OXIDATIONS OF IRON. $31 



fcthers that had scarcely '20 * were not attractable, I con- Unmagnetk 

 eluded, that there was some other cause acting at the same °*| des Wlth lu " 

 time with the oxigen, or perhaps exclusively, to destroy 

 the magnetism. Reflecting on the circumstances, that pre- 

 side over the formation of all these different oxides, I sus- 

 pect, that in these phenomena, as in most of those to which 

 the oxides of iron give birth ? too much has been ascribed 

 to the influence of oxigen, by referring to it effects in which 

 it has no concern. If the loss of magnetism in some red The magnetism 

 oxides of iron be not exclusively owing to a state of extreme division! 

 division, this at least has a more decided influence on it 

 than the presence of oxigen. 



When the magnetic oxide, of which I hare spoken, is Concentrated 

 -precipitated by concentrated alkalis, and without the solu- dovJn°rnagnetic 

 tion having been much diluted by water, the precipitate is oxides : 

 a more or less blackish brown, it does not change by dry- 

 ing in the open air, and it is decidedly magnetic. If, on dilute solutions 

 the contrary, the solution and the alkali be diluted with donot ' 

 water, which has been boiled a long time to remoye every 

 suspicion of superoxidation, the precipitate is red, like all 

 those called oxides at a maximum ; and if it be dried in the 

 open air, or by a gentle heat, like the preceding, it gives 

 no signs of magnetism. Now we cannot ascribe this differ- 

 ence of colour and of magnetism to a different proportion 

 of oxigen ; for if we try the experiment with two equal 

 parts of oxide, we shall find, that the weight of the red 

 oxide is the same as that of the magnetic. The difference of 

 magnetism therefore, like that of colour, depends on the 

 difference of density, or the greater or less distance be- 

 tween the particles of the two precipitates. 



In fact, when the solution is concentrated, the particles This is owing to 



of the oxide touch each other, or at least are much nearer the s . ta,e of a P" 

 , , , . . . .,.,,,, proximation of 



together, than when the solution is diluted with water : the particles, 



and this difference of approximation is in the ratio of the which is m th 5 



inverse ratto of 

 bulk of the two solutions, since the distribution of ih& oxide the quantity of 



in both cases is uniform. Let us suppose, that the differ- the menstrti " 



ence of approximation be in the ratio of one to ten • or 3 



* Those obtained from the green solutions, of which I have 

 spoken in the course of this Paper. See p.;273« 



J£ 2 yrhich. 



