A Physico‐chemical Study of the Propertiesof Humic Acids and Their Changes During Humification

Summary Humic acids extracted from decomposing plant and peat core samples and changes in them during the process of humification were investigated in terms of their elementary composition, the acidity and the equivalent weight, the infra‐red, visible and ultra‐violet spectra and the shape and size of the molecules and their weight. With progressive humification in peat and decomposing plant samples, increases were noted for the carbon content and the aromatic character of the humic‐acid molecules and in the number of their alcohol and ether groups, aliphatic side chains and double bonds, while decreases were observed for the hydrogen content, the molecular weight, the equivalent weight, and the hydrophilic character of the humic acids and possibly to a minor extent also for the ionization constant and the alkoxyl and alkimide groups. It was noticed that the presence of charcoal and, to a minor extent also, of clays in decomposing plant material promoted the formation of humic acids which were very similar to those found in older peat deposits, while the presence of ash did not seem to have much effect. Humic acids derived from different peat materials were found to be very similar in structure and composition, but when different types of plant material were mixed, the humic acids formed during the first stages of decomposition were very similar to those from more decomposed samples containing only the separate components.