LONDON Royal Society, November 8.—A. C. G. EGEBTON and F. LL. SMITH: Estimation of the combustion pro ductions from the cylinder of the petrol engine (1). An engine was fitted with a valve so that gases could be extracted at any stage during the compression and working stroke. By analysis of the gas it was confirmed that ‘knock’ is associated with accelerated flame velocity, but only in the last portion of the gas to burn. Some combustion occurs in the neighbour hood of the valve prior to arrival of flame. The aldehydes reach their maximum concentration (1 in 500) at the moment when flame reaches the valve, the substances behaving as peroxide (1 in 10,000) slightly earlier. Aldehydes were not responsible for the production of ‘peroxide’ or the ‘knock’. Certain organic peroxides were found to be powerful ‘pro-knocks‘. A. C. G. EGEBTON, F. LL. SMITH and A. R. UBBELOHDE: Estimation of the combustion products from the cylinder of the petrol engine (2). The experiments were extended to the study of the be haviour of different hydrocarbons and other kinds of fuel, the ‘aldehyde‘ a ‘peroxide‘ formed at various stages being determined by special methods. The substance behaving as peroxide is mainly nitrogen peroxide and the peak in the curve of con centration which occurred before the top dead centre is partly explained by the presence of traces of sulphur. Nitrogen peroxide alone does not act as a pro-knock, whereas organic nitrites are strong pro-knocks. Nitrogen peroxide is, however, formed in greater amounts under knocking conditions and quite early in the stroke. A. R. UBBELOHDE and A. C. G. EGEBTON: Estimation of the combustion products from the cylinder of the petrol engine (3). The behaviour of various types of organic peroxides towards various reagents was investigated. By taking advantage of the different rate of reaction of the various peroxides on potassium iodide, it was possible to determine them in presence of nitrogen peroxide. Diethyl and ethyl hydrogen peroxide and acetyl peroxide were found to be violent pro-knock substances. The mol fraction needed to produce pronounced knock was 10-5. A peroxide of apparently similar type to ethyl hydrogen peroxide was detected in the gases from the engine cylinder when run under knocking conditions on pure paraffin hydro carbons in much the same concentration. H. JONES: Application of the Bloch theory to the study of alloys and of the properties of bismuth. A qualitative explanation is given of the variations of the crystal parameters within the s and 7) phases observed by Owen and Pickup, and also of the electron-atom ratio at which the e phase begins (Hume-Rothery's rule). A Brillouin zone is found for bismuth containing five electrons per atom. The theory shows why bismuth does not form a co-ordination lattice. The con ductivity of alloys of Bi, Sn, and Bi Pb are considered; the observed variation with composition leads to a determination of the ‘overlap’ of the Fermi surface into the second zone. From this the diamagnetism of pure bismuth and of Bi Sn, Bi Te alloys are deduced, as is also the magnetostriction, in good agreement with experiment.