586 



BRIDGMAN. 



dii'ectly measured at several points. These values, which are some- 

 what more self consistent than usual, are shown in Figure 3. At low 

 pressures (high temperatures), the form with the larger volume is 

 more compressible, but as we go along the transition curve to higher 

 pressures and lower temperatures, the difference of compressibility 

 become less, and finally reverses sign in the neighborhood of the 

 region of rapid curvature. Below 70° the modification stable at the 

 higher temperature is the more compressible. This is perhaps what 

 one might be at first inclined to call the normal behavior, but it is to 

 be noticed that there are two opposite factors here. It is natural to 

 think that the phase of greater volume, as well as the high tempera- 

 ture phase would be the more compressible. Evidently both of these 

 things cannot happen at the same time on this curve. At low pres- 



<-.0„6 



12345678 9 

 Pressure, kgm./cm.^ x 10^ 

 Silver Nitrate 



10 



Figure 3. Silver Nitrate. The observed differences of compressibility 

 between the two phases. 



sures it is the phase of greater volume which is the more compres- 

 sible, but at high pressures it is the high temperature phase which is 

 the more compressible. The relations in this regard at the high 

 pressure end of the curve are similar to those on the melting curve of 

 water and ice I, where water, although of smaller volume, is more 

 compressible than ice. It should be remarked that this reversal in 

 the sign of the compressibility is not to be regarded as remarkable 

 in view of the sudden change of direction of the transition curve. 

 The transition curve is unusual in this respect; one may expect 

 unusual features in the behavior of the two phases to correspond. 



The differences of the expansion and of the specific heats may be 

 calculated from the difference of compressibility, and are shown in 

 Table II. The difference of expansion runs roughly parallel to the 



