132 M. Bertkier on Forge Scales* [Aug. 



slight disengagemeut of hydrogen gas, which lasted only a few 

 seconds, and evidently proceeded from some minute grains of 

 metallic iron, accidentally mingled with the forge scales. The 

 same scales assayed in the dry way w^th one-fifth of their 

 weight of earthy glass, gave metallic buttons whose weight 

 varied from 0*75 to 0*78. If we compare these results with 

 those which an oxide composed of two atoms of protoxide, and 

 one atom of peroxide would give, we find an almost perfect 

 identity : for such an oxide would contain 



Protoxide 0*642 - 2/«; or Iron, 0-745 - 100 

 Peroxide 0-358 - F ^ ; or Oxygen, 0-255 - 0-344- 



I believe this therefore to be the true composition of the forge- 

 scales. 



According to these results, we must henceforth reckon four 

 oxides of iron, in which the quantities of oxygen combined with 

 the same quantity of iron are respectively : : 6 : 7 : 8 : 9. 



This oxide is formed whenever iron is in contact with a more 

 oxygenated oxide at a white heat, or when heated in contact 

 with the air so as not completely to oxidate it. 



It is necessary to observe that some forge-scales give, on 

 analysis, much less than 0*35 of peroxide; but in that case 

 they are not pure, but contain a mixture of scoriae, which is 

 discovered by the jelly it produces with concentrated acids. 

 As these scorise are silicates of protoxide of iron with a great 

 excess of base, the presence of from 0*02 to 0*05 of sihca may 

 diminish the proportion of peroxide nearly one-fifth. Perhaps 

 it may be objected to my hypothesis of the composition of 

 forge-scales, that a mixture of deutoxide and metallic iron, or 

 its protoxide, would give the same analytical results as those 

 which I obtained with my presumed new oxide ; but if the 

 scales be such a mixture, it is very extraordinary that the ingre- 

 dients should always be found in the same proportion ; I shall, 

 however, obviate these objections by the detail of some facts, 

 which in other respects also I think are not uninteresting. 



If the forge-scales were a mixture of deutoxide of iron and 

 metallic iron, they would contaih 0*09 of the latter ; but then 

 their specific gravity would be much greater than it really is, 

 since that of the deutoxide is more than 4-7, and that of iron 

 7*5. Moreover, when we treat a mixture of very fine iron 

 filings and the pulverised deutoxide or peroxide, with muriatic 

 acid, the iron dissolves before the oxide with evolution of hy- 

 drogen gas, and we find in the solution quite as much peroxide 

 as there would have been without the admixture of the metallic 

 iron. Hydrogen gas does not reduce this peroxide ; now, since 

 the forge-scales contain one half less of peroxide than of pro- 

 toxide, we should admit, from that circumstance, that they 

 contain half their weight of metallic iron, which it is impossible 



