62 LEAD 



Thirty-five tons of similar slag smelted with hot blast consumed 300 cubic feet of 

 air per minute. 



Labour cost 378 



Coke, 5 tons, 17 cwts., at 24s. 6d. . . .734 

 Turf for heating air, 11 loads, Is. 8d. . . . 18 4 



Total . 11 9 4 



From which it will be seen that, with one-quarter part less air, a quarter part more 

 slag was melted per week, and a saving of expense of nearly 10s. effected. 



The loss of lead experienced in smelting by the slag-hearth is, however, very 

 great, even under the most favourable circumstances ; and it has, consequently, of 

 later years been gradually superseded by the Castilian furnace, which will be shortly 

 described. Many large and well-conducted establishments still however continue to 

 employ the slag-hearth, and when well constructed and skilfully managed, the loss 

 arising from volatilisation may be considerably reduced. 



Castilian Furnace. Within the List few years a blast-furnace has been introduced 

 into the lead-works of this country which possesses great advantages over every other 

 description of apparatus which has been hitherto employed for the treatment of lead 

 ores of low produce. This apparatus, although first employed in Spain, was invented 

 by an Englishman (Mr. W. Goundry) who was employed in the reduction of rich 

 slags in the neighbourhood of Carthagena. 



This furnace is circular, iisually about 2 feet 4 inches, or 2 feet 6 inches in diameter, 

 and is constructed of the best fire-bricks, so moulded as to fit together, and allow all 

 the joints to follow the radii of the circle described by the brick-work. Its usual 

 height is 8 feet 6 inches, and the thickness of the masonry invariably 9 inches. In 

 this arrangement the breast is formed by a semicircular plate of cast iron, furnished 

 with a lip for running off the slag, and has a longitudinal slot, in which is placed the 

 tapping-hole. 



On the top of this cylinder of brick-work a box-shaped covering of masonry is 

 supported by a cast-iron framing, resting on four pillars, and in this is placed the 

 door for feeding the furnace, and the outlet by which the various products of com- 

 bustion escape to the flues. The lower part of this hood is fitted closely to the body 

 of the furnace, whilst its top is closed by an arch of 4J-inch brick-work laid in 

 fire-clay. The bottom is composed of a mixture of coke-dust and fire-clay, slightly 

 moistened, and well beaten to the height of the top of the breast-pan, which stands 

 nearly 3 feet above the level of the floor. Above the breast-pan is an arch so 

 turned as to form a sort of niche, 18 inches in width, and rather more than 2 feet in 

 height. 



When the bottom has been solidly beaten, up to the required height, it is hollowed 

 out so as to form an internal cavity, communicating freely with the breast-pan, which 

 is filled with the same material, and subsequently hollowed out to a depth slightly 

 below the level of the internal cavity. The blast is supplied by three water tuyeres, 

 3 inches in diameter at the smaller end, 5J inches at the larger, and 10 inches in 

 length. Into these the nozzles are introduced, by which a current of air is supplied 

 by means of a fan or ventilator making about 800 revolutions per minute. The blast 

 may be conveniently conducted to the nozzles through brick channels formed beneath 

 the floor of the smelting-house. 



The ores treated in this furnace ought never to contain more than 30 per cent, of 

 metal, and when richer, must be reduced to about this tenure by the addition of slugs 

 and other fluxes. In charging this apparatus, the coke and ore are supplied stratum 

 super stratum, and care must be taken so to dispose the coke as not to heat too 

 violently the brickwork of the furnaces. In order to allow the slags which are pro- 

 duced to escape freely into the breast-pan, a brick is left out of the front of the 

 furnace at the height of the fore-hearth, which, for the purpose of preventing the 

 cooling of the scoriae, is kept covered by a layer of coke-dust or cinders. From tho 

 breast-pan the slags flow constantly off over a spout into cast-iron waggons, where 

 they consolidate into masses, having the form of truncated pyramids, of which the 

 larger base is about 2 feet square. As soon as a sufficient amount of lead is accu- 

 mulated in the bottom of the furnace, it is let off into a lateral lead-pot, by removing 

 the clay-stopper of the tap-hole situated in the slot of the breast-pan, and, after 

 being properly skimmed, it is laded into moulds. When, in addition to lead, the 

 ore treated likewise contains a certain portion of copper, this metal will be found 

 in the form of a matt floating on the surface of the leaden bath. This, when suffi- 

 ciently solidified, is removed, and, after being roasted, is operated on for tho copper it 

 contains. 



The waggons in which the liquid slag runs off are frequently made to traverse 



