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An infra-red study of the rutile surface has shown that hydroxyl groups and physisorbed water may be removed by thermal activation, and water vapour is readily cheniisorbed at room temperature to produce a reversible surface. A model for the surface based on the (1 10) plane of r u t h has enabled interpretation of the spectra indicating two types of hydroxyl groiips represented by bands at 3700 and 3670 cm-' with the latter being the thcrnially labile species. The oxide shows strong retention of physically adsorbed water inolecules at temperatures up to 300°C.

t The " energy gap " is the term AE in the equation for the conductivity K = KO exp (-Ae/2kT) and is usually given in electron-volts (see ref.(17)). The earlier paper 4 gave A 4 2 values in kcal/mole, listed as E.

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An examination has been made of the effect of temperature on the d.c. electrical conductivity of a number of crystalline organic powders. Many substances show a semiconductivity possessing a definite activation energy E. In the uncompressed state, the " activation energy " E is largely influenced by crystal contacts. Under compression, a lower value of E is obtained which is probably characteristic of the crystals themselves. It is suggested that the excited orbitals of the 7~ electrons in the isolated molecule are combined to give non-localized orbitals stretching throughout the crystal. 2E is then the energy gap between the highest filled band or molecular level and the conduction band. Its value is discussed in terms of single electron transitions in the isolated molecule, and the overlap of 7~ orbitals between neighbouring molecules. The semiconductivity of three globular proteins is also examined in a preliminary fashion.

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