272 Dr. Schoenbein*s Experimental llesearches ofi a peculiar 



times its volume of water, it will still render an iron wire in- 

 active, though in this case, as might be expected, some time 

 is required for obtaining the effect. But if a common iron 

 wire is first immersed in water containing so little of nitric acid 

 as scarcely to change the colour of blue litmus paper, and af- 

 terwards plunged into the solution of mercury, it will preci- 

 pitate the latter metal. It is, indeed, quite extraordinary how 

 far this influence of the acids, favouring metallic precipita- 

 tion, extends. I mixed a strong solution of neutral proto- 

 nitrate of mercury with 1000 times its volume of water, and 

 in the same proportion I diluted common nitric acid. By 

 putting the wire first into the acidulated water, it always 

 acquired the property of decomposing the diluted solution 

 of mercury on being plunged into it. Common muriatic 

 acid, even 4000 times diluted with water, produced the same 

 effect. Though it is a well-known fact that some free acid 

 contained in metallic solutions favours the precipitation of one 

 metal by another, still I am not aware that any chemist has 

 as yet stated any particulars regarding the extent and cause 

 of this ir lu-iice. The peculiar action of acids mentioned 

 seems to be intims'ely connected with the subject of my re- 

 searches on the ac'i n of iron upon nitric acid, and to afford 

 a case similar to that presented by inactive iron in its bearing 

 to strongly diluted nitric acid. In one of my published papers 

 on the subject, I have stated that inactive iron loses its pe- 

 culiar cond'tion by being put into diluted nitric acid; the 

 same thing takes place in the case before mentioned. Com- 

 mon iron wire is of itself inactive in a solution of a neutral 

 salt of mercury, but is rendered active by being subjected to the 

 action of acidulated water previously to its immersion in the 

 solution. According to Mr. Faraday's views the acid must 

 produce the effect spoken of by cleaning the surface of the 

 wire, that is to say, by dissolving some film, with which even 

 a common wire must be supposed to be covered ; but for 

 reasons already alluded to, 1 cannot entertain the opinion of 

 this distinguished philosopher, even in this case. 



The view I have taken of the subject leads me to ascribe 

 the effect in question to chemical excitement in the metal 

 occasioned by the acidulated water. As iron having only for 

 a few moments been immersed in diluted acid decomposes the 

 neutral solution of mercury, it might 'be supposed that this 

 metal should act in the same manner in a solution made some- 

 what acid. But I found this not to be the case. A solution 

 of pernitrate of mercury obtained by saturating nitric acid, 

 sp. gr. 1*35, with peroxide of mercury, was mixed with its 

 own volume of the same acid. A common iron wire put into 



