Theory of Surface Forces. 527 



the formula 6= ? of van der Waals, the equation (24) 



v — b 



becomes 



dp? v RT , v 



rtu a (v — by 



(29) 



Fig-. 8. 



nr 



/ ERGFPK-theorFsotfv. f 

 '' EUWVK-p t -v Curve 

 gurfacGNHllGMN* SLFGMl 



J SF'FW 



VAxis 



In the points of the capillary layer which respectively 

 correspond with the points H, F, and K in fig. 8, and 

 where fJt> = fii, we have thus 



dv ~ V > 



and in the points H, W, and K of the curve HUWVK, 

 which presents the relation between p 2 and v (the p 2 —v 



curve) the tangent is thus parallel to the v-axis. Because -J-? 



has the same sign as the difference //,— r i l (see equation 29), 

 p 2 diminishes between H and W and increases between 

 W and K. Further we have, in differentiating (29), 



d 2 p 2 _ v 2 RT dp RT y + b 



dv 2 a (v — b) 2 dv a{v — b) 2 v — b 



(/*,-/■»). . (30) 



For the points of the capillary layer which correspond 

 respectively with the points Gr and P of fig. 8, the equation 



2N2 



