MEMOIR XIX.] MODIFIED CHLORINE. 273 



now, if this part of the process be conducted properly, 

 it will be seen that the modified chlorine commences to 

 unite with the hydrogen and the salt water rises in that 

 tube. But the unmodified 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- 

 comes slowly modified by the action of the daylight im- 

 pinging on it, union takes place. From this, therefore, 

 we perceive that chlorine which has been exposed to 

 the sun will unite promptly and energetically with hy- 

 drogen ; but chlorine that has been made and kept in 

 the dark shows no such property. 



As I doubt not this remarkable experiment will be 

 repeated by chemists, I will add that the only point to 

 which attention in particular is to be given is in the 

 final exposure to the light. This must not be too feeble, 

 or the action will be tedious; but the direct sunbeam 

 must be sedulously excluded or an explosion will result. 

 A room illuminated by one small window looking to the 

 north answers very well. It need scarcely be added that 

 care must be taken that both tubes are illuminated alike. 



II. The Change in the Chlorine is not Transient. 



Now it might be supposed that this apparent exalta- 

 tion of the electro-negative properties of the chlorine is 

 only a transient thing, which would speedily pass away, 

 the gas reverting to its original condition. 



To show that this is not so, modify some chlorine in a 

 tube as before. Place it for an hour or two in the dark 

 along with the tube of unmodified chlorine with which 

 it is to be compared, then to both add hydrogen. Ex- 

 pose them as in the former experiment to the daylight, 

 and the result will turn out as before; the modified 

 chlorine forming hydrochloric acid at once, and the un- 



modified refusing to do so. 



S 



