Dr. Schoenbein on the Action of Nitric Acid upon Iron. 2.59 



agreeing in every particular; and differing from the characters 

 assigned to oxide of donium only as regards the extent o*' 

 solubility in ammonia and its carbonate. This substance? 

 according to Mr. Richardson, when combined with potash 

 and sulphuric acid, affords a salt which crystallizes in octo- 

 hedra : this furnishes additional confirmation of its identity 

 with alumina. 



It is to be regretted that Mr. Richardson did not test his 

 solution with ferrocyanate of potash, as the characteristic blue 

 colour produced by this test would doubtless have directed , 

 his attention to the possibility of its being merely a mixture 

 of alumina and iron, and not, as he supposed, a new sub- 

 stance. 



I have not tried any experiment on its reduction to an ap- 

 parently metallic state, owing, partly to my not having any 

 donium remaining in my possession, and partly to my belief 

 that the preceding experiments will serve to show that the 

 supposed donium is nothing more than alumina containing a 

 trace of peroxide of iron. But I may, perhaps, be allowed to 

 hazard the conjecture, that the slate blue colour of the pow- 

 der obtained by means of hydrogen gas, was owing to the 

 reduction of the peroxide to the state either of protoxide, or 

 of metallic iron. 



St. Thomas's Hospital, Sept. 17, 1836. 



LIII. Further Observations on the Action of Nitric Acid upon 

 Iron. By Dr. Schoenbein.* 



¥ HAVE already remarked that nitric acid, which generally 

 '■ attacks iron with violence, has no action upon an iron wire, 

 one end of which, before its immersion in the acid, has been 

 heated to dullness. From experiments since made, I find that 

 the action is dependent on the quantity of water combined with 

 the acid. This quantity I have not yet accurately ascertained, 

 but 1 find that acid of the sp. gr. of 1*36 diluted with 15, .'30, 

 60, 120, 240, 480, and 960 times its volume of water attacks 

 an iron wire heated at one end in the same manner as when 

 not heated, and that the oxidated iron falls off by degrees into 

 the acid without being dissolved in it. 



Diluted nitric acid acts upon iron wire protected by pla- 

 tina or gold in the same manner as when the end of the wire 

 is heated. Many chemists state that iron is not acted upon 

 by ordinary nitric acid when diluted with three times its vo- 



« Communicated by Dr. Faraflay. Sec pp. .^S, 57, and \2:i, 

 2 G2 



