230 On the Oxidation of Metals in general, 



same recent solution of tin entirelv decomposes corrosive 

 sublimate and revives the mercury, not only taking the oxy- 

 gen from it, but even the muriatic^ ac.d. Thence it also hap- 

 pens that the acid sqlphate of white iron transforms itself 

 in part, byabsorbmg oxygen from the atmosphere, into green 

 acidulated sulphate, and assumes a slight red tint; thence it 

 happcna at last, that this satne salt, when it is only acidu- 

 lated, becomes troubled all at once upon pouring aerated 

 water into its solution : several other phaenomena depend 

 tipon the same cause; but, should I insist longer on this 

 branch, I shonld wander too far from the subject on which 

 I propose to treat. 



Like the two other acid sulphates, the red acid sulphate 

 of iron is almost colourless ; it takes a very strong colour, 

 and reddens vvhen its excess of acid is saturated in part by 

 potash ; by adding a greater quantity of a salifiable base, a 

 neutral sulphate is precipitated from it, which is, however, 

 susceptible of being decomposed by the alkalis : it separates, 

 as well as all the highly oxygenated salts of iron, sulphur 

 from hydrogen, and returns to the state of a very acid green 

 or white sulphate of iron; it yields no crystals upon evapo- 

 ration : the iron changes it into a less oxygenated sulphate. 

 I have but little to say of the highly oxidated neutral sul- 

 phate : it is yellow and insoluble; this is the sulphate which 

 in time, by exposure to the air, is precipitated from solu- 

 tions of green or white acidulated sulphate : this is also the 

 sulphate which is deposited when the solution of green aci- 

 dulated su!j->liate of iron is evaporated, and which from being 

 red becomes almost colourless, because then it passes to the 

 state of acid sulphate ; it is this salt, in short, which chemists 

 formerly look for 9, particular oxide, and which induced them 

 to admit a yellov/ oxide of iron, as intermediate between the 

 red and the green. 

 . The action of the muriatic and nitric acids upon iron re- 

 sembles much that of the sulphuric acid ; that of the muri- 

 atic acid does nut differ at all, but the acid muriates of iron 

 are not so well characterized as the acid sulphates; the mu- 

 riate when littiC oxidated crystallizes very well, and the cry- 

 Btals.formed from it are of a fine green; but when the solu- 

 tion 



