272 MODIFIED CHLORINE. [MEMOIR XIX. 



exhibit after they have been exposed to light ; we still 

 require to know what are the properties they possess 

 before exposure to such influences. 



Natural philosophers will also find an interest in 

 these phenomena, for they finally establish for the chem- 

 ical rays two important facts: 1st, that those rays are 

 absorbed by ponderable bodies; arid, 2d, that they be- 

 come latent after the manner of heat. Some years ago 

 I endeavored to prove that these things held for a com- 

 pound substance, the iodide of silver (Phil. Mag., Sep- 

 tember, 1841). 



For reasons which will be obvious as the description 

 proceeds, I shall speak of chlorine which has been ex- 

 posed to the beams of the sun as modified chlorine. 



I. Description of the Experiment. 



In two similar glass tubes place equal volumes of 

 chloidne, made from peroxide of manganese and hydro- 

 chloric acid by lamplight, and carefully screened from 

 access of daylight. Expose one of the tubes to the full 

 sunbeams for some minutes, or, if the light be feeble, for 

 a quarter of an hour : the chlorine in it becomes modi- 

 fied. Keep the other tube during this time carefully in 

 a dark place ; and now, by lamplight, add to both equal 

 volumes of hydrogen gas. These processes are best car- 

 ried on in a small porcelain or earthenware trough, filled 

 with a saturated solution of common salt, which dis- 

 solves chlorine slowly; and to avoid explosions operate 

 on limited quantities of the gases. Tubes that are eight 

 inches long and half an inch in diameter will answer 

 very well. The two tubes now contain the same gaseous 

 mixture, and only differ in the circumstance that one is 

 modified and the other not. Place them, therefore, side 

 by side before a window, through which the entrance of 

 daylight can be regulated by opening the shutter; and 



