and the Properties of Liquids. 567 



As we shall frequently have to refer to the general 

 equations for the internal heat of evaporation and surface 

 tension deduced in a previous paper, they will be placed in 

 this paper in a form convenient for our purpose. The heat 

 of evaporation L is given by the equation 



771 |_W, W, U, VJ \ X c 1 cJ Z\ 



-»,[P1.^).^. • • (l) 



where 

 and 



= Xa^{n + w) 2 + u 2 + " 2 



r 



z^ — xi ^{(n + u-) 2 tw 2 + r}, 



m denotes the molecular weight of the liquid, and Sy/mi the 

 sum of the square roots of the atomic weights of a molecule, 

 T is the temperature of the liquid and T e the critical 

 temperature, x a and x\ are the distances of separation of the 

 molecules of the liquid and saturated vapour respectively, 

 and Xc the distance at the critical temperature. If the 

 critical density and the density of the liquid and saturated 

 vapour be denoted by p c , p u and p 2 respectively, we have 



/wiY /3 /my/3 , fmV 



=w ' *»=U ' and * j= w 



The symbol .)» S in the equation is an integral and 



\_n, w, u, v_] 



summation operator between given limits applying to the 

 quantities n, w, w, and r, on its right-hand side : we are not 

 concerned with its exact form in this paper. This equation 

 follows from an investigation by the writer *, taking the 

 attraction between two molecules to be given by 



. /. T\ (Vm,) 2 

 MS'tJ-— *— • 



where z is their distance of separation. This law of 

 attraction was deduced from surface tension and heat of 

 evaporation data, which leaves the form of the function 



* 2 (£.' e) 



arbitrary t- 



* Phil. Mag. May 1910, pp. 793-795. 

 t Loc. cit. pp. 791-793. 

 2 P 2 



