﻿148 Vernation of Triple-Point with Hydrostatic Pressure. 



solid and one for the liquid. The difference of the slopes of 

 these curves at their point of intersection will be given 

 exactly by the equation 



dT " 



dT 



dT 



where the specific volumes of the liquid and solid are repre- 

 sented by u 2 and u ± . Fig. 3 is such a diagram. 



The locus of the triple-point. 



On this diagram the vapour-pressures are shown for two 

 hydrostatic pressures differing by dp. Their point of inter- 

 section shifts from C to C owing to this change of pressure, 



Fig. 3. 



«»+!$** 



and the temperature of the triple-point shifts from r to t or 



dT 

 through the amount -r dp Draw a vertical through C 



cutting the lower curve at A, and draw a horizontal through 

 C cutting this vertical at B. Then 



AC' = AB + BC 

 or 



(~^\ dn= - **, / feg\ -fe 3 



\ *P h 



dp 



*P 



*{' 



VSJ, V^ T 



\} + iw\ d **> 



as can be seen by inspection of the figure. 



* This can be obtained at once from the general expression for the 

 total differential of the vapour-pressure in passing from one triple-point 

 to another : 



dp 



dT 



dp 1 dT 



