7» Proctfsfar maktng Steel iy Cementation. 



of the extremities of the furnace as well as of the cafe, it is ufual to form a hole, by which 

 a bar may be taken out when it is fuppofed that the cementation may be fufficiently ad- 

 vanced. The workman judges from the colour, and the blifters on its furface, whether the 

 fteel be perfe£l. If he cannot depend on his judgment in this refpeft, trial is made of this 

 fteel by hardening and breaking it. If the cementation have not penetrated as far as the 

 centre, it is eafy to diftinguifli, by the fibrous fraclure, that part which Hill retains the nature 

 of iron. 



When the fteel is taken out of the cementing furnace, its furface is covered vt'ith inequa- 

 lities and blifters, whence it is called blifter fteel. In this ftate its frafture prefents very- 

 large facets, and refembles brittle iron of a bad quality. Before it is brought to market it is 

 ufually forged into flat bars feven or eight lines broad ; after which it is fiiffered to cool in 

 the air without plunging it in water. By this treatment its grain becomes much clofer. 



As the extremities of the bars thus converted into fteel are ufually flawed and lefs per- 

 feft, they are cut off and forged together in faggots. This fteel is ufed for inftruments of 

 agriculture. If the fire have not been fufficiently a£live, or kept up for the proper time, 

 the bars are not cemented to the centre ; whence they become of unequal hardnefs, efpe- 

 cially if they be not very carefully forged. When the fire has been too intenfc, the fteel be- 

 comes too brittle, and difficult to be managed on account of its having diflblved too large 

 a quantity of charcoal. Yet it is impoflible to eftablifli any rule for the management of 

 the firj:, becaufe it muft vary according to the form and fize of the furnace, the number 

 and thicknefs of the bars, and the nature of the fuel. 



The form and magnitude of the furnaces vary confiderably in the different works where 

 iron is cemented. The objefts to be aimed at are, to give the furnace a degree of folidity 

 which ftiall enable it to refift a great number of operations, tocaufe the flame and heat to 

 circulate equally on all fides of the cafe, and to produce the greateft quantity of heat with 

 the fmalleft expence of fuel. 



One very important obfervation refpe£llng the extent of dimenfions which may be given 

 to thefe furnaces is, that no advantage, or at leaft very little, in the confumption of fuel is 

 obtained by enlarging thefe dimenfions, becaufe it is neceflary that the whole of the heat 

 (hould be fuffered to diffipate at the end of each operation. The cafe is very difl^erent in 

 other manufadlories where the accumulated heat may ferve for fuccefllve proceffes ; for the 

 whole of fuch fuel as is employed in raiCng the temperature to the neceflary degree in cafes 

 of interruption would be entirely loft. 



Prudence demands, that he who is defirous of improving or extending the arts fliould not • 

 blindly be led away by the feduftion of projefts. It is proper to begin the operations on a 

 fmall fcale, in order to render the pradice familiar, before furnaces of a certain magnitude 

 are conftru£ted *. 



(To beconfludedy with Annotations, in our next. J 



* Reference is here made in the original to drawings of furnaces ; one contrived by Jars for cementing 

 three or four hundred weight of fteel } another of the furnace at Newcaftle ; another heated by wood, toge- 

 ther with fome defignt relative to the manipulations at Carinthia. None of thefe, however, arc annexed » 

 the memeir. K. 



6 IV. Obfervations 



