Table of contents

The attempt to discover the atomic arrangement in the protein molecule seems very ambitious. Ever since Bernal first showed that crystals of protein gave x-ray diffraction pictures, it has been clear that a protein molecule of a given type is a structure with a definite individual form, the x-ray diffraction spots are very sharp and reproducible and extend to regions corresponding to interatomic distances. The molecules are, however, of great complexity It has been a triumph of x-ray analysis to pass from simple substances like rock salt to such molecules as strychnine or penicillin with about one hundred atoms. We are now trying to analyse a molecule such as haemoglobin, which contains ten thousand atoms The reward, if an analysis were completed, would be great, because the determination of any one protein would undoubtedly cast a flood of light on the character of these bodies, which Nature has selected as the basis of living matter.

Work on protein is going on in a number of centres. I wish to speak here in particular about the work on haemoglobin which has been going on in Cambridge for the last twelve years under the direction of Dr Perutz More x-ray data for haemoglobin are available than for any other protein Though still a long way short of the goal, considerable advances have been made recently, so great as to encourage us to hope that the problem is soluble and even that a solution lies not far ahead

Experimental methods have been developed for creating and observing single spherical cavities in water and certain organic liquids Rapid photography permits motion analysis to be made

The cavities show several cycles of expansion and collapse during their lifetime of a few milliseconds At each volume minimum a sharp pressure maximum occurs in the liquid

It appears that these cavities form initially on minute gas nuclei in the liquids, and the existence of these nuclei is essential for the type of cavitation studied The relation of cavity life to maximum diameter is discussed.

An account is given of measurements on the reversible changes in magnetization accompanying change in temperature in annealed nickel, and the results are discussed in relation to the work of Bates and others on the temperature changes produced by adiabatic changes in magnetization (the magneto-caloric effect). It is found that at relatively high fields, where the magneto-caloric effect is mainly reversible, the results are in good agreement with those obtained from direct magneto-caloric measurements, while for low field values a quantitative separation of the reversible and irreversible components of the magnetocaloric effect has been carried out The result of an analysis of the reversible heating effect is compared with the estimate given in the theoretical investigation of Stoner and Rhodes, and it is suggested that, over the low field range considered, rotational processes predominate.

A special apparatus has been used to draw wires of various metals at temperatures between - 183°c and 100°c, and to measure their resistances at the temperature of drawing The change of resistivity with deformation was found to depend on the temperature of deformation relative to the recrystallization temperature. The results explain qualitatively the apparently anomalous resistivity increases previously reported for tungsten and molybdenum It is suggested that a unified theory of the effect of deformation on the resistivity of both pure metals and alloys can be based on stacking faults.

It is shown that sharp yielding can be observed in previously unstrained zinc crystals by means of bending experiments devised to avoid premature overstraining of the specimen. This resolves a difficulty in the interpretation of previous tensile experiments on crystals which show the yield phenomenon

Evidence is given confirming that the yield point in zinc is due to nitrogen in solution The theoretical prediction that a yield point should appear in a susceptible crystal without the necessity for any prior deformation is verified experimentally, and an explanation is given of the observation that a yield point may appear in a specimen even though free dislocations have been introduced subsequent to ageing

Under certain conditions the yield point values in zinc decrease as identical strain-ageing treatments are repeated, and a smooth stress-strain curve is ultmately obtained This is attributed to an accumulation of work hardening which causes the dislocation density to increase to such an extent that the dislocations can no longer be effectively anchored by the available nitrogen atoms The difference between this behaviour and that of iron on repeated strain ageing is discussed

A method is described by which metallic wires can be subjected to easily measurable but very pronounced asymmetrical temperature gradients without straining the wire The electromotive forces developed by the application of symmetrical and asymmetrical gradients to annealed `thermopure' platinum wire and specially prepared cables of copper wire, at both high and low temperatures, have been measured at many points along considerable lengths of wire Precautions to minimize or eliminate spurious effects enabled measurements significant to 0 01 μv to be taken

The results provide no justification for the supposition that an asymmetrical temperature gradient thermoelectric effect exists, under the conditions of investigation, which cannot be explained in terms of inhomogeneity effects The nature of these effects is discussed and some evidence is provided which indicates that the variation in the Thomson thermoelectric potential with strain and impurity is significant