of Hydrogen and Chlorine under the influence of Light. 401 



The date of the first and last observations I have not recorded, 

 having omitted them in my rough notes. But the value for the 

 rate of action at 11° taken in January 1904 agreeing nearly with 

 the value at 12'5° in November 1903, gives a sufficient guarantee 

 that the quality of the gas mixture evolved during that time had 

 not altered. The same acid was used all through the experiments 

 for generating the mixture experimented on. The observation at 

 46° is not a good one, as appears from the curve Fig. 2. It will 



40 



i s 



■ t 



O 10 20 30 40 60 60 



Fig. 2. 



be noticed that for this observation the gas mixture had cooled 

 from the former observation at 50° C. It was found afterwards 

 that after cooling it takes a longer time for the state of maximum 

 sensitiveness to be reached than after heating. This is probably 

 owing to the fact noticed by Bunsen and Roscoe, that an excess 

 of Hydrogen in the mixture produces a much greater effect in 

 retarding the action than an equal excess of Chlorine. After 



