522 
P and T do not change, from the equilibrium (#p)= M + Fa 
being in stable condition, the phase /,41, and from the equilibrium 
(M,4i)= MH Ff, the phase F,, then the equilibrium J/ remains, 
which must be then also stable. Each point of the stable part of 
the curves (/,) and (1,44) represents, therefore, also a stable point 
of curve (ML); the curves (M), (¥,) and (F,41) are situated, therefore, 
with respect to one another as in fig. 2. 
Consequently we find the following : 
1. The two indifferent phases have the same sign, or in other 
words: the singular equilibrium JZ is transformable into the inva- 
riant equilibrium and reversally. Curve (J/) is monodirectionable, 
the three singular curves coincide in the same direction | fig. 1}. 
2. The two indifferent phases have opposite signs or in other 
words: the singular equilibrium J/ is not transformable. Curve (J/) 
is bidirectionable; the two other singular curves coincide in opposite 
direction [fig. 2]. 
It appears from the previous considerations what changes have 
to be applied to the general P,7-diagramty pes. 
1. When the two indifferent phases /, and F4 have the same 
sign, then the curves (/,) and (#4) belong to the same bundle. 
Consequently we may let two succeeding curves coincide in each 
bundle of the P,7-diagram. When in fig. 3(V) A, and A, are the 
indifferent phases, then the curves (A,) and (A,) coincide, in 
fig. 3(V) the curves are not indicated by (A,), (A,) ete. but, omitting 
the parentheses, by A,, A, ete.]; when A, and 4, are the indifferent 
phases, then the curves (A,) and (A,;) coincide; when A, and R, 
are the indifferent phases, then the curves (/2,) and (A) coincide; 
ete. Those coinciding curves represent then the singular curve (J/) 
at the same time, as in fig. 1. 
In .fig. 1 d(V), therefore, the curves (S) and (Q) or (P) and (7) 
may coincide; in fig. 2 g(V) the curves (A) and (B) or (B) and (C) 
or (£) and (F) or (Ff) and (G). 
Consequently a coincidence of two curves in the same direction is 
only possible in P,7-diagrams with one or more morecurvical bundles. 
2. When the two indifferent phases ij and #4: have opposite 
sign, then the curves (/,) and (#44) belong to different bundles 
and in such a way, that the stable part of the one curve is situated 
next to the metastable part of the other curve. In fig. 3(V), there- 
fore, (A;) and (f#,) or (R,) and (B,) ete. may coincide in opposite 
direction. Those coinciding curves represent then the singular curve 
(M) at the same time, as in fig. 2. 
