MEMOIR XXL] INFLUENCE OF LIGHT UPON CHLORINE. 3^3 



Perhaps it may have been that the insolation to which 

 they submitted the chlorine was not continued sufficient- 

 ly long, or perhaps the light was not sufficiently intense. 

 My opinion was founded on three different conditions of 

 the experiment 1st. On the behavior of chlorine itself 

 confined over salt water ; 2d. On the effect of a mixture 

 of chlorine and hydrogen in equal volumes as disengaged 

 from hydrochloric acid by a voltaic current; 3d. On the 

 action of a solution of pure chlorine in distilled water. 

 In each of these instances, the active properties imparted 

 to the chlorine by exposure to light were plainly per- 

 ceptible for a long time after. Indeed, I infer from the 

 experiments of those chemists that they found the effects 

 to continue for a certain brief period. If they do so 

 continue, though only in a momentary manner, after the 

 light has been shut off, I do not see in what other man- 

 ner we are to explain the result than on the principle of 

 a change in the relations of the chlorine. In this inter- 

 pretation it is very well known that Berzelius coincided 

 in his account of my experiments in the Annual Report 

 for 1847. 



At first I thought that there was a general analogy 

 between the case of chlorine thus thrown into an active 

 state and that of iron in its passive condition. An iron 

 wire which has been made passive will quickly revert 

 to the condition of activity if submitted to any jarring, 

 vibration, or other trivial disturbance; its passive state 

 being in one sense permanent, though very easily lost. 

 But subsequently I found many reasons for supposing 

 that the impression is of a much more lasting nature, 

 and resembles that on phosphorus after a similar expos- 

 ure to the indigo rays. As an illustration of what is 

 here meant, I may relate that having obtained a thin 

 stratum of perfectly white phosphorus between two 

 pieces of glass, I exposed it to a motionless solar spec- 



