pressure along curve (PF) increases at rising temperature, decreases 
at lowering temperature. Curve (/’,) may go, therefore, starting 
from the invariant point, towards higher P and 7’, or towards lower 
P and 7, consequently’ in opposite direction. In order to define 
the P,7-diagram we have to use therefore still other properties. 
For this we take: 
1. the equilibria which are formed at an isentropical reaction 
with increase of volume, go towards lower pressures, starting from 
the invariant point; those, which are formed with decrease of 
volume, go towards higher pressures. ; 
2. the equilibria, which are formed at an isovolumetrical reaction 
with increase of entropy (consequently on addition of heat) go towards 
higher temperatures, starting from the invariant point; those, which 
are formed with decrease of entropy (consequently on withdrawing 
of heat) go towards lower temperatures. 
We now write the isentropical and isovolumetrical reactions (7) 
and (8): 
Ge AN ua are Wnts) OAT ROE) 
TRO An TE re a + tne ne Pnte=0 0 ; Ay (13) 
in which we take the coefficients of the phase /’, positive; further 
we assume that in both the equations the phases are written in 
such order of succession, that the condition : 
[ty SU, ode lp Seca Dl = eds) 
is satisfied. 
Now we may write for (11): 
dP dP dP Ay (15) 
= = U == == = EE WOE esi 5 J 
ie Gel NET ame FRR) AV 
When in (14) all the values of w are positive, then it follows from 
(15) that the direction-coefficients of the curves in the invariant point 
are either all positive or all negative. When we take into considera- 
tion absolute values only, then follows: 
dP dP dP 
(Ee) << Ha all |e BAG) 
When g,‚...t, 4 are positive and Mp». Unk? negative, then it 
follows, when we take into consideration absolute values only: 
dP dP dP dP 
a a fl Coed Eeen (17 
(Ge) = = (Gr), 4.” eae > Gel. oe 
In thi al t IL 1 ler tl ag 
Meth S3i[— may be as well larger as smaller than | — |. 
an) iy ay : 5 P 
