422 Facts about Iron. 



condition of iron after fracture must not be taken as necessarily 

 showing in what state it existed before fracture occurred. Dr. 

 Percy tells us that " when a piece of iron which has been 

 melted, and which is largely crystalline, is cautiously hammered 

 at a suitable temperature into a shape adapted for rolling, and 

 then rolled into a bar, not too thick, it will present either a fibrous 

 or a crystalline fracture, according to the manner of breaking 

 it, and especially the duration of the act. After nicking it to a 

 slight depth on one side with a cold chisel, and then bending 

 it slowly backwards from the line of the nick, the fracture will 

 be highly fibrous, and may be almost silky. On the other 

 hand, if it be nicked all round, and suddenly broken in the line 

 of the nick, the fracture will be crystalline, with, it may be, 

 only here and there an indication of fibre." 



We have stated that the modern processes for smelting 

 iron on a large scale produce cast, or carburized iron, and this 

 will be readily understood from Dr. Percy's explanations. 

 " The furnace being in operation, or, as it is technically termed, 

 in blast, iron-yielding materials (of which the essential part is 

 oxide of iron), flux (generally limestone), and fuel, are con- 

 tinually thrown in at the top, so that the interior may be kept 

 filled up nearly to the filling holes, while slag, or " cinder," 

 and cast iron continually accumulate in the hearth at the 

 bottom, the former flowing out over the dam, and the latter 

 being allowed to escape at intervals through the tapping hole." 

 The oxygen of the air blown in to constitute the blast forms car- 

 bonic acid with the carbon of the fuel, and this gas, passing 

 into the state of carbonic oxide, readily reduces the oxide of 

 iron. The ore, or iron oxide, is reduced as it descends in the 

 furnace, and as it falls towards the lower and hottest part of 

 the furnace the metal " becomes carbonized, and converted into 

 cast iron, which trickles down in a molten state to the bottom." 

 The iron not only acquires a large dose of carbon in this pro- 

 cess, but likewise takes up all kinds of impurities that are pre- 

 sent, mid thus needs subsequent treatment to decarbonize it, 

 .■mil remove extraneous matters. An expensive and very 

 laborious treatment of cast iron is resorted to in our large 

 works for the purpose of obtaining (lie metal in a malle- 

 :iUe state. This is technically called " puddling," and " consists 

 essentially in stirring abont pig-iron molten on the bed of a 

 reverberatory furnace, heated by flame, until it becomes con- 

 verted into malleable iron, through the decarbonizing action of 

 the oxygen of the air circulating through such a furnace." One 



of tin- most remarkable inventions for decarbonizing pig-iron 

 is that of Mr. Bessemer. The pig-iron is melted in a suitable 

 furnace, and jets of air are Ihen introduced. As the inventor 

 states, "the nir expanding in volume, divides itself into glo- 



