664 
4. Anodic formation of silverhalords. 
Let us suppose the case that a silver anode is placed in a solution 
of sodium chloride with an excess of sodium nitrate, so that only 
the diffusion of the chlorine ion is to be taken into account, not its 
migration. On anodie polarisation the chlorine ions will be discharged 
at the silver, and then give AgCl. When, however, the current 
density is so great that fewer chlorine ions diffuse towards the 
anode than corresponds to this current density, also silver ions will 
go into solution. Strictly speaking the latter always takes place, 
because silver chloride is not absolutely insoluble, and therefore 
not all the AgCl formed will remain on the anode, but will go 
into solution for a small part. 
In the following way we now arrive at an equation of the current 
potential line for anodic polarisation of silver in NaCl. 
For a given current density there prevails at the anode a certain 
chlorine ion-concentration c‚o, and a certain silver ion-concentration 
Ca. The product of these values is equal to the solubility product 
of silver chloride 
Cia 024 == L. 
Not only at the anode, but also in the diffusion layer and in the 
whole liquid the solution is saturate with AgCl, hence 
C,C,=L 
holds everywhere. 
In the diffusion layer c, and c, lave values which are a function 
of the distance « to the anode, in the rest of the liquid they have 
a constant value, which we denote by C, and C,. 
Now per unit of time a certain quantity of chlorine ions arive 
through diffusion at the anode, there disappear per unit of time a 
certain quantity of silver ions; the sum of these two quantities, 
multiplied by the charge per gramme ion, gives the current density. 
Here the quantity of ions passing through a section of the diffusion 
layer, is not the same for every section as it is in the preceding 
cases, for bere also silver chloride must deposit, which causes 
chlorine ions and silver ions to disappear in equivalent quantities. 
If we now consider a volume of the diffusion layer between a 
section at a distance 2 from the anode, and another at a distance 
x + dre, the quantity of silver ions or chlorine ions passing through 
the first section will in general not be equal to that passing through 
the second. 
D de 
1 1 
will 
Through the section z a quantity of chlorine ions — 
d 
