( 196 ) 



third point of intersection on the liquid branch of the other branch. 

 With increase of T the two points of intersection on the left- 

 hand branch coincide in the point for which x is found from 



f da \— 2 d * a 

 [dx) " 3 a ~dx* 



Everything shows that at the temperature of the 



<Pp 



double point that part of the line = runs through the double 



dvdx 



Fig. 35. 



point that lies beyond the minimum volume. With T lower than 



that of the double point this part of the curve remains entirely in 



the unstable region. 



If we try to ascertain on what it depends whether the value of 



1 da 1 db 



x which corresponds to = is smaller or larger than that 



a dx b dx 



, /"daY 2 d*a ,,,.,., 



for which — |= — a — we may, to decide this, substitute the 

 \dxj 3 dx' J 



value of x which follows from the second of these equations, in : 



da db 



b a — . 



dx dx 



If we then find a positive value for this form, the first case 



