Results of Crystal Analysis. 419 



The absolute dimensions of the lattice and the parameters 

 will be 



a' = 7-88 x 10" 8 cm., 



5-69 xlO" 8 cm., 



Zj = — a '= 3*17 XlO" 8 cm., 

 I = y~c r = l-76xl0- 8 cm. 

 The sides OP or QR of the tetrahedron (l c ) : 



! 



l c = %' = r53xl0- 8 cm. 



7T 



The distances Op\ Po", etc., from the C to the H atom : 

 Op' =f.lc= 0-77xl0- 8 cm. 



The distance between the carbon atom and one of its 

 hydrogen atoms may probably be a little greater : perhaps 

 the most probable value would be about 10 ~ 8 cm. 



For the side of the cubic lattice of NH 4 I, we found 



7-20 xlO" 8 cm. | 



Comparing this value with those found for a' and c' for 

 N(CH 3 ) 4 I, there is apparently no simple relation. One 

 reason is obvious, and is simply this : 



Inside a volume equal to the volume of the elementary 

 lattice of N(CH 3 ) 4 I there are only two molecules, while the 

 lattice of NH 4 I contains four. In spite of this fact, however, 

 one molecule will on an average nearly take up the same space 

 in the direction of tlie C axis. We might find the sides of a 

 prism similar in form to the elementary lattice, but only 

 containing one molecule ; then we should get 



.. „ ^ TT f Side of the base . . 6'26 x 10" 8 cm. 



For N(OH 3 \Ll n . u ,n . , . 1A _ 8 



v 6 4 [Height of the prism . 4*o2 x 10 8 cm. 



For NH 4 I . . Side of the cube . . 4*54 X 10~ 8 cm. 



We see that the height of the prism in the first case 

 is nearly equal to the side of the cube in the latter. This is, 

 in fact, merely the well-known relation between the topic 

 parameters, as shown in Table I. But it is, indeed, quite 

 remarkable that a molecule takes up the same space in the 



