as connected with the Theory of Substitutions. 353 
and then transferring both to the dark, and measuring the oxygen 
which collected at the end of a day, I found in the former one 
twelfth of what was collected in the latter. 
VIII. In agiven quantity of chlorine water, the decomposition 
in the dark corresponding to a given exposure to the light having 
been performed, and the proper quantity of oxygen evolved, and 
the phenomenon ended, it can be reéstablished from time to time, 
as long as any chlorine is found in the liquid, by a renewed ex- 
posure to the sun. 
In a glass vessel like Fig. 3, which, indeed, was nothing more 
than one of Liebig’s drying apparatus, I placed a sufficient quan- 
tity of chlorine water to fill the larger vessel, and also the vertical 
tubes half full. After exposing this to the light for a certain time, 
until decomposition had fairly set in, I placed it in the dark, and 
found that for several days it gave off gas,—the quantity contin- 
ually diminishing. Finally, no more gas wasevolved. But the 
liquid still contained free chlorine, as was shown by its color. I 
therefore again exposed it to the sun, and repeating the former 
observation, found that it evolved gas for several days in the darks 
A third exposure was followed by the same result. 
The form of this vessel renders it very convenient for these ex- 
periments ; because when sufficient gas has collected for the pur- 
pose of observation, it is easily removed by inclining the instru- 
ment, without the necessity of introducing fresh quantities of 
liquid. 
Having found, as has been said, that the rapidity of the decom- 
position depended to a certain extent on the temperature, it 
seemed desirable to determine whether heat alone could bring 
about the change. 
IX. The decomposition of water by chlorine is not brought 
about by mere elevation of temperature when the liquid is set in 
the sunbeam,—although heat accelerates, it does not give rise to 
the phenomenon. 
Ist. I raised by a spirit lamp the temperature of one of the 
bulbs nearly to its boiling point, until so much gas was given off 
that all the liquid was expelled from the tube to the bottle be- 
neath. If at this temperature, which probably was higher than 
200° Fahr., chlorine had been able to decompose water, an equiv- 
alent quantity of oxygen would have been produced ; but on al- 
lowing the apparatus to cool, all the gas was re-absorbed, with 
