J. Nicklés on the Passivity of Nickel and Cobalt. 347 
Art. XXXIV.—On the Passivity of Nickel and Cobalt; by 
M. J. Nickxés. 
Te singular property of iron of becoming less oxydisable in 
contact with fuming nitric acid, has engaged the attention of 
many chemists and physicists. Since its discovery by Keir, it 
has been examined from different points of view by Herschell, 
Faraday, Schénbein, Buff, de la Rive, Andrews, Mousson, Mil- 
lon, Beetz, and Bollmann. The researches of these investigators 
have shown that iron may become passive not only in contact 
with fuming nitric acid ; it acquires this property also on blueing 
it in the flame of a lamp, or on touching it with a plate of plati- 
num, while it is plunged in nitric acid not fuming. 
The same effect is produced when the iron is put in connection 
with the positive pole of a galvanic battery. As evidence of the 
modification which it undergoes under these circumstances, the 
iron does not precipitate sulphate of copper when it is used as the 
anode of a galvanic element; oxygen is disengaged around it, 
without attaching it; in contact with diluted nitric acid, it remains 
unaltered, but it becomes again active when after being taken 
from the acid, it is put into water 
Similar facts may be observed to a greater or less extent with 
nickel and cobalt drawn into wire. The wire of these metals 
used in the experiments was chemically pure ; it was prepared by 
M. H. Sainte Claire Deville, by a process of heating of his inven- 
tion,* who also analyzed it. — 
fuming nitric acid, both of these metals acquire a passive 
State only of short duration ; but the passivity becomes permanent 
when, after blueing them in the flame of an alcohol lamp or on a 
charcoal fire, they are plunged while hot into this acid, in which 
Case, they act in every respect like passive iron, except that they are 
less negative than in nitric acid. They can however, communi- 
cate their passive state to active iron plunged in nitric acid not 
fuming, and so arrest the energetic action that is produced by the 
acid, 
_ Platinum is always negative with respect to these three metals 
In the passive state, and either of these last is negative with re- 
Spect to the same in the active state. 
The preservation of iron against attack in sulphate of copper, 
observed by M. Schénbein, has not been obtained out of the gal- 
Vanic current; in all my experiments, the passive iron becomes 
promptly covered by metallic iron. 
ave also examined the electro-chemical relations of iron, 
nickel and cobalt in the active and passive states, in contact with 
different acids as well asa solution of potash in water. ‘The neg- 
ative character of passive iron is really very decided only in 
* See this Journal, xv, 424, 
