655 
The same quantity of ions must be discharged per second at 
1 cm’. of area of the cathode. The charge of this quantity of ions 
is therefore equal to the current density d 
96500 | C—e 
a reen : 
a TE ’ 
"86400 9 
T= Vi pe EE 
J 
and by combination of (1) and (2) we get: 
E=e + mee log (¢- ene jk Rong Se Wet) 
n 4 Erle DS 
A similar equation holds for the anodic polarisation. 
5 ta CG 3 ; 
Here d—1.117 D- Tia where Ca represents the concentration of 
€ 
the metal ions at the anode. 
The anodic and the cathodic polarisation may also be represented 
by the same equation, when the current density at one of the elec- 
trodes, e.g. the cathode, is taken negative. 
Then we get: 
. = 6H, 
EN (À 
J 
and 
0.058 hes dd 
B =e + —— "log (ca oe ar PE C5) 
In figure 1 the general course of this line is represented by a. 
Positive current densities here refer to the anode, negative ones to 
the cathode. It is seen from the course of the line that with decreas- 
ing values of the potential the current density at the cathode approaches 
to a limiting value. This current density, which cannot be exceeded, 
bears the name of limiting current. The value of this current density 
follows from (4). 
The smallest value that c can have, is 0; hence the greatest value 
for the cathodic current density: 
Di 
C “ 
CKitimit = — 1.717 D 5 eon sn Jeen Sese 
This ecathodie limiting current is, therefore, proportional to the 
concentration of the ions in the electrolyte, and to the diffusion 
coefficient, and in inverse ratio to the thickness of the diffusion layer. 
There does not exist a limiting current in the same sense at the 
anode. When, however, anode and cathode have the same area, the 
current density is the same for them. Hence : 
