The furnaces where iron is melted out of the ores, are tall towers of iron plates bolted together and lined thick with fire clays that will not melt. The furnaces are often as tall as a six or eight story building. They stand together in a group, each one plumed with black smoke and at night with smoky flames. A stranger coming into Chicago or Pittsburg by night, might think these cities had volcanoes from the glow of fire in the sky above the furnaces.

The inside of a blast furnace is the shape of a gigantic bottle turned upside down. An elevated railroad runs from the dumps of ore, coke and limestone in the vast yards to the tops of these furnaces, and from one to another. On a railed balcony at the top of each are men who see that the furnaces are properly filled. A car load of coke is dumped in, then limestone, then ore, making sandwiches of them. More material is put in, in the same order and amounts, until the furnace is filled. A fire is kindled at the bottom, below the small neck of the bottle. Soon the coke is on fire, a blast of warm dry air is forced through the furnace, and everything inside melts together in a white heat, just as the sugar, milk and butter melt together and boil when you make candy.

When a furnace is ready to be drawn a hole at the bottom is opened. Out pours a bubbling, copper-colored river of fire, into a deep ditch of dry sand. Of all the things that were put into the furnace the iron is the heaviest, so the liquid iron falls lowest in the stream, letting the melted rock and ashes rise to the top. Twenty feet or more from the furnace the ditch is dammed. A hole at the base of the dam lets the iron through into a smaller sand canal. The lighter slag flows away on top into slag cars and is carried to dumps.

The iron runs in a golden stream to a great bed of sand under a shed roof. The bed is pitted with holes a couple of feet long and as deep as a man's arm is thick. These pits, or pockets in the sand, are in regular rows. The iron runs down channels into the pockets. Soon the whole bed is a glowing garden. The pools turn to a sulphur yellow, then to gray and silver as they cool. When they are cold they are clubs of iron. They are raked from the sand and stacked in the yards like cord wood. Those clubs are iron "pigs," or pig iron, and are ready to go to market.

Pig iron is bought by factories to turn into rails, bridge and building iron, machines, engines, locomotives, rods, wire and nails, sheet iron, iron plates for war vessels, guns and cannon, farm machinery and tools, knives, and the thousand and one things of iron and steel that the world uses, from carpet tacks to war ships. Pig iron is simply raw material for making many kinds of iron and steel. You know your mother can make ever so many things out of white flour, by mixing different things with it and cooking them in various ways. So pig iron is melted again and made into cast, or wrought or galvanized iron, and many grades of steel, from bridge and rail steel to the finely tempered kinds used in watch springs and razors. It can be cast in molds, rolled into rails and sheets, drawn into rods and wire, and hammered on forges. Some iron works make only locomotives, some sewing machines, some knives and razors, some sheet iron, or wire, or nails, or plows, or stoves. So foundries and mills need a great many of those little iron pigs.

One of the most interesting kinds of iron manufacturing is the making of steel rails in the rolling mills. In Pittsburg and Chicago rolling mills are owned by the same companies that melt the iron out of the ore in the blast furnaces. As soon as the iron pigs are cold they are loaded on cars and sent over a railroad track in the yards to other furnaces to be made into steel. This time they are melted in big, pear-shaped pots fifteen feet high and eight feet across. The pots of thick boiler-plate bolted together, are lined with fire clay and swung on beams so they can be tipped over. As the pig iron in the pot melts, an air blast is forced through and makes it boil furiously. Certain things are put into it to change the iron to steel. As it boils crimson flames leap in the air. The flames turn orange, then yellow, then white, then an electric blue-white. At that point the pot is tipped and the dazzling, blue-white, molten steel is poured into oblong moulds.

Each block, or ingot, of steel has enough in it to make a steel rail one hundred feet long. When the ingot is cold it is sent over the yard railroad again to the rolling mill. There it is heated to a bright red, and as soft, nearly, as putty. Tumbled from the furnace onto a travelling table of iron bars, it is suddenly gripped by enormous iron rollers like some giant clothes wringer with grooves in the rolls, and forced through the grooves. There it is squeezed and lengthened and sent on through one smaller hole after another.

The old forge of Vulcan in the burning mountain could not have been hotter, or full of such thunderous crashes, of quivering air and flying sparks as a modern rail mill. The workmen are big men ; they are stripped to the waist, and streaming with sweat. With long iron rods they turn and push and guide the glowing blocks of steel from one set of rolls to another. They never speak, for no human voice could be heard in the roar and crash. The last rolls begin to shape the lengthened block into a rail with a broad flat bottom, a curved top and grooved sides. It grows longer and longer, and more perfectly shaped, as it nears the end of the journey. At last it is laid on an iron grating to cool.

Today iron and steel are taking the place of wood and brick and stone in building ships, bridges and fireproof skyscrapers. They are used in the finest palace cars, in making oil tanks, service pipes, bath tubs, expanded lath for plastering, pressed sheets for ceilings and walls, and for lining tunnels. The subway, or underground railway in New York is a double steel tube. Bridges and elevators are hung on wire rope. In old, old times men used stone hatchets. That was called the stone age. Then there was a bronze age when copper was made. Our time is called the iron age because we have learned to do so many things with iron. See Iron, Steel, Rolling Mills.