372 APPLIED SCIENCE 



413. Action of the Fluxes. When the fuel is burning, a 

 strong blast of hot air of a temperature of 1200 F. is forced 

 through the tuyeres (pronounced iweers) at the bottom of the 

 furnace. The blast of air acts on the burning fuel causing 

 an intense heat which gradually melts the iron. In order to 

 make the iron ore melt easily, limestone called a basic flux 

 or sand, an acid flux, etc., is added to the coke fuel. The 

 flux combines with the earthy materials of the ore and causes 

 them to melt at a lower temperature. When the iron ore con- 

 tains a great deal of limestone it is said to be basic in character 

 and sand is used as a flux ; when the ore contains clay, the flux 

 must be of a limestone nature. In each case, the sand, clay, 

 and limestone unite at a red heat to form a salt called slag. 



The space inside the blast furnace below the tuyeres is 

 called the crucible. Here the metal separates from the slag. 

 Immediately above the crucible, the diameter of the furnace 

 is made wider to provide for the contraction in the volume of 

 the charge before melting. The sides of the furnace slope 

 gradually from the top to allow for the expansion of the 

 charge as it heats up before fusing. When the flux unites 

 with the earthy material (called garigue) of the ore it forms a 

 glassy matter (called slag), setting free the iron. As the iron 

 melts or fuses, its high specific gravity causes it to fall to the 

 bottom of the furnace. When a suitable quantity has ac- 

 cumulated it is allowed to flow out of a tap-hole onto a sand 

 bed along a large groove called a sow, from 'which at right 

 angles it enters smaller grooves or hollows, forming the molds 

 for the pigs. When the iron cools it is broken up into lengths 

 suitable for shipping to foundries and is known as pig iron. 



414. Chemistry of the Blast Furnace. The glassy slag 

 is formed by the combination of the alumina, silica, and lime 



