ABSTRACT
Humic matter as defined earlier is composed of a variety of substances that can be obtained by fractionation on the basis of their solubility in alkaline and acidic solutions. The first humic substances isolated were compounds soluble in bases, acid solution and water. They were extracted in Sweden by Berzelius (1839), who assigned them the names of crenic and apocrenic acids, the fulvic acids of today. This investigation was continued by Mulder (1840), a former student of Berzelius, who in the following years isolated additional humic fractions. On the basis of color and solubility, Mulder (1862) classified them into (1) crenic and apocrenic acid, the yellowish to brown fractions soluble in water, (2) ulmic acid and humic acid, the brown and black fraction, respectively, soluble in alkali but insoluble in acid, and (3) ulmin and humin, the fractions insoluble in alkali, acid and water. Mulder’s accomplishment was followed twenty-seven years later by the discovery of hymatomelanic acid, isolated by Hoppe-Syeler (1889) as the ethanol-soluble fraction of humic acid. Since then no further achievements of major importance can be noticed in the study and isolation of humic substances until Oden’s (1914; 1919) concept surfaces at the start of the twentieth century. Considered by many scientists as based on a more solid scientific foundation, it is in essence a revision of Mulder’s classification. Oden recognizes (1) fulvic acid, which replaces the use of the terms crenic and apocrenic acid, (2) humic acid for the fraction soluble in alkali and insoluble in acid, (3) hymatomelanic acid, a name used earlier by Hoppe-Syeler (1889) for the humic acid fraction soluble in ethanol, and (4) humus coal, for replacing humin and ulmin.
