270 Dr. Schcenbein*s Experimental Researches on a peculiar 



metals above mentioned is placed in the same solution, hav- 

 ing likewise one of its ends raised above the surface of the 

 liquid, copper will be precipitated as soon as the free ends 

 of both wires are made to touch one another. This mode of 

 changing the state of iron is exactly the same as that by which 

 a similar change of condition of this metal may be effected 

 with regard to nitric acid. Now, all these facts evidently prove 

 that the peculiar condition of iron, whatever the cause of it 

 may be, is always destroyed by the chemical action of metals 

 brought into contact with iron when in the inactive state. 

 There is certainly one singular fact, which seems to indicate 

 as if contact independently of and unconnected with chemical 

 action could of itself occasion a change of state in iron. It 

 has been already stated, that copper brought in some of the 

 ways mentioned into contact with an inactive iron wire, which 

 is immersed in the copper solution, renders the latter metal 

 active. Now copper of course cannot be precipitated from 

 the solution of blue vitriol by copper; the chemical action of 

 this metal upon the copper salt must, therefore, be essentially 

 different from that which is exercised by the more readily 

 oxidable metallic bodies in question. First, I thought there 

 might, perhaps, be some free acid contained in the solution, 

 and by this means chemical action occasioned. To ascer- 

 tain the correctness of this view, I added ammonia to the 

 solution until flakes of oxide of copper were beginning to 

 make their appearance ; but the copper wire acted in such 

 a neutral solution in the same manner as it did in the more 

 acid one ; chemical action consequently does not result from 

 the cause supposed. I think there is only one way left to ac- 

 count for the fact in question. It is well known that copper 

 put into a solution of a salt containing the deutoxide of this 

 metal, unites by degrees with this base, to form protoxide of 

 copper. Although this chemical action is extremely slow 

 and weak, still it is of sufficient power to revive in the inactive 

 iron its dormant affinity for oxygen. 



There is no doubt that, one case excepted, in all others 

 hitherto mentioned, in which passive iron is rendered ac- 

 tive, an electric current is produced, passing from the metal in 

 which chemical action originates, through the solution, into 

 the inactive iron, and from this back again to the first me- 

 tal. It is further obvious, that the direction of the current 

 passing through the inactive iron is opposite to that in which 

 the current moves through an iron wire which performs the 

 function of the positive electrode of a pile. The chemical 

 effects produced upon iron by these different currents being 

 also the reverse of one another, it seems to me that these facts 



