Iron^How Manufactured. 151 



23. Thus they keep putting in layers of ore, 

 limestone, and coal until the whole furnace, 

 which is sometimes sixty feet high, is filled up 

 to the top. As the mass sinks down they put 

 :>n more to keep the furnace always full. The 

 fire burns all through this mass, so that the ore 

 is melted ; a part of which mixes with the heat- 

 ed limestone, making what is called slag, and 

 leaving the iron free to run down below. This 

 the iron is sure to do, because it is heavier than 

 all the other things. 



24. The fire in the furnace is kept up day and 

 night, and on Sundays as well, because if they 

 were to allow the fire to go out, it would take 

 about a week to get it in order again. But the 

 same men do not work at it all the time; 

 there are two sets or gangs of them, and their 

 time is arranged so that each gang shall have 

 the same amount of night-work. Twice a day 

 they let the melted iron run out of the furnace 

 and conduct it along narrow earthen gutters 

 into hollows or molds of sand or iron, about three 

 feet long and three inches wide as well as deep. 



25. These, from their lying side by side like a 

 litter of pigs, are called pig-iron. This is again 

 melted to make anything of cast-iron, and is 

 poured into very smooth earthen molds of the 

 desired shape. All our iron stoves are made of 

 such castings. 



