ASME-Landmark:Nassawango Iron Furnace

The Nassawango iron furnace, built in 1828, was one of hundreds of furnaces that thrived and failed in the 19th century. The Maryland Iron Company (incorporated 1828) built this furnace along the Nassawango Creek roughly four miles northwest of the Pocomoke River to produce pig iron by the cold-blast process. In 1836-1837, the furnace changed ownership several times, until Thomas Spence of Worcester County purchased it and began producing pig iron at a rate of 700 tons a year. Spence is credited with the installation of the hot-blast stove in 1835. Iron was produced at Nassawango until 1847, when labor shortages and poor market conditions forced Spence to shut down the furnace. Lying idle and becoming overgrown, the furnace property was eventually donated in 1962 to the Worcester County Historical Society.

The Nassawango iron furnace is structurally typical of its period while distinctive in several ways: it smelted bog ore; it is principally of brick rather than stone; and, of greatest significance, it is the earliest surviving American furnace that employed the "hot blast." In a hot blast furnace, the combustion process is accelerated by heating (by means of waste gasses) air through a heat exchanger (stove) before it enters the tuyeres (air nozzles), where it is blasted into the furnace. The hotter furnace temperatures decrease the amount of charcoal fuel needed to reduce iron ore. This process—now universally used—greatly increased the production of pig iron at the Nassawango iron furnace. See ASME website for more information