In soil mechanics all of the preparatory techniques relating to clay soils have been standardised. Working in all other branches of science or technology, clay mineralogists have to uncover as best they can techniques from a widely scattered literature or learn from their “older” colleagues. In the present symposium we are to hear about some of the latest methods of preparing clays especially for X-ray and electron-optical study; yet I hope that when the Editor comes to publish these valuable contributions he will also find space to refer to some of the more humble methods of preparing clays; they do not appear to have been collected together before; we know them all by name—the Truog treatment, Mackenzie's method, or the Grim gambit—but where do we find them in printc?

“First catch your clay.” Undisturbed clay samples are regularly taken by engineers and by agricultural clay mineralogists. Moisture content, bulk density and rheological properties depend upon near-perfection in the taking of these samples in the field.

The methods for clay separation described involve dispersion, sedimentation, coagulation, and peroxidation. Modifications to deal with organic soils are also described.

A brief description is given of a vacuum distillation method which, because of the low temperatures involved, does not tend to coagulate the clay when used for concentration of dilute suspensions.

The procedure used for fractionation of soils, rocks, and sedimentary materials involves separation of the clay (less than 2 microns) and silt (2 to 62 microns) by centrifugation. Randomly oriented powders and oriented aggregates of these materials are examined using X-ray diffraction as the principal method of analysis.

General techniques for specimen preparation are described, including formation of supporting films and surface replicas, and methods for dispersion of clays.

A method of extruding powder specimens using a hypodermic syringe is described.

A technique is described whereby powder specimens of controlled volatile content may be obtained for X-ray analysis.

The technique of replica casting of ceramic materials and the various methods of mounting and examination are described. Co-ordination of optical properties of the peels and X-ray analysis is considered. The uses of peels in showing orientation of clays settled under gravitation and also effects of plastic deformation are discussed.

Size graded fractions of ground quartz and other silica minerals are prepared by gravity settling for particles greater than 2 microns Stokes' diameter and by centrifugal methods for smaller sizes. The size distributions of the prepared fractions are determined by counting and sizing with an optical microscope or with an electron microscope. The volume-surface diameter ΣND3/ΣND2 is used both for calculating the specific surface of the fractions and for comparing the projected area diameters used in counting, with the Stokes' diameters.

A focusing X-ray powder camera is described in which the degree of focusing varies with 2θ and can be made a maximum for any one reflection. It is of simple design and has two main uses:—(a) for a routine identification of the main clay mineral groups by their basal reflections, and (b) for the detection of very small amounts of any one crystalline component in a mixture.

The flat-layer method of X-ray diffraction and conditions for focusing are discussed.

A vapour pressure method of glycerol treatment of clays is described and its advantages over normal methods noted.

A method of adapting a 9·0 cm X-ray camera is described