60 



BRIDGMAN. 



shown in Figm-e 1, taken from the data for silver nitrate. It is not 

 however, these curves in which we are primarily interested, but the 

 rate at which the transition runs at constant temperature as a func- 

 tion of the distance measured in kilograms from the equilibrium point. 

 The rate at which pressure changes may evidently be found directly 

 from the tangents to curves like those of Figure 1. In practise the 

 readings were made at frequent enough intervals so that the tangents 



8000 

 Pressure 

 Silver Nitrate 



Fig. 2. 



8400 



5800 6600 



Pressure 



Pliosphorus 



Fig. 3. 



Figure 2. The slope of the curves of Figure 1, expressed as fractions of the 

 total transition per minute, plotted against pressure. Two of the points on 

 the high pressure branch are beyond the scale of the diagram. The total range 

 of velocity on the high pressure branch is 5000 fold. 



Figure 3. Transition velocity of White Phosporus as a function of pressure 

 at 0°. 



may be replaced by the secants connecting successive observations. 

 From the rate of change of pressure we can obtain immediately the rate 

 of transition, that is, the fractional part of the complete transition per 

 unit time, if we know the total change of pressure corresponding to 

 the complete transition from one phase to the other. The total change 

 of pressure is given directly by the curves from which the change of 

 volume has been determined. Such a curve of reaction velocitv from 



