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incongruent sublimationpressure of + F’. This sublimationpressure 
is higher than that of each of the substances / and 4’ separately, 
independent of whether both or only one of them has a stable 
sublimationpressure. 
When we draw in « P,7-diagram the temperatures and the cor- 
responding sublimationpressures of 4, /” and # + #”, we obtain 
three curves. In fig. 1 (VII) aA is the sublimationeurve of #, a’ A’ 
that of ZF’ and a"D that of [+ F”. According to the previous 
curve a“ must of course be situated higher than the curves aA 
and a’K’. Formerly we saw that these curves terminate in A, A’ 
and D; when the formation of liquid fails to come, we can pursue 
them further. 
In the case A the curves ak, a’K’ and aD can be realised in 
stable condition; for this we must bring into a space solid F, or 
I” or F+ F” and we must take care that the solid substances are 
not evaporated completely. In fig. 1 (VID a’A’ is situated above 
ak, the reverse can of course be the case also. 
In the ease 5 only the curves aA and a"D may be realised in 
stable condition, for this purpose we must bring into a vacuum 
F or F+ #’. When, however, we bring /” into a space, then 
solid #” + vapour /” is not formed, but in more stable condition 
F+ F’+ vapour. Consequently we do not determine the sublima- 
tioncurve a’K’ of HF’, but that of “+ F”, therefore, curve a'D. 
We would be able to determine the curve a’A’, only when the 
reaction /#” > /+G failed to come. Further it is apparent that 
curve a’K’ must be situated higher than aX. 
Analogous considerations apply to the case Cas in the preceding 
case 5. 
In the transition case D we assume that 7 coincides with /. 
While the cases A, B, and C may occur at a series of temperatures, 
D occurs at a definite temperature only. In order to understand 
this, we imagine the vapoursaturationcurves of / and ZF’, which 
touch one another in a point # on the line FF’. When we change 
the temperature, we must also change the pressure, in order to let 
the two curves touch one another again; their point of contact 7 
however, shall also get another place on the line #’/”. Consequently 
on change of 7’ not only the sublimation-pressure of # + #’, but 
also thé composition of the vapour r changes. As, therefore, the 
point 7 shifts on change of temperature along the line FF’, it may 
coincide at a definite temperature with /”. The vapoursaturation- 
curve of /” is reduced in this case to the point /” and that of # 
goes through the point /”. The pressure corresponding with this 
