T II E 



LONDON and EDINBURGH 

 PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



♦ 



[THIRD SERIES.] 



OCTOBER 1837. 



XL. On the prepared or peculiar Voltaic Condition of Iron. 

 By Sir John F. W. Herschel, K.G.H., M.A., F.R.S.* 



IN the Number of the Annates for the month of March of 

 the present year, (1833, vol. lii. p. 288,) which I have re- 

 cently received, I find a remark of M. Braconnot upon the 

 manner in which concentrated nitric acid acts, when brought 

 into contact with iron, which brings to my recollection some 

 experiments made several years ago upon the same subject, 

 presenting particularities sufficiently curious to merit a closer 

 examination. I am at present unable to resume my researches, 

 but I think that an account of them will not be uninteresting 

 to your readers, and that it may induce one of them, per- 

 haps M. Braconnot himself, to study in detail the very re- 

 markable phaenomena of the action in question, and to con- 

 nect them with the usual laws of chemical action. 



M. Braconnot says, " filings, or if they be prefered, plates of 

 iron immersed in concentrated nitric acid, do not experience 

 the slightest alteration, and retain all their metallic lustre, so 

 that they are thus preserved from rust. If the same acid be 

 made to boil upon these plates, and it be afterwards supersa- 

 turated with ammonia, it scarcely deposits a few insignificant 

 flocks of oxide of iron." The following are my own observa- 

 tions. (I extract the experiments from a journal dated Au- 

 gust 1825.) 



* From the Annates de Ckimie et de Physique, vol. liv. p. 87, being the 

 paper alluded to by Mr. Faraday in Lond. and Edinb. Phil. Mag., vol. ix. 

 p. 122.; and now inserted to complete the series of papers on the subject 

 to which it relates. 



Third Series. Vol.11. No. 68. Oct. 1837. 2 U 



