Historical Markers
Clinton Furnace Historical Marker
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Clinton Furnace

Pittsburgh Region


Marker Location:
Bessemer Court at Station Square, Pittsburgh

Dedication Date:
September 2, 2004

Behind the Marker

Detail of an abandoned  Bessimer Converter
Pittsburgh: Clinton Furnace, April 15, 2005
Clinton Furnace marked an important advance in increasing the output of bituminous-coke furnaces and spreading these furnaces across Pennsylvania. Clinton Furnace was only the second furnace constructed in Pittsburgh, and the first bituminous-coke furnace. George Anshutz erected a charcoal furnace in present-day Pittsburgh in 1792 but abandoned it two years later. Pittsburgh subsequently became a center for secondary ironworks, such as forges and rolling mills, that finished pig iron produced at furnaces outside the city.

One of the rolling-mill firms, Graff, Bennett and Company, constructed Clinton Furnace in 1859 to integrate its operations backward into iron production. The company initially used coke made from bituminous coal taken from the Connellsville section of the markerPittsburgh coal seam. After its early success, the firm switched to coke made from locally mined coal to reduce costs. The change failed, and Clinton Furnace went back to using Connellsville coke, which had fewer impurities, operated more efficiently, and produced better quality iron.

Clinton Furnace produced 11,000 tons of iron a year. This was an exceptionally high output–more than twice that of the typical anthracite furnace and six times what charcoal furnaces produced on average. Key to Clinton Furnace's huge output was its high blast pressure of eight pounds per square inch. Most furnaces in 1859 drove air under a pressure of three to five pounds per square inch into the bosh where iron ore was smelted. Clinton Furnace's stronger blast greatly improved combustion and output.
Image of the gounds and buildings.
Isabella furnace

Raising the blast pressure was a step toward the later practice of hard drivingiron furnaces, which entailed raising output above the rated capacity of the furnace. The hallmarks of hard driving were boosting the blast pressure as well as increasing the blast temperature and the size of the furnace. The first bituminous-coke furnaces to incorporate all these features were the Lucy and Isabella furnaces, both constructed in 1870 by Pittsburgh ironmasters. These two furnaces were massive, standing seventy-five feet tall as compared to Clinton Furnace, which, at forty-five feet tall, was similar in size to other furnaces in 1859. The Lucy Furnace used a blast pressure of nine pounds per square inch and produced an amazing 26,000 tons of iron in 1874.

Dark oil on canvas of Lucy Furnace with billowing smoking from the stacks. An train engine pulling cars is the left foreground.
Lucy Furnace in Allegheny River Dismantled, by James Bonar, 1932.
After the Isabella and Lucy furnaces proved their value, steel companies adopted the practice of hard-driving bituminous-coke furnaces. Steel firms and ironmasters did not hard drive anthracite furnaces since the structure of anthracite resisted the rapid combustion that hard driving entailed. Instead, steel firms built larger and larger bituminous-coke furnaces with greater blast pressures and hotter blasts, increasing output in the best furnaces to more than 50,000 tons per year by the 1890s.

To further swell output and lower production costs, steel companies developed improved methods of delivering coke and iron ore into furnaces. They replaced the hand-loading of raw materials into the tops of furnaces that dated from the eighteenth century with mechanization that combined skip hoists. They carried materials up the side of the furnace and dumped them into the furnace, with traveling ore bridges that moved iron ore from stockyards to stock houses for transfer to the skip hoists.

The huge bituminous coke furnaces that many steel companies operated by 1900 were a far cry from the bituminous-coke furnaces running when Clinton Furnace went into blast. In terms of output and production costs, they contributed to the advance of bituminous furnaces over anthracite furnaces. In 1875 bituminous furnaces surpassed the output of anthracite furnaces in Pennsylvania. Between 1880 and 1900 the number of furnaces using anthracite or an anthracite/coke mixture fell from 158 to seventy with only 28 percent of the state's total iron-making capacity. On the other hand, seventy coke furnaces accounted for 71 percent of the Commonwealth's iron capacity in 1900, with charcoal accounting for a mere one percent of capacity.

When Graff, Bennett and Company erected Clinton Furnace, few would have envisioned how this step would help transform the iron and steel industries. Opening this furnace was one in a chain of events that contributed to far bigger iron furnaces, the dominance of bituminous-coke furnaces, and the growth of an integrated steel industry, particularly in the Pittsburgh region.
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