POLYMORPHIC CHANGES UNDER PRESSURE OF THE 

 UNIVALENT NITRATES. 



By p. W. Bridgman, 



Received, January 13, 1916. 



TABLE OF CONTENTS. 



Page. 



Introduction 581 



Silver Nitrate 582 



Caesium Nitrate . . . . • 587 



Rubidium Nitrate 590 



Thallium Nitrate 593 



Potassium Nitrate 599 



Ammonium Nitrate 605 



Nitrates with No New Forms 618 



Discussion 619 



Summary 624 



Introduction. 



In this paper the thermodynamic elements involved in the poly- 

 morphic changes of a group of closely related univalent nitrates 

 are given over a considerable pressure and temperature range. The 

 apparatus, the experimental methods, and the methods of computa- 

 tion are in every way the same as were described in a previous paper ^ 

 on a similar subject. 



Particular interest attaches to the group of the univalent nitrates 

 because of the wide occurrence of polymorphism in this group, the 

 unusual number of polymorphic forms, and their complicated rela- 

 tionships. Here, one would expect, is a particularly favorable field 

 in which to look for new forms, stable only at high pressures, which 

 will supply the gaps at atmospheric pressure. It turns out, however, 

 that there are comparatively few new forms in the range reached here : 

 one new form for ammonium nitrate and two for potassium nitrate; 



1 P. W. Bridgman, Proc. Amer. Acad. 51, 53-124 (1915). 



