( 129 ) 



as was carried out above on the /y-line, and so for the p-linê, for 

 which fig. 22 would represent the course of the (jr-line, we have to 



Fig. 22. 



draw a straight line in such a way that its height indicates the 

 middle value of the ordinates of the q-curve. That from the outset 

 we have not followed this course for the determination of the 

 coexisting phases in which the values of x, and ,;•, for given value 

 of p are determined, is due to the fact, that I his way of determina- 

 tion is again possible without correction term only when the whole 

 p-line is found between the two coexisting phases without interruption 

 in the v , «-diagram ; and as for the equilibrium between vapour and 

 liquid phases as a rule this condition is not satisfied, and as it is 

 only by way of exception that the ^-line has split up into two 

 branches, the determination of coexistence by the first mentioned 

 method may as a rule be considered as possible. But nevertheless, 

 in some cases the determination by means of the properties of the 

 value of q, following a p-line, is to be preferred. If we do so in 

 the case discussed for the determination of the coexistence of a liquid 

 phase with a second liquid phase, we must choose every time other 

 />lines, and along each of these plines the course of q as function 

 of x is as drawn in fig. 22 ; and with the simple shape of such a 

 j-line there is only question of a single straight line along which 



qc (■'",— '*i) = I <J dx. The binodal curve for the coexistence of liquid 



l 

 with liquid has therefore a simple shape and is restricted to the 

 stable region. 



