POTENTIALS AT PHASE BOUNDARIES 



193 



hence the total E.M.F. of the chain is 



E = TTi - TTo = RT • In 



"II 



"III 



"IV 



= RT In — 



"IV 



on 



^11 



The potential at the zone of contact 2 is of the character of a 

 diffusion potential, and in most cases may be disregarded as being 

 negligible, especially if it is remembered that the great mobility 

 of the H- and OH-ions, which in aqueous solutions is the important 

 source of all diffusion potentials, is non-existent in oily solvents. 



R. Beutner (1. c.) verified this equation experimentally in the 

 following way: 



Guaiacol, whose specific conductance is 0.1 reciprocal megohms 

 (r.m.), is shaken up with 0.1 M aqueous solution of NaCl. After 

 the distribution equilibrium is established the conductivity rises 

 to 1.2 r.m., an increase of 1.1 r.m. Then another portion of the 

 guaiacol is shaken up with a 0.1 M aqueous solution of dimethyl- 

 anihne hydrochloride. The conductivity rises to 59.0 r.m., an 

 increase of 58.9 r.m. Since the conductances of the various ion- 

 species are not very different, we may take the ionic concentration 

 as being proportional to the conductance. The conductance of the 

 pure guaiacol must be, of course, subtracted. 



Then the E.M.F. of this chain was determined: 



"U 



"in 



+ 



"IV 



The common ion is Cl~, and we obtain 



Cjii 58.9 



= 1; 



"IV 



^u 



1.1 



hence 



E = 0.0001983- T- log 



58.9 

 1.1 



= 0.100 volt 



The observed value was 0.091 volts. 



The figures in table 28 were obtained in a similar way for guaiacol 



