438 



Introduction to the Study of Science 



CHARGING HOPPER 

 / *. . . FLOOR 



HOT AIR 



SLAG 



IRON 



FIG. 143. Diagram 

 of blast furnace. 



impurities from the iron. This is done in blast furnaces (Fig. 

 143) which, constructed of steel lined with fire-brick, are ninety 

 to one hundred feet high and as much as twenty-four feet in 

 diameter. The blast furnace is kept in continuous operation. 

 The raw materials are supplied at the top, 

 and the molten iron removed at the bottom. 

 A modern furnace requires in the course of 

 every twenty-four hours about eight hundred 

 tons of iron ore, four hundred tons of coke, 

 one hundred tons of limestone, and twenty- 

 five hundred tons of air which, heated to 

 1200 F. or 1400 F., is delivered under a 

 gage pressure of eight to sixteen pounds. 

 The iron produced from this charge is usually 

 four hundred tons. How many tons of ore 

 will be reduced in a week? How many 

 tons of coke will be required? How many tons of iron 

 produced ? 



The present method of reducing iron ores is another illustra- 

 tion of the importance of chemistry in modern industry. Until 

 within recent years, ore, coke, and limestone were mixed in 

 accordance with a general recipe which made no account of ore 

 variations or impurities. The iron produced varied in quality, 

 but the recipe remained unchanged. But to-day there is no one 

 recipe for preparing the charges for the blast furnace. The 

 raw materials are subjected to an accurate chemical analysis, 

 and on the basis of the chemical findings proportions of the 

 materials in the mixture are computed. Then all raw materials 

 are weighed and mixed as the analysis requires. The supply 

 to the furnace is exactly controlled. The product is iron of the 

 quality desired. 



The process of reduction. It is the work of the blast furnace 

 to separate the iron from oxygen and from the impurities which 

 the ores may contain. Moisture, organic substances, and carbon 

 dioxid are quickly expelled in the high temperature of the fur- 



