Kjeldahl, Johann Gustav Christoffer

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Kjeldahl, Johann Gustav Christoffer

(b. Jagerpris, Denmark, 16 August 1849; d. Tisvildeleje, Denmark, 18 July 1900)

analytical chemistry.

Kjeldahl’s father was district physician in his native village on the island of Sjaelland; his mother was Johanne Lohmann. He received his schooling at the Gymnasium in Roskilde and then studied chemistry at the Technological Institute in Copenhagen. He passed his state examination “in applied science” with distinction in 1873 and became an instructor at the Agricultural College. There he became acquainted with J. C. Jacobsen, the owner of the Carlsberg brewery, who hired him in 1875 to set up a laboratory for making various technical analyses. Jacobsen soon established the Carlsberg Foundation which helped to found the Carlsberg Laboratory, a scientific research institution. In 1876 Kjeldahl was appointed the director of the laboratory, and he held this position until his death.

Kjeldahl’s name is known above all for the “Kjeldahl method” for the estimation of nitrogen in organic substances. This discovery, of such great value in analytical chemistry, was first made as an auxiliary step in his efforts to develop a method for use in experiments in agricultural chemistry. Yet his method of nitrogen determination is of far greater importance than all of his results in agricultural chemistry. Kjeldahl realized the problem involved in nitrogen determination while investigating protein transformation in beer fermentation.

Lavoisier thought that organic substances consisted solely of carbon, hydrogen, and oxygen, while Berthollet found in 1786 that certain substances of animal origin contained nitrogen. After the experiments of Gay-Lussac and Thénard, Dumas finally succeeded in 1831 in creating a practical method of nitrogen determination, one which required burning and gasometric measurement. As is evident from the contemporary literature, Dumas’s method was “a torment for everyone” because it was so complicated. A suitable wet method had long been sought to replace Dumas’s combustion method. In 1841 Franz Varrentrapp and Heinrich Will created a method in which the substance was heated with barium hydroxide, nitrogen was converted into ammonia, and latter was conducted into hydrochloric acid and precipitated with platinic chloride. Although this procedure was indeed an advance, it was also rather inexact, time-consuming, and costly.

Kjeldahl attacked the problem systematically, starting from James Wanklyn’s observation that under certain conditions potassium permanganate converts the nitrogen in organic bodies into ammonia. This phenomenon, however, occurs only very irregularly. Kjeldahl found that in concentrated sulfuric acid the oxidation and conversion through permanganate take place regularly and quantitatively, and he determined the amount of ammonia by titration. He reported his method to the Chemical Society of Copenhagen on 7 March 1883 (Zeitschrift für analytische Chemie, 22 [1883], 366).

He later added phosphoric acid in order to convert those nitrogenous compounds that had resisted the original method, but this measure was only partially successful. The “Kjeldahl flask” which he constructed in 1888 to simplify the method is still in use today.

Kjeldahl’s method is extremely important for agriculture, medicine, and drug manufacturing, and it is still universally employed in its essentially unmodified original form.

Mention should also be made of Kjeldahl’ work on sugar-forming enzymes. He reported on a previously unrecognized polysaccharide (amylan) in barley, and conducted experiments to distinguish among various kinds of sugar. Although the latter attempt was unsuccessful, he improved the values that were assigned to the reducing capacities of various sugars in the tables employed in analytic calculations.

In 1890 Kjeldahl was elected to the Danish Society of Sciences. Although subject tomorbid depression, he was nevertheless capable of undertaking steady, although increasingly less extended, research, and in his last years he occasionally had to stop working completely. He traveled a great deal for reasons of health, and died of a heart attack while bathing in the sea.


I. Original Works. Kjeldahl’ publications have not been compiled. His most important paper is “Neue Methode zur Bestimmung des Stickstoffs in organischen Körpern” in Zeitschrift für analystische Chemie, 22 (1883), 366; for his work on sugar-forming enzymes see Meddelelser fra carlsberg Laboratoriet, 4 (1895), 1.

II. Secondary Literature.See W. Johannsen, “Johann Kjeldahl,” in Berichte der Deutschern Chemischen Gesellschaft, 33 (1900), 3881; R. E. Oesper, “Johan Kjeldahl and the Determination of Nitrogen,” in Journal of Chemical Education, 11 (1934). 457; St. Veibel, “Johan Kjeldahl” in Journal of Chemical Education, 26 (1949), 459; H. Lund, “Scandinavian Contributions to Chemistry,” in Selecta chimica12 (1953), 3; A. J. Ihde, The Development of Modern Chemistry (New York, 1964), p. 296; and F. Szabadváary, History of Analytical Chemistry (Oxford, 1966), p. 298.

Ferenc SzabadvÁry