a7id partkuiarlij the Oxidation of Iron. 225 



heral principle of combustion, a multitude of different com- 

 binations, I am persuaded that metals, which we regard with 

 reason as analogous bodies, are not more susceptible than 

 the others of a multitude of different degrees of oxidation. 



If we are permitted to entertain doubts on this view of the 

 subject, we may certainly have some upon the nature of the 

 oxides in their combinations with acids ; and even if this 

 *truth had not been long admitted by chemists, some general 

 observations would suffice to place the subject in a clear 

 point of view. Let us take a glance, however, of each of 

 these oxides, and attentively consider the oxides of iron, 

 which are the principal objects of this memoir. Here 

 every thing demonstrates, that in combinations of this sort 

 the oxides are constant. Although cobalt, nickel, lead, 

 zinc, gold, and platina, are all the bases of several oxides, 

 yet in all the salts which they form they are always equally 

 oxidated: thus the oxide is blue in all the salts of cobalt, 

 green in those of nickel ; it is white in those of bismuth, 

 zinc, and lead ; and it is gray in those of silver, yellow in 

 those of gold, and brown in those of platina: it varies, to 

 be sure, in the salts of antimony, tin, mercury, copper, and 

 iron; but still with several of them it is only certain of their 

 oxides that can unite with acids. Two white oxides of an- 

 timony alone are susceptible of this combination — the white 

 volatile oxide and the white oxide of the second degree j the 

 white oxide at the maximum is not attackable, except by 

 the muriatic acid : still, however^ if it is not in a state of 

 very minute division, the muriatic acid dissc Ives it with 

 great difficulty, and always by partly passing to the state of 

 oxygenated muriatic acid. Tin, inercury, and copper, like 

 antimony, do not fofm saline combinations with the acids, 

 but under two states of oxidation ; tin in the state of a gray 

 and a white oxide, mercury in the state of a black and a red 

 oxide, and copper in the state of a yellowisli white and a 

 brown oxide. 



Hitherto it was thought that it was tiie same case with 

 iron, and that in all the salts which it was susceptible of 

 forming, the oxide was always green or red. Some chemists, 

 however, have admitted an intermediate oxide : they believed 



Vol. 24, No. 95. April 1 306. P that 



