as connected with the Theory of Substitutions. 357 
By arranging a series of tubes containing a mixture of these 
gases in the spectrum, it was found that the gases situated in the 
indigo space went into union first. 
These various experiments enabling us thus to trace to the 
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 not 
possessed by chlorine which has been made and kept in the dark. 
In proof of this fact, I may cite an experiment from the Philo- 
sophical Magazine for July, 1844. 
“Tn two similar white glass tubes place equal volumes of chlo- 
rine which has been made from peroxide of manganese and mu- 
riatic 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 earthen- 
ware trough, filled with a saturated solution of common salt, 
which dissolves chlorine slowly, and to avoid explosions, ope- 
rate on limited quantities of the gases. ‘Tubes that are eight 
inches long and half an inch in diameter will answer very 
MBE iS hx; 
“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 is conducted prop- 
erly, it will be seen that the tithonized chlorine commences 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 becomes slowly tithonized by the ac- 
tion of daylight impinging on it, union at last takes place. From 
this therefore we perceive that chlorine which has been exposed 
to the sun will unite promptly and energetically with hydrogen, 
but chlorine which has been made and kept in the dark shows 
no such property.” ' 
Vol. xxix, No. 2.—July-Sept. 1845. 46 
