Wychojf — Crystal Structure of Alahandite. 245 



necessary to assign a value to f{d/n). An approach to 

 the correct form of this function seems to be furnished 

 by writing 



f{d/n) = {d/n)\ 



Introducing this approximation and remembering that 

 the intensity of the powder reflection from a kind of face 

 is given by the product of the intensity of reflection from 

 one of the faces into the number of like planes, such 

 calculations yield for the four strongest lines. 

 For the grouping (II) : 



Plane Order [n) d/n I Intensity (of powder reflection) 



100 2 0.500 6,670 40,000 units (arbitrary) 



110 2 .354 2,460 29,600 

 120 2 .223 1,325 31,800 



112 2 .204 1,115 26,800 



For the grouping (III) : 



Plane Order [n) d/n I Intensity (of powder reflection) 



111 1 0.577 4,680 37,400 

 110 2 .354 3,333 40,000 



113 1 .301 1,270 30,500 



112 2 .204 1,111 26,700 



The estimation of intensity and measurement of spac- 

 ing for the four strongest lines in the powder photograph 

 furnish 



Measufcd 



d/n 



Calculated 



for the Plane 



n 



Estimated 

 Intensity 



2.61 All. 



1.84 



1.17 



1.06 





2.60 A.U. 

 1.84 

 1.16 

 1.06 



100 

 110 

 120 

 112 



2 

 2 



2 

 2 



10 

 8 

 6 

 5.5 



From a study of these measurements it is evident, 

 assuming of course that four molecules are associated 

 with the unit cell, that the arrangement of the atoms of 

 alabandite is described by (II) or by such values of u and 

 u' in either (I) or (IV) that the arrangement approaches 



