Electrodialysis of the Colloidal Soil Material and the Exchangeable Bases ,-

Recent investigations in the Bureau of Soils have shown that the colloidal material present in any soil contains 10 or more elements in widely varying proportions (19). Various attempts to fractionate the material into substances of more definite composition have not met with much success. However, dialysis of the material indicated that one colloid held about 1 per cent of its constituents less firmly than the remainder. Long-continued treatment apparently removed all the lime, soda, and sulphur but only a small part of the magnesia, potash, and other elements. It was thought that further evidence concerning the firmness with which the different constituents are held in the colloid might be obtained by electrodialyzing the material. Electrodialysis is similar to ordinary dialysis, but is much more rapid and effects a separation of the diffusible ions of opposite charge. The mass of data that has been accumulated on base exchange in soils indicates that the colloidal soil material must contain a fairly definite part of its bases in a reactive condition. It was therefore important to compare the bases that can be removed by electrodialysis with the quantity removable by base exchange with a salt solution. PREVIOUS WORK