as connected with the Theory/ of Substitutions. 331 



transferred to a graduated vessel and measured. I satisfied 

 myself, by several variations of this arrangement, that the 

 small quantity of water introduced from time to time when 

 the gas bubble escaped from the end of the tube c, exerted no 

 essential influence on the phaenomenon. The following Table 

 shows the amount of gas evolved in the dark during the pe- 

 riods indicated. 



The bulb having been exposed to the sunshine, in ten mi- 

 nutes the evolution of gas commenced, and in an hour 'lO? 

 cubic inch having collected, this was cast away and the ar- 

 rangement placed in the dark. To prevent the undue escape 

 of the chlorine, a piece of flat glass, </, was laid on the open end 

 of the tube c. In each successive hour the quantity of gas 

 given in the following Table was then evolved: — 



1st hour . . -0162 



2nd -0159 



3rd -0086 



4th -0060 



5th -0038 



6th -0031 



and for four days afterwards gas was collecting in the bulb in 

 diminished quantities. 



V. This evolution of gas in the dark is not merely a gra- 

 dual escape of oxygen originally formed whilst the solution 

 was exposed to the sun, but is traceable to an influence conti- 

 nuously exerted by the chlorine, arising in properties it has 

 acquired during its exposure to the rays. 



If a bulb which has been exposed to the sun be raised by a 

 spirit-lamp to such a temperature that its gaseous constituents 

 are rapidly evolved, its extremity dipping beneath some of the 

 same solution in the bottle, after allowing a sufficient space of 

 time for the disengaged chlorine to be re-dissolved, and the 

 oxygen be turned out of the bulb, it will be found, on keeping 

 the arrangement in the dark, that oxygen will slowly disen- 

 gage as before. 



Now there is every reason to believe that any small amount 

 of oxygen dissolved in the liquid would be expelled with the 

 chlorine at a high temperature. We therefore have to infer 

 that the chlorine, after this treatment, still retains the quality 

 of causing the decomposition steadily to go forward. 



The oxygen which thus accumulates in the course of time 

 in the dark, after an exposure to the sun, does not arise from 

 any portion of that gas held in a state of temporary solution, 

 nor from peroxide of hydrogen, nor from chlorous acid in the 

 liquid undergoing gradual decomposition. From any of these 

 states a high temperature would disengage it. 



