Close-up view of a lime glass tube, part of an apparatus used to investigate the thermionic emission from platinum films sputtered on glass at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. In chemistry, the term "thermionic" is commonly used to describe a substance or value related to or operated by electrons emitted from materials at high temperatures.

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.