2 TSfEWBERY. Recefit Work oji Overvoltage. 



The standard electrodes used were— 



Hg. HgO. N . NaOH for alkali solutions. 



Hg. Hg^'SO^. N. H2SO4 for acid or sulphate solutions. 



Hg. HggClg. N . KCl for chloride or nitrate solutions. 



Cathodic (hydrogen) overvoltages are calculated on the 

 basis of the hydrogen electrode as zero; anodic (oxygen) over- 

 voltages, with the oxygen electrode as zero, the difference be- 

 tween the two being taken as 1.13 volt. 



MetaJ overvoltages (during metal deposition) are all calcu- 

 lated from the single poltential of the metal itself, taken as zero 

 in the given electrolyte. 



For comparison 0(f results the following values were taken : — 



Hg. HgO. N. NaOH. ... N. NaOH. Hg ... 0.93 volt. 



Hg. HggSO^. N. H0SO4 ... N. H2SO4. H2 ... 0.70 „ 



Hg. HggCls. N. KCl. 

 Hg. N. H2SO4 ... 



N. H2SO4. H, 



Absolute 



Absolute 



0.56 

 0.27 



Cathodic Overvoltages in Normal Sulphuric Acid. 



