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Further Results on the Mineralogical Subdivision of Soil Separates by Means of Heavy Liquid Specific Gravity Separations¹

ABSTRACT

Following the work previously reported regarding the mineralogical subdivision of soil material by means of heavy liquid specific gravity separations, an attempt has been made to improve the procedure. The special centrifuge tube previously described for specific gravity separations was redesigned so as to be of simpler construction and of larger capacity.

The results of specific gravity separations of various mechanical separates of soil and nontronite are given. Petrographic methods were employed to check the sharpness of the separations in the case of material of particle size greater than 1.0µ in diameter. Quantitative separations of the mineral groups in sand and silt fractions were effected. In the case of coarse clay (particles 2.0 to 0.2µ in diameter) the separations were quantitative except for traces of talc and biotite in the lighter fractions. The bulk of the base exchange material in the Lufkin clay, and in nontronite, was found in the specific gravity fraction 2.18 to 2.33. It was also found that the quantity of minerals of low specific gravity increases greatly with diminishing particle size.

The results obtained in this study indicate that separation by means of the specific gravity procedure outlined, offers considerable promise as a means of separating and concentrating the mineral species in not only the coarser but also the finer soil separates. This should be of great help in mineralogical studies of soil material by the use of petrographic, chemical. and x-ray methods.

¹ Contribution from the Department of Soils, University of Wisconsin, Madison, Wisconsin. Published with the permission of the Director of the Wisconsin Agricultural Experiment Station. This work was supported in part by a grant from the Wisconsin Alumni Research Foundation.

² Research Assistant and Professor of Soils, respectively. The senior author is now Research Assistant Professor of Soils at Iowa State College. The writers are indebted to Dr. C. D. Jeffries for petrographic examination of the specific gravity separates.