POLYMORPHIC TRANSFORMATIONS OF SOLIDS. 



97 



has also remarked on the sharpness of the transition at atmospheric 

 pressure. The essential agreement of Wahl's and my results at high 

 pressures for the width of the band of indifference, by methods entirely 

 different, would seem to indicate some real physical significance in the 

 absolute values found by us, characteristic of the substance, and not a 

 property of the particular form of apparatus. The width of the II-III 

 band was distinctly greater than that of the I-II band, being from 

 70 to 100 kgm., while that of the I-IIT band was less, 11 to 33 kgm. 

 There seem to be no previous determinations of either AV or AH for 

 the transition. 



The data do not justify any attempt at estimating Aa, A^, or ACp. 



Silver Iodide. — This substance was Eimer and Amend's purest, 

 used without further purification. Only one filling of the apparatus 

 was necessary in getting the high pressure points, and one for the low 



J1234567 

 Pressure, kgm./cm.^ x 10* 

 Silver Iodide 



Figure 21. Silver Iodide. The observed equilibrium temperatures and 

 pressures. 



pressure points. The transitions ran cleanly, and gave no such 

 trouble from lag as was found by Tammann.^^ The dry powder was 



13 G. Tammann, "K. and S," p. 302, and ZS. f. Phys. Chem. 75, 733-762 



(1911). 



