( 3 ? ) 
Bv To this we answer that a real longitudinal plait is only possible 
I for a mixture of two different substances which are not in internal 
^equilibrium with each other, as e. g. for phenol and water. For 
then there is for a series of temperatures “three-phase-equilibrium” 
~ possible (liquid I, liquid II, vapour). For if we denote these three 
I phases by A, B, and C, we have (**>)« = (p x )& = (fi x ) c ; (fi 2 ) a = 
for the three-phase-equilibrium, i.e. four independent relations between 
the 5 quantities p, T,x a ,x b ,x c , so that for any arbitrarily chosen 
I value of T the pressure (vapour pressure) p, as well as the three 
^concentrations x a , x b , and x c are entirely determined. We know that 
then the temperature at which three-phase-equilibrium is possible, 
ranges from the lowest temperatures to the so-called critical tem- 
I perature of complete mixture, where two phases become identical. 
In our case, however, it is different. In consequence of the internal 
equilibrium between the two kinds of molecules (simple and complex 
ones) we have not to deal with two substances in the sense of the 
theory of phases, but only with one substance, of which the internal 
molecular state is entirely determined in consequence of the equilibrium 
of association. Here only three-phase-equilibrium is possible at one 
temperature (the so-called “triple point”) — in perfect accordance 
with the ordinary scheme for a simple substance, (see fig. 4 of the 
plate of part. 1 of this paper). For now for three-phase-equilibrium 
we have the relations (**,)„ = = (^ between the molecular 
potentials of the 1 st component (e.g. the complex molecules), but at 
the same time in each of the phases p a = p,, the relation of equili¬ 
brium between the two kinds of molecules. Then it follows naturally 
that (p s ) a = (fi 2 ) b — ( fij ) c i s a is 0 fulfilled for the 2 nd component. So 
there are here 5 independent relations (viz. the two relations 
— (fO& = (p x ) c and the three relations (*i,)« =4 (p,) a , (^) 6 — f 
(^ == (p 2 ) c ) between the 5 quantities p, T, ft, ft, and ft, so that 
for three-phase-equilibrium nothing remains indefinite, and besides 
the three degrees of dissociation ft, ft, and ft also the (vapour) 
pressure and the temperature are perfectly determined. 
The phenomenon studied by us agrees, therefore, entirely with 
the appearance of a triple point for a simple substance at one definite 
temperature, and had nothing to do with the appearance of aiongi- 
tudinal plait for a binary mixture, for which three-phase-equilibrium 
is possible for a series of temperatures. So there is no question of 
real so-called imperfect miscibility. For a binary mixture the concen¬ 
tration .r may be changed at pleasure -, for a simple substance with 
internal equilibrium we eannot change 0 arbitrarily. For an ordinary 
binary mixture two different phases appear on imperfect miscibility 
