58 Mr. Faraday on a peailiar Voltaic Condition of Iron. 



escent by itself, it has the same properties and relations as that 

 to which the power has been communicated from other wires. 



If a piece of ordinary iron wire be plunged wholly or in part 

 into nitric acid of about specific gravity 1-3 or 1-35, and after 

 action has commenced it be touched by a piece of platina wire, 

 also dipping into the acid, the action between the acid and the 

 iron wire is instantly stopped. The immersed portion of the 

 iron becomes quite bright, and rcmaiiis so, and is in fact in the 

 same state, and can be used in the same manner as the iron 

 rendered inactive by the means already described. This pro- 

 tecting power of platina with respect to iron is very constant 

 and distinct, and is the more striking as being an effect the 

 very reverse of that which might have been anticipated prior 

 to the knowledge of M. Schoenbein's results. It is equally 

 exerted if the communication between it and the iron is not 

 immediate, but made by other metals ; as, for instance, the 

 wire of a galvanometer ; and if circumstances be favourable, 

 a small surface of platina will reduce and nullify the action of 

 the acid upon a large sui-face of iron. 



This effect is the more striking if it be contrasted with that 

 produced by zinc ; for the latter metal, instead of protecting 

 the iron, throws it into violent action with the nitric acid, and 

 determines its quick and complete solution. The phfenomena 

 are well observed by putting the iron wire into nitric acid of 

 the given strength, and touching it in the acid alternately by 

 pieces of platina and zinc : it becomes active or inactive ac- 

 cordingly; being preserved by association with the platina, 

 and corroded by association with the zinc. So also, as M. 

 Schoenbein has stated, if iron be made the negative electrode 

 of a battery containing from two to ten or more pairs of plates 

 in such acid, it is violently acted upon ; but when rendered 

 the positive electrode, although oxidized and dissolved, the 

 process, comparatively, is extremely slow. 



Gold has the same power over iron immersed in the nitric 

 acid that platina has. Even silver has a similar action ; but 

 from its relation to the acid, the effect is attended with pecu- 

 liar and changeable results, which I will refer to hereafter. 



A piece of box-wood charcoal, and also charcoal from other 

 sources, has this power of preserving iron, and bringing it 

 into the inactive state. Plumbago, as might be expected, has 

 the same power. 



When a piece of bright steel was first connected with a piece 

 of platina, then the platina dipped into the acid, and lastly the 

 steel immersed, according to the order directed in the former 

 cases by Professor Schoenbein, the steel was preserved by the 

 platina, and remained clear and bright in the acid, even after 



