A single measurement of the adsorption of atmospheric air on a dried, finely-divided solid at − 183°C carried out in a simple apparatus which does not require a high vacuum system, can be related empirically to the specific surface as determined by the Brunauer, Emmett and Teller procedure, with, generally, less than 10 per cent. error. The method is rapid and simple, and therefore suitable for routine use.

Examination of the cation-exchange capacity of a hydrated halloysite from Djebel Debar has disclosed no evidence for the proposed existence of exchangeable interlayer ions. A series of labile halloysite-salt complexes has been prepared. The requirements for effective intercalation of the salt are a high salt concentration in the external solution phase and a cation of low hydration energy.

It is suggested that the exothermic effect which appears on differential thermal curves for certain samples of NH4-montmorillonite may be due to oxidation of the ammonia evolved. Such an effect is suppressed and replaced by an endothermic effect if an inert atmosphere is used.

Sepiolites are rare minerals in Great Britain, there being hitherto only two recorded occurrences. The identity of the present sample has been established by means of X-ray diffraction, differential thermal analysis, thermogravimetry, chemical analysis, and infra-red absorption analysis, and some speculations on its genesis are offered.

Thermal expansion measurements on unfired ceramic clays have provided a useful rapid method of estimating their quartz contents. Reversible thermal expansion measurements on the fired clay reveal changes in composition with firing, notably the development of cristobalite and of the glassy phase.

The utilization of clay minerals in grouting is discussed.

A brief description is given of modifications enabling high spacings to be observed.