DECOMPOSITION BY LIGHT. 



97 



FIG. 2. 



the lamp, were coincident. In the first experiments 

 the two ends of the tube were closed by plates of rock- 

 salt, and subsequently by plates of glass. For the sake 

 of distinction, I call this tube the experimental tube. 

 It was connected with an air-pump, and also with a 

 series of drying and other tubes used for the purifica- 

 tion of the air. 



A number of test-tubes, like F, fig. 2 (I have used 

 at least fifty of them), were converted into Woulf's 

 flasks. Each of them was stopped 

 by a cork, through which passed a[ 

 two glass tubes : one of these 

 tubes (a) ended immediately 

 below the cork, while the other 

 (b) descended to the bottom of 

 the flask, being drawn out at its 

 lower end to an orifice about 

 0-03 of an inch in diameter. It 

 was found necessary to coat the 



cork carefully with cement. In 



the later experiments corks of 



vulcanised india-rubber were in- 

 variably employed. 



The little flask, thus formed, 



being partially filled with the 



liquid whose vapour was to be 



examined, was introduced into 



the path of the purified current 



of air. The experimental tube 



being exhausted, and the cock 



which cut off the supply of 



purified air being cautiously 



turned on, the air entered the flask through the tube 6, 



and escaped by the small orifice at the lower end of 



b into the liquid. Through this it bubbled, loading 

 VOL. i. H 



