624 BRIDGMAN. 



not the same, calling the first 3 and the second 2. It is significant, 

 however, that crystallographically, both these phases are remarkably 

 similar; Wallerant describes both as ortho rhombic, quasi-tetragonal, 

 optically negative. The chief argument against their identity seems 

 to be that they do not form a continuous mixed crystal series, but 

 such a continuous series would be impossible in any e\'ent because of 

 the anomolous behavior of the tetragonal form II. In fact it is the 

 peculiar behavior of the tetragonal form that supplies Wallerant with 

 the argument that the forms II and V of NH4NO3 are identical. On 

 the whole, the evidence does not seem to me conclusive that 3 and 2 

 are not identical; in view of the suggestiveness of the phase diagrams, 

 further crystallographic investigation would be desirable. At any 

 rate it is significant that the phases 3 and 2 are so much alike. 



Further identification of the phases of NH4NO3 is probably not 

 possible; the phases 4 and 5 are not likely to exist in the other nitrates. 

 These phases, if they are capable of existence at all elsewhere, are 

 probably to be found at considerable negative pressures, which we 

 cannot realize experimentally. On the other hand, it would not be 

 strange if NH4NO3 had modifications peculiar to itself. The Radical 

 NH4 cannot be surrounded by so simple a field of force as a single 

 atom of Potassium, Rubidium, Caesium, or Thallium, and it is not 

 surprising if in virtue of its greater complication larger numbers of 

 stable forms are possible. Tutton has found the same behavior 

 among the sulfates. 



Summary. 



The phase diagrams between 0° and 200° and fron^ 1 to 12000 kg. 

 have been determined for NH4NO3, KNO3. RbX03, CsNOs, TINO3, 

 and AgN03. One new phase has been found for NH4NO3 and two 

 new ones for KNO3. The usual thermodynamic data, which include 

 change of volume, latent heat of transition, difference of compressi- 

 bility, thermal expansion, and specific heat, are given. 



AgNOs stands in a class by itself. The nitrates of Rb, Cs, and Tl 

 have closely similar phase diagrams. The more complicated dia- 

 grams of KXO3 and NH4NO3 may be brought into relation with these 

 by a proper identification of the new high pressure forms with the 

 atmospheric forms of RbNOs, CsNOs, TINO3. Additional crystallo- 

 graphical work seems necessary, however, before this identification 

 can be established. It is significant that at high pressures the dia- 



