'05-1 IRON 



manufactured, a magnesian limestone is preferable, but an aluminous limestone should 

 be used where siliceous ore predominates. Chemical analysis alone, can drti-rmine to 

 which class a particular limestone belongs, as there is often' nothing in the external 

 appearance by which a pure limestone may bo distinguished from one containing 40 

 or 50 per cent, of foreign matter. 



Carbonised pit-coal, or coke was. till within the last twenty-five years, the solo com- 

 bustible used in the blast-furnace. Coal is coked either in tho open air or in kilns. 

 In the former, as practised in Staffordshire, tho coal is distributed in circular 

 heaps about 5 feet in diameter by 4 feet high, and the middle is occupied by a l.w 

 brick chimney piled with loose bricks, to open or to leave interstices between them, 

 especially near the ground. The larger lumps of coal are arranged round this 

 chimney, and tho smaller ones towards the circumference of the mass. When (very- 

 thing is adjusted a kindling of coals is introduced into the bottom of the brick 

 chimney, and, to render the combustion slow, the whole is covered with a coat of coal 

 dross, the chimney being loosely covered with a slab of any kind. Openings are 

 occasionally made in the crust, and afterwards shut up, to quicken and retard the 

 ignition at pleasure during its continuance of twenty-four hours. Whenever the 

 carbonisation has reached the proper point for forming good coke the covering 

 of coal dross is removed, and water is thrown on the heap to extinguish the com- 

 bustion, a circumstance deemed iiseful to the quality of the coke. In this operation in 

 Staffordshire coal loses the half of its weight, or two tons of coal produce one of coke. 



In order to prepare larger quantities of coke at once, long ridges are often substi- 

 tuted for circular heaps, the length of which varies with circumstances and the con- 

 sumption of coke ; they sometimes extend to the length of 200 feet. On erecting one 

 of these ridges a string is stretched along the coking station, in tho direction of which 

 large pieces of coal are placed slanting against each other, leaving a triangular space 

 between them, so that a longitudinal channel (ignition passage) is formed, through 

 which the string passes. In arranging the pieces it is necessary to pay attention to 

 the natural stratification of the coals, which should be at right angles to the longitudinal 

 direction of the ridge. Parallel with the first series of coals is placed a second, and 

 then a third, and so on; but the pieces constantly diminish in size until the station 

 measures 6 feet on both sides. Upon this substructure the heap is then made, 

 without particular care in the arrangements, the largest pieces below and the smallest, 

 above, until it has reached a height of about 3 feet. To facilitate the ignition, stakes 

 are rammed in at distances of 2 feet from each other, projecting above throughout 

 the whole length of the ridge, which, when subsequently removed, leave vac-ant 

 spaces for the introduction of burning coal. The ridge, being thus kindled at more 

 than 100 distinct spots, soon breaks out into active combustion. As soon as the burner 

 observes the thick smoke and flame cease at any one part, and a coating of ash 

 making its appearance, he endeavours immediately to stop the progress of the fire by 

 covering it with powdered coal-dust, repeating the operation until the whole ridge is 

 covered, when it is left two or three days to cool ; the covering on the side exposed 

 to the wind should be thicker and increased in stormy weather. When the fire is 

 nearly extinguished, which occurs in two or three days, the coke is drawn. This 

 mode of coking is simple, but not very economical. The fire proceeding from the 

 upper part of the ridge in a downward direction, towards the lower and interior parts, 

 converts the coal in the upper strata into coke before that in the interior has acquired 

 the temperature necessary for charring, and is still in want of a supply of air, which 

 can only be furnished from without, and must not be excluded by a covering. During 

 the time, therefore, that tho inner parts of tho heap are being converted into coke, the 

 outer portions are being uselessly, though unavoidably consumed. For further details 

 concerning coking, see the articles COAI, and COKE. 



The ' blowing-in ' of a coal blast-furnace is an operation which requires much 

 care, and experience. A fire of wood is first lighted on tho hearth; upon this is 

 placed a quantity of coke, and when tho whole is well ignited, the fun 

 filled to the throat with regular charges of calcined ore, limestone, and coke, and 

 the blast, which should at first be moderate, is turned on. At tho works around 

 Merthyr Tydvil, the first charges generally consist of 6 cwts. of calcined argil- 

 laceous ore and 1| cwt. limestone, to 4 cwts. of rich coke; this burden is kept 

 on for about 10 days, it is then increased to 6 cwts. of calcined ore and 2 cwts. of 

 limestone (Truran). The cinders usually make their appearance in about 12 hours 

 after blowing; the metal follows in about 10 hours after, collecting in the hearth to tho 

 amount of 3 or 3 tons in 60 hours after blowing. If all goes on well about 22 tons 

 of metal will be produced in the first week, 38 tons in the second. .">/) in the third, and 

 SO in tho fourth; after 10 or 12 weeks the produce will averago 110 tons. 

 By forcing the furnace in its infancy a much irivater produce of iron may bo obtaiii'-d, 

 though to the injury cf its subsequent working. j\Ir. Trurai; n-litrs the following 

 case in point. A furnace was blown in at the Abcrsychan works with such volumes 



