

278 Mr. William Sutherland on the 



in the handling of solutions until, in the course of some work 

 on the elasticity of alloys, I discovered a relation similar to 

 the above to hold, and this proved to be the immediate clue to 

 the treatment of solutions. 



Let a w be the surface-tension of water, then we have the 

 following equations giving A : — 



A- 1 = X- 1 +(X- 1 -W- 1 )/ti. 



These equations ought to give the same values of A -1 what- 

 ever the strength of the solution may be ; and herein lies a 

 first test of the truth of the principles involved. 



The following values of cA _1 for NaCl are calculated from 

 Volkinamr's data (Wied. Ann. xvii.) for its solution in water 

 at 20° ; iv is taken as 18, although we consider the water 

 molecule to be complex, but this does not affect the purely 

 relative comparison being made : — 



n . . . '105 -084 -052 -035 -017 



cA~ l . . 1*34 1-38 1-47 1-46 V±% 



Considering that the solutions range from saturation down 

 to considerable dilution, the approach to constancy is satis- 

 factory; but it will be noticed that, on the whole, there is a 

 tendency for the value of cA _1 to increase with diminishing 

 concentration, and this same phenomenon is to be seen in 

 the case of almost all Volkmann's solutions, most pronoun- 

 cedly in that of CaCl 2 : — 



n . 



. -091 



•068 



•041 



•021 



•011 



cA- 1 . 



. 2-41 



2-53 



2-77 



2-95 



3-12 



This case shows us that there is a certain amount of incom- 

 pleteness in our theory of the capillarity of solutions, as indeed 

 we ought to be surprised if there were not, when we try to 

 apply our arbitrary definition of the molecular mass of a solu- 

 tion to one which contains 5 b* parts by weight of CaCl 2 to 100 

 of H 2 as the solution for which ?z = '091 does, and also when 

 we assume that the concentration in the surface-layer is the same 

 as in the body-fluid at all strengths up to saturation. If our 

 object were an exhaustive representation of the connexion 

 between the surface-tension of a solution and its concentration, 

 it would be easy to introduce a slight empirical alteration into 

 the above equations to make them exhaustive. For instance, 



