( '^12 ) 



nitril of ambric acid in tlie system : water — alcohol — nitril of 

 arabric acid ") at 4°. 5 two points of inflection. 



1b ■ The line OP is an asymptote of the indicatriv. 



We assume OP as A^-axis, the other asymptote as 5^-axis so that 

 ^ = 0, Cj = and c^ = 0. 



Then the curve of contact is determined by. 



c.py + 'èd.px-" + Cld,p-c,) xy + d,pi/ + . . . = . . (6) 

 So the generatrix OP of the cone touches the curve of contact 



in 0"-). 



We have here thus the case that through point P we can draw a 

 tangent to the line of saturation of the solid substance represented 

 by P. This point of contact, however, being a hyperbolic point, this 

 case can apnear only on the unstable part of the line of saturation. 



IL Point is a parabolic point. 



As is a parabolic point, it follows that c^c^ — — c,' = 0. Point 

 lies thus on the parabolic or spinodal line of the surface. 



II A • The line OP does not coincide ivith the direction of the 

 axis of the parabola. 



In fig. 1 let aOb be the spinodal line, 



cOd the section of the tangential plane in 



with the surface; OY is the tangent in 



the cusp of this section and at the same 



->X ^i*i^6 the direction of the axes. 



We now assume OP as A^- and (>}"as 

 7-axis, so that q=^0, c^ = and Cj = 0. 

 Then we tind for the equation of the curve of contact : 



2.c,px 4- i^Sd^p—c,) .e + 2c/,p.f^ + d,py' + . . . + 



or : 



2c,x + d,y' = (7) 



So the curve of contact touches in the line OY. The direction 

 of the curve of contact in the vicinity of its point of intersection 

 with the spinodal line is therefore independent of the position of 

 the vertex P of the cone. 



1) V. A. H. ScHREiNEMAKERs. Z. f. Phys. Ghem. 27 114 (1898). 



2) See also: H. A. Lorentz. Z. f. Phys. Ghem. 22 523. 



