1267 
It follows immediately from the direction of the tangent which 
is determined by (7) that, as has been said above, the two curves do 
not touch one another in the point 7 on side BC. As this direction 
depends not only on y,, but also on 8, and as @ is different for 
fF and #”’, the two tangents do not coincide. 
V. The equilibrium /#’-+ /” + #"-+ G; G is a ternary vapour. 
We may also distinguish “here two cases, according as the solid 
substances contain together the three components or not. 
1. F, #’ and F" are not situated on a straight line. 
As the three components occur in four phases, the equilibrium is 
monovariant, consequently at each temperature it exists under a 
definite P only and also the vapour has a definite composition. We 
ean understand this also in the following way. We imagine the 
vapour saturationcurves of /, /” and #” to be drawn for any 7’ and 
P; it is evident that as a maximum six points of intersection 
can occur. “Now we change the pressure, while the temperature 
remains constant; a definite pressure 2, will occur, under which the 
three curves go through one and the same point w. Consequently 
the equilibrium /+/”+/"+G occurs under a definite pressure 
P, and the vapour G has then the composition uv. As each curve 
intersects each of the two other curves in two points, P, is higher 
than the sublimationpressure of the three pairs of liquids: MH, F4" 
and /” + F'". Consequently we find: the sublimationpressure of 
FHI + F" is larger than that of “+ #',F + F" and F'+ #” 
and, therefore, also larger than that of /’, #’, and 2". 
Now we can distinguish three cases, according to the position of 
u with respect to the solid substances. 
A. The reaction / + #’ + F”’ 2G occurs. When we bring; 
therefore, the three substances into a space, a part of each of these 
substances evaporates in order to form the vapour G. Consequently 
we have a congruent sublimation of #! + /#” + F'’, 
B. The reaction # + #” 2 F+ G occurs. When we bring 2°, /” 
and /”’ into a space, consequently, in order to form G, only a part 
of / and /” will evaporate, while at the same time solid +” is 
deposited. In order to obtain the equilibrium + /” + #”’ + G, 
we have, therefore, only to bring a sufficient quantity of #4 +” 
into a space. Consequently we have an incongruent sublimation of 
Fh 4h". 
C. The reaction FV Fk’ + F’’ + G occurs. When we bring the 
three solid substances into a space, then, in order to form the 
vapour (, only a part of # will evaporate, while at the same 
84 
Proceedings Royal Acad. Amsterdam. Vol. XVII. 
