as connected mth the TJieory of Substitutions. 333 



evolved gas for several days in the dark. A third exposure 

 was followed by the same result. 



The form of this vessel renders it very convenient for these 

 experiments, because when sufficient gas has collected for the 

 purpose of observation, it is easily removed by inclining the 

 instrument, without the necessity of introducing fresh quantt- 

 ties of liquid. 



Having found, as has been said, that the rapidity of the de- 

 composition 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 phaenomenon. 



1st. I raised, by a spirit-lamp, the temperature of one of 

 the bulbs nearly to its boiling-point, or until so much gas was 

 given off that the liquid was expelled from the tube to the 

 bottle beneath. If, at this temperature, which probably was 

 higher than 200° Fahr., chlorine had been able to decompose 

 water, an equivalent quantity of oxygen would have been pro- 

 duced; but on allowing the apparatus to cool, all the gas was 

 re-absorbed, with the exception of a small bubble amounting 

 in volume to y^^gy of the water. This bubble, which was left 

 after the chlorine was recondensed, I found in three different 

 experiments contained 32, 33, and 36 per cent, of oxygen, 

 the remainder being nitrogen ; but this being nearly the con- 

 stitution of the gas which is dissolved in ordinary water, the 

 source from which the small bubble came was inferred to be 

 the water used in these experiments. 



2nd. One of the bulbs was painted black all over with 

 India ink; its temperature now rose much higher than in 

 former experiments when it was set in the sun, but not a bub- 

 ble of oxygen appeared. 



X. When chlorine-water has been exposed to the sun, the 

 oxygen accumulated in it is readily expelled by raising the 

 temperature. 



Having exposed one of the bulbs used in the last experi- 

 ment until it was actively evolving gas, I raised its temperature 

 with the spirit-lamp until the bulb was full of gas; but on 

 cooling this gas did not all condense, as, in the last instance, a 

 large quantity remained behind : this was oxygen. 



These ninth and tenth facts are of further interest as bearing 

 upon a question which has been much discussed by chemists, 

 — the nature of the bleaching compounds of chlorine. The 

 chloride of lime, and other such substances, probably have the 



