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Various physical properties of an acid-treated Texas bentonite were studied as a ftmction of treatment time. The observed kinetics were pseudo first-order (large excess of acid) and on this basis and the x-ray results a model and mochanisin are proposed that are consistent with observed surface area, exchange capacity, and surface acidity changes. A crude estimation of activation energy gave a value lower than that of Osthaus (1956) but of the right magnitude.

Hectorite, a trioctahedral magnesium montmorillonite, has been synthesized a t atmospheric pressure and reflux temperature. The reaction mixture was the system SiOz/MgO/LizO (or L3)/NazO in a large excess of water. The starting ratios were based on the following formula for the mineral [(LizMg~-z)SisOso(OH)4]z-.xNa+.Li+ has been found to accelerate the crystallization, and reasons for this effect are considered. Lowering of the p H of the reaction mixture by the use of alkali metal fluorides rather than hydroxides, resulting in an increase in the solubility of Mg(OH)z, also caused the crystallization of hectorite to proceed more rapidly. The products containing Li+ and F-proxying for Mg2+ and OH-, respectively, were %und to be most like natural hectorite.The time-dependent data obtained in this work were rationalized on the basis of a postulated appearance of hectorite embryos in the dilute aqueous solution of Mgz+, OH-and SiOz, followed by growth of this material to crystalline hectorite by transfer of components from solution to the solid phase.Strese and Hofmann (1941) also conducted synthesis work in this area. A comparison of the products resulting from the two techniques showed the main difference to be the presence of 001 spacings in the current product. These earlier workars made a point of the lack of 001 reflections. I N T R O D U C T I O NThe Research Project a t Mellon Institute sponsored by Baroid Division National Lead Co. has been directed of late toward the variation of the physical properties of clay minerals as a function of the nature and extent of isomorphous substitution. As a consequence, considerable effort has been expended in the development of techniques for the synthesis of the clay minerals, with emphasis on hectorite.The clay mineral occurring a t Hector, California, was studied by Boshag and Woodford (1936) and by Nagelschmidt (1938). No11 (1936) studied the synthesis (using high-pressure techniques) of magnesium-containing montmorillonite and extended his work to the magnesium end member of the series. Strese and Hofmann (1941) also conducted extensive synthetic work in this area and included a study of the products obtained from an atmospheric pressure approach. A careful x-ray study of the Hector, California, clay is included in their paper. Their approach will be described in a later section of this paper. Incidentally, Strese and Hofmann discount the presence of Li+ in the structure and attribute it to accessory mineral.I n their classification of the montmorillonite minerals, Ross and Hendricks (1945) MacEwan (1951) in his discussion of the montmoriuonite minerals includes hectorite, and establishes the criterion that the 06 spacing for the trioctahedral montmorillonite should be slightly greater than 1.5 A, and slightly less than this value for the dioctahedral series. Pinally, Eitel (1952) describes compounds prepared by solid state reactions, which he terms " hectorites ", and gives the following formula Li2Mg6A12Si6020F4 nLiF, where the LiF is contained between...

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A viscometric study of dilute montmorillonite dispersions, truing for the most part dilution-type capillary viscometers supplemented by a falling-head capillary viscometer, has involved a determination of the concentration dependence of viscosity of such dispersions in both distilled and electrolyte-containing water. The results of the study have been interpreted in terms of a theory of incremental viscosity, and of the SchulzBlaschko (1941) equation. Use of this equation yields good extrapolations to zero concentration for the determination of limiting viscosity number, and permits calculation of " interaction indices " which are considered, for reasons discussed in detail, to be a measure of pa~icie-particle interaction. These indices are related to tha cationic heat of hydration of the electrolyte used, and relationship is demonstrated between the yield stress of a 3 percent montmorillonite-electrolyte-water system and such interaction indices. The recent work of Paekter (1956Paekter ( , 1957 is discussed, and the relation of the results of this investigation to the data of van Olphen (1956, p. 204) is noted.