CARBOXYL AND PHENOLIC HYDROXYL GROUPS IN SOME ORGANIC SOILS AND THEIR RELATION TO THE DEGREE OF HUMIFICATION

The degree of humification of 17 organic soil samples was determined by the pyrophosphate test of Dawson as described by MacLean et al. (5) and the colorimetric method of Kaila (4). The latter procedure, although more laborious, was preferred because of good replication and exclusion of the personal judgment of an observer.Treatment with HCl–HF solution resulted in a significant reduction in the ash content of most samples; concomitant losses of organic matter were less than 5%. The main effect of the HCl–HF treatment was to free carboxyl groups. By contrast, phenolic hydroxyl groups remained apparently unaffected. Carboxyls appeared to be the most reactive groups in these organic soil samples. Infrared spectra of untreated peats and of mucky peats exhibited bands at 1720 cm−1, indicative of the presence of free carboxylic acid groups. These bands were absent in the spectra of mucks. After the acid treatment, however, infrared spectra of mucks showed new strong bands at 1720 cm−1 and decreased absorption at 1625 cm−1, apparently due to the conversion of carboxylate to carboxylic acid groups.The total carbon, hydrogen, sulphur, and oxygen contents were similar for all samples, but peats and mucky peats tended to contain less total nitrogen than mucks.