808 



containing Cl' — Br' and I'-ions, wliicii ions must tiierefore be 

 considered as catalysts for the conversion of pnsslvi' iron into 

 active iron. 



In the conrse of the investigation on llie passivity of iron the 

 qnestioM rose wiiether it would not be possijjle to call forth periodic 

 phenomena for instance by the addition of Cl-ions to the electrolyte 

 during, the anodic polarisation. 



According to our recent views the internal equilibrium in the iron 

 surface is namely disturbed during the anodic polarisation, in con- 

 sequence of this that practically exclusively ferro-ions go into solution, 

 and the comparatively slow internal transformation ferri -» ferro in 

 the iron surface proceeds too slowly to keep pace with the going 

 into solution of ferro-ions. Hence the iron surface becomes richer in 

 ferro-ions and the potential diiference iron elect rtjlyte becomes less 

 strongly negative or positive. 



Let us suppose that the electrolyte is ferrosulphate, and during 

 the anodic polarisation of an iron electrolyte with a very small 

 surface, we add ferrochloride, then the catalytic influence exercised 

 by the chlorine ion becomes noticeable by a decrea.se of the positive 

 potential difference, and when the addition of ferrochloride is con- 

 tinued, a pretty rapid and considerable decrease of the potential 

 difference appears at a given moment, and the iron has passed 

 from the passive state into the active state. 



Without our entering into any further details it is clear that at 

 a velocity of solution of the iron determined by the density of 

 current it must be possible to find a concentration of chlorine ions, 

 at which at a definite moment the chance that the iron remains 

 passive is just as great as the chance that it becomes active oi* vice 

 versa. Let us now suppo.se that at this moment the density of the 

 current is somewhat diminished, then it may be expected thai the 

 transition passive-active takes place, and while the iron-anode in the 

 passive state only goes exceedingly little into solution, the iron, 

 having now become active, will be sent into solution to a very great 

 degree in the form of ferro-ions. Hence the contact, of the Cl'-ions 

 with the iron-surface will diminish, and in consequence of this the 

 i>'on will again be brought back to the passive state. 



As has been said, the iron dissolves but very sparingly in this 

 passive state, and the processes which now take place at the anode, 

 consist first of all in the discharge of the SO^-ions with the subse- 

 quent Os-generation, and secondly in an increase of concentration of 

 the Cl'-ions. This latter process will then again give rise to activation 

 and so on. This supposition was fully confii'med, and as the following 



