The Early Years of the Kjeldahl Method to Determine Nitrogen *

In 1883, in Fresenius' Zeitschrift fur analytische Chemie, there appeared a paper by Johan Kjeldahl of the Carlsberg Laboratory in Copenhagen entitled "A new method for the determination of nitrogen in organic substances."35 This contribution has had an effect upon analytical chemistry in general and especially upon the application of analytical chemistry to agricultural and physiological chemistry that marks it as one of the truly great achievements of science. Only 8 years later, in 1891, Kebler34 prefaced a paper in which he gave a detailed bibliography of the Kjeldahl method, with the statement, "In the history of analytical chemistry, no method has been so universally adopted, in so short a time, as the 'Kjeldahl method' for the estimation of nitrogen." Kebler's bibliography contains no less than sixty titles distributed through many journals. Most of these had also been discussed by Fresenius in the Zeitschrift, often to a length of several pages. To understand the enthusiasm with which the new method was greeted, it is necessary to recall the situation that the investigator of the period faced. It was recognlized that judgments upon the nutritive value of foods for animals and of fertilizers for plants, and upon problems in the metabolism of both animals and plants, as well as the chemical identification of pure nitrogenous compounds all rested upon the analytical determination of nitrogen. For this purpose two fundamental methods were available, the combustion methods of Dumas and of Will and Varrentrapp. Both of these methods had been extensively modified and were almost continually under study in various laboratories (see, e.g., Kreusler40), but both required the services of trained and expert chemists and, although highly accurate, they were slow and extremely inconvenient. The advent of a new principle and of a new technique applicable alike to pure sulbstances, to crude mixtures, and albove all to solutions, and