some New Equations derived therefrom. 35 



Hence according to equation (10), p. 29, 



p a -007425 



P <= (VTPjl = 9 . ( .0033)» = 76 atmos P heres > 



which is the same value calculated according to equation 

 (12), p. 30, as shown by table, p. 31, and very nearly the 

 pressure found by Andrews. 



For methyl acetate, V c = *0096, P c = 47*54, we find in the 

 same manner P c =52 08. 



For propyl alcohol, V c = '0098, P c = 50-16, we find 

 P e = 51*65, and so on. 



For T e , according to equation (16) or (17), we find for 

 carbonic acid, T e = 273°, ;is should be, considering the value 

 of'V c = *0066 is the volume relative to the original volume 

 re lueed to 0° and 760 mm. 



The constant a for carbonic acid calculated above has a 

 somewhat smaller value than the one van der Waals finds 

 (a =-00874). 



The value van der Waals calculates for P c is (for C0 2 ) 

 61 atmospheres. 



IV. 



On a future occasion we will show that the equality of 

 P c . and P le can be proved in an entirely different and 

 independent manner. 



A natural consequence of this equality would be the 

 disappearance of the phenomena of surface-tension and of 

 the latent heat of vaporization at the critical point. For 

 the cohesive forces would be compensated by the thermic 

 pressure, and the transference of a molecule from the in- 

 terior of the fluid to the space over its surface would not 

 require any work against a force. 



But we cannot imagine P c = P lc , and still measure an 

 actual critical pressure P c towards the exterior, unless we 

 assume the law of equality of action and reaction to apply 

 to the cohesive forces, as to all other forces. Thus the 

 surface molecules, attracted by the interior molecules, must 

 exert the same attraction on the latter, equally strung but 

 opposite in direction. 



Between the surface and the interior the thermic pressure 

 would be supported by the cohesive forces, the density 

 would be greatest at the surface and gradually diminish 

 towards the interior. 



If II were the pressure without any molecular attraction 

 throughout the fluid, then the pressure from the interior 



D2 



