707 
call the saturation line of F in figs. 7 and 11 a circumphased and 
that of fig. 12 an exphased one. 
F contracts on melting. An increase in pressure (at constant T) 
will, therefore cause a fusion of solid F, a decrease of pressure a 
solidification of molten F. On decrease of pressure the isothermic 
saturation line of F will consequently form first of all in F and 
then extend at first rapidly and then slowly. 
We now start from such a pressure that a heterogeneous region 
I, does exist, but not yet the saturation line of F. We then have 
fig. 1 from which we must, however, leave out the saturation line 
of F. On lowering the pressure, the liquid line shifts towards F and 
we assume that it has already just passed the point F when the 
saturation line of F appears in the point F. The isotherm then has 
a form as in fig. 5 or 6 in which, however, we must assume the 
curve de to be very close to F. On further reduction of pressure 
the saturation line of F now rapidiy extends round the point F and 
overtakes the liquid-line so that at a definite pressure they come into 
contact with each other. We then obtain an isotherm as in fig. 5 
or 9. In fig. 5 however, we must imagine the saturation and the 
vapour saturation lines of F to be drawn and in such a manner 
that the first curve comes into contact with e d in m, the second 
curve with d, e, in m,. In Fig. 9 we must also imagine the satu- 
ration line of F coming into contact with the curve d e in m. 
On further reducing the pressure fig. 4 or 8 are formed and as 
the velocity of the saturation line of F now becomes smaller than 
that of the liquid-line, these are again converted into fig. 5 or 9. 
Hence on reduction of pressure we obtain a succession of isotherms 
such as: 
fig. 5 — fig. 4 — fig. 5a or fig. 9 — tig. 8 — fig. Ja. 
in which fig. 5a differs from fig. 5, and fig. 9a from fig. 9 in this 
way, that in the figures indicated by a the liquid line ed is removed 
further from point F. Also, as the fig. 5 and 9 occur at higher 
pressures than the fig. 5a and 9a the letters m and m, must be 
considered as being replaced by M and M,. 
From these considerations it now follows 
that the saturation line of F must exist 
under its own pressure as in fig. 13, hence 
exphased; the correlated vapour line may 
be exphased as well as cireumphased and 
may also be situated on tbe other side of F. 
The case may also occur that the satu- 
46 
Proceedings Royal Acad. Amsterdam. Vol. XV. 
