Abstract
Following the previous report, the author studied the visible and ultraviolet absorption spectra of humic acids in alkaline solutions, which were extracted from paddy rice soils, peats and rotten stump by SIMON'S method. The results are summarized as follows : 1. Absorption curves (log κ-λ curves) of these humic acids were very similar in their shape; and the intensity of light absorption increased generally toward the shorter wavelengths. The curves were nearly straight (Fig. 1). 2. When these curves were expressed on the same concentrations of humic acids (0.01% solutions), they were generally not crossed; and there existed a reciprocal relationship between the intensity of light absorption coefficient at a given wavelength and the inclination of the curve to the axis of wavelength. (Fig. 2 and Table 1) 3. Humic acids having smaller light absorption had a weak absorption band in the ultraviolet region, but this band was not found in the case of those having stronger light absorption (Fig. 1). From these results, it may be reasonably said that the mechanism of light absorption of humic aicds is essentially the same, and the intensity of their light absorption corresponds to their degree of humification, that is, the latter can be shown by their absorption spectra.
