DECOMPOSITION BY LIGHT. 105 



luminous rays. The rays which give chlorine its colour 

 have nothing to do with this combination, those that 

 are absorbed by the chlorine being the really effective 

 rays. A highly sensitive bulb, containing chlorine and 

 hydrogen, in the exact proportions necessary for the 

 formation of hydrochloric acid, was placed at one end of 

 an experimental tube, the beam of the electric lamp 

 being sent through it from the other. The bulb did 

 not explode when the tube was filled with chlorine, 

 while the explosion was violent and immediate when 

 the tube was filled with air. I anticipate for the liquid 

 chlorine an action similar to, but still more energetic 

 than, that exhibited by the gas. If this should prove 

 to be the case, it will favour the view that chlorine 

 itself is molecular and not monatomic. 



Production of Sky-blue by the Decomposition of Nitrite 

 of Amyl. 



When the quantity of nitrite vapour is considerable, 

 and the light intense, the chemical action is exceedingly 

 rapid, the particles precipitated being so large as to 

 whiten the luminous beam. Not so, however, when a 

 well-mixed and highly attenuated vapour fills the ex- 

 perimental tube. The effect now to be described was 

 first obtained when the vapour of the nitrite was de- 

 rived from a portion of its liquid which had been ac- 

 cidentally introduced into the passage through which 

 the dry air flowed into the experimental tube. 



In this case, the electric beam traversed the tube for 

 several seconds before any action was visible. Decom- 

 position then visibly commenced, and advanced slowly. 

 When the light was very strong, the cloud appeared of 

 a milky blue. When, on the contrary, the intensity 

 was moderate, the blue was pure and deep. In Briicke's 

 important experiments on the blue of the sky and the 



