Mr. Faraday o?i a 'peculiar Voltaic Cojidition of Iron. 61 



second cup of nitric acid, and then connecting the two cups by 

 a compound platina and iron wire, putting the platina into the 

 first vessel, and the iron attached to it into the second. The 

 second wire acted at the first moment, producingits correspond- 

 ing current, which passed through the first cup, and conse- 

 quently through the first and inactive wire, and affected the 

 galvanometer in the usual way. As soon as the second iron 

 was brought into the peculiar condition, the current of course 

 ceased ; but that very cessation showed that the electric cur- 

 rent was not stopped by a want of conducting power, or a 

 want of metallic contact, for both remained unchanged, but 

 by the absence of chemical action. These experiments, in 

 which the current ceases whilst contact is continued, combined 

 with those I formerly gave, in which the current is produced 

 thouo-h contact does not exist, form together a perfect body 

 of evidence in respect to this elementary principle of voltaic 

 action. ... 



With respect to the state of the iron when inactive in the 

 nitric acid, it must not be confounded with the inactive state 

 of amalgamated or pure zinc in dilute sulphuric acid. The 

 distinction is easily made by the contact of platina with either 

 in the respective acids, for with the iron such association does 

 nothing, whereas with the zinc it develops the full force of 

 that metal and generates a powerful electric current. The 

 iron is in fact as if it had no attraction for oxygen, and there- 

 fore could not act on the electrolyte present, and consequently 

 could produce no current. My strong impression is that the 

 surface of the iron is oxidized, or that the suj^erficial particles 

 of the metal are in such relation to the oxygen of the electrolyte 

 as to be equivalent to an oxidation ; and that having thus their 

 affinity for oxygen satisfied, and not being dissolved by the acid 

 under the circumstances, there isno renewal of the metallic sur- 

 face no reiteration of the attraction of successive particles of the 

 iron on the elements of successive portions of the electrolyte, 

 and therefore not those successive chemical actions by which 

 the electric current (which is definite in its production as well 

 as in its action) can be continued. 



In support of this view I may observe, that in the first ex- 

 periment described by Professor Schoenbein, it cannot be 

 doubted that the formation of a coat of oxide over the iron 

 when heated is the cause of its peculiar and inactive state : 

 the coat of oxide is visible by its colour. In the next place 

 all the forms of experiment by which this iron, or platina, or 

 charcoal, or other voltaic arrangements are used to bring or- 

 dinary iron into the peculiar state, are accompanied by a de- 

 termination of oxygen to the surface of the iron ; this is shown 



