The phenomenon of nonisotropic propagation consists in the spontaneous development of blisters or cells on the surface of a combustion wave. The present experiments on spherical flames and the experiments of Markstein on flames in wide tubes show that the phenomenon is characteristic of nonstoichiometric explosive mixtures in which the deficient reactant constituent is also the constituent of largest diffusivity. This su~gests that the p~enomenon is primarily caused by the effect of diffusion processes on the burning velocity. It IS proposed that III curved areas of the wave that are convex with respect to the burned gas, the burning velocity is reduced because the lines of diffusion diverge, and hence the concentration of the faster diffusing constituent decreases; whereas in concave areas the lines of diffusion converge, and hence the concentration of the faster diffusing constituent increases. In rich mixtures of hydrocarbon and oxygen, additional evidence for the effect is furnished by the emergence of carbon streamers and by characteristic changes of light emission from convex wave areas, showing that the oxygen concentration, and probably therefore the burning velocity, is decreased in these areas below the average for the mixture.

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The decomposition of methane by a beam of electrons having energies between 15 and 100 ev has been studied using methane pressures between and mm of mercury. The products were frozen out on a surface cooled to about -220" C and situated approximately 5 millimeters from the electron beam.Ethane, ethylene, and acetylene were found to be the main products along with smaller amounts of saturated and unsaturated higher hydrocarbons. The results provide some evidence that under these experimental conditions ions do not play a major part in the decomposition and a free radical mechanism has been proposed to explain the formation of the main products. INTRODUCTIONRecently the authors have become interested in the study of chemical reactions in the electric discharge. For many years, the interpretation of the results of such studies was based largely on the reactions of free radicals, ionic reactions not being considered of importance. During the last few years, however, it has been observed, initially by Stevenson (I), that ions frequently have enhanced cross sections for reaction. This has led t o a reappraisal of the role played by ions in radiation and discharge chemistry.As an aid to understanding the decomposition of methane in a discharge, the experimental conditions have been simplified in such a way that many of the experimental parameters could be separately controlled. In addition, an effort has been made to reduce the extent t o which secondary reactions occur by providing for the rapid removal of the products froin the reaction zone. In this way, it was hoped t o obtain some information concerning the primary products of the discharge reaction. An electrically heated (a-c.) tungsten ribbon filament was the source of electrons, the filament being enclosed in a housing with its own pumping for the removal of pyrolysis products. The beam of electrons was defined by apertures 1.5 mm in diameter in a series of Chrome1 A plates. Further alignment and collimation of the beam were obtained by the use of a permanent magnet which provided a uniform field strength of 870 gauss over an area about 4 centimeters in diameter a t the center of the gap. Onto the final collimator (collimator 2) was soldered a hollow brass cone, A, which fitted into the glass tube surrounding the reaction zone. This arrangement caused the major pressure drop to be across the defining aperture in the center of the collimator. The collector served to monitor the electron beam. The collector grid, about 1 mm in front of it, consisted of 90% transparent tungsten mesh and was maintained a t the same potential as the final collimator, thus creating a field free reaction zone 4.5 centimeters in length.The various potentials were obtained from a regulated d-c. supply and were chosen t o give the maximum beam current consistent with stability and reasonable filament 'Manuscript

Studies have been carried out, of the influence of the chlorine content of both aliphatic and aromatic compounds on the structure of the carbon deposits formed on a silica surface by pyrolysis at 850-950 °C. The results show that the more highly chlorinated compounds give rise to carbons in which the crystals are smaller and the preferred orientation and (001) habit of the crystallites are less marked than in those derived from organic compounds containing little or no chlorine. The differences in carbon structure are ascribed to the decreased mobility of the carbon atoms in presence of hydrogen chloride or chlorine.

A study of the thermal decomposition of chlorobenzene shows that two quite distinct mechanisms can operate according to the temperature. Between 770 and 800" C, the main products are hydrogen chloride, hydrogen and p : p'-dichlorodiphenyl ; chlorine atoms and chlorophenyl radicals appear to be the principal carriers involved in a chain cycle in which there is little or no rupture of the aromatic ring. At higher temperatures (800-850" C), extensive ring-breaking occurs and quite large yields of vinyl chloride are obtained ; here, a chain reaction is postulated in which C2HCl fragments are important intermediate species. The occurrence of two competing mechanisms results in a welldefined negative temperature coefficient of reaction rate between 830 and 850" C ; for on account of the increasing thermal instability of CzHCl fragments the ring-breaking mechanism ceases to operate and there is a consequent decrease in the rate of consumption of chlorobenzene by this process. At still higher temperatures, therefore, hydrogen chloride, hydrogen and p : p'-dichlorodiphenyl again become the main products.Pyrolysis of chlorobenzene in the presence of added hydrogen yields products qualitatively similar to those obtained in its absence. The accelerating effect of hydrogen is most marked at temperatures where the ring-stripping mechanism is predominant. It is suggested that hydrogen favours the latter process by preventing recombination of chlorine atoms at the walls, while it hinders the ring-breaking reaction by stabilizing intermediate CZHCl fragments.