20 Metallurgy of Iron. 



and burns like tinder, yielding red oxyd of iron. In order to 

 avoid the inconvenience of this excessive tendency to oxj'dation, 

 the metal is exposed in the process of manufacture to a heat some- 

 what greater than would be required for the reduction.; this ren- 

 ders the sponge more dense, and less liable to oxydation in the air. 



The part of the furnace below the action of the fire is so pro- 

 longed, that the reduced metal in its slow descent, has time to be- 

 come veiy nearly cold before reaching the bottom. It is then re- 

 moved at intervals, by an ingenious arrangement, which enables 

 the operator to cut off, as it were, the lower portion of the mass, 

 without allowing the air to enter into the apparatus. In the case 

 where the ore has been mixed with charcoal, the la-ger masses of 

 metal are now separated from it by a screen, and the smaller by a 

 revolving magnetic machine. 



This spongy metallic iron may be applied to various uses. If 

 we grind it to powder and then submit it to strong pressure, co- 

 herent masses are obtained, which at a welding heat, contract 

 slightly, without losing their form, and yield malleable iron. By 

 this process of moulding, which may be termed a casting without 

 fusion, the metal may be obtained in forms retaining all the sharp- 

 ness of the mould, and possessing the tenacity, malleability and 

 infusibility of wrought iron. The masses thus compressed have iu 

 fact only to be forged, to give wrought iron of the finest quality; 

 and it is found that during the hammering, any earchy matters 

 mechanically intermixed, are eliminated like the scoriae of the 

 iron from the puddling furnace. 



But without overlooking the great advantage of this method of 

 making malleable iron, and moulding it into the shapes required, 

 it is especially as applied to the manufacture of steel, that the 

 metallurgical methods of Chenot deserve attention. In the ordi- 

 nary process, as we have already seen, the bars of malleable are 

 carburetted by a prolonged heating in the midst of charcoal pow- 

 der ; but the operation is long and expensive, and the metal ob- 

 tained by this mo.le of cementation is not homogeneous. Mr. 

 Chenot avails himself of the porosity of the metallic spono-e, to 

 bring the carbon in a liquid state, iu contact with the minutest 

 particles of the iron. For this purpose he plunges the sponge 

 into a bath of oil, tar, or melted resin, the composition of the bath 

 varying according to the quality of the steel which it is desired 

 to obtain. The sponge thus saturated, is drained, and heated in a 

 close vessel. The oily or resinous matter is expelled, partly as a 

 gas, but for the greater part distils over as a liquid, which may be 



