General view of R.J. Connor photographing the spectrum of active nitrogen at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. In chemistry, "spectrum" commonly refers to the characteristic wavelengths of electromagnetic radiation (or a portion thereof) that is emitted or absorbed by an object or substance.

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.