THE INFLUENCE OF IRON AND ALUMINIUM HYDROXIDES ON THE SWELLING OF Na‐MONTMORILLONITE AND THE PERMEABILITY OF A Na‐SOIL

Summary Hydroxy Fe and A1 interlayers reduce the swelling of Na‐montmorillonite in NaCl solutions. A deposit of sesquioxide round an aggregate or orientated flake of clay restricts swelling until the sesquioxide coating is broken by the swelling pressure of the clay. A1 is more effective than Fe. The effect of sesquioxides on the permeability to NaCl solutions of an alkali soil depends on the control of clay swelling in a manner expected from the above results. A sesquioxide coating round a soil aggregate stabilizes the structure until the coating is broken by the swelling pressure of the clay in the aggregate.