OXIDATIONS OF IRON. 273 



with water. As soon as the solution was complete, I preci- 

 pitated one portion of 30 grains by ammonia, washed and 

 drained it as quickly as possible, and dried it at a temperature 

 of about 120° [300° F.]. After it was dry I found it a brown Brown magne- 

 oxide, attracted by the magnet, weighing 36f grains, and tlc oxlAe - 

 pvecipitated red from its solution in muriatic acid. Another 

 portion I precipitated likewise by ammonia ; but with a view 

 to obtain the precipitate red, I diluted the solution with five 

 or six parts of water at 50° [144°] before I added the am- 

 monia. This oxide was in fact red; and when dried ] ike „ . , 



Ked, and not 



the preceding, it was not at all affected by the magnet, magnetic. 

 though it weighed only 36 grains. Lastly, I precipitated 

 the other 30 grains by ammonia likewise, using a very broad 

 vessel, in which I left the precipitate exposed to the air for a 

 month, stirring it twice a day. At the end of this time I The same, 

 dried it like the preceding : it was red, gave no signs of 

 magnetism, and weighed 36*2. The only difference be- Yet all equally 

 tween all these oxides was, that the first was brown and mag- 

 netic, while the others were red, and did not become mag- 

 netic till exposed to a higher temperature. 



Though I perceived in the course of this experiment, This does not 

 that it was not sufficient to establish with accuracy the pro- a5cerlain the 



~ . . , . v . proportion of 



portion ot oxigen, that the green oxide contains in solutions oxigen obsorb- 



o'f iron by acids, on account of the oxigen that must combine ed during solu- 



.,.,..'. . . , , . .. , tion. 



with it during its being dried at so hign a temperature, and 



in a state of such minute division, it confirms two of the prin- 

 cipal results obtained in the oxides by calcination. This 

 process afforded me red oxides that had only *15or *20 of 

 oxigen and the solution produced red oxides that contained 

 only '20 of oxigen, including what was absorbed during the 

 drying. Calcination afforded red magnetic oxides; and so- 

 lution did the same. 



There are two methods of appreciating with extreme ac- Two methods 

 curacy the quantity of oxigen contained in the green oxide of doing tins, 

 by solution. The first, which I should have preferred, if 

 circumstances had permitted me to adopt it, is, to dissolve a 

 given quantity of iron in muriatic acid, and carefully to col- 

 lect the hidrogen evolved; this measured, and for still far- 

 ther certainty burnt in Volta's eudiometer, would give the 

 quantity of oxigen combined with the iron. The second is 



to 



