General view of a Brown Potentiometer and other assorted apparatus and machinery used at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. Potentiometers are used to determine variable potential (i.e. voltage) in a circuit, specifically measuring electromotive force (emf) by balancing it with a known emf. The concept was first developed in 1841 by J. C. Poggendorff and improved throughout the 19th century by Latimer Clark and J. A. Fleming.

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.