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Cation and anion adsorption was studied for the systems sodium bentonite plus zinc chloride, calcium bentonite plus zinc chloride, hydrogen bentonite plus zinc chloride, and for the systems zinc bentonite plus sodium chloride, zinc bentonite plus calcium chloride, and zinc bentonite plus hydrochloric acid.2. The uptake of zinc from zinc chloride solutions involves the ions Zn++, (ZnCl)+, and (ZnOH)+. The release of zinc from zinc clay by sodium chloride and calcium chloride is restricted mainly to divalent zinc.3. Zinc clays possess pronounced anion-exchange properties. The anions Cl-, OH-, and NO3are mutually replaceable. On the surface OHis held more tightly than either NO3or Cl-.4. It is postulated that zinc clay has a mosaic surface capable of independent cation and .anion exchange. The approximate constitution of the mosaic adsorption layer is indicated.5. Some of the zinc adsorbed exists in non-replaceable form. It is suggested that it is inside of empty oxygen and hydroxyl octahedra of the brucite layer of the montmorillonite crystal.

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Summary Egyptian desert soils are generally of coarser texture than Nile alluvium with only slight depositional changes within the same profile. Total N is lower in desert soils than in alluvial soils under similar climatic conditions. On the basis of clay mineral analysis the soils fall into four groups, having (1) kaolinite (Ganah and Kharga), (2) montmorillonite (Beris, Boulaq, Nile alluvium), (3) hydrous mica (Kharga), (4) attapulgite (desert road), as the dominant mineral. The very slight difference in clay mineral composition between the soil and subsoil or parent material indicates that clay minerals in these soils are derived mainly from a pre‐existing sediment. The mechanical analysis and mineralogical study of the heavy mineral fraction showed that the soils of Kharga oasis are either water‐laid sediments (Boulaq and Beris) or wind‐modified (Ganah and Kharga). Whether or not the qualitative similarity of the clay minerals of the soils from mid and southern Kharga with those of the Nile alluvium indicates a genetical relationship cannot be definitely ascertained from this study.