t 456 ] 



XLV. Intelligence and Miscellaneous Articles. 



ON THE EQUATION OF STATE. 



To the Editors of the Philosophical Magazine. 



Sirs, — 

 TN a paper published in the 'Philosophical Magazine' for ilugust 

 -*- 1918 it has been shown that from Boltzmann's theory of 

 entropy we can arrive at an equation of state 



P=-~lQgl-— =« NK0« (1) 



Amongst other applications of this theorem it was shown that 



T?fl ^e 



the value of the critical constant Iv= — -? would be ___ =3-53, 



pcJc c—L 



instead of van der Waals' ,3 and Dieterici's ^ = 3'69. 



o 2 



A table was given showing that in the case of the most of the 



elementary gases the value 3*53 corresponded better with experi- 



mental results than either - or 3-(39. 



3 



The list comprised He, i\ T 2 , 2 , Xe, but not Hydrogen, about 

 which the experimental data were not satisfactory. 



Eecently the critical data for Hydrogen have been re-determined 

 in the Laboratory of Prof. K. Onnes (vide Proc. K, Akad. Weten- 

 schappen, Amsterdam, vol. xx. 1917). 



It has been found that 



e = 33°-18K, d c = '03l0, 1)0 = 12-8 atmospheres ; 



from these data, K=335. 



It is superfluous to add that this value of K is in much 

 better agreement with the value 3-53 than with either the value 

 8 , e 2 



q=2'66 or =3'69, thus corroborating the belief expressed in 

 o 2 



the aforesaid paper that the equation (1), though not final, marks 

 a step in the right direction. 



Megh Nad Saha. 

 University College of Science, Satyei\ t DRA Nath Basu. 



Calcutta, India, 



