708 
ration line under its own pressure and its correlated vapour line get 
each reduced to a point. Both these points then lie with F on a 
straight line. 
This case will occur when the saturation line of F and the liquid 
line when meeting each other in a point (fig. 2 in M, in fig. 5 and 
9 in m) move at that moment from that point towards and from F 
with the same velocity. The same then applies to the vapour line 
and vapour saturation line of F which also meet in a point (M, in 
fig. 2 and m, in fig. 5 and 9). This equality of velocity has, of course, 
also a physical significance, which we will look for. 
We represent the composition and the volume of the solid substance 
F by a, 8 and », that of the liquid by «, % and V and that of the 
gas by 0, yg Vy: 
The equation of the saturation line of F is then given by: 
[((a—ax)r4+ (B— ys] de + [(a—a)s 4+ (8—y) 4 dy=—AV.dP (1) 
and that of the liquid line of the heterogeneous region LG by: 
[ee —e)r ae meee) s|dx + [(e@— #,)s + (y—y,)t]¢dy = Vor dP (2) 
in this: 
0V 
AV=V—v4+(a— ea “+. = 
Oy 
ò Vv 
Vor = y= Vi as (x, ra ae ain Chg) NE 
Ò Oy 
As the two curves (1) and (2) come into contact with each other 
« and y in (1) and (2) are the same and then we have: 
BU Uae ce ae 
= == att I 
tt OL Od, 
If now we write (4) and (2) in the form: 
AV, 
(r + us) dw + (s + ut) dy = — dP 
Oo 
Von 
(7 + us) de + (s + ut) dy = dP 
a 
we notice that the above mentioned circumstance will appear as: 
PV, Vou 
at Bd, 
After substitution of the values AV and Vor we can write for 
this also: 
(aw) V + («—a) V, + (a, — a) v= 0 
or (Bu) V+ (y—-8) VY, + G1 —y) 0 = 0. 
This means that the change in volume which ean occur in the 
reaction between the three phases #, L, and G, which are in equi- 
