CHAPTER VI 



The Electrode Potentials 

 summary of contents 



Nernsfs theory of metal electrode potentials is developed and applied 

 to concentration chains, of which the hydrogen gas chains are the most 

 important for physiological work. The application of Nernsfs theory 

 to chains with various metal electrodes is briefly explained and the 

 electromotive series is described. 



45. The single potential of an electrode 



A metal immersed in a solution generally shows a difference of 

 potential towards the solution. This long familiar fact has been 

 theoretically worked out after the establishment of the ionic theory 

 and developed by Nernst. It has long been recognized that this 

 potential difference between a metal and a solution depends, first, 

 upon the nature of the metal, secondly, upon the composition of the 

 solution, and thirdly, to a small extent, upon the temperature. The 

 composition of the solution refers to the solvent as well as to the 

 solute electrolyte. As the solvent, water alone will first be con- 

 sidered. As far as the electrolyte is concerned, only the concentra- 

 tion of that ionic species is of importance which is capable of yielding 

 ions of the metal involved. All other ionic species which may be 

 present in the solution are immaterial as far as the value of the 

 potential difference is concerned. Thus the potential of a silver 

 electrode towards a 0.001 N AgNOa solution is the same as that 

 towards a 0.001 N solution of AgClOs, or of any silver salt, i.e., if a 

 galvanic chain were to be made of these two electrodes then the 

 resulting E.M.F. = 0. But if one silver electrode is immersed 

 in a 0.01 N AgNOs solution on one side and another silver electrode 

 is immersed in a 0.001 A^ AgNOs solution on the other side, a current 

 will be generated by this chain. Whether or not there be present 

 in these solutions another salt, 0.01 N KNO3 for example, is immate- 

 rial, insofar as this salt does not by chemical reaction alter the con- 



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