336 Prof. Draper on the Allotropism ofChlorine^^ 



In the Philosophical Magazine the same result was estao 

 blished by me in another way. I found that a ray which had' 

 passed through a given thickness of a mixture of equal vo- 

 lumes of chlorine and hydrogen, lost by absorption just half 

 as much of its original intensity as when it passed through the 

 same thickness of pure chlorine gas, a result which obviously 

 leads to the conclusion, that when chlorine and hydrogen 

 unite under the influence of the sun, they discharge function^J 

 which are different, the chlorine an active and the hydrogen a 

 passive function. The primary action or disturbance takes 

 place upon the chlorine, and a disposition is communicatexJfd-^ 

 it, enabling it to unite readily with the hydrogen. ; i f )ni 



By arranging a series of tubes containing a mixtui'e of thescP' 

 gases in the spectrum, it was found that the gases situated 4in^'^ 

 the indigo space went into union first. •'■ '» 'on ?jvh ylod iitdT 

 These various experiments enabling us thus to trace to th^^ 

 chlorine the source of disturbance, I have next to remark, that'^^ 

 chlorine, which has been exposed to the rays of the sun, has 

 gained thereby a tendency to unite with hydrogen, which is *j 

 not possessed by chlorine which has been made and kept iit''^ 

 the dark. 



In proof of this I may cite an experiment from the Philo- 

 sophical Magazine (July 1844). " In two similar white glass 

 tubes place equal volumes of chlorine, which has been made 

 from peroxide of manganese and muriatic 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 which " 

 is in it becomes tithonized. 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 carried on in a small porcelain or earthenware trough, 

 filled with a saturated solution of common salt, which dissolves 

 chlorine slowly ; and to avoid explosions, operate on limited 

 quantities of the gases. Tubes that are eight inches long and 

 halfaninchin diameter will answer very well. The tubes 

 now contain the same gaseous mixture, and differ only in the ;^ 

 circumstance that one is tithonized 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 now, if this part of the process be conducted '-""^ 

 properly, it will be seen that the tithonized chlorine com- 

 mences to unite with the hydrogen, and the salt water 

 rises in that tube. But the untithonized chlorine shows no 

 disposition to unite with its hydrogen, and the liquid in its 

 tube remains motionless for a long time. Finally, as it be- 



