The extraction of naturally occurring free iron oxides from soils and clays with oxalate solutions is distinctly photosensitive. Apparently wave-lengths around 366 mµ, the near ultra-violet region, are the most efficient; this radiation is predominant in the emission of a medium-pressure mercury arc lamp. A qualitative consideration of the dissolution process indicates that in all probability electron transfer from solute to solid via intermediary C2O4− is involved. Such a mechanism may explain the attack of near-neutral oxalate solutions upon natural ferric oxides and the decomposition of the quite resistant hematite in slightly acid media, when irradiated. The reaction appears to be autocatalytic. Electron transfer utilizing thermal electrons may also explain the attack of dithionite ions upon ferric oxides, which was shown to proceed in media above neutrality. Finally, a detailed description of the method is given, including the application for estimating free iron oxides in particle-size fractions obtained during the course of mechanical analysis.

The specific surface areas of three montmorillonite samples, both alone and in admixture with kaolinite, have been measured. The results are discussed in relation to the possible existence of montmorillonite crystals.

The contribution of free iron oxides to positive and negative charge distribution has been studied on soils and synthetic kaolinite-iron oxide complexes over a wide range of pH values. The charge on the iron oxides is pH-dependent, being positive at low and negative at high pH values, respectively, and accounts for a considerable proportion of the pH-dependent negative charge in soils. Iron oxides increase the buffer capacities of all soils and kaolinite-iron oxide complexes. A considerable proportion of the surface of the clay fraction is covered by iron oxides, resulting in a decreased negative charge on the clay. The isoelectric points of iron oxides in soils are considerably higher than those reported for pure iron oxides. A number of the soils studied were isoelectric at their field pH values, so that under field conditions they would be expected to be extremely infertile. Evidence is presented to show that kaolinite has a permanent negative charge, confirming the view that isomorphous substitutions occur.

Examination of clays from surface and basal horizons of four Scottish soils by differential thermal analysis, before and after heating to 600°C and by infra-red spectroscopy indicates that these contain a proportion of highly hydrated amorphous material, resembling allophane in its properties, and that this component is particularly high in clays from the surface horizons with the greatest organic matter content. This conclusion is consistent with the cation-exchange capacities of the clays and with the amounts of silica and alumina extractable from them by hot sodium carbonate solutions. The ratio of silica to alumina in these extracts indicates that the amorphous material is highly siliceous.

Two clays of the kaolinite type, one from Bihar and the other from Kerala, were each separated into particle-size fractions greater than and smaller than 1·4 µ.e.s.d. X-ray diffraction, differential thermal analysis, cation-exchange capacity and moisture absorption determinations and chemical analysis of the fractions showed that the micaceous mineral was concentrated in the fine fraction of one whereas it was mostly in the coarse fraction of the other. The evidence suggests that the mineral in the former belongs to the illite group and in the latter to the mica group.

Some characteristics of the kaolin→metakaolin reaction have been studied by applying nuclear magnetic resonance, X-ray fluorescence, and acid dissolution techniques to samples at intermediate stages of dehydroxylation. Nuclear magnetic resonance spectra enabled the average distance between hydroxyl groups to be computed, while X-ray fluorescence provided information on changes in the co-ordination number of aluminium and acid dissolution demonstrated the reduction in cohesion between individual layers during dehydroxylation. The last technique appears to be useful in studying the development of new solid phases. The main conclusions are that the reaction proceeds in a stepwise manner by complete removal of constitutional water from octahedral sheets and not by the growth of randomly distributed nuclei, that six-fold coordinated aluminium is gradually transformed into four-fold coordinated aluminium, and that the internal surface becomes progressively accessible to the acid reagent as dehydroxylation proceeds. The ‘ring structure’ of the silica layer remains.

This Conference, organized by the Comit6 International pour l'Etude des Argiles (CIPEA) and sponsored by the International Union of Geological Sciences, was attended by some 200 clay mineralogists from 23 countries. The British Clay Minerals Group was well represented, having 17 participants.

The Conference arrangements were very efficierxtly made by Professor I.Th. Rosenqvist and Dr. P. Graff-Petersen, President and Secretary of CIPEA, together with an Organizing Committee appointed by the Swedish Society for Clay Research, who were the official hosts.

Conflicting evidence has been published concerning the occurrence of an oxidation exothermic peak on differential thermal curves for NH4-saturated clay minerals. The present experiments show that this peak is affected by (a) the clay mineral concerned and (b) the nature of the thermocouple, Pt/PtRh thermocouples apparently acting as good catalysts for oxidation of released ammonia.

Complex formation enhances the sorption of various diamines from aqueous solutions by montmorillonite in the presence of copper and vice versa. A distinct difference was observed between chelating and nonchelating diamines. The effects were measured quantitatively, and the resulting structures were investigated by X-ray diffraction tedhniques. No direct correlation was observed between cell height and the configuration of the interlayer complexions; ‘keying’ of organic and organometallic cations into the oxygen surfaces is inferred.

Experiments on a number of clays from different formations show that heating at 375°C for 16 hours removes 90 per cent. or more of the carbonaceous material without removing combined water from the clay mineral. A close relationship is found between percentage loss at 375°C and percentage carbon determined in the carbon-hydrogen furnace.

A Quaternary or Recent tuff or pumice has weathered to an allophanic soil reminiscent of some described by Sudo. The soil has interesting engineering properties. Electronmicrographs show the apparent coalescence of alophane ribbons into a thin platy mineral, probably an early form of hydrated halloysite. The formation of crystals by the coalescence of mosaic crystallites is discussed.

Particle-size analyses of brickearth and Clay-with-flints from Kent, England, are presented. A calcareous sample of brickearth is comparable to loess. In the clay fraction, there is more illite (or glauconite) than kaolin; and there is some chlorite. The clay fraction of the Clay-with-flints consists of smectite, illite and quartz and is probably derived directly from the Chalk. Black sand-grade nodules are manganiferous.