Close-up view of an ultrasonic oscillator with a soil suspension and view of the driving transformer and oil bath containing piezoelectric quartz crystal. This oscillator was used at the U.S. Department of Agriculture's…

Close-up view of the Warburg-Barcroft microrespiration apparatus used to study bacterial nitrogen fixation at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C.

The…

General view of the control panel for the experimental blast furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. The individual visible in the photograph is…

Assorted views of slag being tapped from the experimental blast furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. The individuals visible in the photographs…

General view of the gas-fired smelting furnace used to volatilize (i.e. cause to evaporate or disperse in vapor) potash at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington,…

General view of machinery used to crush ore at the Fixed Nitrogen Research Laboratory's blast furnace plant. A worker identified as "Parker" is seen transferring raw material, presumably ore, from a machine into a…

General view of storage piles of raw material, including greensand, leucite, coke, and limestone, used in the experimental blast furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located…

Three views of Mr. Royster (left) and Travis Hignett (right) tapping slag from the experimental blast furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. Mr.…

General view of Travis P. Hignett (left) and Mr. Royster (right) reading the temperature inside the experimental blast furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in…

General view of Travis P. Hignett examining blowing engines for the experimental blast furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C.

The Fixed Nitrogen…

General view of Travis P. Hignett demonstrating use of the blowing engines for the experimental blast furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. A…

General view of an apparatus used to determine the solubility of gases in liquids at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. Visible in the bath of the…

Two views of the construction of the phosphoric acid furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. This furnace was used to make phosphoric acid through…

General view of an unidentified employee operating an apparatus used to produce x-radiation in order to study nitrogen fixation catalysts at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory…

Close-up view of molten slag emerging from the phosphoric acid furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. The slag consists of waste produced during…

General view of a large-capacity constant temperature bath with a removable glass front used at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C.

The Fixed Nitrogen…

General view of a phosphoric acid furnace in use at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. Phosphorus fumes and molten slag are seen emerging from the furnace…

General view of a phosphoric acid furnace in use at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. Phosphorus fumes are seen emerging from the furnace as part of the…

General view of the hot blast stove, a component of the phosphoric acid furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. The individuals visible in the…

Close-up view of Travis P. Hignett using an optical pyrometer to measure the combustion temperature of coke in the blast furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in…

General view of a glassblower, identified as L. Testa, working in an unidentified U.S. Department of Agriculture facility. Per a 1931 list of technical workers in the Department of Agriculture, Testa worked as a…

Two views of the Royster stoves used for the No. 2 experimental blast furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. According to notations accompanying…

General view of the carbon tube precipitator and spray tower for the experimental blast furnace at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C.

The Fixed Nitrogen…

Two views of the No. 2 furnace and stock piles at a U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory plant. The stock piles likely contained a mix of raw material, including greensand, leucite, coke,…

Two views of the interior of the Engine Room at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory, with both full and partial views of the blowing engines for the experimental blast furnace.

The…