202 HYDROGEN ION CONCENTRATION 



On the other hand in the chain 



the observed E.M.F. value was only 0.005 volts, instead of the 

 calculated maximal value of 0,040 volts; thus we have here an 

 approach to the other hmiting value of R.M.F. = 0. This is due 

 to the fact that, in this case, the anion, the salicylate-ion, is so much 

 more soluble in the oil phase than the cation, that it predominates in 

 the distribution. But being an anion it cannot be fixed, as a cation 

 would be, by the acidic oil. Hence the necessary conditions for 

 the maximal effect are lacking; on the side where the aqueous phase 

 contains more sahcylate-ions, the oil also contains more of them; or, 

 the concentration of saHcylate-ions in the oil phase is not invariable. 



The theoretical considerations which determine whether and how 

 far the E.M.F. approaches this or that limit may be stated as follows: 

 The salt tends to distribute itself between the phases. If this dis- 

 tribution is affected by the simultaneously occurring separation of 

 oppositely charged ions, then the difference of potential arises. But 

 if no or equal electrostatic forces interfere on both sides of the oil 

 phase, then no E.M.F. is developed. 



The last example, with Na-salicylate, presents the simplest case. 

 If the above theory is correct, then it should be experimentally de- 

 monstrable that in this case the common ion can distribute itself 

 according to a definite distribution coefficient and unhindered by 

 other forces. In other words, it must be shown that in those cases 

 where the E.M.F. = the common distribution law for electrolyte 

 is valid and that the ratio of its concentrations in the two phases is 

 invariably independent of the absolute amount present. 



This demonstration was given by Beutner for the chain arranged 

 with salicylic aldehyde and sodium salicylate: 12.5 cc. of salicylic 

 aldehyde were shaken with 50 cc. of a 0.1 molar aqueous solution 

 of sodium salicylate until the distribution equilibrium was estab- 

 lished. The conductance of the oil phase which was originally 

 0.7 r.m. is now 2.56 r.m. On using a 0.5 molar solution of sodium 

 salicylate instead of the 0.1 molar, the conductance is 14.46 r.m. 

 These two observed conductances are in the ratio of 1:5.6, while 

 the ratio of the concentrations of the two aqueous solutions is 1:5, 



