ON THE pXIDES OP IRON. £^9 



modes : Ist, by distilling the solution to dryness, washing jn the oxides 

 the pi^cipitate, and drying; 2ndly, by precipitating the ^^^n'''**^^*'*' 

 oxide by an alkali ; 3dly, by precipitating in the metallic 

 state, by means of iron, the dissolved oxides of other metals, 

 the quantity of oxigen contained m which is already known, 



1st Method. Lavoisier dissolved iron in nitric acid, eva- ^^^^ ^^V^* 

 porated to dryness, and obtained a red oxide, the weight of acid by Lavo- 

 which was from 40 to 50 per cent more than that of the iron ^^^^^'* 

 dissolved. 



Bucholz dissolved iron in diluted nitric acid, evaporated Bucholz, 

 it to dryness, and kept it in a red heat for a quarter of an 

 hour. In three successive experiments the increase was 42 

 per cent. 



Gaeniveau, mine engineer, writes to me from Paris, on and GuenU 

 the 30th of September, 180? : " We also have been em- ^^^"' 

 ployed on the same subject (the oxidation of iron by the ni- 

 tric acid), and we conclude, that the oxide is composed of 

 100 metal with 44 oxigen. We employed the same method 

 as Mr. Bucholz." This experiment appears to have been 

 repeated in the laboratory of the council of mines at Paris. 



Iron dissolved by nitric acid is commonly in the state of Part of the 

 red oxide. Lavoisier says, that, having calcined this oxide befxpe^tedbr 

 to reduce it to the state of ethiops, it lost so much of its heatby Lavoi- 

 weight, as to retain no more than 25 or 30 of oxigen to 100 ^^^^' 

 efiron*. 



It is difficult to place confidence in this result of Lavoi- but this que-?- 

 sier: 1st, becanse there is no indication of his having taken '"^"* ^' 

 the necessary precautions, to oxide completely the metal he 

 dissolved: 2dly, because, according to the experiments of 

 BerthoUet and Fourcroy, the oxide does not part with any 

 of its oxigen to retnrn to the state of oxidule, to whatever 

 temperature it be exposed. 



It remains for us therefore to compare the two results of Comparison of 

 Bucholz and Gueniveau. As it is difficult for us to know J^fjg^^ 

 with certainty, whether the oxide of Bucholz did not still 

 contain some portion of oxidule mixed with it; and whether 

 the iron, which he employed, were perfectly pure ; every 

 thing leads us to prefer the second result, which gives the 

 larger proportion of oxigen. both however having taken the 



- • M6rn. de r Ac des Sciences, i78?, p. 5. 



same 



