( 912 ) 
Fig. 24. 
negative value of a, + a, — 2a,,, which is derived from VAN DER 
Waats’ diagram of isobars by making the points of intersection of 
dp dp RS ee 
Dn 0 and rn 0 interchange their roles of isolated point and double 
point (Cf. van per Waais These Proc. IX p. 629). But so long as the 
experiment has not given us any case of maximum plaitpoint tempe- 
rature, it does not seem desirable to me to dwell any longer on this. 
For it follows immediately from this that in all the examined cases 
certainly no maximum critical temperature of the mixture taken as 
homogeneous can occur. In this respect the circumstances for a 
maximum differ from those for a minimum. As VAN DER WAALS 
rc 
ie ae 
a minimum value of / need 
D 
already observed (These Proc. XI p. 15 
not necessarily be attended by a minimum plaitpoint temperature. 
It migbt be that above the minimum 7%, the plait continues to exist 
for a long time till in the meantime the point that indicates the 
critical temperature of the mixture taken as homogeneous has reached 
ve =O or x1, a case which is not to be considered as impossible 
especially when the minimum 7%, is to be found very near one of these 
values. But when there is a maximum 7%, i.e. when at the higher 
of the two critical temperatures of the pure substances taere are 
still mixtures which are below their 7%, there are sure to be still 
mixtures which are below their plaitpoint temperature, and so 
there will be a maximum plaitpoint temperature. This in connection 
with the fact that the limits of the coexisting phases and of the 
