1197 
1. the total composition of 2. 
2. the composition of each of the phases, of which the equilibrium 
E consists. | 
We shall say that two equilibria have the same phases-compo- 
sition when the phases of both equilibria have the same composition. 
We now take a definite point x of the region / (consequently 
the equilibrium Z under P, and at 7%). Then the equilibrium / 
has either only one definite phase-composition Zr, or two phase- 
compositions EL, and £’; or three viz. E‚, H’, and HE’: etc. We 
may express this by saying that either one, or two or more equilibria 
E belong to the point # of the region Z. 
When only one single equilibrium Z: belongs to each point 2 of 
the region Z, then we call the region one-leafed; when in a part 
of the region two equilibria (ZX, and £’,) belong to each point w, 
then we call that part two-leafed ete. 
As the equilibrium Z, which belongs to a definite point of the 
region EH, may be as well stable as unstable, the region / may 
consist, besides of stable, yet also of unstable leaves. 
When the point x traces the region / of the P,7-diagram or in 
other words, when we give to the equilibrium / all possible phase- 
compositions, then equilibria may occur, which show something 
particular. 
1. The equilibrium £ of m components in » phases passes into 
an equilibrium Z, of n—1 components in 7 phases. [The index 
O indicates that the quantity of one of the components has 
become zero]. 
2. Between the » phases of the equilibrium ME a phase-reaction 
ST PE 0 0 il AN ae) 
may occur. We call this equilibrium . [The index A indicates 
that a reaction may occur}. 
3. Critical phenomena occur between two phases; we call this 
equilibrium x. 
The first case occurs when the quantity of one of the components 
e.g. K, may become zero in all phases. It is evident that the phases 
with constant composition are not allowed to contain this component 
K,, therefore. 
The equilibrium ZE, contains n—1 components in n phases and 
is, therefore, monovariant; consequently it is represented in the 
P,T-diagram by a curve, which we shall call curve £,. This curve 
E, is, therefore, nothing else but a monovariant curve of a system 
with n— 1 components. Consequently it is defined by: 
