950 



IRON 



1225 



One engine, blowing two furnaces making 750 tons of pig-iron per week, gives 11,500 

 cubic foot of blast per minute, at 30 strokes per minute; but when making '800 

 tons, 32 strokes are required. 



The form of the blast-furnaco 

 from the boshes to the throat is 

 exhibited in jig. 1222 as a trun. 

 cone, and such was formerly in- 

 vnriably the construction ; of late 

 years, however, considerable varia- 

 tions have been introduced. In 

 Scotland the body of the furnace 

 frequently is carried up cylindrical, 

 or nearly so, for a considerable 

 height, terminating with the usual 

 truncated cone to the mouth; in 

 other places a curved line is sub- 

 stituted for a straight one. The 

 form adopted in some furnaces at 

 Ebbw Vale and Blaina is shown in 

 fig. 1224 in vertical section, and in 

 fig. 1225 in horizontal section at the 

 tuyere level. 



The diameter of the throat or 

 filling place is a subject of very great importance to the operations of the furnace. 

 Most iron masters are, we believe, agreed as to the impolicy of the narrow tops for- 

 merly adopted ; the waste of fuel in such furnaces, where the width of the throat 

 scarcely averaged one-fourth of the diameter of the furnace, was very great, the 

 average yield of coal to the ton of crude iron exceeding 6 tons ; by enlarging the 

 throat to one-third, the consumption of coal was reduced to 4 tons ; and by continuing 

 the enlargement to one-half, it was reduced to 2 tons. Mr. Truran states that, on 

 reducing the diameter of the throat of a furnace at Dowlais from 9 feet to 6, the 

 make of pig-iron weekly fell off from 97 tons to an irregular make of from 50 to 70 

 tons ; and that while with the 9-feet throat the consumption of coal was 45 cwts. to 

 the ton of iron, it rose with the 6-feet throat to 70, 80, and 90 cwts., the quality of 

 the iron being exceedingly bad. On enlarging the throat to 9 feet, the make, fur 

 a period of six months, averaged over 160 tons, with a good yield of coal and other 

 materials. Mr. Truran appears to question the utility of reducing the diameter of 

 the furnace at the top, which was only adopted in the first place from an erroneous 

 impression that the furnace could be filled best through a contracted mouth ; but it 

 may be questioned whether this widening of the throat may not be carried too far, so 

 as to disperse the heated gases too rapidly, and whether a diameter much greater 

 than one-half of the largest dimensions of the furnace above the boshes can with 

 utility be adopted. On this subject Mr. Kenyon Blackwell says: 



'If that part of the blast-furnace commencing at the point where it attains its 

 greatest width were continued of the same wide dimensions upwards to its mouth, two 

 objectionable results would ensxie : first, the upper part of the furnace would be cooled 

 by the too rapid dispersion of the ascending column of heated gases, and by the entire 

 absence of the reverberating effect of the contracted mouth ; and, secondly, the mate- 

 rials could not be equally spread from the filling-holes over so wide a surface. The 

 diameter of the upper part of the furnace ought, therefore, to be such as will cause the 

 materials thrown in at the filling-holes to distribute themselves equally in their 

 descent over every part of the sectional area of the furnace, and will produce such a 

 reverberation only of heat as shall be sufficient to expel the water and carbonic acid 

 contained in the materials, without consuming any of the carbon of the fuel, which 

 ought to remain intact until it reaches the lower regions of the furnace, where it is 

 vaporised as carbonic oxide, and produces the reactions on which the reduction of the 

 ore depends.' 



An example of the largest and most improved modern type of blast-furnace a- 

 in the Cleveland district is shown in fig. 1226, which represents one of the Newport 

 furnaces at Middlesbrough in a vertical section. The foundation, up to the ground 

 level, consists entirely of brickwork resting upon clay. From this point a circular 

 base is carried to a height of 7 feet in solid brickwork, mainly of iin>-brick. with a 

 ttone curb all round, on which the supporting columns rest. These columns an- 

 18 feet 6 inches in height, averaging 2 feet 4 inches in diameter, with a thickness of 

 metal of 2 inches. They serve to support the structure from the an^li- of the bosli 

 upwards ; the lower part being carried partly by the wrought-iron conical casing, and 

 partly by the brickwork and stanchions which surround the hearth. The whole of the 



