810 



in fig. Ie. Tlie oscillations founil by iis are, as is shown in the 

 drawing, about ten times greater. 



2. 2Vie injiiumce of the (Jl'-ion concmtnttion on. tin' sha/w of the 

 curve of nctivation. 



Another qiiostion whicii likewise incited to research, was this: 



Wlien iron is made j)assive by anodic |Jolarisation, e. g. in a 

 solution of ferro-sulphate, and then I lie current is interrupted, the 

 potential difiTerence diminishes rapidly at first, then it changes little 

 for a short time, after which it finally descends again rapidly. 



This discontinuity has been accounted for by Smits and Ate.n "•), 

 the explanation coming to tiiis that in the transition passive — »■ 

 active a state must be passed through at which two metal phases 

 exist side by side, which, in case electromotive equilibrium continued 

 to exist all the time, would have to give rise to a temporary occur- 

 i-ence of a constant potential ditt'erence. 



When now chlorine ions in the form of ferro-chloride are added 

 to the solution of ferro-sulphate it may be expected that, the 67'-ions 

 accelerating ihe internal transformation in the iron surface, this 

 discontinuity will become less distinct, and a/iparent/i/ vanishes 

 entirely at a certain C/'-ion concentration. 



As the curves fig. 2 show this expectation has been entirely realized. 



It is clear that the discontinuity which seems to have entirely 

 disappeared on the last photo, (/ fig. 2, would manifest itself again 

 clearly, when the velocity of revolution of the registration cylinder 

 was increased. We shall return to this later on. -) 



That these remarkable results recorded here, which strongly 

 support the new views of the passivity, can be stated in such a 

 way that every particularity which tlie different figures contain, is 

 essential to the phenomenon, and is not a consequence of the inertia 

 of the galvanometer, we owe to this that ' the research could be 

 made with Dr. Moll's e.xcellent galvanometer, which through its 

 quick and moreover perfectly aperiodic indication was eminently 

 suitable for these experiments. 



The photographic representations have been made with Dr. Moll's 



1) These Proc Vol. XVII, p. 680. 



Chem Weekblad 31, 678 (1915). 



-) The curve d exhibits a hardly visible thickening on the original photo at the 

 place of the halting-point. In a subsequent communication the infliience of the 

 extent of the iron surface on the periodicity will be more particularly dealt with, 

 and further the periodic passivity at anodic polarisation of iron, the unprotected 

 surface of which is only partially imnierged in a ferro-sulphate solution. 



