Cast Iron, Steel, and Malleable Iron. 583 



rating with the carbon of the iron, carbonic oxide gas, as well 

 as carbonic acid ; and the evolution of these gases causes the 

 well-known ebullition of the whole mass. In this separated 

 state of the molecules, it is very difficult for heat to be brought 

 to act on them ; and it is, in fact, well known to all workmen, 

 that several mettils are the more difficult to re-melt the more 

 minute their state of division. 



Each grain of the iron, not being in a fluid state, by losing 

 the carbon, silicon, &c., is converted into the base of malle- 

 able iron, leaving behind only a skeleton of the grains of 

 cast iron. All the crystalline planes are destroyed ; and 

 therefore, instead of the crystals adhering to each other with 

 their planes of crystallization by a force easily to be over- 

 come^ an innumerable quantity of points of the skeleton of the 

 crystals adhere together in all directions of the adhesive 

 force ; and as we have before observed, that the skeleton 

 grains are naturally not in a liquid state, the spaces formerly 

 occupied by the carbon, silicon, and portions of iron, which 

 have been consumed, are still vacant, consequently the iron 

 in this state exerts a very great decomposing power upon 

 all chemical bodies, as is the case with oxide of iron reduced, 

 at a low degree of heat by hydrogen. This fact likewise ex- 

 plains the circumstance, which I have often observed, that by 

 using bad coals, or when the draught of the furnace is not 

 well regulated, the iron which during the first half of the 

 process of puddling had lost all its sulphur by chemical 

 means, exhibited at the end of the process more sulphur than 

 the cast iron actually contained before the puddling com- 

 menced. 



The vacant spaces in the skeleton grains which constitute 

 the lumps of iron made in the puddling furnaces, are imme- 

 diately closed when brought under the forge hammer, and 

 consequently the decomposing power ceases ; but where the 

 malleable iron thus obtained is again kept at a white heat for 

 a considerable space of time, the closed pores in some mea- 

 sure re-open, and their attractive force towards chemical 

 agents begins to re-appear, and thus, to mention one in- 

 stance, the iron combines in the cementing furnace with car- 

 bon, forming cemented steel, without altering the juxta-position 

 of the silicon and iron molecules in the cemented bar. Such 

 a cemented bar, when exposed to a proper degree of heat, 

 will weld to another similar bar, as the mechanical texture of 

 the iron had not been altered. But it is different when the 

 cemented steel, instead of being softened only, is reduced to a 

 perfect liquid state by melting. In this case the iron and si- 



and I used a similar apparatus, for ascertaining the nature of the escaping 

 gases, after the boiling mass had been mixed with different chemical agents. 



