General view of E.J. Fox demonstrating use of a rotary tunnel to facilitate the absorption of nitric oxides by ground phosphate rock at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. At the laboratory, this process was referred to as the "dry method."

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.