1270 
they intersect one another under the pressure P,, = P, only in two 
points, viz. w and v. It follows from the intersection of these curves 
that the pressure P,, = P, is greater than the sublimationpressure of 
FF, EHF" and fF’ + fF". 
We have seen above that at each temperature a pressure P, = P, 
exists, under which the points /,, /' and /’,", fall in a straight 
line. When this line is situated below the vapourleaf of the S-surface, 
the equilibria: P+ F4 FPF", F+ + "+ G, and #-+ # + 
+" +, oeeur in stable condition. When this line is situated 
above the vapourleaf or when it intersects the vapourleaf, then the 
equilibrium /’+ /’ + PF" is metastable and the equilibria “+--+ #” + 
+ fF" +) are impossible. As transition-case this line touches the 
vapourleaf at a definite temperature 7} and under a corresponding 
pressure P,; the projection 7 of the point of contact is situated on 
the line FF’ EF". The vapoursaturationeurves of F, /” and /" touch 
one another at this temperature and under this pressure consequently 
in the point 7. In this transitioncase the vapourpressure is P,, there- 
fore, not larger but equal to the sublimationpressure of #’-+ 1”, 
FA HF" and fF’ + F". 
When we bring the three substances at a given temperature into 
a space, then vapour is formed, the composition of which is repre- 
sented by a point of the line //”F". It is apparent from this that 
the equilibrium “+ /” + F"+ G, (or G,) cannot arise in this 
way, unless casually the temperature 7} was chosen. Therefore, we 
shall not call the pressure P?,, = P, the sublimationpressure, but the 
equilibriumpressure of /’+- /’ + /'". When we bring together the 
three solid phases into a space, generally, therefore, one of them 
will disappear; then one of the equilibria #4 /” + G, F+F"+G 
or 4’ + FF" HG is formed. Then the pressure becomes also not 
the equilibrium-pressure P, = P,, but one of the lower sublimation 
pressures. 
We may draw the equilibrium “+ /’ + F" + G as well in 
the P, 7, as in the concentrationdiagram. When we draw the com- 
positions of the vapours G, and G, in the concentrationdiagram, 
the points « and v trace a curve on change of 7. Definite Tand P 
correspond with each point of this curve. At the temperature 7 
the points « and wv coincide in the point r of the line FFF". This 
point 7 divides the curve into two parts; with each point w of the 
one branch viz. a point v of the other branch corresponds and 
in this way, that a same 7’ and P belong to these points. Hence 
it follows that along this curve in the point7, Tand P (consequently 
7. and P,) are maximum or minimum. 
