LEWIS AND JACKSON. — POLARIZATION ON MERCURY CATHODE. 401 



The electrolytic cell and the measuring apparatus are sketched in 

 Figure 1. The cell consists of a glass bottle, which is immersed in a 

 thermostat (the latter not shown in the figure). B represents the tube 

 by which the hydrogen enters the cell ; C is the platinum electrode, 

 made of a strip of platinum foil of about thirty square centimeters, plat- 

 inized with pure platinum chloride, carefully cleaned and treated for 

 some time with boiling water, to remove any loose particles that might 



Figure 1. 



otherwise be disengaged by the hydrogen bubbles and carried to the 

 cathode ; E is the exit tube for the hydrogen; D is a tube two millimeters 

 in internal diameter, containing mercury, constituting the cathode. In 

 order to determine whether diffusion processes in the electrolyte jilay an 

 important part in the phenomenon cited, it was our original purpose to 

 vary the height of the mercury in D, and find the effect upon the magni- 

 tude of the current, at potentials insufficient to produce a bubble of 

 hydrogen in the tube.* As a matter of fact, however, we found that 

 after complete saturation of the electrolyte with hydrogen no potential 



* Cf. Caspari, Zeit. pliys. Chem., 30, 89 (1899). 



VOL. XLI. — 26 



