1199 
then we obtain an equilibrium Zro, which belongs as well to the 
turning-line HR as to the limit-line /,. Turning-line and limit line 
touch one another in the point Zpr.o. 
In the ease mentioned under 8 critical phenomena appear between 
2 phases. This is the case when in the equilibrium Z two liquids 
L, and LZ, get the same composition or when a liquid and a gas 
become identical. Then we obtain an equilibrium Zx of n components 
in n phases, of which 2 phases are in critical condition. This 
equilibrium Hx is represented in the P,7-diagram by a curve Ex 
which we call the critical curve of the region. In the vicinity of 
this curve Hx the region is one-leafed. 
Consequently it is apparent from the previous that a bivariant 
region is one-leafed in the vicinity of a limit-line or critical-line, in 
the vicinity of a turning-line it is two-leafed. We shall refer to 
this later. | 
~ 
One- and two-leafed regions. 
A one-leafed region may be limited by limit-lines and critical 
lines, but it may also be unlimited. When the equilibrium / contains 
e.g. only phases of invariable composition, then neither limit-line, nor 
critical line, nor turning-line exists. Consequently the region LF is 
unlimited. [Of course a part of this region becomes metastable at 
higher 7, because another phase is formed e.g. a liquid by melting 
or transformation of solids. When we leave out of consideration 
however the occurrence of other phases, then the region extends 
itself unlimited]. The region may also be unlimited when in the 
equilibrium, besides invariable phases also variable phases occur, 
which do not contain all components | e.g. mixed crystals or a gas]. 
We take an equilibrium H=L+G of a binary system with 
the components A and B, which occur both in the vapour G. Then 
the region ME has two limit-lines Z,. When in Z and G the com- 
ponent A is missing, then we have the limii-line #4— 0, when Bis 
missing, then we have the limit-line HLg— . Consequently curve 
E,4—» is the boiling-point-line of the substance 5, curve Egp—o that 
of the substance A. 
When Z and G have always different composition, then the region 
E=L+G@ has no turning-line; then it may be represented by 
fig. 1 in which ab and ed are the limit-lines. When Z and G 
may get the same composition, so that a reaction 1 = G may occur, 
then also a turning-line ER exists. Then the region may be repre- 
