POLYMORPHIC TRANSFORMATIONS OF SOLIDS. 



Ill 



as computed, without any adjustment. These figures would demand 

 that Hgl2 be abnormal in many respects. On the rising branch of the 

 curve the yellow modification is less expansible than the red, but above 

 6000, on the descending branch, the yellow becomes more expansible. 

 The place at which AjS changes sign need not necessarily coincide with 

 the maximum. In general, however, the phase with the smaller 

 volume, whether at the higher or lower pressure seems to have the 

 higher thermal expansion. AC'p calculated in accordance with the 

 assumption above as to Aa comes out negative, the yellow having 

 the smaller specific heat. But it has already been shown that ACp 

 is particularly sensitive to errors in the assumed value for Aa, and in 



TABLE XII. 



Mercuric Iodide. 



this case there is a direct determination of the specific heat by Guin- 

 chant, from which it appears that the yellow at atmospheric pressure 

 has the larger heat, the difference being 0.0040 cal. At higher pres- 

 sures, ACp calculated with the assumption as to Aa, decreases rapidly. 

 Combining this with the experimental value at atmospheric pressure, 

 we are probably justified in the conclusion that the difference of speci- 

 fic heats becomes less at high pressures. The sign of A^S found above 

 was verified by direct measurement on the rising branch of the curve, 

 but the direct measurements did not give regular numerical results. 



Phenol. This was Kahlbaum's purest, further purified by crystal- 

 lization at constant temperature in the thermostat. Two lots were 

 purified; the first was pure white in color, and the second was very 



