Chemical Force in the Spectrum. 437 



and, as respects the mixture under trial, had become deactinized ; 

 simultaneously the mixture itself had been affected, its con- 

 stituent gases uniting ; and thus it appears that the radiation 

 had undergone a change in producing a change in the ponderable 

 matter. 



The following modification of this experiment shows the part 

 played by the chlorine and hydrogen respectively when they are 

 in the act of uniting :— 



{a) The glass absorption-vessel above described was filled with 

 atmospheric air, and the chemical force of the radiation passing 

 from the lamp through it was determined. It was measured by 

 the time required to cause the index of the actinometer to de- 

 scend through one division : this was 12 seconds. 



(6) The absorption-vessel was now half filled with chlorine, 

 obtained from hydrochloric acid and peroxide of manganese. 

 The chemical force of the ray, after passing through it, was deter* 

 mined as before. It was now represented by 25 4 seconds. 



(c) To the chlorine an equal quantity of hydrogen was added, 

 the absorption -vessel being consequently full of the mixture. The 

 radiation was now passing through a stratum of chlorine diluted 

 with hydrogen; and the point to be determined was whether it 

 had undergone the same or a greater or less loss than in the 

 preceding case, since the chlorine was now uniting with the 

 hydrogen. On measuring the force it was found to be represented 

 by 19 seconds. 



[d) Lastly, the first [a) of these measures was repeated, with the 

 view of ascertaining whether the intensity of the lamp had 

 changed. It gave 12 seconds, as before. 



From these observations it may be concluded that the addition 

 of hydrogen to chlorine does not increase its absorptive powder. 

 Moreover it is obvious that the action of the radiation is expended 

 primarily on the chlorine, giving it a disposition to unite with 

 the hydrogen, and that the functions discharged by the chlorine 

 and by the hydrogen respectively are altogether different. The 

 ray itself also undergoes a change ; it suffers absorption, and 

 loss of a part of its vis viva. 



As to the ray which is thus absorbed. In 1835 I found that a 

 radiation which has passed through a solution of potassium 

 bichromate could not accomplish the union of chlorine and hy- 

 drogen, but one which has passed through ammonio-sulphate 

 of copper could do it energetically. This indicates that the 

 effective rays are among the more refrangible. 



On exposing these gases in the spectrum, the maximum action 

 takes place in the indigo rays (Phil. Mag. December 184?3). 



Recently (1871) some suggestions have been made by M. 

 Budde respecting the action of light upon chlorine. 



