On definite Proportions. 33 7 



excess of ammonia will not in this case be able to throw 

 down the whole quantity of iron ; the precipitate is white, 

 and the liquid standing over it retains its former colour. 

 If we admit the air, the fluid is immediately covered with 

 a blue pellicle, which becomes continually thicker, and ac- 

 quires first a green and then a yellow colour; and the same 

 change of colour takes place in the white protoxide which 

 has already been precipitated. The easiest mode of ex- 

 plaining these appearances would be to suppose that iron has 

 three degrees of oxidation, that the white oxide is in the 

 lowest degree that it is present in these solutions, and that 

 if has in some respects a stronger affinity for the acid than 

 ammonia; but that when tlie air is admitted, it is further 

 oxigenized, is converted into the black or blue oxide, and 

 precipitates. This explanation I have long thought satis- 

 factory. 



If we leave a saturated and recently prepared solution of 

 iron in the muriatic acid, standing undisturbed for some 

 time in a high cylindrical vessel, and exposed to the open 

 air, and then introduce, by means of a glass tube, some 

 drops of caustic ammonia at different heights in the glass, 

 we shall find (he precipitate at the top green, below this 

 blue, still louer grayish blue, dirty white, and lowest of all 

 quite white ; according to the degree in which the oxygen 

 of the air has been absorbed. If we digest iron filings vvith 

 a solution of sal ammoniac in a glass nearly full and well 

 corked, a part of the iron will be dissolved in the sal am- 

 moniac, the fluid will become alkaline, and will deposit 

 blue, green, and yellow oxide, when exposed to the air. 

 But with finery cinder the solution of sal ammoniac under- 

 goes not the slightest change. 



It was probably on this foundation that Thenard consi- 

 dered the uhite precipitate produced in these experiments as 

 a protoxide in its lowest stale of oxygenization ; and as he 

 thought that he found for each oxide salts of different de- 

 grees of saturation, he has hence derived an astonishing 

 number of sulphuric and prussic salts of iron. 



Bncholz, by a series of laborious and ingenious experi- 

 ments, has determined the quantity of oxygen of the prot- 

 oxide of iron to be 23 per cent,, 100 parts of iron com- 

 bining Willi 29-88 of oxygen. If we calculate from the 

 fulphur contained in the sulphuret at a nnnimum, the 

 quantity of oxygen taken up by 100 parts of iron should 

 be 2y4 or 2<)'5. We have further seen that, in the sul- 

 phate ot the protoxide, 100 parts of acid are united to so 

 much of the protoxide as will furnish 99-22 of the red 



Vol. 41. No. ibl. Muij 1813. Y oxide. 



