1395 
stable part of curve (/,), then the complex X can also be converted 
into one single equilibrium only: when more regions extend them- 
selves over it, then also more equilibria may arise. Then it depends 
on the composition of this complex X which of those equilibria 
shall be formed. Of course the concentration-region of those equilibria 
occupy together the whole region of the invariant point. 
Formerly (Comm. 1) we have shown that each tield which extends 
itself over the stable or metastable part of a curve (/) contains 
the phase F,; hence it follows that each equilibrium into which 
the complex Y can be converted, contains the phase 4. 
Consequently we find: when the equilibrium (/,) is converted 
from a metastable condition into a stable one under constant / 
and at a constant 7, then a bivariant equilibrium is formed, in 
which always the phase /, occurs, which was not present in the 
equilibrium (F’). 
At this conversion, therefore, the number of phases is diminished 
with one. This does not take place, however, on account of the dis- 
appearance of one phase from (/°); as at the same time a new phase 
Fis formed, two of the phases, present already, have to disappear. 
Previously we have seen that each bivariant field represents at 
the same time some fields with more than two degrees of freedom ; 
under definite circumstances the equilibrium (/) may, therefore also 
be converted into a tri- or tetravariant ete. equilibrium. Also those 
equilibria always contain the phase / then. 
We shall elucidate this rule by some examples; for this we take 
first a binary system [fig. 2 (IJ. 
When we bring the equilibrium (/) under such a P and at such 
a 7 that it is metastable, then it is represented by a point on the 
metastable part of curve (1) in the region 14. At the occurrence of 
the stable condition consequently (/,) = F, + F, + F, is converted 
into #, + F,. As new phase consequently occurs /’,, while the 
phases #’, and /’, disappear. 
When we bring (/’,) under such a P and at such a 7, that it 
is metastable, then it is represented by a point on the metastable 
part of curve (2), consequently by a point of the fields 12 and 24. 
At the occurrence of the stable condition (/,) = F, + F, + ¥, is 
consequently converted either into /’, + /, or into F#, + F,. In 
both cases, therefore, two of the phases disappear from (/',) and 
the new phase /’, is formed. 
Which of the two equilibria #4 #, or #,-+ F’,, will be formed, 
depends on the composition of the complex; when this is situated 
on the line AB between F, and #,, then only the first can be 
90 
Proceedings Royal Acad. Amsterdam. Vol. XVIII. 
