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The humic substances extracted with a mixture containing 0.1 M each of NaOH and Na4P2O7 were more polymeric, aromatic, and complex than those extracted with 0.1 M aqueous NaOH. Mixture-extracted substances had higher values of extinction coefficients and -COOH contents, but lower values of E4/E6 ratios. Humic acids from Aridic Ustochrept of Hisar had larger particle size and were more aromatic than those from Ustifluvent soils of Morni Hills. The E4/E6 ratio was inversely related with particle weight and volume. The absorption bands of FAs at 1720 and 1280 cm-1 in the IR spectra were sharper than that of HAs, showing that FAs contained more -COOH than HAs. The absorption of light varied in intensity and frequency with the source of humic substances and method of extraction. X-ray diffraction patterns of HAs from three soils showed peaks at 0.75, 0.35, and 0.21 nm owing to their crystalline structures.