Selective Dissolution and Differential Infrared Spectroscopy for Characterization of 'Amorphous' Constituents in Soil Clays

Poorly crystalline inorganic materials were removed from soil clays of different origin and mineral composition by successive treatments with sodium dithionite, 2 % Na 2 CO 3 and 0·5 N NaOH. Techniques are described whereby difference spectra representing the infrared absorption of the materials removed by the treatments can be obtained. These spectra indicate that the materials dissolved are related to the mineral composition of the soil clay. Dissolution of allophanes of different composition was only proved for two volcanic ash soil clays in which these dominated. Layer silicates, probably including kaolin, were dissolved from the clay fractions of the red-brown earth and krasnozem studied. In addition, alumina-rich gel-like material and gibbsite, but no allophanes, were dissolved from another volcanic ash soil clay in which gibbsite and layer silicates are present in considerable amounts.