The “Activation” of Chlorine

Abstract

The large number of papers on the nature of the photochemical reaction between chlorine and hydrogen is evidence of the fundamental significance of this still unsolved problem. That a reaction takes place, especially under the influence of the shorter wave lengths, and that it is the chlorine which is effective in absorbing the radiant energy is established, but almost every concomitant fact has been repeatedly asserted and denied by various investigators. The recent discovery of the ozone form of hydrogen,1 however, suggests strongly that chlorine also may exist in some similar active modification, and calls for a reexamination of the evidence. The work here reported shows that if such an active form exists at all, it returns to the ordinary form within a very small fraction of a second, but that, nevertheless, an increased activity can be imparted to the chlorine by previous exposure to light such that the period of induction of the photochemical reaction with hydrogen is reduced or eliminated, this condition lasting for hours or days, but not indefinitely.William Cruickshank, who first studied this photochemical reaction, observed2 that the reaction is first hesitant, and requires several minutes before it attains a constant maximum velocity. This "period of indue-'