CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



POLYMORPHIC TRANSFORMATIONS OF SOLIDS UNDER 



PRESSURE. 



By P. W. Bridgman. 

 Received, May 1, 1915. 



CONTENTS. 



Page. 



Introduction 55 



Experimental Procedure 57 



The Effect of Impurities on the Transition Lines 59 



The Equation of the Transition Lines 63 



Data 68 



Potassium Sulfocyanide 68 



Ammonium Sulfocyanide 72 



Potassium Sulfide 76 



Potassium Chlorate 78 



Potassium Nitrite 81 



Carbon Trichloride 84 



Carbon Tetrabromide 90 



Silver Iodide 97 



Mercuric Iodide 104 



Phenol Ill 



Urethan 118 



Introduction . 



In this paper data are given sufficient for a thermodynamic specifi- 

 cation of a number of polymorphic transitions between soHds. Besides 

 the transition quantities themselves (change of volume, latent heat, 

 slope of the transition line) it has been possible in a good many cases 

 to give at least a rough approximation to the difference of compressi- 

 bility, thermal expansion, and specific heat of the reacting phases. 

 The field is a comparatively unworked one. Hitherto investigations 

 on polymorphic changes have been concerned for the most part with 

 the temperature of transition at atmospheric pressure. There are 

 not many measurements of latent heat or change of volume even at 

 atmospheric pressure. Still fewer measurements of the effect of pres- 

 sure have been made; many of these are due to Tammann, whose 

 pressure range was considerably lower than that of this paper. The 



