AND SCHONBEIN 21 



in any of the ways described, is placed in the acid, it 

 is again attacked by it if brought into contact with 

 any metal, even iron itself, which is actually being 

 dissolved by the acid. The indifferent wire can, how- 

 ever, be made active even if the part projecting above 

 the liquid (which may be of any desired length) is 

 brought into contact with the similarly projecting 

 part of the active wire. For example in the accom- 

 panying figure 1 let a b be the vessel containing the 

 nitric acid, c d the indifferent, and e f the active wire. 

 If now the point c of the wire c d is brought into 

 contact with the point e of e /, the immersed portion 

 of c d at once becomes active, as also happens if / 

 touches d. The same thing occurs likewise if c is 

 connected with d by any metallic wire. 



If the nitric acid is very dilute none of these 

 phenomena happen. After arriving at these results 

 I was curious to see how an iron wire would behave 

 in nitric acid if it was made the positive pole of a 

 voltaic circuit. My experiments on this point have 

 led to the following results. If the negative pole of 

 a cup apparatus of fifteen elements is connected with 

 nitric acid of specific gravity 1-35 by means of a 

 platinum wire, and one end of a common iron wire, 

 of which the other is attached to the positive pole, is 

 plunged in the acid, this wire remains perfectly in- 

 active and possesses generally all the properties of 

 the wires of which I have spoken above. Thus a 

 wire of this kind when separated from the positive 

 pole is not attacked by ordinary nitric acid. But if 

 1 There is no figure in the letter. 



