POLYMORPHIC TRANSFORMATIONS OF SOLIDS. 



77 



more irregular than usual. The same cause produces an even greater 

 irregularity in the AJ' values; we have here a large percentage error 

 due both to the extreme smallness of the change and the necessity for 

 a considerably wider extrapolation than usual. To reduce this error 

 as much as possible, the measurements of AV were made with both 

 increasing and decreasing pressure. 



The very small change of the volume and the comparatively large 

 lag of the reaction combine to make impossible measurements of the 

 rate of the reaction. After the reaction had once started, it ran to 

 completion within the time required for the dissipation of the ordinary 

 heat of compression. 



The experimental results are shown in Figure 9, the computed 

 values for AH and AE in Figure 10, and the numerical values in Table 



12 3 4 5 

 Pressure, kgm./cm.' x 10' ' 

 Potassium Sulfide 



Figure 9. Potassium Sulfide. The observed equilibrium temperatures 

 and pressures and the changes of volume. 



IV. The beha^•ior of the various quantities is like that of a typical 

 liquid. 



There are no other values for comparison, since it was not knoA\Ti 

 before that KoS is dimorphic. 



The direct measurements of the difference of compressibility are 

 irregular and inaccurate, but the probability is that the low tempera- 

 ture form of K2S is the more compressible, the difference of compressi- 

 bility being of the order of O.O5I . This means that the low temperature 

 form is also more expansible, and has the higher specific heat. The 

 difference of expansion is of the order of O.O48, and of the specific heats 

 of the order of 3 kgm. cm. per gm. 



