383 



of the discharge of (he SO'\-ions with the subsequent 0, -generation, 

 and further of a concentration increase of the halogen-ions, activation 

 will again make its appearance througli this latter- process at a 

 given moment etc. 



This surmise was perfectly confirmed, and using Dr. Mou/s 

 excellent galvanometer, we photographed some exceedingly regular 

 periodic curves, the maxima and minima of which differed 1.74 

 Volt in situation. These graphs were, howevei-, still incomplete in so 

 far that the lines of time still failed. 



In our further researches we made use of a jihotographic registra- 

 tion arrangement with time-signal-apparatus manufactured at this 

 laboratory, so that also the time-lines are visible on the new photos, 

 and accordingly a better idea of the regularity of the phenomenon 

 can be formed. 



We intend to answer several other questions by means of this 

 arrangement, but before proceeding to do so we will first give a 

 photographic representation of the phenomenon of the periodic 

 passivity, under about the same circumstances as before, but now 

 with registration of the time. 



This photograph is gi\'en in Fig. 1. The potential difference again 

 ranges here from about — 0,3 Volt with respect to the 1 norm, 

 calomel electrode in the active state, to about f 1,4 Volt, in the 

 passive state, the current density retrogi-essing from 33 m.Amp. to 

 28 m.Amp. per cm'. Since the time-lines, which are at a distance 

 of 3,3 seconds from each other, are now also di-awn, the regularity 

 of the phenomenon can be much better observed than before. The 

 maxima lie 6,15 seconds apart. Fig 1 shows further that the iron 

 was only a short time active, and comparatively long passive. The 

 electrode was sealed in as before, and 1,5 cm. long, and the 

 siphon of the auxiliary electrode was halfway of the height of the 

 electrode. The solution contained 0,72 gr. mol. FeSO^ and =t 0,014 

 gr. mol. Fed 3 |)er litre solution. 



The content of FeCl^ was, thei-efore, much smaller than before, 

 hence the |)eriüdicity appeared hei'e already at a smaller current density. 

 Fig. 2 refers to an experiment with the same electrode, but taken 

 with a slightly smaller current density, viz. 30 — 25 m.Amp. As is 

 very apparent from this photograph, this has caused the periods to 

 become longer, and the time during which the iron was in active 

 slate to become about equally long as the time in which the iron 

 was passive. 



It is remarkable that when we endeaxour to proceed in the 

 same direction, atid try to make the active state last siill longer 



25* 



