Blast Furnace

Three rivers - the Allegheny, Monongahela, and Ohio - join in Pittsburgh, making the city a natural site for the building of bridges. But the Smithfield Street Bridge stands apart from other Pittsburgh bridges for several reasons: it replaced structures by two well-known bridge engineers, Lewis Wernwag and John A. Roebling; it was the first use in America of the lenticular - or lens-shaped - truss design; and it was one of the first major bridges in the U.S. built primarily with steel.

When erected by Peter Grubb to smelt the rich iron ore of the nearby Cornwall ore banks, this stone-built blast furnace was typical for its time, producing about 20 tons of pig-iron and cast-iron products a week. A major reconstruction in 1856 to 1857 produced important changes: the furnace itself was enlarged; the blast-air bellows were replaced by a pair of wooden cylinder "blowing tubs"; the waterwheel that had powered them was replaced by a 20-horsepower steam engine; and a pair of waste-heat boilers to supply the engine was built into the open stack of the furnace.

These engines, built by Cooper & Co., of Mount Vernon are among the oldest surviving agricultural steam engines to show the evolution from the portable, skid-mounted engine (ca. 1860) to the horse-drawn engine (1875), through the self-propelled but horse-guided engine (1875) and finally to the self-propelled, self-steered traction engine (1883). Such engines powered the conversion to mechanized farming, which was a great hallmark of the Industrial Revolution.