WILLIAM SIEMENS, F.R.S. 2QI 



steam or for heating the air blown into the blast furnaces ; but 

 fliis utilization represents only a small proportion of the value of 

 the coke or charcoal charged with the ore into the furnace ; 

 whereas a much cheaper material might be employed for the pur- 

 poses just named. The introduction of hot blast was unquestion- 

 ably a very great improvement in blast furnace economy, because 

 the heat thus introduced is obtained by means of the perfect com- 

 bustion of fuel, and, in reducing the combustion necessary within 

 the furnace, the quantity of products of combustion as compared 

 to a unit quantity of ore is greatly reduced, the effect being that 

 the incoming ores have a relatively greater capacity for absorbing 

 the sensible heat from the products of combustion, which latter 

 must therefore issue from the top of the furnace at a lower 

 temperature. 



Relying upon this argument, I am inclined to believe that the 

 consumption of coke in a blast furnace must materially diminish 

 with increased temperature of blast without limitation of degree, 

 and in this respect I venture to differ from my friend Mr. 

 Lowthian Bell, who maintains that mere increase of capacity of 

 furnace up to a certain limit produces the same effect as increase of 

 temperature of blast, and that no beneficial effect can be obtained 

 by increasing the temperature of blast beyond 515 C. In taking 

 however, the best examples of blast furnaces, the products of com- 

 bustion escaping from the top, four parts out of five, as CO with- 

 out counting the N, and at not less than 350 C. of sensible heat, 

 carry with them fully two-thirds of the heat they would be capable 

 of producing, if they were burnt to carbonic acid. 



In my former lecture I described a plan of reducing iron oxides 

 by feeding them, mixed with carbonaceous materials, into a rever- 

 beratory furnace through inverted hoppers of fire-clay, the inten- 

 tion being to effect the reduction of the iron ores into spongy 

 metal during their descent, and the fusion of the spongy metal so 

 produced on the open hearth of the furnace, pig metal being used 

 to facilitate the fusion. It was found, however, that the quantity 

 of heat that had to be transmitted through the sides of the fire- 

 clay hopper was so great that the process of reduction proceeded 

 very slowly, and the hoppers themselves were rapidly destroyed by 

 the intense heat of the furnace. The reduction of the metallic iron 

 in closed chambers of this or any other form which I have tried 



u 2 



