1350 



tliaii the other part of the soliUions. After the current has been 

 broken the iron surface is transformed witli pretty great velocity 

 jn the direction of the internal eqnilibrium, and as it is surrounded 

 by a solution that contains fewer ferri-ions than the solution outside 

 the boundary layer, the potential of the iron will now be more 

 negative than before the anodic polarisation. This state can, however, 

 last only a very short time, for the ferri-ions ditfuse from outside 

 into the't)oundary layer, in consequence of which the potential must 

 again become less negative, and will rise to the original value. 



For a right understanding of the matter it is useful to study the 

 subjoined diagram. 



Time 



The line ABC represents the course of the potential of iron after 

 anodic polarisation, when it is immersed in the solution of a ferro- 

 salt, which is practically free from ferri-ions. Immediately after the 

 anodic polarisation the iron is pretty greatly disturbed, but this 

 disturbance diminished at tirst with great velocity, and afterwards 

 more slowly. The curve AB'C also indicates the course of the 

 potential of iron after anodic polarisation, but now after a small 

 quantit} of a ferri-sall has been added to the preceding solution. 

 At tirst the potential descends rapidly, to below the tinal value. If 

 the liquid in the boundary layer had been entirely free from fern- 



