Action of Iron upon Solutions of some Metallic Salts, 2G9 



jected to the influence of a current. This remarkable fact has 

 been observed by Sir John Herschel, and more recently by 

 Mr. Faraday and myself. IT, for instance, a common iron 

 wire, having been made inactive by repeated immersions in 

 common nitric acid, is put into a solution of blue copper vitriol, 

 not the least chemical action takes place. It is true that it 

 happens sometimes that such a wire precipitates copper at 

 the moment of its being plunged into the solution, but in such 

 a case the inactive state of the metal had ceased previously to 

 immersion. Now whether iron is or is not in its peculiar con- 

 dition may easily be ascertained by the appearance of the 

 surface of that part of the wire which had been immersed in 

 nitric acid. If the surface is bright, the wire is inactive; if 

 yellowish brown, the metal has assumefl its common state, 

 and will consequently act upon the copper solution in the 

 usual manner. The peculiar condition of iron with regard to 

 the copper solution can be destroyed in different ways. In 

 the first place it may be destroyed by making an inactive iron 

 vibrate. If such a wire is wetted by the said solution, and 

 afterwards rather violently struck against any solid body, for 

 instance against a table, immediately after the shock a film of 

 copper will make its appearance along the whole wetted sur- 

 face of the wire *. According to the results of my experiments, 

 published in several periodical works, inactive iron is rendered 

 active with regard to nitric acid by the same means. In the 

 second place the active state of iron may be reproduced by 

 touching the inactive metal with a metal which acts chemically 

 upon the solution of the copper salt. If an inactive wire is 

 whetted by this solution, and then touched, on any point of the 

 part wetted, with a piece of common iron, zinc, cadmium, tin, 

 lead, arsenic, or even copper, the precipitation of copper in- 

 stantaneously takes place at the point of the iron wire where 

 contact had been effected, and this action rapidly extends itself 

 over the whole part of the wire which is covered with the so- 

 lution. It is a matter of course that the same effect can be 

 obtained by touching the inactive iron wire within the solu- 

 tion of the copper salt with the same metals. But the pecu- 

 liar condition of iron may be changed into the common state 

 without immediately touching those parts of the metal which 

 are surrounded with the copper solution. If, for instance, an 

 inactive wire is put into the solution so as to allow part of it 

 to rise above the level of the fluid, and if a wire of any of the 



• This remarkable fact, considered by itself at least, tends to confirm 

 Prof. Faraday's impression as to the cause of the peculiar voltaic state of 

 iron. — Edit. 



