VELOCITY OF POLYMORPHIC CHANGES BETWEEN SOLIDS. 



61 



above and below is shown in Figure 2; this was obtained directly 

 from the original curve shown in Figure 1. 



Curves like these giving the time rate of transformation as a func- 

 tion of pressure were computed from the data and plotted for all the 

 substances for which the time rate could be measured. A few ex- 

 amples of these for different substances are shown in Figures 3, 4 and 5. 



To completely present all the data would mean to give all the 

 curves like these, a pair of curves corresponding to every observed 



.07 



.06 



0) 



3 

 C 



a 



c 



S 05 



.04 



a. 



be 



c 



C3 



.03 



02 



,01 



7500 8000 



Pressure 



KCIO, 



.00 

 2750 3250 



Pressure 



NH SCN 



Fig. 4. Fig. 5. 



Figure 4. Transition velocity of Potassium Chlorate as a function of 

 pressure at 200°. 



Figure 5. Transition velocity of Ammonium Sulfocyanide as a function of 

 pressure at 0°. 



pressure and temperature point of the transition curves. Such a 

 complete presentation would demand a prohibitive amount of space, 

 and would be of little significance, because the precise form of the 

 curves depends on the dimensions of the particular apparatus. There 

 are, however, certain features common to all the curves which will 

 be discussed here. By making abstraction of these essential features, 

 each curve may be rei^resented by a single point. The various repre- 

 sentative points for a single substance may then be collected into a 

 single diagram, and curves drawn through them. To every transition 

 curve there corresponds, therefore, a pair of curves giving the main 



