1222 
We will choose the new system F+ L’ + G’ in such a manner 
that it is in equlibrium at the temperature 7’ and the pressure 
P+dP. Then, as follows from our previous communications, 
dx, dy, dv, and dy, are determined by: | 
(we — a) r + (y—B8)s] da + [(w —a)s + (y — 3) t] dy = AdP 
eer + (y,—a) 8] de + [(e,—a) s + (WB) 1] dy =(A4C) dP 
and two corresponding equations which determine dz, and dy, 
From this we find: 
E (rt —s’) dw = — (sAr +t A) dP E (rt—s*) dy = (rAz+sA,) dP 
E (r,t, —8,7) da,=(s,Az, +t, Ay,)@P E (r,t,—8,") dy, = — (7, Ax, +8, dy AP. 
After substitution we find: 
Ar + Bededy + tty mn + Bard Ay + en 
m q A EE 
rt — s? r,t, —8,’- dP 
so that A and dP must have the opposite sign. 
In the above relation 4 represents the change in volume if both 
systems are compared at the same pressure P; if, when the new . 
system is taken at the pressure P+ dP, the change in volume is 
represented by 4', we get: 
A'=A+ giles ae 
dP 
in which Vz represents the total volume of the new system at the 
pressure P. From this follows that A’ and 4 have always the same 
sign and A' and dP always the opposite one. 
Let us now consider the system /’+ L + G at a constant tem- 
perature, namely the saturation line of / under its own vapour 
pressure and its conjugated vapour line. These are respresented in 
fig. 7 (1), 11 (I), 12 (D and 13 (I) by the curves Mamb and M,a,m,)h,. 
We now take the system S—= F+ L+G which is stable at 
the pressure P and the system S’ = F+ L’ + G’ which is stable 
at the pressure P’. If now the volume of S’ is smaller than that 
of S, P’ will be greater than P; if the volume of S’ is greater 
than that of <S, P’ will be smaller. 
Reversally, if P’ is greater than P the volume of S' is smaller 
than that of S; if P’ is smaller than P the volume of S’ will 
be greater. 
All this applies, as we have noticed previously, if S and S’ can 
be converted into each other and when P and P’ differ but little. 
We now omit from the system S the vapour so that we retain 
F +L only. We now ean distinguish two chief cases, depending 
on whether a phase reaction is possible, or impossible, between the 
three phases of the system + L + G, 
