DEFINITION OF TERMS. 



173 



iron. Steel is iron combined with a small 

 portion of carbon, and has been for that> 

 reason called carburetted iron. The pro- 

 portion of carbon has not been ascertained 

 with much precision. 



From the analysis of Vaiiquelin, it 

 amounts, at an average, to ^l^ part. Mr. 

 Clouet seems to affirm that it amounts to 

 j\ part; but he has not published the 

 experiments which led him to a propor- 

 tion which so far exceeds what has been 

 obtained by other chemists. That steel 

 is composed of iron combined with pure 

 carbon, and not with charcoal, has been 

 demonstrated by Morveau, who formed 

 steel by combining together directly iron 

 and diamond. At the suggestion of Clouet, 

 he enclosed a diamond in a small crucible 

 of pure iron and exposed it, completely 

 covered up in a common crucible, to a 

 sufficient heat. The diamond disappear- 

 ed, and the iron was converted into steel. 

 The diamond weighed 907 parts, the iron 

 57800, and the steel obtained 56384 ; so 

 that 2313 parts of the iron had been lost 

 in the operation. 



From this experiment it follows, that 

 steel contains about -^^0^ its weight of 

 carbon. This experiment was objected 

 to by Mr. Mushet, but the objections 

 were fully refuted by Sir George Mc- 

 Kenzie. Rinman, long ago, pointed out 

 a method by which steel may be dis- 

 tinguished from iron. When a little 

 diluted nitric acid is dropt upon a plate of 

 steel, allowed to remain a few minutes, 

 and then washed off, it leaves behind it 

 a black spot; whereas the spot formed 

 by nitric acid on iron is whitish green. 

 We can easily see the reason of the black 

 spot ; it is owing to the carbon of the 

 iron which is converted into charcoal by 

 the acid. This experiment shows us, 

 that carbon is much more readily oxidhz- 

 ed when combined with iron than when 

 crystallized in the diamond. Cast iron 

 is iron combined with a still greater pro- 

 portion of carbon than is necessary for 

 steel. The quantity has not yet been 

 ascertained with precision ; Mr. Clouet 

 makes it amount to | of the iron. The 

 blackness of the color and the fusibility 

 of cast iron, are proportional to the 

 quantity of carbon which it contains. 

 Cast iron is almost always contaminated 



with foreign ingredients: these are chief- 

 ly oxide of iron, phosphuret of iron, and 

 silica. It is easy to see why iron is ob- 

 tained from its ore in the state of cast 

 ircn. The quantity of charcoal along 

 with which the ore is fused, is so great 

 that the iron hasan opportunity of saturat- 

 ing itself with it. The conversion of cast 

 iron into wrought, is effected by burning 

 away the charcoal, and depriving the iron 

 wholly of oxygen: this is accomplished 

 by heating it violently while exposed to 

 the air. Mr. Clouet has found that when 

 cast iron is mixed w'ith i of its weight 

 of black oxide of iron, and heated violent- 

 ly, it is equally converted into pure iron. 

 The oxygen of the oxide, and the carbon 

 of the cast iron, combine and leave the 

 iron in a state of purity. The conversion 

 of iron into steel is effected by combining 

 it with carbon. This combination is per- 

 formed in the large way by three differ- 

 ent processes, and the products are dis- 

 tinguished by the names of natural steel, 

 steel of cementation, and cast steel. 



Natural steel is obtained from the ore 

 by converting it first into cast iron, and 

 then exposing the cast iron to a violent 

 heat in a furnace while its surface is 

 covered with a mass of melted scoriae 

 five or six inches deep. Part of the car- 

 bon combines with the oxygen which 

 cast iron always contains, and flies off in 

 the state of carbonic acid gas. The re- 

 mainder combines with the pure iron, 

 and constitute it steel. 



This steel is inferior to the other spe- 

 cies; its quality is not the same through- 

 out; it is softer, and not so apt to break; 

 and as the processes by which it is ob- 

 tained are less expensive, it is sold at a 

 lower price than the other species. It is 

 obvious that iron and carbon are capable 

 of combining together in a variety of dif- 

 ferent proportions. When the carbon 

 exceeds, the compound is carburet of 

 iron or plumbago. When the iron ex- 

 ceeds, the compound is steel or cast iron 

 in various states, according to the propor- 

 tion. All these compounds may be con- 

 sidered as subcarburets of iron. The 

 hardness of iron increases with the pro- 

 portion of charcoal with which it com- 

 bines, till the carbon amounts to about 

 J^ of the whole mass. The hardness is 



