31& 



ON THE OXIDES OF IRON. 



Proust's ac- 

 co'int of the 

 oxides of iron, 



U^iVal meaning 



^^I have just received a coj^y of, Thomson'^ System' df 

 Chemistry translated by Rifiaut. I opened the first volume^ 

 and read with eagerness the tenth section, which treats of 

 iron. The details published in that section were the more 

 interesting to ml!, as I have been for these two years' era* 

 ployed by the minister of the Interior, to describe the art 

 of extracting iron from its ores, and to explain the dif. 

 fcrent operations, which it iindergbes before it is brought 

 iuto the comsnercial world in the states of cast iron, iron, 

 and steel. You may guess my astoiushmcnt, M'hen I read 

 the following passage. ' The peroxide of iron is also 

 found native in great abundance. Froust proved it to he 

 composed of 48 parts of oxigen and 62 of iron. Con^e.. 

 que^Ulij the protoxide, Ziehen converted into red oxide absorbs 

 0-40 cf oxigen ; or, zchich is the same thing, the red oxide 

 is composed of QQ-b parts of black oxide, dnd S^'b parts of 

 oxigen. One hundred parts of iron, zohen converted into a 

 protoxide, absorb 37 parts of oxigen, and the oxide weighs 

 ld7;,zchen converted into pe,r oxide, it absorbs 55 addi- 

 tional parts of oxigen, and the oxide rseighs 192-3. 



" Proust has not said, in any work that I know, that 

 the red oxide is composed of 48 parts of oxigen and 52 

 of iron. What may have led Dr. Thomson into errour 

 isj that in i\\e memoir of the celebrated chemist of 

 Madrid, published in vol. xxiii, p. 85, of the Annalcs 

 de Chimie, it is stated, that he announces the existence of 

 the two oxides of iron, the one at -^-J-^ of oxigen, the other 

 at -,%^^. As it is not said in any ai^ficle of the memoir, 

 whether the 48 of oxigen were in the 100 of oxide, or 

 cpiilbined with 100 of metal, this manner of expressing 

 the proportion of oxigen has left a kind of uncertainty in 

 the minds of those chemists, who have made no experiments 

 01^ the proportion of oxigen in the oxide of iron. The 

 learned British chemist, who certainly , has made no experi- 

 nicnt to resolve the question, has adopted the simplest 

 meaning of the fraction -^f^; and this has occasioned the 

 errour in the passage, which I have quoted :" 



Mr. Hassenfratz then proceeds to show, that in other 



of his fractional pjjy^s ^f jjjg writings Proust js in the habit of denoting by 

 the numerator of his fraction the quantjty of oxigen, and 



by 



