( 505 ) 

 (admixture), J/j that of the other substance^ wliile 



F—, 



dr- J \dy- J ydv d,r 



The equations (1) determine on tlie ip-surface a curve which 

 according to Kuknkn (1. c. }). 6) 1 call the gravitation-curve '). 

 From (J) we derive: 



M,{l-.v)+M^x 



dv /OiA /*' 



d.Vgr \^-vJijT /^ö^fA M^{l—.v)-^M^.vfd''i^y\ /dhp 



ÜI' J L' \a.i'öv } yoi-" 



From this equation it follows that at the plaitpoint z= ( — ) , 



d,i^gr \d-vJpT 



hence the gravitation-cur\e touches the isobar, and accordingly also 



the spinodal curve, for which F = 0. Then also at the following 



point of the gravitation-curve which passes through the plaitpoint, 



dv /öy\ 



to the lirst approximation - — = — 1 or at the plaitpoint 



d^v /ÖV 



By means of this we have for a point of the gravitation curve 

 which passes through the plaitpoint, in the neighbourhood of the 

 latter: 



in which equation the differential quotients of F and r must be 

 taken at the plaitpoint. If here wo put .VTfji small, we may reduce 

 this form using reductions as in Comm. N". 75, § 7 (Proc. Dec. 

 'J 901), to the tirst approximation to: 



^ = — V (•'■—•^'T/aY — , T^r^- ' 



d.>:JvT 



in which relation the differential quotients of p must be taken at 

 the critical point of the simple substance. 



^) Gomp. also Kuenen, 1. c. Fig. 2. 



~) This has been demonstrated for the gravitation-curve on tlie vj/-surface for a 

 constant mass in a different manner by Kuenen, 1. c. p. 8. 



39 

 Proceedings Royal Acad. Amsterdam. Vol. VI. 



