A slight modification to Bascomb's procedure for determining cation exchange capacity makes it applicable to gypsic soils even when the gypsum content is as high as seventy percent. The modification involves a second titration of the final extract made specifically for calcium and which is necessary to correct the magnesium titration. All practical evidence shows that gypsum is not dissolved by the preliminary barium chloride treatments, due to a protective coating of barium sulphate subsequently removed by the final, acid treatment. re]19730821