الفهرس 
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Abstract
There is increasing need for the preparation of solids
in the state described as ”active”.
Such active solids are
used in a variety of purposes e.g. for use as adsorbents for
gases or liquids, or as catalysts. In other cases, the solids need to be brought into an active state in order to react or dis- solve with a sufficiently rapid rate.
A variety of materials that has been called clays, have been widely used in pure and applied fields as insulators of heat and sound, ion exchangers, catalysts, catalyst fillers and for cracking of petrolium oil. The chemical analysis of clays shows them to be essentially silica, alumina and water, frequently with appreciable quantities of iron, alkalies and alkaline earths.
The following classification of the clay minerals was suggested on the bases of currently available data on the structure and composition of the various clay minerals. 1. Amorphous
Allophane group.
ii. Crystalline
A Two-layer type (sheet structures composed.