of the Liquid and Gaseous States of Matter. 677 



must be equal to pji/, or ap\=Upi, and therefore h' = api. 

 Since the internal latent heat of evaporation L is given 

 by L = L' — L" we have L = a(pi — p 2 ), where a is constant. 

 But this equation for the latent heat does not agree with the 

 facts, and a is therefore not a constant. This is shown by 



Table L, which contains the values of ■ at different 



P1-P2 



temperatures for a number of liquids ; the values of this 



quantity or a, it will be seen, decrease considerably with 



increase of temperature. 



Table I. 





Ethyl oxide. 



Carbon tetrachloride. 1 



Methyl formate. 



T. 



L 



Pl~p2 



T. 



L 

 Pj-P2 



T. 



L 



Pl~( J 2 



T. 



L 



P1-P2 



T. 



L 

 Pi — Pa 



T. 



L 

 Pi— Pa 



273 



117-1 



393 



100-2 



273 



29-6 



473 



25-3 



273 



1129 



443 



89-5 



313 



109-9 



433 



934 



393 



27 4 



513 



244 



1 



323 



107-6 



483 



73-4 



353 



104-7 460 



88-7 



433 



26-4 



553 



22-1 



403 



956 



486-5 



68-1 



From the equations of condition for equal roots of v we 

 obtain 



RT 

 PcV ° m2'6tf 



But the constant 2'6ti is too small, its value we have seen 

 ought to be 3*7. Van der Waals' equation thus satisfies 

 only imperfectly two important conditions. The equation of 

 state given in this paper satisfies these two conditions besides 

 one other, and should therefore be in better agreement with 

 the facts than van der WaaiY. Moreover, it is more general 

 in form and has a definite theoretical basis. 



The equation of state given in this paper was developed 



taking <j>2\—i@) or K in the expression for the attraction 



between two molecules as a function of the temperature only, 

 in support of which we obtained some evidence. It will be 

 of interest to develop an equation of state taking K a 

 function of p and thus independent of the temperature. 

 It should be observed that when the equation of state is 

 applied to a liquid and its saturated vapour, it does not 



