84 Mr. J. Kam on Molecular Attraction and 



or reduced to 0° C. and 760 mm. 



1 3 1 



n c — — 



and 



v c -/3 2v c 



p c =l- (eqs. 20&21) 



for gases with T c > 273. 



For gases with T c <273 we should find for the same- 

 reason: 



_ 273/T. _ 273/T; 



c ~ v-^ Pc ~ 2v c ' 



and v c is in both cases the reduced volume. 



This view is entirely in accordance with the formula 



v 



for gases like H 2 , 2 , N 2 , &c. at temperatures T above 273. 



For expressing /3t and j3 in /3 Te as fraction of the volume 1 

 at IT = 1 and the critical temperature T c , we have 



T c /T _T c /273_ 1 



n= 



n . /3 T n _&q n. £ T ' 



in which n . /3 T; &c. are the " free spaces." 

 It is evident that 



T C /273 _ R.T.T C /T 



n./3 n./3 



i. e. equal to the pressure of the gas at T and the " reduced 

 volume "(w+1) fy. 



III. 



Reduced Isothermals and Reduced Border-curve. 



For every saturated vapour-pressure p c we have one 

 temperature but either two or three volumes. Where in 

 our equations T 2 is found it only appears as a volume factor. 

 In fact, as is shown by equations (D) and (E), the temperature 

 divides out, and the volumes are determined by the value 

 of p, the pressure of the saturated vapour. 



If, following van der Waals, we make 



p= e.pc, 



v = n . v c , 



