EFFECTS OF PRESSURE ON NITRATES. 017 



unusual feature, because IV is the phase stable at higher pressures and 

 lower temperatures. That the relation of the compressibilities of II 

 and IV is unusual might be also suggested by the fact, already men- 

 tioned, that the change of volume becomes greater at the higher 

 pressures. The other differences between I, II, IV, and VI may be 

 obtained by a combination of the values given above. The experi- 

 mental data were not accurate enough to allow a statement as to the 

 variation of difference of compressibility with pressure on the transi- 

 tion line; the above values are average values. No direct values 

 were obtained on the short lines II-III and III-IV. 



I was also able to obtain fairly satisfactory measurements of the 

 difference of thermal expansion of III, IV, and II at 77 kgm. II is 

 more expansible than III, the difference being 0.000038 cm.^ per gni., 

 and IV is more expansible than III by 0.000115. Here again, the 

 behavior of IV is anomalous, being more expansible than a phase 

 stable at a higher temperature. The thermal expansions at atmos- 

 pheric pressure have been measured by Bellati and Romanese ^* 

 and by Behn.^^ One may deduce from the data of Bellati and 

 Romanese, although the authors themselves do not give the computa- 

 tion, that the expansion of IV is 0.000222 cm.^ per gm., that of III 

 0.000134, and that of II 0.0001165. The differences between these 

 vahies do not agree at all with the values which I have found, in fact 

 they would make II less instead of more expansible than III. The 

 values of Behn I have computed from a diagram which he gives; he 

 himself does not give the computations. From his data I would 

 make the expansion of II 0.00041 cm.^ per gm., that of III 0.00036, 

 that of IV 0.00048, and that of V 0.00037. The differences between 

 II and III and between III and IV will be seen to agree remarkably 

 well with the values which I found above. There seems to be no 

 doubt that IV is more expansible than III, and that II is more ex- 

 pansible than III. 



The specific heats at atmospheric pressure has been measured by 

 Bellati and Romanese.^* They find for IV 0.407 cal. per gm., for III 

 0.355 cal., and II 0.426. Here again IV is abnormal, its specific heat 

 being greater instead of less than that of the high temperature phase. 

 If now we compute in the regular way the differences of compressi- 

 bility and specific heats at atmospheric pressure, using the values 

 which may be deduced from Table VII for the variation of the change 

 of volume and the latent heat with pressure along the transition curve, 

 and assuming my direct experimental values for the differences of 

 thermal expansion, we shall find that II is more compressible than 



