( 625 ) 
and which is denoted by B' and £', and by doing the same with 
the point B ZE. In the same way fig. 2 leads to fig. 3. But the way 
in which this separation must take place is different for these two 
transitions. What happens in one case in the left-hand point, takes 
place in the other case in the right-hand point. 
The coinciding of the points B' and LH’ is represented in fig. 2 
on the spinodal curve; also the coinciding of the points 5 and 
E. The spinodal line is namely the curve which is denoted thus 
— — — —, and which runs through the points BD L'PDRCQ BE. 
That the coinciding must take place on the spinodal curve might be 
anticipated from the characteristic which we have used to distinguish 
between main plait and branch plait. We had to consider Q as 
top of a branch plait, if the rolling tangent plane, arrived at the 
position A’ A", reached the spinodal curve on the side of A” when 
rolled further, so in the space lying within the top Q. On the 
contrary P was the top of a branch plait when this happened on 
the other side. For the case that there is symmetry between the 
two tops P and Q, the meeting of the spinodal curve must take 
place on both sides simultaneously. But we might also have taken 
as criterion for the main plait, that the main plait is such a plait 
for which the points Band £' are separated *). The comparison of 
these two criteria leads to the fact that the coincidence of the points 
B' and £" must take place on the spinodal curve. But as long as 
the two tops P and Q are present, whatever the character of these 
tops may be, there is a third plaitpoint, viz. the point F, belonging 
to a composition of the binary mixture which lies between the com- 
positions belonging to the points P and Q. 
In the figs. 4, 5 and 6 the complete (p, #) curves have been given 
for the coexisting phases. Fig. 4 for a temperature which is little 
higher than 7, and at which Q is still the top of the branch 
plait, and fig. 6 for temperatures below 7’, at which P is still the 
top of the branch plait. Fig. 5 represents the transition temperature. 
I may assume as known that the differential equation for this (p,) 
curve is: 
075 
Cee Ci DR Te) ER Ad et a ee dE) 
Òz pT 
Whenever that the (p,v) curve has a point in common with the 
; es 
spinodal curve 
02 >T 
= 0), p is a maximum or a minimum. This 
1) Cf. Wiskundige opgaven enz. IVde deel, 5de stuk, Vraagstuk CXXXIX, where it 
is also demonstrated, that the branches of the binodal curve which touch in B'E, 
have the same curvature. Also the conjugate ones, which touch in BE. 
