( 824 ) 
Fig. 41. 
isobars. The isobar which passes through the point 3, has its convex 
side turned towards the v-axis in this point, has a point of inflection 
in its course to the point 1, and touches the line joining the points 
3 and 1 in this point. But then the point 2 lies in such a way that: 
iS ae (= set 
Pel &,—2, de, ok Det, #,—2, 
is negative. In fig. 41° the p‚z-line is drawn for the temperature for 
which this is the case. At again a somewhat higher temperature the 
p,«-line has the shape of fig. 41°. Then mixtures for which the value 
ee, can show the double retrograde condensation. A favourable, 
if not the most favourable case occurs if the points for which 
v,,—9 and v,,=0, lie in the same line normal to the a-axis. 
At somewhat higher temperature, i. e. when the p,a-line has the 
_ position of fig. 41¢, the opportunity is past. Then v,,=0, and 
