36 



On van der Waals' Equation. 



would be supported towards the surface and diminished in 

 the opposite direction, with the value of the attraction P 1? 

 if there were any such attraction. — i. e. the pressure in the 

 surface-layer would become II 1 = II + P 1 , and the pressure 

 at the surface and in the interior would become 



p=n-p 1; 



as illustrated by our diagram (fig. 2). In particular, if" 

 Pc = P lc we should thus have 



or 



n=p c +p lc =2P c =2P ]c , 



r c = Pic =2^11. 



'B$ 



— ^ — '->*£- 



Fig. 2. 



p*a-p, 



ri*n*p p^ 

 *> </ — ^ 



p=n-f* 



No matter how great P f , the pressure in the interior must 

 be transmitted undiminished towards the surface. But the 

 pressure between surface and interior is increased and 

 attains at the critical state (thus for P c = P lc ) a value 



n 1= n+Pi c =3P c . 



The force opposing 11! is identical with the " Intrinsic 

 pressure " of Laplace in the case of liquids. 



Instead of causing an increase of pressure in the interior, 

 the cohesive forces are the means of such increase betioeen 

 surface and interior equal to their numerical value, and of a 

 decrease of pressure in the interior of that equivalent. This, 

 however, does not affect our equations (A) and the following. 

 For the gas-pressure P is equal to the pressure II the gas 

 would exert if there were no molecular attraction, minus 

 the value of that attraction P l9 i. e., 



p=n-p 1; 



or 



P + 



R.T 



(v+by 



Additional evidence in support of this view will be 

 brought forward on a future occasion. 



