Open AccessThe displacement by ultra violet light of the explosion limit in a chain reaction
Author(s) -
Cyril Norman Hinshelwood,
Klaus Clusius
Publication year - 1930
Publication title -
proceedings of the royal society of london. series a, containing papers of a mathematical and physical character
Language(s) - English
Resource type - Journals
eISSN - 2053-9150
pISSN - 0950-1207
DOI - 10.1098/rspa.1930.0176
Subject(s) - limiting , tube (container) , chemistry , oxygen , chain reaction , thermodynamics , critical point (mathematics) , explosive material , materials science , analytical chemistry (journal) , photochemistry , physics , chromatography , composite material , organic chemistry , mathematics , engineering , mechanical engineering , mathematical analysis
Mixtures of phosphine and oxygen at the ordinary temperatures do not react appreciably in the course of several days if the pressure is respectively above or below one of two critical values. If the pressure is between these values the gases explode with a bright flash. This behaviour can be explained by assuming that the oxidation is a chain reaction. The lower limiting pressure is that at which chains begin to multiply more rapidly than they are broken by the walls of the vessel, as shown by the fact thatp 0 2 .p PH 3 at this point is inversely proportional to the square of the diameter of the cylindrical containing tube. The upper limiting pressure is that at which the deactivation in the gas phase becomes great enough to prevent the chains from multiplying, and is independent of the diameter of the tube. Moreover the oxygen rather than the phosphine is the principal deactivating agent. In a tube of diameter 2 cm., and with an equimolecular mixture, the lower critical pressure is of the order of 1 to 2 mm.; the upper critical pressure would be about 0⋅2 atmosphere. Dalton discovered that if a stable mixture above the upper limiting pressure is exposed to ultra-violet light a rapid but non-explosive interaction occurs; and that suitable illumination thus provides a means of controlling the initial process upon which the development of the chains depends. It seems, therefore, that an investigation of the manner in which the critical explosion limits are influenced by ultra-violet light might lead to a deeper understanding of the mechanism of chain propagation. The present paper deals with the lower pressure limit.