The Photosensitised Explosion of Hydrogen-Oxygen Mixtures in the Presence of Chlorine

Abstract

A RESULT of some interest has recently been obtained relative to the explosion of hydrogen and oxygen by the photosensitising action of chlorine in light from the mercury vapour lamp transmitted by glass. The experiments were initially carried out at a temperature of about 300° C. with the view of testing the possibility of the initiation of a hydrogen-oxygen chain mechanism by the hydrogen atoms produced in the hydrogen chloride synthesis. When 280 mm. of a mixture (2H₂ + O₂) was exposed in a cylindrical glass reaction vessel to light from a mercury lamp, no effect was observed. If chlorine in increasing quantities was added, a sharp limit of chlorine pressure was found, above which a practically instantaneous and quantitatively complete explosion of the hydrogen and oxygen to form water occurred. Below this limit a rapid reaction between the hydrogen and chlorine occurred, which was complete in a few minutes, only a trace of water formation, if any, being observable. The limit of chlorine pressure was exceedingly sharp and could be fixed with precision to one or two mm. In the particular apparatus used it was 135 mm. at 300° C. The experiments were then carried out at other temperatures, the quantity of hydrogen-oxygen mixture always being adjusted to a constant molar concentration in the reaction bulb. It was found, contrary to initial expectation, that the hydrogen-oxygen explosion could be sensitised down to room temperature, though a much greater chlorine pressure was required at this lower temperature. In the accompanying graph (Fig. 1) is plotted the limiting chlorine pressure, reduced to 0° C., required to sensitise the explosion of (2H₂ + O₂) at constant molar concentration corresponding to a total pressure of 156 mm. at 0° C.