MEMOIR XIX.] 



MODIFIED CHLORINE. 



277 



TABLE I. 



Many years ago M. Berard made experiments on the 

 explosion of chlorine and hydrogen, and concluded from 

 his results that it was brought about by the violet ray. 

 This was at a time when the methods of making these 

 experiments were less exactly known. It is a very easy 

 matter to prove that in reality the indigo is the active 

 ray, and that from a maximum point which is in. the in- 

 digo, but towards the blue, the effect gradually dimin- 

 ishes to each end of the spectrum. 



The following table gives the calculated approximate 

 intensity of the chemical force for each ray, deduced 

 from the foregoing experiment : 



TABLE II. 



There is a great advantage which experiments con- 

 ducted in this way possess over those depending for 

 their indication on the stains impressed on daguerre- 

 otype plates or sensitive papers. In those cases we ob- 

 tain merely a comparative contrast for different regions 

 of the spectrum; in this we have absolute measures de- 

 termined by a definite chemical effect and the rise of a 



* Even after the longest exposure I had the means of giving it, no movement took 

 place in the tube in the extreme red, and I am doubtful about that in the red and 

 orange. 



