EFFECTS OF PRESSURE ON NITRATES. 619 



back to 1857/^ says that LiNOs is trimorphic. Other authorities, 

 Groth included, do not mention this, however, and the supposed 

 polymorphism is doubtless to be explained as due to the transition 

 points of the hydrates, because LiNOs crystallizes with H2O. I made 

 especially careful search for other forms, isothermally at 20° and 200° 

 to 12000 kg., and at constant volume between 100° and 160° at ap- 

 proximately 3000 kg. and between 30° and 160° at 8000 kg. 



Hg2(N03)2+H20 does not crystallize isomorphously with the other 

 univalent nitrates. The anliydrous salt showed no new form at 20° 

 or 90°. At the higher temperature there was probably some decom- 

 position; temperature was not raised higher for fear of further de- 

 composition. The salt crystallizing with one molecule of water 

 probably has a transition point at 20° at 8000 kg. ; no other tempera- 

 ture was tried. The substance is a difficult one to investigate, because 

 beside containing water of crystallization it is hygroscopic. It is 

 difficult to remove the absorbed moisture without dehydration. The 

 material deserves further investigation, however. 



Hg(N03)2 was the first of the nitrates tried which was not univa- 

 lent. I know of no cases of polymorphism among this class; there 

 is no particular reason to expect other forms at high pressures. 

 Hg(N03)2 showed nothing new at 20° to 12000; on heating to 180° 

 at 1000 kg. it decomposed with almost explosive violence, depositing 

 metallic mercury throughout the apparatus. 



Pb(N03)2 is stated by xA-rzruni ^^ to exist as a mineral in two forms. 

 I found no new form up to 12000, however, at 20° or 200°. 



A1(N03)3 was tried at 20°, 100°, and 200° with no effect. After 

 the run it was found to have decomposed into a brownish mass, 

 actively deliquescent. It was somewhat moist before the run. 



Discussion. 



IVIost of the facts described in this paper are collected and exliibited 

 qualitatively in Figure 16, which shows the phase diagrams, pressure 

 against temperature, and indicates other data also. The drawings 

 are made with some exaggeration, so that the direction of curvature 

 of each transition line may be readily' noticed. The arrows on the 

 lines show the directions in which Av decreases numerically. An a, (3, 



17 P. Kremers, Pogg. Ann. 92, 520 (1854) and 93, 23 (1854). 



18 A. Arzruni, Phj'sikalische Chemie der Krystalle. Vieweg und Sohn, 

 Braunschweig (189-3), p. 42. 



