General view of a colorimeter used to analyze nitrogen dioxide at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. With regards to chemistry, colorimeters are used to measure the absorbance of particular wavelengths of light by a specific solution and should not be confused with the tristimulus colorimeter, which is used to measure colors in general.

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.