30 Mr. J. Kam on van der Waals* Equation and 



At the critical state Y c =2b and (A) becomes 



P + JL-! 



c 96 2 ~26' 



a quadratic equation, really a special form of (C^;. Writing 

 it in the form 



we 



find 



h2 -k h+ wr^ 



,_ 1 /( 1 {* a 



"-IF^V tip, J ~9P7 



and as b naturally has only one value, 



6= 4E and {4fJ 2 -9F c = °' 



or 



b*= — 

 9P £ 



We thus get the two values 

 1 

 2V C 

 and 



P c =-— or 2P c V c = l = constant, . (12) 



Pc ~9& 2 ~(V c + 6) 2 ~' :Ple ( 13 ) 



The accuracy of equation (12) is demonstrated by the 

 figures of the table on the next page, taken from "Landolt- 

 Bornstein," ' PJiysikalische Tabellen, Berlin, 1905, pp. 181-186 

 The values marked * are borrowed from Handbucli der 

 Physi/c, A. Winkelmann, vol. iii. Leipzig 1906, pp. 859-868. 



Equation (12), 



2P e .Y c =l (constant) 

 or 



II C .V C = 1 (constant), 



n being the total pressure a gas bears, shows the interesting 

 fact that the law of Boyle-Mariotte is true again for the 

 critica] state. 



Naturally, if during the course of the experiment mole- 

 cules have either dissociated or condensed, we must find 

 deviation over and above such as caused by the errors of 

 observation made in determining P c and V c . 



At the critical state, small changes of pressure cause large 



