the mixed 
( ?«‘J 
the stable and metastable solid equilibria s t q and s x n meet 
crystal lines ep and dm of the pseudo-binary system. 
In case of nionotropy these meetings between the unary and the 
pseudo-binary system do not take place under but above the unary 
melting-point temperature, and this is the reason that in this case 
the second line for the solid inner equilibria everywhere indicates 
metastable states. 
I started from Gibbs’ principle of equilibrium, which states that 
with constant temperature and pressure a number of substances 
arranges itself in such a way that the thermodynamic potential is 
a minimum; and then I showed how sharply the relation between 
the pseudo-binary and the unary system can be defined also in this 
way, when we bear in mind that a state of inner equilibrium must 
always lie in the minimum of a potential line. 
Further the case was considered that the three-phase temperature 
lies between the melting points of the substances A and B. After 
having discussed the phenomena of enantiotropy and monolropy also 
for this case, I finally pointed out that when A and B are miscible 
in all proportions in the solid state, heterogeneous allotropy is excluded, 
and only homogeneous allotropj' can occur, unless unmixing occurs 
in the pseudo-binary system at lower temperature. 
Discussion of the curves of inner equilibrium. 
After this introduction which seemed indispensable to me to make 
the reader acquainted with the main faqts, I will consider fig. 1 a 
little more ciosely and discuss the curves of inner equilibrium. 
It follows from the course of the curve S' a S\ that it is assumed 
here that over the corresponding range of temperature the equilibrium 
shifts towards B with increase of temperature, and so that 
Or in words that the transformation from the left to the right is 
endothermic. 
With application of the equation: 
dlnK _ Q 
~dT~ B T- 
we know therefore that Q is positive in the assumed case. 
Neglecting the external work we can split up Q into two differen¬ 
tial heats of mixing, one of which has the negative sign, because 
it is a ease of un mixing, and further into a heat of transforma- 
don, SO: 
