76 SCIENCE PROGRESS 



predicted, the gaseous products of interaction of nitric oxide 

 and chlorine were gradually dissolved by the water in the 

 actinometer, so that the effect of adding the nitric oxide dis- 

 appeared after several days, even when the insolation vessel 

 was not exposed to light. In this respect, nitric oxide differs 

 in its behaviour from nitrogen chloride, which will remain for 

 months in the presence of moist chlorine and hydrogen and only 

 decomposes at an appreciable rate at a higher temperature or 

 under the influence of light. An idea of the magnitude of the 

 effect of nitric oxide can be gained from the following experi- 

 ment. A measure of nitric oxide, equal to ^s of the total 

 volume of the mixed gases, was admitted to the insolation 

 vessel : the mixture was exposed to the light of a glow lamp 

 during half an hour, in which period there was no detectable 

 movement of the index. If the original mixture had been 

 exposed to the light during the same length of time, about one- 

 third of the electrolytic gas would have been converted into 

 hydrogen chloride. After the illumination of half an hour, 

 the mixture was allowed to remain in the dark during two and a 

 half hours and then re-exposed to light ; during twenty-five 

 minutes there was no interaction. The actinometer was then 

 left during thirteen hours in the dark ; on exposure to light 

 there was an instantaneous formation of hydrogen chloride. 

 The movement of the index was at first slow but it gradually 

 increased until the sensitiveness of the mixture was almost as 

 great as that observed before the nitric oxide had been added. 



The inhibitory effects of chlorine dioxide and of ozone are 

 comparable with that of the product of interaction of chlorine 

 and nitric oxide. Even in the dark, the ozone completely dis- 

 appears after a few hours, owing to its extreme instability in 

 the presence of chlorine. The oxygen from the decomposition 

 of the ozone of course reduces the sensitiveness of the mixture 

 of chlorine and hydrogen but is not capable, like ozone, of 

 almost, if not completely, preventing the formation of hydrogen 

 chloride. The destruction of the ozone appears to take place 

 more rapidly in the light than in the dark. 



The known inhibitors, therefore, are oxygen, nitrogen 

 chloride, nitrosyl chloride or nitrogen peroxide, chlorine peroxide 

 and ozone. They are all oxidising substances with moderately 

 unstable molecules, the one with the most stable molecule, 

 namely oxygen, being by far the weakest inhibitor. Chemically 



