898 



STEEL 



This steel is very useful for ships' plates, being very strong and rigid, and thus re- 

 quiring less weight of metal ; it may also eventually be used for rails and a great 

 variety of purposes, for which at present strong charcoal or scrap iron is used. 



The Paal process may be considered as an improvement upon natural steel, the 

 object being as far as possible to carbonise the iron fibres which this kind of steel 

 always contains. The process is based upon the old one of Vanaccio : it consists in 

 plunging iron into a bath of melted metal. The carbon of the metal combines with 

 the iron, and in a very short, time converts it into steel. This process was carried 

 further by Vanaccio, who contrived to add wrought iron to the metal until he had 

 decarbonised it sufficiently ; this was found to produce a steel, but unfit for general 

 use. That produced by plunging iron into metal was found to be a very hard steel on 

 the outside, but iron within ; while that produced by adding iron to the metal was 

 found too brittle to be drawn. The Paal method, however, was a decided improvement 

 in the manufacture of refined natural steel. The packets, as already described in the 

 refinement of natural steel, are welded and drawn to a bar ; whilst hot they are 

 plunged into a bath of metal for a few minutes, by which the iron contained in the 

 raw steel becomes carbonised, and thus a more regular steel is obtained than that 

 produced by the common process. The operation requires great care, for if the bars 

 of steel be left in the metal too long they are more or less destroyed, or perhaps 

 entirely melted. 



The foregoing kinds of steel may be classed under the first head of natural steel, 

 being manufactured from the crude iron direct. 



The next process is the production of steel by introducing carbon into malleable 

 iron which is the reverse of the process already described. The iron to be converted 

 is placed in a furnace, stratified with carbonaceous matter, and on heat being applied 

 the iron absorbs the carbon, and a new compound is thus formed. 



At a very early period charcoal was found to harden iron, and to give it a better and 

 more permanent cutting edge. It seems probable that from hardening small objects 

 bars of iron were afterwards submitted to the same process. To Reaumur certainly 



1904 



1905 



belongs the merit of first bringing the process of conversion to any degree of per- 

 fection. His work contains much information on the theory of cementation ; and 



although his investigations are 

 not borne out by the practice of 

 the present day, yet the first prin- 

 ciples laid down by him are now 

 the guide of the converter. Our 

 furnaces are much larger than those 

 used by Reaumur, and they are 

 built so as to produce a more uni- 

 form and economical result. The 

 furnace of cementation in which 

 bar iron is converted into blistered 

 steel is represented in figs. 1903, 

 1904, and 1905. 



It is rectangular, and covered 

 in by a semicircular arch, in the 

 centre of which there is a circular 

 hole left, 12 inches diameter, which 

 is opened when the furnace is 

 cooling. It contains two chests, called 'pots',' c, c, made either of fire-stone or fire- 



