The partial and apparent molal volumes of K-bentonite in pure water and in 0·5 M KCl were determined using pycnometer density data. The values obtained were found to increase with particle concentration. Theoretical values of the electrostatic contribution to the volume of particles calculated from an assumed model based on the electric double layer theory, gave values different from those found experimentally. This is explained as due largely to the uncertainties in the value of the clay specific surface area as well as to the assumed ideality of the model used.

Adsorption and desorption of cationic surfactants, cetyl pyridinium bromide, cetyl trimethyl ammonium bromide, dodecyl pyridinium bromide on bentonite, kaolinite and illite, and their diffusion through a bentonite membrane have been studied.

The binding of these compounds on the mineral surface takes place much beyond the exchange capacity. For excessive saturations with long chain compounds like these, the chains stand erect to the surface. A correlation of area per exchange site and area associated with surfactant molecule on clay surface also supports this view. The increase in the extent of adsorption with the size of the organic cation is due to an increase in the van der Waal's forces between clay and surfactant molecule. Isosteric heats of adsorption at different stages of surface covered with surfactant have also been determined and the same was found to pass through a minimum point. Larger ions desorb less, owing to the lesser solubility and larger contribution of dispersion forces.

Permeability of these surfactants and energy of activation of the diffusion process through the H- bentonite membrane has also been investigated. Diffusion of these cations takes place via exchange positions through the membrane and the order is exactly the reverse of their adsorption on the clay surface.

A study of the weathering of micaceous clays in some Norwegian podzols, includes semiquantitative estimates of minerals in the concentrated clay fractions which show a decrease in the amounts of illite and chlorite, and an increase in vermiculite and mixed-layer minerals upward in the profile. Illite, the dominant mineral at depth, weathers to hydrobiotite in the surface horizon of the profile. Subsequent weathering of hydrobiotite in this portion of the profile produces trioctahedral vermiculite and smectite, or intergrade smectite-chlorite.

Calculated diffraction profiles for interstratified kaolinite and montmorillonite have been used to determine the composition of clays reported from Poland, Japan and Mexico. The predicted layer proportions determined from the curves and by other methods are in close agreement for the first two but a higher kaolinite content than that originally proposed is obtained for the Mexican clays.

The construction is described of a heating stage for examining oriented clay specimens in a Philips' diffractometer. The stage, which is simple and cheap to make, is interchangeable with standard specimen holders, operates over the range 20—265°C and does not require the diffractometer to be specially modified. The maximum temperature attained at the surface of the specimen collapses freely-expanding Mgsaturatcd vermiculite and prevents re-expansion of layer silicate minerals once they have been collapsed.

The use of HF digestion to concentrate minerals of the plumbogummite group is discussed. Prolonged treatment is shown to result in solution of plumbogummite minerals, and in precipitation of HCl-insoluble, complex fluorides. These yield X-ray diffraction spacings that may be confused with those of plumbogummite minerals. The presence of fluorides in digestion residues is confirmed by X-ray diffraction, DTA and by identifying the products formed when such residues are heated to 600°C.

The cation exchange capacity (C.E.C.) of nontronite was determined by titrating the acid clay, prepared by the action of H-resin on nontronite, in water and some nonaqueous solvents. The base-titratable acidities of the acid nontronite, freshly prepared as well as aged, were found to be greater than the acidities extractable with 1 N NaCl; the difference was attributed to the non-exchangeable pH-dependent component of C.E.C. In the freshly prepared sample, H+ and Fe3+ ions were the only exchangeable cations. Ageing produced basic Fe ions which were exchangeable and whose amount increased at the cost of H− and Fe3+ ions. Whatever the age, the total quantity of these exchangeable cations corresponding to the total isomorphous charge, remained constant. The amount of the pH-dependent acidity also remained unchanged. A likely mechanism to account for the observed pH-dependent component of the C.E.C, of nontronite is suggested.