Published online by Cambridge University Press: 27 March 2009
1. A historical review of the dye adsorption method for the estimation of soil colloids is presented, and the method is criticised chiefly from the point of view of the isoelectric theory.
2. A procedure for the detection of hydrous alumina in soils is described, involving the demonstration of the isoelectrio point of hydrous alumina by means of preferential dye adsorption in suspensions of various pH values.
3. Satisfactory results were obtained with a mixture of acidic Biebrich Scarlet and basic Iodine Green. The former is adsorbed by hydrous alumina only on the acid side of its isoelectric point, and the latter only on the alkaline side.
4. The characteristics of an ideal dye for use in studies such as those described are tabulated.
5. The applicability of the mixture of dye-stuffs finally selected is demonstrated for a series of soils of varying basic ratio, and including examples of lateritic soils and clays.