34 ADAMS AND WILLIAMSON : PHYSICAL CONSTANTS OF MUSTARD GAS 



be seen that the compressibility measurements of table i were 

 extended by about 500 megabars into the region of undercooled 

 liquid. At ordinary pressures the melting point of the sample 

 used is 13.9°, but although it was a carefully purified and color- 

 less preparation, a slight variation in pressure during melting 

 was observed. This indicates a small amount of impurity re- 

 maining in the material and doubtless the melting point of pure 

 dichloroethylsulfide at P = i is a few tenths of a degree higher 

 than the figure here given. 



45 



40 



35 



30 



O 



O 

 US 

 Q 



UJ 



q: 25 



< 

 q: 



UJ 20 



LU 



15 



10 



500 



1000 



15C0 



2000 



2500 



PRESSURE MEGABARS 



Fig. 2. The small circles in this figure represent the freezing points at various 

 pressures. The smooth curve drawn through the circles is slightly concave toward 

 the pressiu^e axis. 



In order to test for the possible existence of other sohd modi- 

 fications of this substance, the pressure on it was increased to 

 12,000 megabars at 38°; but no new^ forms were discovered. 



From the data contained in table 2 we may calculate by the 

 Clausius-Clapeyron equation the latent heat of melting. Thus 



Ai/ = o.o239i7(Fi— F.)dP/d7, 



where AJf is the latent heat in calories per gram, T is the absolute 

 temperature, Vi — F, is the change of volume on melting in 



