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Diffusion coefficients are measured for physical absorption using a laminar jet apparatus. The COz+water system is examined over a wide temperature range. The systems NzO+water and N20+water glycerol are examined at constant temperature over a wide range of concentrations of glycerol solutions. A modified Stokes Einstein equation is proposed. Values of diffusion coefficients are obtained with an error of about 1 "/,.

Optoacoustic spectrometry can be employed to obtain data concerning the spectral absorption characteristics and thermal diffusivity of small solid samples. Theoretical expressions have been developed to relate the optical and thermal properties of such samples to the amplitude and phase of the signals observed in optoacoustic spectrometry when using dispersive and non-dispersive techniques. The validity of these expressions has been examined by using transparent and opaque materials with widely differing thermal diffusivities.

A simple single-beam spectrometer suitable for the study of optoacoustic spectra from small solid samples is described and the design of a suitable sample cell is reported. The performance characteristics of the spectrometer have been evaluated using different types of sample. A preliminary assessment of the predicted advantages of optoacoustic spectrometry over conventional techniques of ultravioletvisible absorption and reflectance spectrometry for solid samples has been made.

The frictional characteristics of keratin fibres are anisotropic. The most obvious characteristic feature is that the frictional work required to slide one fibre over another is greater in the direction tip-to-root than the converse; this is the socalled differential friction effect (DFE). This paper describes a series of experiments where fine polymer (polyethyleneterephthalate) and carbon fibres are slid in the two directions with a range of normal loads over cleaned human, camel, guanaco and llama hairs in order to quantify the DFE. These hair fibres exhibit a range of asymmetrical cuticular structures which have been characterised using electron microscopy. It is suggested, in keeping with established wisdom, that it is this topographical asymmetry which is responsible for the DFE. An analytical model is developed and evaluated in order to rationalise the origins of the DFE. The model combines various precedents from contact mechanics, the adhesion theory of friction and earlier studies of friction. The predictions of the model are consistent with the experimental data.