These five blast furnaces were the heart of the plant for many decades, with as many as three operating at one time. They ran continuously day and night, seven days a week, and required constant feeding of materials. To make one ton of pig iron, a furnace required 1 ton of coke, 2 tons of iron ore or pellets, ½ ton of limestone, and about 4 tons of heated, pressurized air. Iron ore, a rocky mineral mined from the earth, coke, a high-carbon fuel obtained from processing coal, and limestone, a mineral that acted as a flux and captured impurities in iron, were brought to the furnace in transfer cars and hopper cars, dumped into storage bins below the trestle, and hoisted by skip cars up the inclined track to charge the furnace in layers. Hot, pressurized air was blown into the furnaces, and as the coke burned, the inside of a furnace reached over 3000 degrees Fahrenheit. Hot gases rose through the descending ore, coke, and limestone, left through large pipes, and were cleaned for further use as a fuel.
