IRON 



3058 



IRON 



The Blast Furnace. In ancient times iron 

 was smelted in pots of clay. The ore was 

 broken up and placed in alternate layers with 

 charcoal. Then clay was plastered over all, 

 small holes being left at the top and bottom 

 for the draft; this was originally secured by 



LOADING ORE IN MINNESOTA 



locating the furnace near the top of a hill 

 where the prevailing winds would blow up 

 through it, but later a goat-skin bellows was 

 employed. Softened by the intense heat, the 

 iron would flow through the lighter cinders and 

 waste matter and would drop to the bottom of 

 the furnace and after several hours could be 

 taken out in a lump. This method, however, 

 so imperfectly separated the iron from its ore 

 that in modern England it has been found 

 profitable to smelt the slag (which is the mix- 

 ture of cinders and waste) left from the ancient 

 Briton furnaces. 



The blast furnace of to-day, though much 

 larger and more elaborate than the primitive 

 one, works in a similar way. It is a steel- 

 enclosed cylinder of fire brick perhaps a hun- 

 dred feet high. Into it, after a coke fire has 

 been built, a charge of ore, coke and limestone 

 is poured. The last material is included to 

 bind together the slag so that it will flow out 

 of the furnace. A blast of warm air is blown 

 into the furnace from near the bottom and, 

 together with the gases which the fire separates 

 from the solid materials, passes off through a 

 pipe at the top. Sometimes this combination 

 of air and other gases is then sent through a 

 dust catcher and used as fuel to run the engines 

 which compress the original charge of air. If 

 the fire in a blast furnace is allowed to die 

 out, the charge becomes so solid that no air 

 can again pass through it to smelt it, and 

 the furnace has to be pulled down. 



Below the point at which the air enters the 

 furnace there are two holes, the upper to 



flush out the slag, the lower to let out the 

 heavier molten iron. About every four hours 

 the latter is drawn off, but the slag is tapped 

 more frequently to prevent its rising to the 

 point where the blast of air enters. 



The ordinary charge of a blast furnace con- 

 sists of four parts of ore, two of coke, and one 

 of limestone, through which eight parts of air 

 are forced. From this total only two parts of 

 iron and one of slag result, over half of the 

 solid materials passing off in gases. Coke is 

 the usual fuel, because it is economical and 

 because it will sustain the weight of a heavy 

 charge without being crushed so that the air 

 cannot pass up through the mass. A charcoal 

 furnace could not be more than about forty 

 feet high, but charcoal, because of its different 

 chemical effect, is still superior for smelting, 

 certain qualities of iron. 



Pig Iron. In the older plants the iron as it 

 comes out of the blast furnace flows through 

 a trench of sand into little branch trenches, 

 where it hardens in bars called pigs. In many 

 of the newer foundries the pigs are formed by 

 machinery, the molten metal running into 

 molds which are moved on a chain through 

 cold water and dumped into waiting cars. 

 Pigs are seldom more than ninety-five per cent 

 iron, for they contain in addition carbon, man- 

 ganese, phosphorus, sulphur and silicon, in 

 varying quantities. Each of these elements is 



GREAT LAKES ORE BOAT 

 This type of vessel is built 550 to 600 feet in 

 length. It will carry 10,000 tons of ore. 



described in its proper place elsewhere in this 

 work, and some of their effects upon iron are 

 told later in this article. 



Pig iron might be called the raw material of 

 the iron and steel industry. From it most of 

 our steel and other forms of commercial iron 

 are made. Where steel companies have their 

 own blast furnaces the pig iron is generally put 

 into the converters for transformation into 

 steel while still molten, to save the expense of 

 reheating. 



Cast Iron. The ornamental brackets on 

 school desks and on stoves are examples of 



