312 INFLUENCE OF LIGHT UPON CHLORINE. [MEMOIR XXI. 



MEMOIR XXL 



ON THE INFLUENCE OF LIGHT UPON CHLORINE, AND SOME 

 REMARKS ON ALCHEMY. 



From the Philosophical Magazine, November, 1857. 



CONTENTS : Modification of chlorine by the sun-rays. The modification 

 is not transient. Alchemical attempts to modify metals. Exposure 

 of silver chloride to a burning-lens. The resulting silver is not acted 

 upon by nitric acid. 



SEVERAL years ago I observed that when a mixture 

 of chlorine and hydrogen is exposed to light, union does 

 not occur at once, but that a certain time must elapse 

 during which absorption takes place, the combination 

 then proceeding in a uniform manner. 



It is by the chlorine that this absorptive agency is ex- 

 ercised, the indigo ray being mainly concerned. And 

 not only is it that ray which is thus absorbed : to it 

 must be attributed also the subsequent combination. 



Among several other facts connected with this subject, 

 which may be found in the Philosophical Magazine 

 (July, 1844), The American Jownal of /Science, Vol. 

 XLIX., and other publications of that time, there is one 

 to which I would particularly direct attention. Chlo- 

 rine which has been exposed to the sun has obtained 

 properties not possessed by chlorine which has been 

 made and kept in the dark, and the change is by no 

 means transient. It lasts for many hours, and even days. 



In their recent examination of this fact, Professor Bun- 

 sen and Dr. Roscoe do not appear to regard the modifi- 

 cation in question as being of so permanent a nature. 



