420 Mr. H. Davies on some Applications oj the 



all the above liquids approximately obey Maxwell's law, it is 

 probable that the values of: K are higher than the best 

 modern determinations would give for them. 



4. The Co-volume and Intrinsic Pressure of Liquids. 



The term (y — b) in the various equations of state is termed 

 the co-volume. Further, " b " is the volume at the absolute 

 zero of temperature. Taking, as in my previous paper, 

 Gruldberg's value for the ratio of the density at absolute zero 

 to the critical density as 4, it follows that b = % . V c . Again, 

 from (la) above 



whence 



V,=.JaT e .V^ 



The co-volume is consequently given by 

 r,-&=J(2«T.-l) 



4 \2T c -£ ) 



= ~«T (10) 



V 



Since b — —-. This immediately gives 



Vl =b(i+*T). ..... (ii) 



If a were constant this would be the ordinary linear relation 

 between v t and T ; but it must be remembered that a is a 

 function of T. The equation of state for a liquid can b© 

 written in the form 



(p + ^Xv-b) = RT, 



where p is the external and it the internal or intrinsic 

 pressure. If p is neglected in comparison with it and (y — b) 

 written as (/> the equation becomes 



7r<£ = ET (12) 



On substituting the value of (j> from (10) it follows that 



7r= ^ (13) 



