POLYMORPHISM 



553 



The solubilities in chloroform, in which both forms dissolve 

 much more freely, were therefore determined at temperatures 

 in the neighbourhood of io°. 



Solubility of the Enantiotropic Forms of Phthalylphenylhydrazide in 



Chloroform 

 Temperature. 



5° 

 8° 



9° 

 io a 

 n° 



15° 



• 25 



The solubility curves are given in fig. 2. By plotting on a 

 large scale and intrapolating, it is seen that the transition point 

 lies a little above 9'4°. 



1 8 q 10 11 



Temperature. 



FlG. 3. — Phthalylphenylhydrazide in chloroform solution. 

 p.T. = pale yellow form. d.y. = deep yellow form. 



The extremely slow rate of transformation near the transi- 

 tion point and the very slight difference in density of the two 

 forms did not allow the observational or dilatometric methods 

 of determining the transition point to be employed. 



