THE HUMIC ACIDS EXTRACTED BY VARIOUS REAGENTS FROM A SOIL: II. INFRA‐RED, VISIBLE, AND ULTRA‐VIOLET ABSORPTION SPECTRA

Abstract

The infra‐red, visible, and ultra‐violet absorption spectra of humic acids extracted from a red‐brown earth by various reagents, are described. The variations in the intensity of various absorption bands in the infra‐red spectra are related to the method of extraction, yield, and titration data. For example, the humic acids extracted by milder reagents give rise to spectra which show relatively weak aliphatic C‐H absorption whilst the intensity of the bands arising from oxygen‐containing groups (carboxyl and ketone carbonyl) is relatively strong. The opposite behaviour is shown by the corresponding bands in the spectra of humic acids extracted by stronger reagents. The intensities of other infra‐red bands are also considered. The optical density of the C═O band at 1720 cm−1 in the humic‐acid spectra and of the carboxylate ion band at 1380 cm−1 in the spectra of the K salt is linearly related to the exchange capacity. The presence of carboxyl groups ionizing above pH 7 and extending to as high as pH 11, is demonstrated. Copyright © 1967, Wiley Blackwell. All rights reserved