THE ORGANIC MATTER OF THE SOIL 138 



acid, humic acid, or crenic acid exist in the soil, one name 

 has persisted in soil literature — that of humus and 

 humic acid. The word humus, as already indicated, 

 does not relate to any definite compound, but to the 

 great mass of primary and secondary products of bio- 

 logical and chemical organic decay taking place in the 

 soil. One of the men whose work established beyond 

 a doubt the fact that humus was not a definite compound 

 was Van Bemmelen. 1 His investigations still further 

 showed that the soil humus was largely in a colloidal 

 condition, and therefore exhibited properties quite dis- 

 tinct from those shown by crystalloids. 



In recent years investigation has again been directed 

 toward the immense field opened by the overthrow of 

 the Mulderian school. Baumann, 2 by his researches, 

 has shown freshly precipitated humus to possess properties 

 which are largely colloidal in nature. Among these char- 

 acteristics are high water capacity, great adsorptive power 

 for certain salts, ready mixture with other colloids, power 

 to decompose salts, great shrinkage on drying, and coagula- 

 tion in the presence of electrolytes. Jodidi 3 has studied 

 the composition of the acid-soluble organic nitrogen in 

 peat and in mineral soils. The nitrogenous compounds 

 thus obtained can be divided into the following 

 groups : — 



1 Van Bemmelen, J. M. Die Absorptions Verbindungen 

 und das Absorptionsvermogen der Ackererde. Landw. Ver- 

 suchs. Stat., Band 35, Seite 67-136. 1888. 



2 Baumann, A. Untersuchungen iiber die Humussauren. 

 Mitt. d. K. bayr. Moorkulturanstalt, Heft 3, Seite 53-123. 

 1909. 



3 Jodidi, S. L. Organic Nitrogenous Compounds in Peat 

 Soils I. Mich. Agri. Exp. Sta., Tech. Bui. 4, November, 1909. 

 Also, The Chemical Nature of the Organic Nitrogen in Soil. 

 Iowa Agr. Exp. Sta., Research Bui. I, June, 1911. 



