Action of Iron upon Solutions of some Metallic Salts, 273 



this acid solution had no action upon it, and assumed its pe- 

 culiar condition. I could put even twenty volumes of nitric 

 acid to it, without producing any action. But I must not omit 

 to state the singular fact, that there is in this respect a great 

 difference between a wire flhich is cleaned and one which is 

 not. If, for instance, a common iron wire has only once passed 

 through a piece of linen or cloth, it will be acted upon by the 

 acid solution containing only one volume of nitric acid, whilst 

 an uncleaned one is not affected at all. This difference is the 

 more remarkable, as an uncleaned wire is much more violently 

 attacked by mere nitric acid than a clean one. Another fact, 

 still more singular, is, that different parts of the same piece of 

 an uncleaned wire are sometimes differently acted upon by the 

 same acid solution of mercury, one part being, for instance, 

 entirely inactive, whilst another contiguous to it proves to be 

 highly active. I call this fact a very singular one, because 

 every bit of a whole roll of iron wire is acted upon in common 

 nitric acid. When an iron wire cleaned or not is plunged into 

 the solution of mercury containing from 30 to 50 times its vo- 

 lume of nitric acid, it will be affected, and continue to be acted 

 upon if left in the solution ; but when it is again taken out of 

 the fluid and held for hardly a second in the air, after its re- 

 immersion it will prove entirely inactive. It is surprising, 

 that almost the same results are obtained at very different 

 degrees of temperature. I heated a mixture containing 20 

 volumes of nitric acid and one volume of the solution of per- 

 nitrate of mercury to its boiling-point. The end of an iron 

 wire put into it was certainly acted upon, but by withdrawing 

 it only for a few moments from the solution it was rendered 

 inactive, so that it could afterwards be reimmersed in the 

 nearly boiling acid fluid without being attacked by it. A cer- 

 tain proof that the metal acquires, even at this high degree of 

 temperature, its peculiar inactive state is, that when put into 

 a solution of blue vitriol, or into mere common nitric acid, it 

 does not in the least act upon these substances. In making 

 these experiments I frequently observed the curious fact, that 

 the iron wire immersed in the nearly boiling acid solution 

 loses its inactive condition as soon as it is a little raised so 

 as to expose to the air a very small part of that portion of 

 wire which has been immersed in the fluid ; but though this 

 is often the case, it is not invariably so. 



The results which I have obtained from experiments made 

 with iron wire and an acid solution of mercury much diluted 

 by water, are likewise worthy of being stated. One volume of 

 a very strong solution of neutral protonitrate of mercury, five 



Third Series. Vol. 10. No. 61. April 1837. 2 N 



