254 METALS 



twiers, the three bjast tubes of which connect with a common tube that 

 extends round, by the passage g g, (figs. 1, 3,) in the form of a semi- 

 circle, and receives the blast through the tube p. The dotted circle 

 within corresponds to the inner outline of the fife brick lining of the 

 widest part of the furnace. 



The melted iron runs into the lower part of the hearth, and is covered 

 by the cinder. It is prevented from running out by the damstone c 

 (figs. 2, 3) ; and farther to hinder the metal from being forced out by 

 the blast, clay is rammed beneath the tymp around the twiers and upon 

 the surface at k, where it is retained by heavy iron plates. These 

 plates are raised every few hours to allow the cinder to run off, which 

 passes out over the damstone, along the (lust-plate, c i, (figs. 2, 3.) The 

 metal is drawn off every twelve hours at the lower level a, through an 

 aperture at the bottom of the damstone. 



Great economy in making iron has of late been secured by heating 

 the blast to three to six hundred Fahrenheit. The cooling effect of the 

 vast volumes of air thrown into the furnace is avoided ;* and this is ab- 

 solutely necessary when anthracite coal is used, as is the case in many 

 works of recent construction. In the view above given,/, f y (fig. 2 7 ) 

 represent two (out of three) passages in the upper part of the furnace, 

 by which the waste flame is led off, first to heat boilers at W, W, (fig. 

 1,) and then to a hot-oven chamber, o. In the last there is a great 

 number of iron pipes, arranged in series ; the blast by the action of the 

 engine, is thrown through all the pipes in succession, and after being, 

 thus heated, flows on to p, (fig. 3,) whence it passses to the twiers, (t, t, 

 t.) When the engine is separated from the furnace, the oven is usually 

 placed upon the front side (instead of back) of the top, and the flame 

 passes in by a single aperture. The works here figured are situated 

 upon a side hill. It is important that the blast should not be too great, 

 as it wastes the metal by oxydation ; and at the same time it should be 

 sufficiently copious to supply the requisite qantity of oxygen. 



The first step in the process of reduction, consists in roasting the ore 

 to drive off any volatile ingredients, and open its texture. This is effect- 

 ed by piling the ore in heaps, made of alternate layers of coal or coke 

 and ore, covering up the heap loosely with earth . and firing it. The 

 carbonic acid, if it contains any, the moisture, and any sulphur present, 

 are thus expelled, and the ore is in a looser state for reduction. The 

 mrnace is filled with coal and slowly heated up — ten or twelve days 

 being required for this, to avoid the effect of too sudden heat on the fur- 

 nace. The charge, next to be added, consists of coal, the roasted ore, 

 and limestone, (if this be the flux,) in certain proportions, and it is car- 



What is said of the hot blast 1 Describe the method of heating the 

 engine, and air of the blast. Mention the several steps in the process 

 f reduction. 



* The weight of air thrown into a Glasgow furnace in 24 hours, has 



een estimated at 6192 cwt., or 6292 cubic feet per minute, while the 



hoi": weight of coke, ore and limestone added in the same time, was 



nly 666£ cwt. In ordinary cases, the weight of the air is at 'east four 



imea as much as that of the charges. 



