EFFECTS OF PRESSURE ON NITRATES. 607 



not thought of this trick of procedure at the time the measurements 

 in the neighborhood at the triple points I-II-IV-VI were made, and 

 some error is introduced into the actual data which it would have been 

 possible to avoid if the measurements had been repeated. However, 

 the values of the changes of volume at these points seem to be indi- 

 cated with sufficient certainty. At low pressures, where the method 

 is that of varying temperature at constant pressure, lag is not so 

 troublesome, and repetition was not necessary. The low pressure 

 point on the curve I-II was not repeated; the repeated points at low 

 pressure for the transitions II-III and III-IV were in substantial 

 agreement with the first determinations. 



The experimental \'alues for the eciuilibrium pressures and tempera- 

 tures and the transition curves are shown in Figure 13, the experi- 

 mental points and the curves for the change of volume in Figure 14, 

 the computed values for the latent heats and the change of internal 

 energy in Figure 15, and the numerical values are collected in Table 

 VII. In the equilibrium diagram the points of both runs, in 1913 

 and 1914, have been included, but in the change of volume diagram, 

 only the points of 1914 have been given. The irregularities of the 

 early points for Av were so great that it was almost hopeless to attempt 

 to obtain any information from them. 



Several features of these diagrams require special comment. The 

 phenomenal steepness of the melting line is to be noticed. The point 

 on the melting line at 200° was determined experimentally, but for the 

 point at atmospheric pressure I have adopted the value of Lehmann.^^ 

 An attempt to determine this point directly did not give satisfactory 

 results, because of decomposition. This decomposition could be 

 plainly detected at 200°, producing a rounding of the corners of the 

 curves, so that the value for the change of volume cannot be counted 

 on with much certainty. At the melting point at atmospheric pres- 

 sure the decomposition was so much greater that it did not seem worth 

 while to attempt to calculate a probable value for the change of 

 volume at atmospheric pressure. The decomposition at atmospheric 

 pressure has been found by other observers also; Behn ^^ states that 

 it is noticeable at temperatures as low as 100°. It would seem, how- 

 ever, that this decomposition is an effect chiefly found only when the 

 liquid phase is present, or at least that it is effectively prevented by 

 the higher pressures, because no trace of it was ever found on any of 

 the transition curves between solids, even as high as 200°. 



13 O. Lehman, ZS. Kryst. 1, 97-131, (1877). 



