystallographic symmetry. On the basis of recorded 

 face development it has been customary to assign to 

 cuprous oxide, with the same structure, an enantiomor- 

 phic hemihedry. It has been suggested 7 that this enantio- 

 morphism could be explained if one or both of the kinds 

 of atoms occupied positions slightly displaced from that 

 of (a). Since in the arrangement of their atom positions, 



7 W. H. and W. L. Bragg, X-rays and Crystal Structure, p. 157 (London, 

 1916). 



