12 



nitrogen by the action of nitrous acid. Dojarenko (1902) working 

 with humus from seven Russian soils found appreciable quantities 

 of amino nitrogen. Unlike previous investigators he determined 

 the amount present quantitatively, and assumed all of the 

 amino nitrogen was present as amino acids. He also made deter- 

 minations of the ammonia by distillation with magnesium oxide, 

 and obtained the amide nitrogen by hydrolysis with dilute hydro- 

 chloric acid and subsequent distillation of the ammonia formed 

 with magnesium oxide. 



B. The Humus Theory of Grandeau. 



A tremendous impetus was given to the study of soils by the 

 work of Grandeau, because he believed that the ammonia extract 

 of soils contained the nutritive substances essential for the life 

 of the plant and for the fertility of the soil. The theory that the 

 humus extract was of such value had a great deal to do with re- 

 tarding the development of the study of the organic matter of the 

 soil. 



The method of Grandeau (1872) is essentially the one in use 

 at the present time in America for the determination of humus. He 

 elaborated a method for the estimation of the "matiere noire" of 

 the soil by first leaching the soil with dilute acid in order 

 to set the humus free from its combination with the alkaline earths, 

 removing the excess of acid by washing with water, then moisten- 

 ing the soil with ammonia and allowing it to stand for a short 

 time (three to four hours, cf. Grandeau 1877, p. 149), after which 

 the humus solution was displaced by repeated washings with am- 

 moniacal water. The dark brown solution so obtained was evapor- 

 ated to dryness in platinum, weighed, ashed, and the amount of 

 "matiere noire" and of ash recorded. Grandeau regarded the humus 

 ash as an integral part of the humus. He believed that the organic 

 matter which dissolved was responsible for the fertility of the soil, 

 apparently not so much because of the carbon and nitrogen con- 

 tent, as for the high percentage of phosphoric acid and potash in 

 the humus ash. 



The views of Grandeau w r ere never generally adopted in Eu- 

 rope although often accepted by individual workers, but have been 

 more generally accredited in America, due to the sponsorship of 

 certain parts of Grandeau's humus theory by the late Professor 

 Hilgard. The American investigators, e. g., Hilgard (1906), Ladd 

 (1898), and Snyder (1895, 1897, and 1901), however, do not report 

 the humus ash as an integral part of the humus but call only the 

 volatile portion humus. They consider that the humus is, in part 

 at least, combined in the soil with inorganic substances ; these 

 compounds are called "humates" and to their abundance and pro- 

 duction has been ascribed an important part of the maintenance 

 of soil fertility. 



Hilgard (1906) regarded the humus of the soil as a definite soil 

 product, formed from vegetable material in the soil under the in- 

 fluence of fungus and bacterial growths ; this conversion being 



