384 



by diiiiiriisliiiig the current density siill more, this can only be main- 

 tained for a short time, and a state soon sets in again as reproduced here. 



Periodic passivity in experiments with iron electrodes 

 that luere not sealed in. 



The following experiment was made with an electrode that was 

 not sealed in, but in which an iron electrode was simply immer- 

 sed 1.5 cm. deep into the electrolyte, the siphon of the auxiliary 

 electrode being placed (juite at the bottom against the iron electrode. 

 In this case (here was always an activating influence, starling from 

 the iron at the height of the liquid level, but in preliminary experi- 

 ments we had already found that this activating influence did not, 

 however, prevent the iron at the bottom of the electrode, which 

 was 1,5 cm. long, from exhibiting pretty regular periodic passivity. 



Fig. 3 shows the result obtained in this experiment. The pheno- 

 menon is, indeed, not quite so regular as with the sealed-in elec- 

 trodes, but the difference is not great. 



Periodic passivity at dijker ent heights under the liquid level. 



We will now examine what is the behaviour of a non-sealed 

 electrode at different heights under the liquid level. 



F'or this purpose experiments were made with an electrode which 

 was immersed much deeper, viz. more than 5 cm. under the liquid 

 surface. When the auxiliary electrode was again placed quite at the 

 bottom, a pretty regular periodicity was observed, just as in case 

 of less deep immersion ; this is shown by Fig. 4. When the auxiliary 

 electrode was placed 1.5 cm. above the lower end against the iron 

 electrode, the activating influence exerted from above, was already 

 very clearly noticeable. Thus Fig. A^a shows that though the pheno- 

 menon IS still regular, the character of the curve has been greatly 

 modifled. The periods are much shorter and the passive state lasts 

 very short, and what is very remarkable, now a longer duration of 

 the activity than of the passivity can be maintained. 



In the following experiment we have |>laced the auxiliary elec- 

 trode halfway up the immersed part, hence ± 2.5 cm. from the 

 bottom, and under these circumstances still greater modifications 

 were found, consisting in this that the iron did not always become 

 equally strongly active, and that regularly two less active states 

 were followed by a more active one, or that alternately a more 

 active and a less active state followed, as is clearly shown by Fig. 



