Close-up view of molten slag emerging from the phosphoric acid furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. The slag consists of waste produced during the furnace acid process. One of the first commercial techniques for making phosphoric acid, the so-called furnace acid process dates back to the 1890s and is a high-temperature, energy-intensive process that uses large amounts of electrical energy to separate phosphorus from phosphate rock.

The Fixed Nitrogen Research Laboratory (F.N.R.L.) was established at American University in 1919 under the directorship of Arthur B. Lamb. Initially part of the War Department, the F.N.R.L. was the successor to several wartime initiatives to develop a secure domestic supply of nitrate compounds necessary for the manufacture of explosives during World War I. With a staff of about 110 individuals, including 35 to 50 chemists, the F.N.R.L. focused on the manufacture, production, and development of products of atmospheric nitrogen, including munitions and fertilizers.