322 Prof. Draper on the Influence of Light upon Chlorine. 
itself, confined over salt water; 2nd, on the effects of a mixture 
of chlorine and hydrogen in equal volumes, as disengaged from 
hydrochloric acid by a voltaic current; 3rd, 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 ex- 
posure to light were plainly perceptible 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 
hight has been shut off, I do not see in what other way we are 
to explain the result, than on the principle of a change in the 
relations of the chlorine. In this interpretation it is very well 
known that Berzelius coincided, in his account of my experi- 
ments 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 sub- 
mitted to any jarring, vibration, or other trivial disturbance ; its 
passive state being im 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 exposure 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 motion- 
less solar spectrum, and found that it turned of a dark brown 
colour in those spaces on which the more refrangible rays fell, 
the effect reaching a maximum under the indigo ray. The fixed 
lines of Fraunhofer were very prettily depicted as white streaks, 
particularly the larger ones at H. I kept this sample of phos- 
phorus for several years without its showing any disposition to 
resume the active state. 
Professor Bunsen and Dr. Roscoe dwell very appropriately on 
the disturbing effects of minute quantities of extraneous gases, 
mingled with chlorine, on photo-chemical induction. No one 
who has used a tithonometer can have failed to make a similar 
remark. My attention has been directed to that subject in its 
more general aspect ; and I will ingenuously confess that I have 
made several attempts at the transmutation of metals, on the 
principle of compelling them, by the aid of solar light, to be dis- 
engaged from states of combination, in the midst of resisting or 
disturbing media. 
The following is a description of one of these alchemical 
attempts. In the focus of a burning-lens, 12 inches in dia- 
meter, was placed a glass flask 2 inches in diameter, containing 
