POTENTIALS AT PHASE BOUNDARIES 207 



The nature of the oil in the middle phase is not quite as immaterial 

 as might appear from this tabular summary, for the differences 

 between the individual ions within the series are accentuated to 

 various degrees depending upon the oil. Thus, if the oil is of an 

 acid character (either by itself or in virtue of an added oil-soluble 

 organic acid), then the differences between the cations are strongly 

 marked, while those between the anions are shght. In a basic oil 

 (or with an added organic base) this effect is reversed, as would be 

 expected from the stated theory. 



But apart from this general rule specific effects of the nature of 

 the oil manifest themselves. Thus in a chain with NaCl at one 

 end and Na2S04 at the other we should expect from the above rule 

 the Na2S04 side to be negative. Such is the case with o-, m-, p- 

 cresol, phenol, guaiacol, acetophenone, acetoacetic ester (all of which 

 jdeld an E.M.F. of 20-30 millivolts); aniline, toluidine (which yield 

 even higher E.M.F. values). On the other hand, benzaldehyde and 

 salicylaldehyde give E.M.F. values of nearly zero, while with cin- 

 namic aldehyde, anisaldehyde and benzophenone even a positive 

 charge of the Na2S04 side was found. Evidently the above rules 

 are obeyed b}- all of those oils which are definitely acid or basic in 

 character in virtue of NH4 or OH-groups; while with oils of a 

 chemically indifferent character the relationships are not so un- 

 equivocal, which is quite comprehensible in view of our earlier 

 explanations. 



58. The electromotive series of the oils 



We have hitherto considered chains in which the asymmetry of 

 arrangement lay in the difference between the two aqueous phases. 

 But chains can be had whose aqueous phases are of the same com- 

 position and whose oil phase is asymmetrical, the latter consisting of 

 two oils, as, for instance, 



I II III 



Aqueous phase | Oil I Oil II I Aqueous phase 



Such chains, with the two aqueous phases being identical, jdeld an 

 E.M.F. obviously caused by the potential difference between the 

 single potentials I and III. As for example, in the chain 



Calomel electrode 



in 0.1 N KCl in 



water 



Cresol 



Benzaldehyde 



Calomel electrode 



in 0.1 N KCl in 



water 



