Nature and Distribution of Humic Matter
Most of the pioneers in humic science named above are also chemists, physicians (medical doctors), or pharmacologists. Both Achard and Vauquelin were not researching humic acids but were looking for chemicals. Vauquelin, for example, was a pharmacologist and was looking for therapeutic pharmaceuticals for treatment of ulcers and cancers as can be noticed from the title of his published report (Vauquelin, 1797). Using the brown cell sap, called scientifically exudates, of elm trees, he succeeded apparently in isolating a black substance that he called ulmin (from Ulmus sp. the Latin name for elm trees), providing fuel for the present-day idea of formation of humic compounds within live plant bodies, as indicated above. In solid condition, this substance, called ulmin, is insoluble in water and assumes physical characteristics reflecting a shiny metallic black luster, similar to humic-like compounds obtained earlier by Achard from the alkali extraction of peat (Achard, 1786). Sprengel (1826), on the other hand, was at first indeed studying humus and its influence on plant nutrition and growth. He is known for the distinction of humus into acid and mild humus as
discussed earlier in Section 188.8.131.52. However, at a later stage, he apparently abandoned his humus theory and developed the inorganic or mineral theory in plant nutrition. Sprengel was credited, in fact, for being the first to formulate the law of the minimum in plant nutrition. Liebig has allegedly only popularized this fundamental law, and proposals are recently floated around to rename the law as the Sprengel-Liebig law of the minimum (Van der Ploeg et al., 1999).