994 IRON 



coals are then introduced from above, and tho necessary supply of air admitted to 

 the generator through the lower air-chest. When these coals have been thorouuhly 

 ignited, the generator is filled with coals, and a very moderate supply of air admin ni 

 through the tuyeres below (for the generation of the gas), and those over the bridge 

 (for its combustion) until the furnace is dried, when the supply of air at both places 

 is increased, so as to raise the hearth to the temperature necessary for baking it 

 thoroughly, upon which, about 40 cwts. of iron are introduced ; the metal being dis- 

 tributed over the whole hearth as uniformly as possible, and the size of the pieces 

 being selected with the view to expose as much surface as possible to the flame. 

 The fusion of the charge of metal is effected in about three hours, the coal owd 

 amounting to about 3f cubic feet per hour. The gas-generator is always kept filli-d 

 with coal, and the supply of air admitted from below is diminished by a regulation 

 of the valve, whenever fresh coal is supplied, as tho latter, at first, always yields gas 

 more freely. The arrangement of the upper row of tuyeres effects the combustion 

 of gases just as they pass from the generator on to the hearth. The hottest portion of 

 the furnace is of course near the fire-bridge, i.e. where the blast first meets with the 

 gases. During the melting process the iron is shifted occasionally, so that the cooler 

 portion near the flue may in its turn become melted without loss of time. When 

 the iron is ascertained to be thoroughly fused, about 5 Ibs. of crusted limestone are 

 thrown over its surface for the purpose of converting the dross which has separated 

 into fusible slag. The two side tuyeres are now introduced into the furnaces through 

 the^ppenings above alluded to, the width of the nozzle employed depending upon tho 

 power of the blast used. The air rushing from these tuyeres impinges with violence 

 upon the iron, and the two currents meeting an eddying motion is imparted to tho 

 fused metal. In a short time the motion produced in the mass is considerable ; tho 

 supernatant slag is blown aside by the blast, and the surface of the iron thus exposed 

 undergoes refinement, while it changes continually, the temperature of tho whole 

 mass being raised to a full white heat, by the action of the air. Tha iron is stirred 

 occasionally, in order to insure a proper change in the metal exposed to the action of 

 the blast. A shovelful of limestone is occasionally thrown in (the total quantity 

 used being about 1 per cent, of the crude iron employed). The slag produced is ex- 

 ceedingly fusible, and is allowed to remain in the furnace until the metal is tapped, 

 and on cooling it separates from it completely. 



The duration of the treatment in this furnace after the metal is fused, varies from 

 two hours and a half to five hours, according to the product to be obtained. For 

 the preparation of perfectly white iron, the treatment is carried on for five hours. A 

 sample is tapped to examine its appearance when it is believed to be sufficiently 

 treated. 



When the charge is to be withdrawn from the furnace, the side tuyere nearest the 

 tap-hole is withdrawn, so that the blast from the opposite tuyere may force the metal 

 towards the hole. The fluid iron, as it flows from the tap-hole is fully white hot, and 

 perfectly limpid ; it chills, however, very rapidly, and soon solidifies. A few pails 

 of water are thrown upon those portions of the metal which are not covered with tho 

 slag, which flows out of the furnace, the object being to cool it rapidly, and thus 

 prevent the oxidation of any quantity of iron. The loss of metal during the treat- 

 ment is said not to exceed 5 per cent. 



With regard to the purification which the iron undergoes in the gas reverberatory 

 furnace, it appears to be confined chiefly to the elimination of carbon and silicium, 

 the amount of sulphur and phosphorus undergoing but little alteration, as appears from 

 the following analyses (Abel) : 



Pig-iron Refined iron 



Silicium .... 4'66 .... 0*62 

 Phosphorus . . , 0'56 .... 0-50 

 Sulphur . . . 0-04 .... 0'03 



Nevertheless, the iron thus refined is highly esteemed for all castings which nro 

 required to possess unusual powers of resistance ; some experiments made to ascertain 

 the comparative strain borne by therefined metal, and the same metal as obtained from 

 the blast-furnace, showing the strength of the former to bo greater by one half than 

 that of the latter. 



The Operation of Puddling. In the year 1783 and 1784, Mr. Henry Cort of Gnsport. 

 obtained two patents, one for the puddling, and the other for the rolling of iron. ' I>i^- 

 coveries,' says Mr. Scrivenor, 'of so much importance in tho manufacture, that it 

 must be considered the era from which we may date tho present extrusive au>l 

 flourishing state of the iron trade of this country.' 



The object of Mr. Cort's process was to convert into malleable iron, cast or pig- 

 iron, by means of- the flame of pit-coal in a common air furnace, and to form t 



