( 240 ) 
7. Survey of tfie possible shapes of the plaitpoint curve. 
We shall give a summary of the possible shapes of plaitpoint lines, 
for so far as they might be actually found in our investigations, so 
without considering all the cases to which the theory leads (e.g/for 
cases as helium and water). This summary has been chiefly derived 
from the above mentioned investigations of van der Waals, to which 
we must refer for further particulars. There also T,x and v,x projections 
are found of the plaitpoint lines discussed here in p,T projection. 
We first consider the case that the region of non-miscibility does 
not extend to the region of the critical temperatures liquid-vapour. 
The simplest imaginable case is this that at a certain temperature a 
small closed plait is formed on the spinodal curve of the transverse 
plait, which extends, and exceeds the limit of the stable region, 
remaining closed towards the sides of the small volumes all through 
according to our supposition mentioned on p. 237. At higher tempe¬ 
rature this plait contracts again, it retreats again within the trans¬ 
verse plait, and at last disappears on the spinodal curve of the 
transverse plait in an heterogeneous double plaitpoint. Or strictly 
speaking: it disappears on the spinodal curve, since in this case there 
is only question of one spinodal curve. Whether in this case we 
should speak of a longitudinal plait, or only of a branch plait which 
forms and disappears again, depends on this whether in the nomen¬ 
clature we pay special attention to the binodal curve, or to the 
spinodal one. For the above reason (appearance of the solid state) 
we cannot as a rule reach experimentally the point where the plait 
egresses into the stable region, but only that where it retreats again 
mtd the metastable one, therefore we call this case that of the “retreat”. 
Fig. 1 represents the p>projection of the plaitpoint line for this 
case schematically *). AB is the plaitpoint line vapour-liquid, CD the 
plaitpoint line of the longitudinal plait with two cusps' (heterogeneous 
double plaitpoints) and a maximum of the pressure, situated at the 
highest pressure E which the plaitpoint turned towards the small 
volumes reached after its egress from the transverse plait. So at 
higher pressure than ^non-miscibility cannot be brought about in 
any way. The line FG indicates the three-phase-pressure; F and G 
are critical end-points, of which, as we said, generally only G is to 
be realized. 
Of course it is not excluded that F and G draw nearer together, 
*) *“ this % ure and in figures 2 a and 2b the point A must be taken as lying 
to the fcjght of D and I. 
