The famous Homestead mills make armor plate for battleships. At Braddock are steel works, where great furnaces turn out enough rails in a year to span the United States from the Atlantic to the Pacific. The great Carnegie Steel Company has its headquarters in the city of Pittsburgh and leads the world in the production of structural steel, steel rails, and armor plate. [Illustration: BLAST FURNACES OF THE CARNEGIE STEEL COMPANY] [Illustration: MINERS AT WORK] Perhaps your knife blade is made of steel manufactured in one of the huge factories in this busy district. The car tracks of your town, the street-car wheels, and the great locomotives, to say nothing of the heavy steel beams and girders of your fireproof buildings, may all be products of this mighty workshop. [Illustration: IN A MODERN COAL MINE] [Illustration: THE ENTRANCE TO A COAL MINE] Pittsburgh coal is used all over the country. The near-by mines form a great underground city, whose dark passageways, far below the surface of the earth, are lighted by tiny electric lights. More than fifteen thousand men find employment in this weird city. Day after day the brave miners go down into the mines, never sure that they will see the sunlight again, for many are the perils of mining. Who has not read of the terrible disasters caused by suffocation from fire damp, by flood, the falling of walls, or the explosion of coal dust? Small particles of coal dust are constantly floating in the mines, and much is stirred up by the cars used to carry the coal to the outside world. A tiny spark may ignite this dust and cause it to explode with terrific force. Sometimes even the presence of much oxygen in the air will make the dust explode, tearing down great blocks of coal which bury the poor miners or stop up the passageways so that there is no escape unless the victims are dug out before they die. [Illustration: SCENE IN A COAL MINE] [Illustration: PITTSBURGH COAL IS SENT ALL OVER THE WORLD] But the world must have coal, for, used for our great boilers, it drives our powerful locomotives, sends mighty vessels plowing across the ocean, and supplies the power which turns the wheels of industry, both great and small. Yes, the world must have coal. So Uncle Sam, in pity for the miners who brave these awful dangers, has bought a mine at Bruceton, a short distance from Pittsburgh. There the government is making experiments to find out the causes of explosion, aiming in this way to protect the miners by lessening their dangers. [Illustration: THE CITY OF PITTSBURGH] Much of the coal is made into coke by burning out certain gases in open-air ovens. Thousands of these ovens are located in the Pittsburgh district, and their fires at night illuminate the country for miles. The coke is used as fuel in the steel furnaces of Pittsburgh, Cleveland, Chicago, and other cities. [Illustration: THE BUSINESS DISTRICT]