of the Liquid and Gaseous States of Matter. 669 



In a previous paper* it was shown that the internal latent 

 heat of evaporation L of a liquid is given by 



where p v and p 2 denote the densities of the liquid and 

 saturated vapour respectively, and A, and A 2 are constants 

 each of which is the same for all liquids at corresponding- 

 temperatures. This equation is based on the law of attraction 

 between molecules, given at the beginning of the paper. The 

 equation may be written 



L = L'-L", 



where L , = Ai '■ 



and 



(S) <*^ 



m \m/ 



From the way the above equation has been obtained, 

 it follows that L' denotes the internal latent heat o£ evapora- 

 tion of a liquid into a vacuum, and L" the internal latent 

 heat of evaporation of the saturated vapour into a vacuum. 

 The equation (2) for the intrinsic pressure may now be 

 written 



P n = P L'K S , (4) 



where T ^ _ K 2 



and is therefore a constant which is the same for all liquids 



at corresponding states. At low temperatures L" is small in 



comparison with L', and the above equation may then be 



written -r, T -^ 



r n = pLii^ 3 . 



An equation similar to equation (4) may be very simply 

 obtained if we make the supposition that matter does not 

 consist of molecules but is evenly distributed in space. Let 

 the attraction of a large mass of liquid, making this sup- 

 position, on a slab of liquid of unit area and thickness dz at 

 a distance z from the surface of the liquid, be yfr(z)dz, in a 

 direction at right angles to the surface of the liquid. The 

 attraction on a cylinder of unit cross-section and infinite 

 length standing with one of its bases on the surface of the 



liquid will therefore be J^(~) .dz ; and this is equal to the 

 intrinsic pressure. "o 



* (a) pp. 704-795. 



