8o SCIENCE PROGRESS 



demonstrated that nitrosyl chloride had no influence on the 

 thermal interaction of chlorine and carbon monoxide but that 

 at high, as well as low, temperatures, it reduced to a negligible 

 value the responsiveness of the mixture to light. The kind 

 of chemical inhibition under discussion is therefore essentially 

 and exclusively a photo-phenomenon. If a substance owed 

 its effectiveness as an inhibitor to its property of combining 

 with an unknown catalyst, instead of to its capacity to modify 

 and degrade the vibrational energy of the system, then we 

 should expect it to retard the thermochemical as well as the 

 photochemical change. 



We shall now pass on to the consideration of the bearing 

 on the theory of the relation which has been found to subsist 

 between the partial pressure of the oxygen contained in a 

 mixture of chlorine and hydrogen and the sensitiveness of the 

 mixture to light. It has been shown that if the proportion 

 of oxygen be small, the sensitiveness (i.e. the velocity of 

 formation of hydrogen chloride for constant intensity of 

 illumination) is almost inversely proportional to the amount 

 of oxygen present in a given volume. 1 This result is in 

 accordance with the assumptions that the degradation of the 

 vibrational energy which causes the interaction of the chlorine 

 and hydrogen is entirely effected by the oxygen and that the 

 rate of degradation is proportional to the concentration of the 

 oxygen. An interesting and obvious deduction from the 

 experimental result just stated is that if the relation continue 

 to hold for infinitely small concentrations of oxygen, a mixture 

 of chlorine and hydrogen entirely deprived of oxygen would 

 be infinitely sensitive. It has recently been shown that the 

 same relation does not hold between the sensitiveness of a 

 mixture of carbon monoxide and chlorine and the content 

 of oxygen if the value of the concentration of the oxygen be 

 large; 2 when the partial pressure of the oxygen is relatively 

 great, the doubling of the concentration has very little effect 

 on the sensitiveness of the mixture ; thus, in the case of a 

 mixture which contained 25 per cent, of oxygen the sensitive- 

 ness was 0745, whereas in one which contained 50 per cent, of 

 oxygen (the concentration of the chlorine and carbon monoxide 

 being the same) the sensitiveness was 0733. This result 



1 Chapman, MacMahon, Trans. Chem. Soc. 1909, 95, 960. 



2 Chapman and Gee, Trans. Chem. Soc. 191 1, 99, 1726. 



