274- Dr. Scbcenbeiii's Experimental Researches on a peculiar 



volumes of nitric acid, sp. gr. 1-35, and 200 volumes of water 

 were mixed together. A piece of cleaned iron wire put into 

 this solution did not precipitate mercury. By plunging such a 

 wire into water slightly acidulated, its power of acting upon the 

 salt of mercury, as above mentioned, is instantaneously called 

 forth. The wire having once acquired this power retains it; 

 provided, however, it be called into play at intervals of time 

 not much exceeding a second or so. But if the wire after 

 having been active in the solution is taken out of it, cleaned 

 from the adhering mercury, and Itjft exposed to the air only 

 for a ^evf seconds, it will have lost its property of precipitating 

 the last-named metal, and rest entirely inactive in the solution, 

 whatever length of time it may remain immersed in it. This 

 remarkable and sudden change of the condition of iron is most 

 likely due to some action of the air; for if the wire, being still 

 in its active state with regard to the solution of mercury, is 

 put into water or hydrogen gas, it preserves its precipitating 

 power. I have not yet put iron into other mediums than those 

 mentioned, nor have I examined whether moisture has any- 

 thing to do with the phaenomenon. At any rate this subject 

 seems to me in many respects sufficiently interesting to de- 

 serve further investigation. Before passing to another sub- 

 ject, I have still to mention some facts connected with those 

 just spoken of. An iron wire which proves to be entirely 

 inactive in the last-mentioned solution of mercury, is not so 

 with regard to a solution of blue vitriol or to common nitric 

 acid ; for a wire which does net throw down mercury, pre- 

 cipitates copper, or is violently acted upon by the said acid. 

 From chemical reasons we are led to expect that the very 

 contrary should take place, the affinity of copper Tor oxygen 

 being much greater than that of mercury; that is to say, 

 we should think the mercury salt easier to be decomposed by 

 iron than the copper Salt. It seems, therefore, as if the ano- 

 malous fact does not result from the action of common affinity. 

 Another fact worthy of remark is, that iron acts quite differ- 

 ently upon the neutral nitrates of mercury dissolved in al- 

 cohol or aether, from what it does upon the aqueous solutions 

 of the same salts. In the former case iron always precipitates 

 mercury and never turns inactive, whilst, as above stated, in 

 the latter case the contrary takes place. If an iron wire, hav- 

 ing been rendered inactive by immersion in an aqueous solu- 

 tion of the mercury salt, is put into alcohol or aether con- 

 taining the same salt, it loses its peculiar condition and re- 

 turns into its active state. 



I think it not quite irrelevant to the subject treated of in this 



