881 
taking place in the iron surface, and it will therefore entirely depend 
on the velocity with which this ionisation takes place, whether a 
disturbance, i. e. in this case an ennobling of the metal surface 
and attending it a decrease of the negative potential difference, occurs. 
Now we had found already two years ago’) that it is indeed pos- 
sible to disturb the internal equilibrium in the iron surface in the 
way indicated here, and it has further appeared that as was to be 
expected, the degree of the disturbance depends 1. on the: velocity 
with which the liquid is stirred; 2 on the concentration of the 
ferri-ions, and 3 on the temperature. 
When this had been ascertained, we have made attempts to 
earry the disturbance through a solution of a ferri-salt so far that 
the iron became passive. As a ferri-salt we chose ferri-nitrate, 
because it had appeared to us that the nitrate ion exercises a nega- 
tive catalytic influence on the setting in of the internal equilibrium. 
Experiments made at the ordinary temperature with iron elec- 
trodes cemented with sealing wax in a glass tube, at first gave a 
negative result with a single exception. In the meantime we heard 
from Messrs. Ornstein and Morr, who, induced by our research, 
had also occupied themselves for some time with the passivity of 
iron, that they had succeeded in making a thin iron wire fused 
into glass, passive by immersing it in a solution of Fe(NQ,),. 
On continuation of the investigation it now appeared that our 
negative result up to then was probably owing to our cementing 
the iron electrode, and that when the cement does not perfectly 
exclude from all contact the part of the iron covered by this material 
including all capillary rifts and cracks, a passification probably fails 
to take place in a solution of Fe(NO,),, in consequence of seeding 
originating from the non-passive parts which are all the same in 
contact with the solution. By bestowing the greatest care on the 
cementing we succeeded accordingly in obtaining iron-electrodes 
which become almost instantaneously passive on immersion in a 
solution of fe(NO,), at the ordinary temperature. 
This result may also be reached by fusing the iron in, as Messrs. 
Ornstein and Morr did. Then use must be made of enamel, because 
else no perfectly isolating fusing can be brought about on account 
of the great difference in expansion coefficient between glass and iron. 
This method of passifying iron also succeeds with iron electrodes 
of greater dimensions. Then the iron is suspended on a platinum 
1) Versl. Nat. en Geneesk. Congres Amsterdam April 1915. Z. f. phys. chem. 
40, 723 (1915). 
