Results of Crystal Analysis. 



397 



From the intensity measurements we easily find that the 

 face-centred lattice of N can be made to cover th^ lattice 

 by a displacement al'2 parallel to one of the cube sides. 

 Thus the N and I lattices are in the same relative opposition 

 as the Na and CI lattices in rock-salt. 



Fig. 1. 



OtHj 1. 



NJCH^ /. 



(100) 



i I i 

 1 i i 



' I I 



: i : , : 



(100) 



' ! 1 I 



1 

 1 



' 1 1 , 



(MO) 1 



i i 

 i i 



!- i. : . . 



(110) 



1 



1 1 ' 



1 1 1 



" 1 ' 



' 1 ' ' 

 1 1 



1 l 



i r ' 



(001) ' 



1 ' » 





l I [ 

 I t l 

 I i i 

 1 I c 



i i » 



(101) 



J 

 1 

 1 



: i 



1 i _._.!__ 



(Hi) 





i i ■ 



V I 

 ! 1 

 I I |l 



(111) 



i ' 



i i 



i | 



0.1 



0.2 



0.3 



0.1 



0.2 



0.3 



If we do not take into account the small reflecting-power 

 of hydrogen, this arrangement mentioned would give a 

 normal distribution of intensities for the faces (100) and 

 (110) in agreement with observations. 



In the (111) face the N atoms are situated in planes 

 midway between the I planes, which will produce a 

 diminution of the intensity of the first and third order 

 spectrum, which is also clearly brought out by the experiments. 



With regard to the H atoms, their reflecting-power is 

 probably too small to enable any experimental determination 

 of their exact position. Most probably the four atoms which 

 belong to each molecule are placed in the corners of a tetra- 

 hedron with the N atom in the centre, and in sue!) a way 

 that the lines from the N atom to any of the four H atoms 

 are parallel to one of the diagonals of the cubic lattice. 



Phil. Mag. S. 6. Vol. 33. No. 197. May 1917. 2 E 



