393 
We shall now imagine that a tangent plane for solid-fluid rolls 
over the y-surface, and we choose as solid substance the first com- 
ponent. At very low temperature the curve which is deseribed by 
the tangent plane on the y-surface, will lie entirely on the right- 
hand side of the figure. So it will not come in contact with the 
longitudinal plait, if it should be present already. This condition has 
been represented by the curve a in figure 1; it intersects the bino- 
dal of the transverse plait, and this point of intersection indicates 
the liquid of the three-phase equilibrium S + L, + G (we denote 
by L, the liquids lying on the righthand of the longitudinal plait), 
Now on rise of temperature the possibility presents itself that the 
binodal solid-fluid comes in contact with the longitudinal plait. If 
this is the case contact will take place, and this can happen no- 
where else than in the plaitpoint. This is easy to see, as in case of 
contact in another point of the longitudinal plait a second liquid 
would have to coexist with the solid substance, and so no contact, 
but intersection would have to take place. This condition of contact 
has been represented by curve 6. So the fluid phases coexisting with 
solid yield a line 6, which passes through the stable plaitpoint of 
the longitudinal plait, and intersects the transverse plait in two 
points, of which again only the liquid point has been indicated in fig. 1. 
Then at higher temperature an intersection follows in four points. 
Two points of intersection with the longitudinal and two with the 
transverse plait then lie on the line solid-fluid; so at this tempera- 
ture there are two stable three-phase equilibria 5 + L, + L, and 
26 
Proceedings Royal Acad. Amsterdam, Vol. XV. 
