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VI. One critical end-point lies on AS, the second on BM (points 
and q ,, of fig. 1). This case, in which both the melting-point avid 
the maximum sublimation point have disappeared, was already dis¬ 
cussed by Prof. Smits in the cited paper. 
The above cases, which have been derived on the assumption that 
the vapour pressure of the compound lies between that of the com¬ 
ponents at the same temperature, in which, therefore, the liquid- 
vapour surface above the melting-point gradually descends from the 
first to the second component, may be easily derived for systems 
with compounds which are less resp. more volatile than the two 
components, which then gives rise to the appearance of a line of 
minimum, resp. maximum pressure on the liquid-vapour surface. 
By combination of the preceding cases-double intersections may occur, 
one of which was discussed in the cited communication. 
When we consider when the cases mentioned can occur, it appears 
that the chance for the occurrence of ease III will be the smallest, 
as the generally slight differences in pressure and temperature of 
minimum melting-point and maximum sublimation point render an 
intersection of three-phase line and critical line between these points 
improbable. So the cases II, III, and IV, where such a situation is 
met with, will only be rarely found, if they really occur at all ; I 
have not succeeded in finding an instance of these cases. 
The three remaining cases have this in common that they may 
all occur for compounds which are little soluble in one or both 
components. In all the systems where 1 have found critical end-points, 
this was really the case. Of the investigated systems the following 
belong to 
Type I: Hydrochloric acid-Ammonia; Hydrogen sulphide-Ammonia; 
Carbonic acid-Ammonia. 
Type V: Ammonia-Sulphur dioxide. 
The system hydrochloric acid-ammonia, for which it did not seem 
improbable that type VI would hold on account of its melting-point 
not being known, appeared to belong to type I, as I could ascertain 
that when chloride of ammonium was heated a three-phase line was 
found which extended from about 520° — 560°. 
Of these systems only that of hydrogen sulphide and ammonia is 
suitable for a quantitative investigation of the spacial figure, though 
this system, too, is open to great experimental difficulties in conse¬ 
quence of the action of mercury on hydrogen sulphide, which is only 
to be counteracted with the greatest difficulty. Yet 1 have succeeded 
