156 MOLECULAR GROUPING 



increases c by 0-019 or * OI 3> but also a by 0*026 or oo22. 

 It is then natural to assume that with the configuration 



K 



OH P OH 



II 

 O 



the line passing through K O P=O gives the direction 

 of the principal axis c, so that the enlargement due to 

 substitution of NH 4 for K only lengthens the principal 

 axis, whereas that due to the substitution of As for P 

 produces an expansion in all directions. 



OXFORD : HORACE HART 

 PRINTER TO THE UNIVERSITY 



