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Samples of three purified illites, one pursed montmorillonite, and one natural clay containing montmorillonite, quartz, and limonite were heated at successive temperatures up to 1400°C.The changes that take place in the clay minerals, illite and montmorillonite, when they are heated at various temperatures up to 14OO0C. are discussed.X-ray and optical determinations were made on all samples. Exchange and Swelling of Montmorillonite on Preheating." 2. Ver. deut. Chem., Beihefte No. 35, 10 pp. (1939). FIG. 1.-Indices of refraction and representative X-ray diffraction patferns of sample (1). The more prominent lines of various phases are designated as follows: I = illite, Q = quartz, S = spinel, and M = mullite. Vol. 23, No. 8

The structures of the clay minerals are reasonably well known, but greater detail and more precision are needed if the properties of clays and soils are to be fully understood. For example, the selective adsorptive and catalytic properties and the reaction with organic materials vary with the character of the clay mineral, but the structural factors that control such properties are not well understood. Research is urgently needed on the structure of pure clay minerals and on the reactions of pure clay minerals with organic and inorganic materials. Much past research on clay-mineral reactions has little fundamental value because the clay that was used was composed of a mixture of minerals which were not well characterized. It is not a simple matter to find pure samples of many of the clay minerals, and to a considerable extent progress depends on finding such pure minerals or preparing them in the laboratory.

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