704 
The curve Mam b represents the solu- 
tions which, at a given temperature are 
saturated with F under their own pressure; 
the compositions of the vapours are indi- 
cated by the curve M, a, m, b,. We may, 
‘ / 
MS “9 therefore, call the curve M amb, the iso- 
( ; : 
cm 9 thermic saturation line of F under its own 
ig. 7. 
vapour pressure and M, a, m, b, its con- 
jugated vapour line; where no mistake is possible we will omit 
the adjunct “isothermic”. | 
As a rule, the saturation line of F at a certain constant pressure 
P and the saturation line of F under its own vapour pressure will 
differ but little, so that, practically, we may substitute the one for 
the other; as to exceptions for temperatures in the vicinity of the 
melting point of the compound F to them we will refer later. 
We have already stated above that the saturation line of F, under 
its own vapour pressure, must exhibit a point with a vapour pres- 
sure maximum and another with a vapour pressure minimum; the 
first is represented in Fig. 7 by M, the second by m. On the con- 
jugated vapour line, there occur, of course also two points M, and 
m, of which M, represents the vapour with the vapour pressure maxi- 
mum and m, that with the vapour pressure minimum. The arrows 
on both curves indicate the direction of the increasing vapour pressure. 
The points F, M and M, are, of course, situated on a straight 
line and agree with the isothermic-isobaric diagram of Fig. 2; the 
points F, m and m, which are of course also situated on a straight 
line, agree with the isothermic-isobaric diagram of Fig. 5. 
We have assumed above that on lowering the pressure the diagrams 
3, 4 and 5 succeed each other, or in other words that the points a 
and b of Figs. 3 and 4 had already coincided in a point m of Fig. 5 
before the vapour region had extended to over F. If, however, the 
vapour line has already passed point F before aand b of Fig. 3 or 4 
coincide we get an isotherm as in Fig. 8 which, however, does. 
not differ essentially from Fig. 3 or 4. On further reducion of the 
pressure Fig. 3 is converted into Fig. 9. The vapour saturation line 
of F now meets the vapour line e, d, in m,; the saturation line of 
F not drawn in Fig. 9 meets the liquidline ed in m. The vapour 
saturation line of EF represents the stable, the saturation line of F 
the metastable conditions. The points F,m and m, are, of course, 
again situated as in Fig. 5 on a straight line; as, however, these 
points are situated, in the two figures, differently in regard to each 
