IRON, 



fracture will be ; and as this is not com- 

 pletely remedied by the subsequent tem- 

 pering", it is advisable to employ the least 

 heat capable of affording 1 the requisite 

 hardness. It is a circumstance worthy of 

 remark, that steel has a less specific gra- 

 vity when hardened than when soft; but 

 there are no circumstances upon which a 

 probable connection between these two 

 properties, namely, the increased hard- 

 ness and the diminished specific gravity, 

 can be made out. 



If the cementation be continued too 

 long, the steel becomes porous, brittle, of 

 u darker fracture, more fusible, and inca- 

 pable of being forged or welded. On the 

 contrary, steel cemented with earthy in- 

 fusible powders is gradually reduced to 

 the state of forged iron again. Simple 



K ignition produces the same effect ; but is 



t attended with oxidation of the surface. 

 The texture of steel is rendered more 

 uniform by fusing it before it is made 

 into bars ; this is called cast steel, and is 

 rather more difficultly wrought than com- 

 mon steel, because it is more fusible, and 

 is dispersed under the hammer if heated 

 to a white heat. 



The conversion of iron into steel, either 

 by fusion, viz. the direct change of crude 

 iron into steel, or by cementation of bar- 

 iron, presents many objects of interesting 



, inquiry. From various experiments of 

 Bergman, it appeared that good crude 

 iron, kept for a certain time in a state of 



[, fusion, with such additions as appeared 

 calculated to produce little other effect 



L than that of defending the metal from 

 oxidation, became converted into steel 

 with loss of weight. These facts are con- 

 formable to the general theory ofVan- 



* dermonde, Monge, and Berthollet : for, 

 according to their researches, it should 

 follow, that part of the carbon in the 

 crude iron was dissipated, and the re- 



m mainder proved to be such in proportion 

 us constitutes steel. The same chemist 



[ cemented crude iron with plumbago, or 



I carbonate of iron, and found that the 

 metal had lost no weight. Morveau re- 



. peated the experiment with grey crude 

 iron. The loss of weight was little, if any. 

 The metal exhibited the black spot by the 



j application of nitric acid, as steel usually 



] does, but it did not harden by ignition and 



t plunging in water. Hence it is conclud- 

 ed, that it was scarcely altered : for crude 



I iron also exhibits the black spot, and can- 

 not by common management acquire the 

 hardness or' steel. 



From the experiments of the three 

 excellent chemists last mentioned, it ap- 

 pears that the grey crude iron consists 



principally of iron, with as much carbon 

 as it can dissolve in the strong heat of the 

 smelting furnace. They have shown 

 also, that it deposits part of this addition, 

 when cooled in contact with an iron bar 

 immersed in the bath. This separation 

 must be general in the ordinary or gra- 

 dual way of cooling, whence the grey co- 

 lour must arise from the blue white co- 

 lour of the iron mixed with the black of 

 the carbon. And this grey colour is also 

 in a degree perceived, when soft close- 

 grained steel is broken. These circum- 

 stances lead to an inference, that hard 

 steel may in a certain respect differ from 

 that which is softer by the intimate com- 

 bination of a larger proportion of carbu- 

 ret. This accounts for the whiter and 

 more metallic aspect of hardened steel, 

 than of such as is soft. For the former con- 

 tains less of disengaged carburet. Hence 

 also we may account for the greater hard- 

 ness of steel, which has been made quite 

 hard, and then let down by tempering to 

 a certain colour, than of steel merely 

 heated to that colour, and pluugedin wa- 

 ter. For, in the first method of harden- 

 ing, a sufficient degree of heat is given 

 to produce combination between part of 

 the disengaged carburet and the iron, 

 which in the latter does not take place. 

 If the carburet be merely sufficient to sa- 

 turate all the iron at a moderate degree of 

 ignition, the hardness will be considera- 

 ble ; but the steel will be easily degraded 

 to tlie state of iron by frequent ignition. 

 Such steel, in its hard state, will be very 

 uniform in its texture, not excessively 

 hard in its temper, but disposed to take a 

 very fine firm edge, which will not easily 

 be broken or injured by violence. These 

 are accurately the properties of the Eng- 

 lish cast steel, which is of so uniform a 

 nature, as to be distinguished by its con- 

 choidal or glassy fracture. When the dose 

 of carbon in steel is greater, it will bear 

 a greater heat without degradation, inso- 

 much that it may be welded like iron. 

 Its hardness will also be capable of a 

 higher degree; and if this degree, pro- 

 duced by a stronger ignition, be not given, 

 the edge of the tool will never become 

 fine and smooth ; and even at this higher 

 degree, with all the advantage of subse- 

 quent tempering, it will be less smooth 

 than that of the cast steel, and more dis- 

 posed to break. Steel of this kind is bet- 

 ter adapted for the construction of ham- 

 mers, vices, hatchets, leather-cutters' 

 knives, and other instruments, wherein 

 the edge is either stout, or sudden blows 

 unnecessary, or the construction demands 

 frequent heating and welding. 



