ELECTROMOTIVE FORCES IN PYRIDINE 



Getman and Gibbons 9 measured the electrode potentials, trans- 

 port numbers and conductivities in solutions of silver nitrate in 

 methyl alcohol, ethyl alcohol, acetone, and aniline. They con- 

 cluded that certain abnormalities in non-aqueous solutions may 

 be attributed to the formation of complex solute-solvent com- 

 pounds which dissociate more or less gradually with the dilution. 



The first systematic study of electrode potentials and electro- 

 motive forces in mixed solvents was reported by Pearee and 

 Farr. 10 They determined the electromotive forces of concentra- 

 tion cells and the electrode potentials of silver against its ions 

 in water, methyl alcohol and ethyl alcohol and in their binary 

 mixtures at both 0° and 25°. From the close agreement between 

 the observed and calculated values of the electromotive forces it 

 was shown that the Nernst equation can be applied not only to 

 solutions in non-aqueous solvents, but also to solutions in binary 

 mixtures of these solvents. The electrode potentials are rela- 

 tively greatest in methyl alcohol and least in aqueous solutions, 

 the corresponding values in ethyl alcohol occupying an inter- 

 mediate position. Further, the values of the electrode potentials 

 are highest in the most concentrated solutions. In all cases they 

 decrease rapidly with dilution at first and then subsequently the 

 decrease proceeds almost linearly with further dilution. 



The electrode potentials in the binary mixtures of the alcohols 

 obey the law of mixtures. In the binary mixtures of water and 

 the two alcohols, the electrode potentials increase slowly at first 

 with addition of alcohol from the value in pure water up to mix- 

 tures containing about seventy-five per cent of the alcohol and 

 then more rapidly with further increase in the proportion of the 

 alcohol. 



The temperature coefficients of the electrode potentials are 

 positive for solutions in both alcohols and their binary mixtures. 

 Those in ethyl alcohol and the aqueous mixtures containing sev- 

 enty-five per cent and fifty per cent ethyl alcohol, increase with 

 dilution throughout, while those in methyl alcoholic solutions 

 pass through a minimum value. The temperature coefficients in 

 the water and the seventy-five per cent aqueous mixtures are 

 negative throughout, becoming more negative with increasing 

 dilution. The influence of the water as manifested by the tem- 

 perature coefficients of the electrode potentials is displaced to- 

 ward higher dilutions as the proportion of the alcohol in the 

 mixture is increased. 



"Ibid. 36, 1630, 1914. 



10 Jour. Physical Chem., IS, 729, 19H. 



