Molecular Thermodynamics. 633 



If the limiting form has really been reached by Lewis and 

 Linhart in the few such cases investigated, this expectation 

 would not appear to have been realized, but the data can 

 scarcely be regarded as very satisfactory. 



Owing to the electrostatic forces being four times as great 

 in this case, we should expect the limiting form to be 

 attained only at much greater dilution than in the case of 

 univalent binary electrolytes. 



Now when we consider a mixture of ions of different 

 valencies, the corresponding calculation of %%r(f)(r) becomes 

 somewhat more complex. Milner's intermediate functions 

 f 7l (ni), 9n(m)i and s{m) become modified and less simple. 



Lewis has propounded an empirical rule which is equiva- 

 lent to substituting for C* (the total equivalent concentration) 

 of the preceding, a quantity S t - called the " ionic strength " 

 and given by 



S^iStfA., (103) 



where x s is the valency of the ion species (s) . 



It is probably not incompatible with a generalized form 

 of Milner's calculation that this rule should have a certain 

 limited validity as an approximation in practice, but whether 

 it is anything moro is rather doubtful. 



Chemical reactions in Electrolytic Solutions. 



In dilute solutions non-electrolytes behave as perfect 

 solutes for which 



|*=#.-Blog*. ...... (104) 



Not so ions, for which, as we have seen, 



supposing only ions of the same valency are present. 



Now from general theory (equation (21)) in any equi- 

 librium with regard to the virtual chemical change £Sn s we 

 have 



s!*.8 Ms =0. 



When all the participants are solutes obeying (104) this 

 gives, as we have seen (and as Planck showed in the 

 case where the solvent is not " associated " or polymerized), 



