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case if in the ternary system liquid + vapour, a singular point 
occurs and when the saturation curve of F passes through this 
point..,As in this case «=e, and y=y, it follows from (11), as 
R becomes intinitely large, that : | 
dP D M,—H 
eid ae (14) 
eC EER 
We have noticed above that ifthe straight line ZFZ, passes through 
point A of fig. 5, its conjugated vapour curve must pass through - 
D and F and that with the liquid A a vapour F is in equilibrium. 
Hence, we have for the point K #,=a and y,=8. As R now 
becomes — 1 it follows from (11) that: 
AMOR IRS aw: St ie 
eeen leed 
The above formula also determines the sublimation line a K of the 
compound # (fig. 4) If, in fig. 5 the straight line ZFZ, passes 
through the point 4, the corresponding P,7’-curve in fig. 4 must 
meet the sublimation curve aA in the point AK. We now give in fig. 
1 different positions to the straight line Z/Z,; to each position 
appertains a definite /, 7-curve in fig. 4 so that we can draw in 
this figure an infinite number of P, 7-curves. From our previous 
considerations it now follows that a// these (1 will refer later to a 
single exception) meet the melting point line /d of the compound 
F in the point / and that one only meets the sublimationcurve a K 
in the point A. The latter takes place when the straight line ZFZ,, 
in tig. 1 passes through the point A. All other P, 7-curves in fig. 4. 
proceed ahove the point A, or in other words: at the upper subli- 
mation temperature 7, of the compound / the vapour pressure of 
each system: solid /’-+ liquid + vapour is greater than the vapour 
pressure of the solid substance /’. 
Different P, 7-curves, besides coming into contact in /’ with the 
melting point curve // will also meet the three-phase line FK. 
Although all this is evident from what has been said previously, 
we will still consider a few of these points in another manner. 
On warming the solid compound /’, this, as mentioned previously, 
proceeds along the sublimation curve a & of fig. 4 until the upper 
sublimation point KX is attained; then the equilibrium: solid # + 
liquid + vapour is formed which proceeds along the three-phase 
line KF of fig. 4 until the melting point line Ad has been obtained. 
We have already noticed previously that the liquid and vapour 
continually alter their composition therewith and we may now ask 
what curves they proceed along in fig. 1. 
