80 



KINETICS OF CHEMILUMINESCENCE 



but visible light.* The intensity of the chemiluminescence of hydrazine 

 appears to be independent of oxygen concentration. This is interesting 

 as luminol and the DPD's in general can be thought of as substituted 

 hydrazine. This being the case, it should not be surprising if both 

 were to undergo many of the same reactions, which suggests that the 

 DPD's undergo a similar weakly luminous reaction with ferricyanide 

 in the absence of oxygen. 



i 50 



Oxygen (ml) 



Fig. 2. Intensity versus time curve for luminol being oxidized by ferricyanide in 

 the presence of oxygen. 



It was found by Bremer ( 1953 ) that if oxygen was admitted after 

 the ferricyanide and luminol have been allowed to react under anaero- 

 bic conditions, the solution would emit a reasonably bright light. The 

 present authors have been able to confirm this observation and, in 

 addition, have found that if a few minutes is allowed to elapse 

 between the mixing of the luminol and ferricyanide, no light is pro- 

 duced. The importance of Bremer's observation will be discussed later 

 in connection with the proposed mechanism. The second observation 

 is important in that it indicates that ferricyanide does react with 

 luminol in the absence of oxygen. This is proof that there is at least 

 one other reaction route besides the chemiluminescent one involving 

 oxygen. The experiments just described indicate that, in any case, 



* Unpublished work of the present authors. 



