302 Mr Stromeyer on Metallic Iron and its Oxides. 



temperature. He affirms that the protoxide is first inflamed, 

 and that the caloric emitted by it sets fire to the metallic iron, 

 in consequence of which combustion takes place rapidly through 

 the whole mass. 



In addition to these interesting remarks, the Professor ob- 

 serves, that there are only two proper oxides of iron, name- 

 ly, the blue or protoxide, and the red or peroxide. He con- 

 firms the opinion of Proust, that the black oxide, whether 

 formed by the direct combustion of iron, or by passing the 

 vapour of water over ignited iron wire, is not a distinct oxide, 

 but a combination of the two others. He adds, also, that the 

 proportion of the oxides to one another, in the black oxide, is 

 variable, the relative quantity of each being dependant on the 

 duration of the process, and on the temperature at which it 

 is conducted. 



M. Magnus has replied to the observations of Professor Stro- 

 meyer in the same Number of PoggendorfFs Journal. After 

 repeating and varying his former experiments, he draws from 

 them the two following conclusions : First, that the combus- 

 tion of iron does not arise from the presence of the protoxide, 

 but is occasioned by the porous condition of the metal. Se- 

 condly, that iron at a temperature between the boiling point 

 of mercury and the degree at which zinc fuses, is completely re- 

 duced by hydrogen, and that, according to his experiments, 

 no deoxidation at all takes place at a lower temperature. 



This le es us theref ore in the dark as to the real cause of 

 the spontaneous combustion of iron. It is clear from the second 

 conclusion of M. Magnus, either that he must have committed 

 some oversight, or that Stromeyers protoxide cannot be formed 

 in the way which that chemist has described. The character of 

 Stromeyer is too well known to leave a doubt as to his accu- 

 racy ; and we, in particular, have good reason to know that 

 he is right on the present occasion, having, in his laboratory, 

 so long as four or five years ago, both seen the blue oxide of 

 iron, and witnessed its formation. 



