ACTION OF WATER ON IRON. JsOO 



most important I'esult which the carbon in iron, especially cast 

 iron, plays during its solution. 



It is established that carbon exists in cast iron, steel, &c. 

 in two states : as graphite or crystallized carbon, disseminated 

 in its mass, giving it brilliancy of fracture, softness, porosity, 

 and fluidity in fusion ; and as a definite carburet, combined with 

 a portion of the iron chemically, and mixed mechanically with 

 the remainder. 



Now, in the decomposition of iron so circumstanced by air 

 and water, whether in presence of an acid or not, besides the 

 combination of oxygen furnished both by the air and water with 

 the metal, other reactions take place. Nitrogen and hydrogen 

 are both set free, but they may or may not be both evolved. The 

 nitrogen combines with part of the hydrogen to form ammonia, 

 which, according to circumstances, is evolved, or combines with 

 the oxides of iron produced. 



But it is probable, from the experiments of Thenard and 

 Despretz, that an azoturet of the undissolved metal may also be 

 formed. Iron at a higher temperature is unquestionably capable 

 of decomposing ammonia and combining with azote, so as to aug- 

 ment its weight by 0'12. But in addition, as the combined car- 

 bon is set free from the iron in a nascent state, it seizes upon 

 a portion of the evolved hydrogen, and forms a highly volatile 

 and odorous oily hydrocarbon, while some of the uncombined 

 or suspended graphite, also set free in a highly divided state, 

 combines with another portion of the hydrogen and with oxy- 

 gen, and produces an extractive mattei- — apotheme of Berzelius, 

 and which differs little from ulmic acid in its reactions. This 

 latter deposits as a brown substance, soluble in alkalis, &c., 

 and combmed ivith all the magnesia and silica due to the 

 amount of their bases, which the iron may have contained, if 

 any. The volatile oily hydrocarbon is partly dissipated with the 

 hydrogen evolved, partly swims upon the surface of the fluid, 

 rendering it irridescent, and is partly held absorbed by the 

 porous mass of oxides, carbon, and ulmic acid resulting from 

 the whole reaction. Hence we see that the simple decomposi- 

 tion of cast iron by air and water may give rise to no less com- 

 plex a result than the following formula indicates : — 



(FeC^ + C + %i + M^g) + (HO -f- N^O) = {¥e^O^+YeO) 

 + (F.,03 + 3HO) + (H + C,.H,.) + (CeoHgoOjs? + SfOg f M^-O) 

 + C. 



And here several of the substances commonly present in cast 

 iron are omitted ; if these be included, or an acid present, the 

 result will of course be still further complicated. 



s 2 



