VOLUME AT ABSOLUTE ZERO 31 



But according to what precedes (p. 21), 



&=r$F Al 



therefore F = iF*; 



i. e. equally a constant ratio between the volume at the 

 critical point and the critical volume, only ^ instead of the 

 experimental |. 



6. Volume of the Liquid at Loiv Temperature 1 . 



By applying the three empirical rules (i) as to critical 

 density, (2) density at the absolute zero, (3) of the rectilinear 

 diameter, a good insight may be obtained into the volume 

 relations of liquids at temperatures such that the density 

 of the vapour may be neglected by comparison with that 

 of the liquid, i. e. at temperatures not very close to the 

 critical point. 



The law of rectilinear diameter connects the liquid and 

 vapour densities (D L and D v ) by the equation 



in which, according to (2), for 



so that a = 



and for T = T t , D L = D C = D k . 



Therefore 



^ K t-^A: <-'-- > m 



k 



so that 



T k T k 



and if D v is negligible 



i T k V k T k 



in which, according to (i), 



7, - 



~ 



37 * 



1 D. Berthelot, Compt. Rend. 128. 606. 



