THE 
LONDON, EDINBURGH ann DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE. 
[FOURTH SERIES.] 
NOVEMBER 1857. 
XXXVII. On the Influence of Light upon Chlorine, and some 
remarks on Alchemy. By Joun W. Dravzr, M.D., Professor 
of Chemistry and Physiology in the University of New York*. 
< pamaa years ago I observed that when a mixture of chlo- 
rine and hydrogen is exposed to light, union does not oceur 
at once, but that a certain interval must elapse, during which 
absorption takes place, the combination then proceeding in a 
uniform manner. 
It is by the chlorine that this absorptive agency is exercised, 
the indigo ray being chiefly influenced. And not only is it that 
ray which is thus absorbed : to it also must be attributed the sub- 
sequent combination. ; 
Among several other facts connected with this subject, which 
may be found in the Philosophical Magazine (July 1844), the 
American Journal of Science, vol. xlix., and other publications 
of that time, there is one to which I would particularly direct 
attention. Chlorine which has been exposed to the sun has ob- 
tained properties not possessed by chlorine which has been made 
and kept in the dark; and the change is by no means transient, 
but lasts for many hours and even days. 
In their recent examination of this fact, Professor Bunsen and 
Dr. Roscoe do not appear to regard the modification in question 
as being of so permanent a nature. Perhaps it may have been 
that the insolation to which they submitted the chlorine was not 
continued sufficiently long, or perhaps the light was not suffi- 
ciently intense. My opinion was founded on three different 
conditions of the experiment :—1st, on the behaviour of chlorine 
* Communicated by the Author. 
Phil, Mag. 8. 4. Vol. 14, No. 94, Nov. 1857. ¥ 
