Close-up view of the mounting frame and driving mechanisms of the fertilizer distribution testing apparatus used in the U.S. Department of Agriculture's Fertilizer Machinery Laboratory located at the Arlington…

General view of assorted equipment and apparatus in the Constant Humidity Room at the the U.S. Department of Agriculture's Fertilizer Machinery Laboratory located at the Arlington Experimental Farm in Rosslyn…

General view of the indoor soil track used in the U.S. Department of Agriculture's Fertilizer Machinery Laboratory located at the Arlington Experimental Farm in Rosslyn [Arlington], Virginia. Measuring 9 feet wide by 70…

General view of the air-conditioning equipment used in the U.S. Department of Agriculture's Fertilizer Machinery Laboratory located at the Arlington Experimental Farm in Rosslyn [Arlington], Virginia. This particular…

General view of the fertilizer distribution testing apparatus used in the U.S. Department of Agriculture's Fertilizer Machinery Laboratory located at the Arlington Experimental Farm in Rosslyn [Arlington], Virginia. The…

Exterior view of the U.S.D.A.'s Agricultural Engineering Laboratory located in Beltsville, Maryland. The laboratory was predominately used for practical investigations related to plants and fertilizers in support of the…

General view of the machine shop at the U.S. Department of Agriculture's Fertilizer Machinery Laboratory located at the Arlington Experimental Farm in Rosslyn [Arlington], Virginia. Established by an act of Congress in…

Exterior view of an unidentified United States Department of Agriculture building. The building is believed to be part of the U.S.D.A.'s Agricultural Engineering Laboratory facility located in Beltsville, Maryland.

Exterior view of the Fertilizer Machinery Laboratory at the Arlington Experimental Farm in Rosslyn [Arlington], Virginia. Established by an act of Congress in April 1900, Arlington Farm served as the main field…

Two views of the component parts of an apparatus used to grow higher plants in a sterile medium at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C.

The Fixed Nitrogen…

Two views of culture samples used to study the effect of boric acid on the production of nodules upon the roots of soy beans grown under pure culture conditions at the U.S. Department of Agriculture's Fixed Nitrogen…

General view of culture samples used for an experiment to determine if corn can secure its nitrogen from the air if grown in the presence of nitrogen-fixing bacteria. This experiment was conducted at the U.S.…

Two views of a thermocouple apparatus and assorted components, including a micro-spot welder and soldiering pencil, at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. …

General view of an apparatus used for the spectroscopic study of the mechanism of nitrogen fixation in the electric arc at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington,…

Two views of assorted apparatus at the Fixed Nitrogen Research Laboratory's Urea Plant. Urea is a water-soluble powder form of carbonic acid frequently used as a fertilizer and feed supplement. The individuals present…

Two views of Dr. Kuentzel studying the thermal and catalytic decomposition of azomethane at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C.

The Fixed Nitrogen…

Four assorted views of a thermostat and equipment used to determine the compressibility of gas at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. In chemistry,…

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…

Close-up view of the assembly of an apparatus used for sterile cultures of taller green plants at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C.

The Fixed Nitrogen…

Close-up view of a sterile culture of small phanerogams, also known as spermatophytes or seed plants, at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. The…

Close-up view of an alsike clover plant at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C. Notably, the root of the plant is growing from the pedicel (i.e. the stem…

General view of the microapparatus and assorted laboratory equipment used to study bacterial nitrogen fixation at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C.…

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 an apparatus used to grow plants under sterile conditions at the U.S. Department of Agriculture's Fixed Nitrogen Research Laboratory located in Washington, D.C.

The Fixed Nitrogen Research Laboratory…

General view of assorted apparatus used in the Steel Corrosion Laboratory at the U.S. Department of Agriculture's Fixed Nitrogen Research facility located in Washington, D.C. Apparatus include a constant volume…