( 649 ) 



metastable and unstable equilibria solid-fluid in the T, «-figures drawn 

 up by van der Waals 1 ), and the v, x~ and ^«-figures drawn up 

 by Smits 3 ). Van der Waals himself has already pointed out a defect 

 in those figures 3 ), viz. that the spinodal curve falls here within the 

 connodal one, whereas in reality it falls far outside it at low tem- 

 peratures ; but it is not this that I have in view. 



Let us first take the p, «-figures. According to them the complica- 

 tion which the binodal curve solid-fluid shows for tern peratures below 

 the triple-point, will disappear in this sense that at the triple point 

 a new complication makes its appearance with three phase pressure, 

 horizontal and vertical tangent, that then these two complications 

 together give rise to the existence of' a detached closed branch which 

 contracts more and more, and at last disappears as isolated point. 

 It is clear that in this way it is supposed that the complication can 

 only disappear above the triple point, and not in the triple point 

 itself', or in other words, that when the triple point is passed, always 

 another three phase pressure is added to the existing one, and that 

 these two more or less high, but always above the triple point 

 pressure and the triple point temperature concur and disappear. Or 

 expressed in another way still, it has been supposed in these figures 

 that there is always found a temperature maximum in the three 

 phase line. In the light of the considerations of our preceding com- 

 munication this supposition is by no means legitimate. But apart 

 from this there rise serious objections against these views. First of 

 all, if these views are held, it is impossible to see what the shape of 

 the binodal curve solid-fluid must be when the solid substance is the 

 more volatile component. Moreover all through the succession of the 

 p, x- figures the binodal curve solid-fluid has only one point in common 

 with the axis x = 0. Now it is, however, known, that for the com- 

 ponents themselves, so for the concentrations x =. and x = 1 the 

 p, ^-diagram of fig. 1 holds (see the plate), i.e. at the triple point 

 temperature there exists by the side of the triple point pressure C 

 a second pressure of equilibrium solid-fluid (viz. of an unstable 

 phase) C', and above and below the triple point temperature these 

 exist even two such pressures, one of which indicates metastable 

 equilibrium, the other unstable equilibrium. But then the binodal curve 

 solid-fluid for the mixture will not have to cut the axis of the 

 component which becomes solid, once, but three times. And finally 

 the p, «-figures of Smits and the T, .t'-figures of van der Waals 



1 ) These Proc. VIII p. 193. 



2 ) These Proc. VIII p. 196. 



3 ) loc. cit. p. 05. 



44* 



