ESR investigations of humic acids

Investigations of humic acids (HA) extracted from fossil Danish peat and so il samples have confirmed that by the ESR method it is possible to distinguish between HA formed under acid conditions (raised bog peats, mor) and HA originating from more alkaline environments (fen peat, mull), as suggested by Atherton et al. (1967). An analogous classification for recent soils (mor and mull) does not seem to be possible in our case, however, presumably because the samples contain relatively simple organic molecules (originating from partly humified material) in addition to the HA fraction. - With the ESR technique no differences can be observed between diffe rent mor types (coprogenous mor, mycogenous mor), and variation in the degree of humification of raised bog peats seems only to influence the intensity of the ESR signal.