MEMOIR XX.] THE ALLOTROPISM OF CHLORINE. 30} 



rose in the tube c. But in the other, which had not 

 been exposed to the sun, no movement took place until 

 the gases had had time to be modified by the light com- 

 ing through the open shutter. 



When care has been taken to have the gases made 

 quite dry, and, owing to the narrowness of the tube , no 

 aqueous vapor has had time to contaminate the gas in B, 

 so that no water is present to condense the hydrochloric 

 acid as it forms, a little delay may be occasioned in the 

 liquid rising in the tube, the chlorine of which was ex- 

 posed to the sun. But after a time a mist arises in the 

 neighborhood of the water in the narrow tube, due to 

 the hydrochloric acid condensing, and then the process 

 goes forward with regularity. 



It appears, therefore, that chlorine by exposure to the 

 sun contracts a tendency to unite with hydrogen which 

 is not possessed by chlorine which has been kept in the 

 dark. 



On the Allotropism of Chlorine, or its Passive and Act- 

 ive States. 



In what, then, does this remarkable change impressed 

 by indigo rays upon chlorine consist ? This is the ques- 

 tion immediately arising from the phenomena we have 

 had under consideration. 



To this I answer that when chlorine has been thus in- 

 fluenced its electro-negative properties are exalted, and 

 it has passed from an inactive to an active state. 



It is now fully established that a great number of the 

 elementary bodies undergo similar modifications. Many 

 of them can exist in no less than three different states, 

 and these peculiarities are impressed on the compounds 

 to which they give rise. To these peculiarities Berze- 

 lius directed the attention of chemical philosophers 

 in his Memoir " On the Allotropism of Simple Bodies, 



