Rust Preventing Power op Certain Electrolytes. 7 
tain electrolytes, and a sufficiently large current is passed, then the 
iron does not dissolve, but oxygen is evolved on its surface, just 
as would be the case with a platinum or gold pole. The surface 
of the iron retains this passive condition fairly indefinitely if it is 
taken out of the solution and the surface is washed and dried. The 
question arises: is it possible to transform the surface by this means 
so that it may resist corrosion permanently ? and another question is : 
since iron frequently must be used in contact with water and salt 
solutions, is it possible to find certain salts which, when added to 
the solution, may affect the surface so that it may be kept perma- 
nently passive? These are the particular questions that I have ad- 
dressed myself to in connection with my experiments and concern- 
ing which I wish to report here. 
In brief, the detail of the experimental procedure was the 
following: A clean, definitely measured portion of metal surface 
(several samples each of wrought iron, cast iron, and steel were 
tried) was exposed to anodic action under conditions which assured 
uniform distribution of the current over the surface. 
Different electrolytes were employed (See list below) and the 
liquid was admitted to the pole and stirred in such a manner that 
during any one determination the composition of the solution in 
contact with the surface remained absolutely the same — it was not 
changed by the products of the electrolysis, because these were re- 
moved by passing the electrolytes through the apparatus in a con- 
tinuous stream. In all experiments air was removed at the begin- 
ning and excluded during the progress of the experiment, because 
oxygen is the particular substance the action of which upon the 
surface produces the phenomenon of passivity. The current density 
and the corresponding electric potential of the metal under observation 
were recorded. The solutions used were sulphates, chlorides, nitrates, 
fluorides, chromates, chlorates, bromates, iodates, perchlorates and 
hydroxides. These were used in definite concentrations. Some of 
these solutions were also used with the addition of definite slight 
amounts of alkali or of acid. Also several mixtures of two electro- 
lytes were employed. 
The behavior of the metals under these conditions showed conclu- 
sively that the passive condition is due to a cover formed by the 
liberated oxygen. It is quite certain now that a very thin coat of 
metal oxide at least is produced, and this together with a film of 
oxygen gas which is held by this oxide coat as a skeleton, protects 
and isolates the metal surface from the electrolyte. However, this 
coating is never homogeneous, and at the “cracks” or interstices the 
metal is exposed to the electrolyte and undergoes the usual action. 
