Kjeldahl flask

This Kjeldahl flask was made by Schott & Genossen. In 1883 Danish chemist Johan Kjeldahl (1849–1900) of the Carlsberg Laboratory published the Kjeldahl method. It was the first accurate, simple, and speedy way to determine nitrogen content in organic matter.
Kjeldahl’s employer, Carlsberg Laboratory, had been originally established as a place for scientific research to perfect the process of beer making. Later, the laboratory took on a broader mission to contribute to pure research. The need for the Kjeldahl method grew from his analysis of the protein content of grains for beers at different stages—from germination to fermentation as beer wort. Analyses of nitrogen content can be used to quantify the amount of protein in a sample, and protein content of grains influences the volume of beer they produce.
The Kjeldahl method proved to have wide-ranging applications and was quickly adopted by scientists from a variety of fields. In the mid-2010s, the method (with minor modifications) was still in use for purposes ranging from analysis of protein in foods to nitrogen content in soil samples. To “Kjeldahl” a sample has become a verb in chemical parlance, considered by some the greatest honor bestowed by the chemical community.
Along with his method, Kjeldahl’s name also became attached to a piece of laboratory equipment he developed in 1888. The long-necked, round-bottomed flask was ideal for avoiding splashback when heating solutions. Splashback was a threat during the first step of the Kjeldahl method—which requires heating the sample in concentrated sulfuric acid.
Glastechnisches Laboratorium Schott und Genossen (Glass Technology Laboratory, Schott & Associates), later the Jenaer Glasswerk Schott & Gen. (Jena Glassworks, Schott & Associates), was founded in 1884 by Otto Schott (1851–1935), Ernst Abbe (1840–1905), Carl Zeiss (1816–1888), and Zeiss' son Roderick.
In 1881 Schott, a chemist from a family of glassmakers, and Abbe, a physicist with an interest in optics, formed a research partnership. Together they hoped to perfect a chemical glass formula for lenses in optical instruments like microscopes and telescopes. Their original goal was to develop glasses of high quality and purity with consistent optical properties. As their research expanded, they eventually developed the first borosilicate glasses. Their strength against chemical attack and low coefficient of thermal expansion made them better suited to the harsh circumstances of the chemical laboratory than any other glass.
Jena Glass quickly became a success among the scientific community, widely considered the best on the market until World War I.
Baker, Ray Stannard. Seen in Germany. Chautauqua, N. Y.: 1908. http://hdl.handle.net/2027/nyp.33433043165608.
Burns, D. Thorburn, and W. I. Stephen. “Kjeldahl Centenary Meeting.” Analytical Proceedings 21, no. 6 (1984): 210–20. doi:10.1039/AP9842100210.
Cauwood, J.D., and W.E.S. Turner. “The Attack of Chemical Reagents on Glass Surfaces, and a Comparison of Different Types of Chemical Glassware.” Journal of the Society of Glass Technology 1 1917): 153–62.
Hovestadt, Heinrich. Jena Glass and Its Scientific and Industrial Applications. London, New York: Macmillan, 1902.
Pfaender, H. G. Schott Guide to Glass. Springer Science & Business Media, 2012.
Sáez-Plaza, Purificación, Tadeusz Michałowski, María José Navas, Agustín García Asuero, and Sławomir Wybraniec. “An Overview of the Kjeldahl Method of Nitrogen Determination. Part I. Early History, Chemistry of the Procedure, and Titrimetric Finish.” Critical Reviews in Analytical Chemistry 43, no. 4 (2013): 178–223. doi:10.1080/10408347.2012.751786.
Sella, Andrea. 2008. “Classic Kit: Kjeldahl Flask.” Chemistry World. http://www.rsc.org/chemistryworld/Issues/2008/May/KjeldahlFlask.asp.
Walker, Percy H. Comparative Tests of Chemical Glassware. Washington, D.C.: 1918. http://hdl.handle.net/2027/mdp.39015086545707.
Currently not on view
Object Name
date made
after 1884
Schott and Genossen
overall: 12 in x 3 1/2 in; 30.48 cm x 8.89 cm
ID Number
catalog number
accession number
Science & Scientific Instruments
See more items in
Medicine and Science: Chemistry
Science & Mathematics
Science Under Glass
Data Source
National Museum of American History, Kenneth E. Behring Center


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