S84 



>iETALLIC 0XlBAT10H,i 



Degrees of oxi 

 dation in me- 

 tals constant, 

 determinable 

 hy the salts 

 tkey form, and 

 numerous. 



Colours of me- 

 tallic salts do 

 not indicate 

 those of the 

 oxides they 

 contain. 

 Iron has no 

 yellow oxide, 



but green, red, 

 and white. 



Each oxide 

 produces two 

 sulphates, 

 making six in 

 all. 



Aciclulous sul- 

 phate of white 

 iron. 



VI. 



Considerations on the Oxidation of Metals in general, and on 

 that of Iron in particular. By IM. Then arc* 



■ JL HE object of the auihor in this memoir is to show, that 

 the degrees of oxidation in metals are constant, and deter- 

 minable particularly by the nature and properties of the salts 

 they form. These different degrees of oxidation are frequently 

 pretty numerous, as in antimony, iron, and manganese. 



He adverts to the principle but lately known to chemists^ 

 that the colours of salts do not always indicate those of the 

 metallic oxides they include ; and this principle he applies to 

 the study of the different oxides and sulphates of iron. Though 

 he does not admit the existence of the yellow oxide of iron^ 

 which has been adopted from the observation of some yellow 

 salts of this metal; he distinguishes in it three degrees of oxida- 

 tion, namely, the green oxide, the red oxide, and a third made 

 known by M. Thenard himself, which is white, and less oxided 

 than either of the other. This is the first obtained, when we 

 decompose a fresh solution of sulphate of iron by means of an 

 alkali. On this occasion we see a white oxide thrown down, 

 which quickly turns green, and even red, by absorbing oxi- 

 gen. - 



This white oxide is capable of producing two different sul- 

 phates by combining with two different proportions of sulphuric 

 acid : and as these two degrees of saturation are equally capa- 

 ble of taking place with each of the other oxides, we have six 

 sulphates of iron, observes M. Thenard, very distinct from each 

 other, and of importance to be known, on account of the vari- 

 ous and delicate uses to which this salt is applied in the arts. 

 The following, are the names and characters of these six sul- 

 phates : 



1. Acidulous sulphate of white iron. This is the white 

 oxide just mentioned, combined with a little sulphuric acid in 

 excess. Its colour is a deep bottle-green. It is the sort most 

 common in the shops. 



* Bulletin des Sciences, August, 1805, p. 223. 



2, Acid 



