Mr. Faraday on a peculiar Voltaic Co?idition of Iron. 59 



the platina was separated from it, having, in fact, the proper- 

 ties of the inactive iron. When immersed of itself, there was 

 at first action of the usual kind, which, being followed by the 

 appearance of the black carbonaceous crust, known so well in 

 the common process of examining steel, the action immediately 

 ceased, and the steel was preserved, not only at the part im- 

 mersed, but upon introducing a further portion, it also remained 

 clean and bright, being actually protected by association with 

 the carbon evolved on the part first immersed. 



When the iron is in this peculiar inactive state, as M. Schoen- 

 bein has stated, there is not the least action between it and the 

 nitric acid. I have retained such iron in nitric acid, both 

 alone and in association with platina wire for 30 days, without 

 change ; the metal has remained perfectly bright, and not a 

 particle has been dissolved. 



A piece of iron wire in connexion with platina wire was 

 entirely immersed in nitric acid of the given strength, and the 

 latter gradually heated. No change took place until the acid 

 was nearly at the boiling-point, when it and the iron suddenly 

 entered into action, and the latter was instantly dissolved. 



As an illustration of the extent and influence of this state, 

 I may mention, that with a little management it can be shown 

 that the iron has lost, when in the peculiar state, even its power 

 of precipitating copper and other metals. A mixture of about 

 equal parts of a solution of nitrate of copper and nitric acid 

 was made. Iron in the ordinary, or even in the peculiar state, 

 when put into this solution, acted, and copper was precipitated; 

 but if the inactive iron was first connected with a piece of pla- 

 tina dipping into the solution, and then its own prepared sur- 

 face immersed, after a few seconds the platina might be re- 

 moved, and the iron would remain pure and bi'ight for some 

 time. At last it usually started into activity, and began to pi-e- 

 cipitate copper, being itself rapidly corroded. When silver 

 is the metal in solution, the effect is still more striking, and 

 will be referred to immediately. 



I then used a galvanometer as the means of connexion be- 

 tween the iron and other metals thus associated together in 

 nitric acid, for the purpose of ascertaining, by the electric cur- 

 rents produced, in what relative condition the metals stood to 

 each other; and I will, in the few results I may have to describe, 

 use the relations of platina and zinc to each other as the terms 

 under of comparison by which to indicate the states of these 

 metals various circumstances. 



The oxidized iron wire of Professor Schoenbein is, when in 

 association with platina, exactly as another piece of platina 

 would be. There is no chemical action, nor any electric cur- 



