Blast-furnace

(für'nas.) [A.S. blæst.] (Metall.) A huge structure (Fig. 86) about 50 or 60ft.high, built of ma ive masonry, and lined internally with fire-brick, used in iron-works for smelting iron-stones or ores. Since it would be impo ible to obtain a sufficiently high temperature with the natural draught of this furnace, air is forced into it at the bottom, under a presFig. 86.-BLAST-FURNACE. sure of 3 or 4 pounds upon the inch, through 3 tuyère pipes, the nozzles of which pa through apertures in three sides of the furnace. On considering the enormous quantity of air which pa es through the blast furnace, it will be seen that it occasions the lo of a considerable amount of heat. In order to economize the fuel, hot-blast furnaces are fed with air of which the temperature is raised to about 600° Fahr., by pa ing it through heated iron pipes before allowing it to enter the blast-furnace. The higher temperature which is thus attained permits the use of uncoked coal, which would not have given enough heat in a cold-blast furnace, and the same quantity of ore may be smelted with le than half the coal formerly employed. [s. 97]