ON THE OXIDES OF inOIT. 381 



to a red heat, it is convorted into red oxide. This furnishes nUricacidand 



•ii ii .1 1 /• • ,. ,1 ,• e ' converted iulo 



US with another method of estimating the quantity of oxigen ^^^i, 

 in black oxide. of iron. Bucholz had recourse to it, and 

 found, that 100 parts of black dy.ide are by this treatment 

 converted into 110 of red oxide*. On repeating the ex- 

 periment, I found it attended with more difficulty than I This experi- 

 cxpected. It is not easy to procure black oxide in a state "^'^'^'' *^'*^"'** 

 of purity. My first trials diflored so much from each other, 

 that I was obliged to conclude, that my black oxide contained 

 some red oxide mixed with it. Another difficulty is to 

 dissolve black oxide of iron in nitric acid. It resists the 

 action of that acid with great obstinacy, even when in the 

 state of a fine powder. After repeated failures, I at last 

 succceeded in obtaining results, which agreed with each 

 other. The following I consider as the most accurate of The most 

 these. 16'77 grains of pure black oxide were dissolved ju accurate 

 nitric acid. The solution was evaporated to dryness, and 

 the dry mass exposed to a red heat, in a platinum crucible. 

 It weighed 19-1 grains. Hence 100 grains of black oxide 

 by this treatment would have been converted into 113-8y 

 grains of red oxide. Now if red oxide be a compound of 

 100 metal and 45 oxigen, it is obvious, that 113-89 grains 

 of red oxide contain 78*5 graiiis of metal, therefore 100 

 parts of black oxide are composed of 78-3 metal and 21-3 gave simifar 

 oxigen, or the oxide consists of 100 metal combined with 27 ie««>lt^^i^^» ifae- 



° preceduj,!j. 



oxigen — a result which agrees very nearly with that deduced 

 from the two proceeding sets of experiments. 



4. I introduced 300 grains of polished iron wire Iron wire coa- 

 ioto a porcelain tube, placed the tube in a furnace ^lO"- ^j^^^^^'^'.^^ ^^. 

 zontally, heated it to redness, and then causeda current of liteam, 

 steam to pass through it for several hours. T3y this process 

 it is well known that the iron is converted into black oxide, 

 while hidrogen gas is evolved in abundance. The evolution of 

 this gas is accounted for by the decomposition of the steam. 

 The oxigen is conceived to unite with the iron, while the 

 hidrogen passes off in the form of gas. By this method I 

 expected to be able to ascertain directly the increase of 

 weight, which takes place when iron is converted into black • ' ' 



oxide. But I was disappointed. Though the experiment.? Results unsatis- 



factorv. 

 *Jou:na], vol. xxv, p. 334. 



were 



