ABSTRACT
Humic substances, the dark-colored organic compounds which are present in practically all soils and sediments, have been the object of scientific inquiry for more than 200 years. In the classification of humic substances three different fractions are defined operationally on the basis of their solubility in acid and base: humic acid, fulvic acid and humin. The humic substance fraction which is insoluble in sodium hydroxide, and therefore remains in the soil or sediment after extraction, is called humin. A comparison of the humic acids is isolated by NaOH and by MIBK from a sphagnum bog in Massachusetts. All of the humic acids yield the same fractionation pattern when fractionated on Sephadex gels, and the C-13 NMR spectra of all fractions fit into the same general categories. No doubt, in many instances, the humic substances actually form bilayer membranes around mineral grains; however, in other cases, they are present as vesicles or micelle-like aggregates.
