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Specific Surface Determination by Duo-Interlayer and Mono-Interlayer Glycerol Sorption for Vermiculite and Montmorillonite Analysis¹

ABSTRACT

In a new method for specific surface determination, montmorillonite is made to sorb exactly two interlayers of glycerol (a true monolayer on each planar surface) at 35° C. in a vacuum of < 1 mm. of Hg. Vermiculite sorbs only one interlayer under these conditions. Both montmorillonite and vermiculite sorb only a mono-interlayer of glycerol at 110° C. in a previous method. The two analytical methods thus give the amount of glycerol corresponding to the second interlayer in montmorillonite, and this makes possible quantitative analytical determination of montmorillonite and of vermiculite.

To illustrate, Wyoming montmorillonite sorbs 21.1% glycerol at 110° C., and 41.6% at 35° C. in vacuum, which gives an analysis of 98% montmorillonite, whereas Colorado vermiculite sorbs the same amount of glycerol under both these conditions, equivalent to only a monointerlayer. The presence of fine amorphous material in montmorillonitic fine clays is revealed by a higher specific surface than obtained with 100% montmorillonite. Dissolution of the allophane from Black Cotton soil (India) resulted in a specific surface analysis of 94% montmorillonite (5 to 10% kaolinite is present). Ladybrook fine clay fraction (Queensland, Australia) showed 90% montmorillonite and 10% of mono-interlayer expanding mineral.

Contribution from the Dept. of Soils, University of Wisconsin, Madison, supported in part by the University Research Committee through a grant of funds from the Wisconsin Alumni Research Foundation. Presented before Div. II, Soil Science Society of America, Lafayette, Indiana, Aug. 6, 1958.

² Graduate Assistant and Professor of Soils, respectively.

Received for publication February 9, 1959. Accepted for publication March 27, 1959.