290 THE SCIENTIFIC PAPERS OF 



prove to you that upon theoretical grounds the blast furnace is 

 open to very grave objections, inasmuch as it produces iron com- 

 bined with nearly all the objectionable substances contained in 

 the materials used, that only expensive fuel, such as coke, can be 

 employed, and that its combustion is necessarily imperfect. 



Plate 45 shows the distribution of temperature in the blast 

 furnace, as given by Mr. Lowthian Bell in a paper read by him 

 before the Institution of Civil Engineers, in 1872. 



It shows that the reduction of the metallic oxides to spongy 

 iron is accomplished within the first 20 feet of their descent 

 in the furnace, and at a comparatively low temperature. This 

 upper zone is followed by one where the limestone is decom- 

 posed and the carburisation of the spongy metal is commenced. 

 Between this second zone and the zone of fusion in the boshes of 

 the furnace a zone of great magnitude intervenes, where apparently 

 no other change is effected than an increase of temperature of the 

 spongy metal, but where in reality a very powerful reducing action 

 is accomplished of substances which had much better not be joined 

 to the iron. It is well known that almost all the phosphorus con- 

 tained in the iron-stone, the lime-stone, and the coke is here 

 incorporated with the spongy iron. The silica is reduced to its 

 metallic condition, and, together with sulphur, arsenic, and other 

 bases which may be present, combines with the iron. The final 

 action in the blast furnace consists only in fusing those reduced 

 substances and forming the slags which envelop and protect the 

 fused metal. 



As regards the fuel question, it will be observed that the result 

 of the combustion in the blast furnace is for the most part car- 

 bonic oxide, and that the heat developed in this combustion 

 amounts to only 2,400 heat units per pound of pure coke con- 

 sumed, whereas a perfect combustion (to carbonic acid) of the 

 same coke would be attended by the development of 8,000 heat 

 units. It is practically impossible to obtain more than one-fifth 

 of carbonic acid to the carbonic oxide issuing from the top of the 

 blast furnace, and taking also into account that the gases leave 

 the top of the blast furnace at 350 C., it may fairly be asserted 

 that only one-third of the heat-producing power residing in the 

 coke is utilised. A portion of the heat thus left undeveloped may 

 .be used, it is true, in burning the gases for the generation of 



