86 Dr. R. D. Kleeman : Determinations of the Law of 



to which it corresponds must therefore also contain an 

 arbitrary function, 



Fig. 2. 



Kext let ns consider the determination of the law of 

 molecular attraction from surface tension data. The surface 

 tension of a liquid may be defined as the work done against 

 the molecular attraction per cm. 2 of new surface formed in 

 cutting a thick slab of liquid into two parts and separating 

 them by an infinite distance. If the liquid is surrounded by 

 vapour of density p 2 we may suppose that an amount of 

 matter of density p 2 remains stationary in space when the 

 slabs are separated, which is equivalent to separating two 

 slabs (not surrounded by vapour) each of density (p 1 —p 2 )*. 

 Let the equation of the surface tension of a substance for 

 any value of {pi—p 2 ) or p B , deduced from a knowledge of the 

 law of attraction between 1he molecules, be A^^ (T, /j 3 ). 



* This is strictly admissible only if matter consists of molecules in- 

 finitely small in size, but devia ions due to this not being the case ■will 

 occur only when the liquid and vapour have nearly the same density as 

 occurs near the critical point. 



