1818 
Chemistry. — “Zguilibria in Ternary Systems” VIT. By Prof. 
F. A. H. SCHREINEMAKERS. 
Up to now we have only considered the occurrence of a single 
solid substance /’; we will now take the ease when a second solid 
substance /” also appears. 
Tet us first investigate what happens if a mixture of both 
substances /” and /” is brought together. 
If, at a low temperature, we introduce a mixture of the substances 
F and /” in an evacuated space, a vapour G is formed causing the 
equilibrium + /” + G to appear. The vapour G is of course 
represented by a point of the line FF. 
According to the composition of the vapour G or in other words 
according to the position of the three points in regard to each 
other, the following reactions can occur at a supply or with- 
drawal of heat or at a change in volume, P and 7’ being constant. 
1. If the point G is situated between / and /” the reaction 
F+ I’ =G occurs. Hence, if / and F’ are placed in an evacuated 
space a part of each of the solid substances evaporates. We will 
call this a congruent sublimation. 
2. If the point /” is situated between / and G the reaction 
IF’ 2F+4@ takes place. Hence, if both substances are placed in 
an evacuated space only a part of /#” will evaporate while solid /’ 
is being deposited. The formation of vapour is, therefore, accom- 
panied by a transformation of /” into £. We will call this an 
incongruent or transformation sublimation. 
3. If the point /’ is situated between /#” and G the reaction 
FZ +G occurs. This case is quite analogous to that mentioned 
sub 2. so we call this also an incongruent or transformation 
sublimation. 
4+. As a transition case between 1 and 2 or 3 the point G 
can also coincide incidentally with /” or with /. 
At an elevation of temperature, the vapour pressure of the system 
U 4 Fk’ + @ increases when G, of course, alters its composition; 
hence, in a P,T-diagram we obtain a curve such as aD of fig. 1 
which we will call the sublimation: curve of F+ F”. If, between 
the three phases occurs the reaction mentioned sub 1 we call 
a'D a congruent, if the reaction mentioned sub 2 or 3 takes place 
we call a" an incongruent or transformation sublimation curve. 
It is evident that the one part of a curve may be a congruent and 
the other part a transformation sublimation curve. 
On further heating the system /’-+ /” + G a temperature 7'p 
