. 
1388 
all equilibria in this point must be the region of the invariant 
equilibrium, consequently the whole quintangle, over curve (1) still 
the region 184 has to extend. 
In the same way it is apparent that over curve (2) still the region 
245 has to extend itself; for equilibrium (2) is the quadrangle 
1453 and the whole quintangle is quadrangle 1 458 + triangle 245. 
Let us take a ternary system, of which the concentration- and 
the P,T-diagram are represented by fig. 3 (II) and 4 (Il) [We have 
to bear in mind, as is already communicated several times that 
figs. 4(11) and 6 (Il) must be changed mutually.| The concentration- 
region of the invariant point is now the quadrangle 1352, the 
sum of the regions, represented by a point in fig. 4 (Il) must, there- 
fore, be equal to quadrangle 1352. When we take e.g. a point 
between the curves (1) and (2), this point represents the equilibria 
124, 154, 245, and 345; we see that those equilibria do overlap 
in fig. 3 (Il) and that they form together the quadrangle 1352. 
Also we see at once that no region is allowed to extend itself 
over curve (4); for the equilibrium (4) = 1+ 2 +8 + 5 occupies 
already the whole quadrangle 1352. Also we see at once which 
regions extend themselves over the other curves; let us take e.g. 
curve (2). As this curve represents the equilibrium (2)—1+3-+4-+5, 
consequently quadrangle 1453, the regions 124 and 245 have 
{o extend themselves over curve (2). It follows viz. from fig. 3 (ID): 
quadrangle 1 258 quadrangle 1453 + triangle 1 2 + + triangle 
245. 
We see also the confirmation of these rules with the applications 
of these considerations to fig. 5 (II) and 6(II) and to the figures, 
relating to quaternary systems (Communication III). In the P,7- 
diagrams of the quaternary systems the different regions are not 
drawn; the reader may deduce them however easily in the way 
formerly described. The P,7 diagram with its regions of fig. 6 (II) 
is represented in Communication IV by the symbolical diagram 3. 
We can prove the first of the rules mentioned above in the follow- 
ing way. We assume that a point Q of a P,7-diagram represents 
the equilibria S, and S,. When the concentration-regions of S, and 
S, coincide, then every point within this coinciding region can 
represent as well the equilibrium S, as S,; at the temperature and 
a 
under the pressure represented by the point Q consequently the 
reversion S, ZS, may take place. As temperature and pressure 
remain unchanged with this reversion, of the two equilibria S, two 
and S, the one is metastable with respect to the other. Let us limit 
ourselves to stable conditions, then it follows that the concentration- 
2 
