CONSTITUTION AND TEMPEEATURE ON MAGNETIC SUSCEPTIBILITY. 263 



and i is the resultant intensity of magnetization induced in the direction of the 

 external field. The compressibilities will now be different along and perpendicular to 

 this direction, and the change of volume should be proportional to i 3 for the particular 

 value of the applied field. This result agrees with experiment* 



We can see in a general way how the sign of (5V on crystallization may sometimes 

 be positive and sometimes negative. Usually the molecular packing in the crystalline 

 state will be closer than that in the liquid state, but it may happen that the 

 configuration of the molecule is such that, when the parts which have the strongest 

 magnetic attraction for each other are in the position of minimum potential energy, 

 the packing is more open than in the liquid state. The appearance of the internal 

 fbrcive on crystallization will in this case be accompanied by expansion. In the former 

 case the appearance of the internal forcive will be accompanied by contraction. 



The region of stability of the crystalline state is represented on the pressure 

 temperature diagram by a closed area (fig. 2). 



Vitreous 



Fig. 2. 



This area will in general be divided into four quadrants by the loci of the lines 

 <?V = and L = 0, where (5V is the change of volume on crystallization and L is the 

 latent heat. 



In the four quadrants the following conditions hold : 



If the melting-point is at some point along the arc AB of the first quadrant, 

 increase of pressure raises the m.p. and <SV and L are positive. This corresponds 





VOL. ccxx. A. 



* NAGAOKA and HONDA, ' Phil. Mag.,' vol. 46, p. 268, 1898, 



2 o 



