In September 1850, Philadelphians George L. Lewis and Samuel Fox Fisher, together with Charles Lennig, a German Quaker and successful chemical manufacturer, chartered the Pennsylvania Salt Manufacturing Company on this site. The location was chosen for its abundant salt and coal, the two main ingredients of soda ash, and for its access to the Pennsylvania Main Line Canal, which from 1829 to 1865 linked the site with eastern and western markets. In 1852 Penn Salt began producing soda alkali for Cincinnati soap-makers and soon introduced Natrona Refined Saponifier, individually packaged caustic soda or lye for home soap making, which brought the company its first profit. That product helped inspire the town's 1862 name change from East Tarentum to Natrona, from the Greek natron, meaning soda. Penn Salt later used cryolite to extract materials used in the 1880s to refine aluminum, and until the plant closed in 1959 it manufactured a wide range of products, including Natrona Oil, bleaching detergents, refrigerants, pesticides including DDT, and chemical defoliants used in the South Pacific during World War II. The company was important to the U.S. war effort, and in 1943 Natrona ranked third on a captured Nazi demolition target list of American sites. The district's distinct character came partly from Penn Salt's Philadelphia and Quaker origins. Natrona developed as a company town that was paternalistic but more benevolent than many western Pennsylvania coal-patch and steel towns: the company paid the rent of families whose fathers served in the Civil War, supplied water, light, and power, and provided land for early churches. Its architecture was also distinctive, especially the Gothic Revival housing on Federal Street. Including the company store, the district's 150 surviving structures were part of a larger complex built by Penn Salt for its workers, with the oldest homes on Federal Street dating to the fall of 1850, and together they preserve one of western Pennsylvania's most enduring and unusual industrial communities.