484 



TATE AND FOOTE : ANODE FALL OF POTENTIAL 



voltmeter measurements must appear somewhere between the 

 probe and the cathode. 



The second assumption which may be made, and which the 

 writers believe they have proved to be the correct explanation, 

 is that the probe wire carrying a current does not take up the 



3ooa 



Zooo ■ 



Nickel Probe 

 Main Current, o.9 Amp 

 Area of Probe, 0.3 cm 3 



loco 



•5" 10 is 



Current from Probe (Amps * Z9Z5~) 



Fig. 2. Relation between the surface resistance and the current 



potential of the space surrounding it. This would be the case 

 if the probe were surrounded by a high-resistance film. Such 

 films are known to exist 2 at the cathode, but the writers are not 

 aware of measurements showing the presence of films at the 

 anode. Any surface resistance of the probe must be due to its 

 functioning as a secondary anode since the probe acts as a 

 cathode through a metallic circuit alone. 



In order to show the existence of a surface film at the probe, 

 the apparatus was arranged as illustrated by figure 1. 



The true anode drop was measured by using a potentiometric 

 method, suggested by Dr. Swann, by adjusting the slide wire c 

 for zero current in the galvanometer G and observing the read- 



2 Skinner. Loc. cit. 



