Intelligence and Miscellaneous Articles. 



455 



induced, not only by the contact of fuming nitric acid, but also when 

 the iron is blued by the spirit-lamp, or when it is touched with a 

 piece of platinum whilst immersed in non-fuming nitric acid. The 

 same effect is obtained when the iron is attached to the positive pole 

 of a voltaic battery. 



In consequence of the modifications which it undergoes under 

 these circumstances, iron does not precipitate sulphate of copper 

 when it is employed as the anode of a voltaic element ; oxygen is 

 evolved around it without attacking it ; it bears contact with aqueous 

 nitric acid without alteration, but becomes active again when it is 

 plunged into water after being taken out of the acid. 



The same thing takes place more or less with nickel and cobalt 

 when drawn into wire. In contact with fuming nitric acid these 

 two metals only acquired a passive state of very short duration, but 

 their passivity becomes permanent, when, after bluing over the flame 

 of a spirit-lamp or a charcoal fire, they are plunged whilst hot into 

 this acid ; they then behave exactly like passive iron, except that 

 they are less negative than that metal in nitric acid. They never- 

 theless communicate their passive state to active iron immersed in 

 non- fuming nitric acid, and arrest the violent attack of the acid on 

 the metal. 



Platinum is always negative in regard to these three metals when 

 rendered passive, and each of the latter is also negative in regard to 

 the three active metals. The neutrality of passive iron in sulphate 

 of copper, pointed out by Schb'nbein, could not be reproduced out of 

 the circuit ; in all the experiments the passive iron was soon sur- 

 rounded with metallic copper. 



The examination of the electro-chemical relations of iron, nickel 

 and cobalt, in their active and passive states in contact with different 

 acids and with a watery solution of potash, gave the following results. 

 The negative character^ of passive iron is really distinct only with 

 nitric acid ; in the other liquids employed in these experiments, the 

 positive electricity is transferred to the iron instead of emanating 

 from it. In solution of potash the relations were the same with the 

 active as with the passive metals, which would seem to indicate that 

 the passivity of these metals is destroyed, by this alkali. This, how- 

 ever, is not the case ; for if after immersion in potash the metals 

 are again brought into contact with nitric acid^of spec, gray. 1*34, 

 they again acquire their passive state, and are not attacked by the acid. 



The following table gives the relations of iron, nickel, and cobalt 

 in both states, commencing with the positive and concluding with 

 the negative metal, the experiments being made with the liquids 

 indicated : — 



Comptes Rendus, August 16, 1853, p. 284. ; . 



