( 640 ) 
From the series of p,a-diagrams we might still see, that the 
boundary-curve of the two liquid phases with the plaitpoint Q below 
the temperature, where 1 and 2 coincide (in M’), does not come 
within the boundary-curve vapour-liquid, as Kuenen *) thinks, but has 
entirely vanished. In fact, there is no reason to suppose, that in M' 
decrease of pressure should cause again permanent separation (if 
that state were realisable), as apparently Kurnen thought that he had 
“undoubtedly” to expect with mixtures of triethylamine and water *). 
What he has observed in another case with propane and methylalcohol®), 
must be ascribed in my opinion to this, that the expansion just above 
the (upper) critical point has caused the temperature to fall a little, 
so that he came on the (metastable) part of the two liquid curves, 
which lies below the threephase-pressure. But when the cusp was 
reached, the metastable equilibrium became immediately stable, and 
by further expansion homogeneous liquid and vapour reappeared. 
Because increase of pressure in this case too favours the mixing, as 
appears from fig. 7 and from the p, z-diagrams, the plait on the y- 
surface will have turned its plaitpoint Q also to the side of the small 
volumes. Fig. 10 gives a schematical representation of the successive 
transformations of the two plaits, or rather of the transversal plait, 
for we can regard again with van DER Waats the longitudinal plait 
as a transformed transversal one. 
In fig. 7 we see, that increase of pressure raises the critical points 
Q, at least in the beginning, if the curve M'C, should present 
a maximum; and from the p, a-diagrams, that these critical points 
will be again in that case /ower critical points, just as in fig. 1 between 
the minimum and the maximum in the curve of the critical points Q. 
Equally in the case of the second general type the threephase- 
pressure may be either between the vapourpressures of the two 
components, as in the case of C,H, and the mentioned alcohols, in 
which case the composition of the vapour-phase will be not between 
that of the liquids — or may be /zgher than that of the components. 
Then there is again a mazimum-vapourpressure after the coinciding 
of the two liquid phases below the lower critical point, and the 
composition of the vapourphase is between that of the liquid layers *). 
1) Phil. Mag. 1. c. p. 645. 
2) Id. p. 652. 
3) Id. p. 646. 
4) That at the coinciding of the two liquid phases 1 and 2 in M’ the vapour- 
phase does not necessarily coincide with 1 and 2, has been already remarked by 
Kueyen, and still earlier has been deduced by me theoretically for an analogous case 
