532 Prof. Draper on the Allotropism of Chlorine, 



VI. The evolution of gas is not of the nature of a fermen- 

 tation, for when it once sets in tlie molecular motion is not 

 propagated from particle to particle, but only affects those 

 which were originally exposed to the rays. 



Let a bulb be filled with chlorine-water which has been ex- 

 posed to the sun, and in a second bulb place a quantity of the 

 same liquid equal to about one-third of its capacity. Fill the 

 remaining two-thirds with chlorine water which has been 

 made and kept in the dark, and after keeping both bulbs in 

 obscurity for some days, measure the volumes of gas they con- 

 tain. If the qualities of chlorine which has been changed by 

 exposure were communicable by contact or close proximity 

 from atom to atom, we might expect that both the bulbs would 

 yield the same quantity of gas, but this is very far from being 

 the case; and in such an experiment I found that the bulb 

 containing the mixture gave only one-fourteenth of the gas 

 contained in the other. 



VII. The quantity of gas which thus collects in the dark, 

 depends on the intensity of the original disturbance, which in 

 its turn depends on the time of exposure to the rays, to their 

 intensity, and other such conditions. In other words, the 

 rays are perfectly definite in their action, a long exposure 

 giving a larger amount of subsequent decomposition, and a 

 short exposure a lesser amount. 



On exposing a bulb filled with chlorine-water to the rays 

 until bubbles of gas began to appear, and a second one until 

 the decomposition had been actively going on for a quarter of 

 an hour, and then transferring both to the dark, and measu- 

 ring the oxygen which collected at the end of a day, I found 

 in the former one-twelfth of what was contained in the latter. 



VIII. In a given quantity of chlorine-water, the decompo- 

 sition in the dark corresponding to a given exposure to the 

 light having been performed, and the proper quantity of oxy- 

 gen evolved, and the phaenomenon ended, it can be re-esta- 

 blished from time to time as long as any chlorine is found in 

 the liquid, by a renewed exposure 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 

 quantity 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 continually diminishing. Finally no more gas was 

 evolved ; but the liquid still contained free chlorine, as was 

 shown by its colour. I therefore again exposed it to the 

 sun, and repeating the former observation, found that it 



