A Photoelectric Investigation of the Cool Flame of Ether

Abstract

A method is described, in which the light from a cool flame under the form of a static, uniform glow is measured as a function of time by means of a multiplier photo‐tube and a single‐sweep cathode‐ray oscillograph. The circuit embodies an a.c.—d.c. amplifier and a slow sweep. Cool flames of diethylether‐oxygen mixtures in a Pyrex cylinder 4.6 cm in diameter have been studied under the following range of conditions: 180–250°C, 0–150 mm and 5–95 percent ether. The pulsating glow, which lasts about 1 second, shows two and sometimes more maxima. The generally accepted lower pressure limits appear as regions of feeble but smoothly decreasing intensities. Under the conditions of our experiments, the temperature coefficient is negligible. Both intensity and integral emission increase regularly with the concentrations of the reactants and are maximum at 50 percent ether by volume, the variations being roughly symmetrical with respect to the partial pressures of either component. Variations of pressure and composition cause regular but considerable changes in the shapes of the oscillograms. Light and pressure pulses follow each other closely, suggesting that the latter are of mainly thermal origin and that the light intensities reflect the instantaneous reaction rates. The glow lasts longer in the wider vessels. In the presence of the reaction products, it either fails to appear or emits the normal amount of light. A preliminary analysis of the quantitative data is given and possible interpretations, in terms of oxidation mechanisms, are discussed.