IRON 947 



to be to consume more coal than wide ones, inasmuch as in Pennsylvania and through- 

 out the whole west, where narrow tops are preferred, the consumption of charcoal per 

 ton of iron is from 160 to 180 bushels, while in the State of New York, and further 

 east, where the furnace throats are wider, the consumption is from 120 to 130 bushels. 

 Another subject which demands the strictest attention is the regulation of the blast. 

 A weak soft charcoal will not bear a much greater pressure than from half a pound 

 to five-eighths of a pound to the square inch ; strong coarse charcoal will bear from 

 three-quarters of a pound to a pound ; and again, it may be laid down as a rule, that 

 the larger the throat in proportion to the boshes, the stronger ought to bo the blast, 

 and that a narrow top and wide boshes, while they permit a weaker blast, involve the 

 loss of much fuel. In every case a careful roasting of the ores at charcoal furnaces 

 will prove advantageous ; this is the surest means of saving coal and blast, and of 

 avoiding more annoyances in the working of the furnaces. 



The above account represents the form of blast-furnace as constructed at the time 

 of the former edition of this work. Other modifications have since been introduced 

 mainly in the direction of increased size, and the avoidance of strongly -contracted 

 slopes as sudden changes in dimensions. 



English Process of Iron-making. The 'Mineral Statistics ' gives us the quantity of 

 pig-iron produced in Great Britain in the year 1872, as follows : 



Tons 

 Northumberland . . . . . . 38,766 



Durham ' . ' . 760,172 



Yorkshire, North Eiding . . * ^ f 1,122,114 

 Do. "West Eiding . . . . ! ,' >; 148,636 

 Derbyshire. .' . . : .<;-... -4- .,> ' . 283,375 

 Lancashire . . . - f : .; ^. . 524,041 

 Cumberland . . . *'.-.. 440,575 



Shropshire , ; ' : * T - 133,046 



North Staffordshire , '- . . . 275,925 

 South Staffordshire and Worcestershire -. ." 673,470 

 Northamptonshire and Lincolnshire . 96,413 

 Gloucestershire, Wilts, and Somerset . . . 97,481 

 North Wales . . . , . . . 54,698 

 South Wales . . ... . . 1,002,623 

 Scotland 1,090,000 



Of the Blast-Furnace. The blast-furnaces at present in use are of various sizes, 

 being from 35 to 90 feet in height, and at the boshes, or widest part, from 12 to 30 

 feet. The internal form commonly adopted consists essentially of two frustums of 

 cones meeting each other at their bases, at the point where the widest part or the top 

 of the boshes is situated. From this point the furnace gradually contracts both 

 upwards to its mouth, and downwards to the level of the tuyeres below. The hearth, 

 properly speaking, is that part of the furnace only which receives the fluid metal 

 and cinder, as they fall below the level of the tuyeres. It forms a short prolongation 

 from that point of the lower inverted cone. From the boshes upward the width 

 gradually decreases to the tunnel-head, which varies from 7 to 9 feet in diameter, 

 according to the size of the furnace. The hearth is generally a cube, from 2^ to 3 

 feet square. The air is introduced by one, two, or three small apertures, called 

 tuyeres. When two tuyeres are used, the orifices of their blow-pipes are about 3 

 inches in diameter, and the pressure of the blast is from 2 to 3 lbson the square 

 inch. To prevent the tuyeres from being melted by the intense heat to which they 

 are exposed, a stream of cold water is caused constantly to flow round their nozzles 

 by an arrangement which will be immediately understood by an inspection of fig-. 

 1221, which represents a sec- 

 tion of a tuyere nozzle thus 1221 

 protected, the cold water en- 

 tering the casing by the tube 

 a, and the hot water run- 

 ning off by the tube b. The 

 upper part of the furnace 

 above the boshes is called 

 the cone or body. It is 

 formed by an interior lining 

 of fire-brick, about 14 inches 

 in thickness, between which 

 and the exterior masonry is a casing of fine refractory sand compactly rammed in, 

 air-holes being left for the escape of aqueous vapour. In the base of the furnace 



3 P 2 



