LEWIS AND JACKSON. — POLARIZATION ON MERCURY CATHODE. 415 



old, and they must therefore be regarded as preliminary to a more 

 thorough investigation. Since, however, circumstances prevent a con- 

 tinuation of our work at this time, we publish the results so far obtained. 



Summary. 



The polarization observed when hydrogen is deposited electrolytically 

 upon a mercury cathode is studied, the apparatus being designed to 

 exclude as fully as possible all impurities and all side-reactions. 



The polarization curve up to 0.7 volt is regular and shows no break in 

 continuity. The relation between potential E and current 1 is given 

 very exactly by the equation E — A log Ix B where A and B are con- 

 stants. 



The theory of this logarithmic equation is discussed. 



It is shown that the polarization cannot be due to the slowness of dif- 

 fusion either of hydrogen-ion to the electrode or of the hydrogen away 

 from the electrode, but must be due to some intermediate reaction. 



A theory is proposed concerning the nature of this reaction. 



The effect of temperature on the polarization is considered. 



Certain unexpected phenomena accompanying the polarization are 

 discussed. 



