The lower pressure limit in the chain reaction between hydrogen and oxygen

Abstract

Previous investigations have shown that above 460°C. there are two pressure limits between which the combination of hydrogen and oxygen takes place explosively and outside which it may abruptly become extremely slow. Practically difficulties have hitherto hindered a detailed study of the conditions governing the position of the lower limit. A modification of the earlier experimental arrangement has allowed these difficulties to be overcome, and the influence on the limit of hydrogen-oxygen ratio, vessel diameter, temperature and presence of inert gases has been investigated. The influence of these various factors corresponds in general to that found in other reactions which exhibit limit phenomena. The results are consistent with the hypothesis, already put forward and discussed, that the lower limit is that pressure where reaction chains cease to be broken at the walls of the vessel as rapidly as they are started by the “branching” of existing chains. The method of experiment was simply to prepare in A (fig. 1) a mixture of appropriate composition, measure off a small proportion of it in the capillary pipette B, and then to allow the contents of B to stream into the evacuated silica reaction vessel C. The coefficient of sharing between B and C was determined by a special calibration. C was heated in a horizontal electric furnace provided with a quartz window. If the calculated final pressure in C was below the limiting value nothing was seen when a pipetteful of mixture was added, while if it was above the limit a flash was observed. The temperature of C was measured with a thermocouple.