72 FRAGMENTS OF SCIENCE. 
A glass tube 3 feet long and 3 inches wide, which had 
been frequently employed in my researches on radiant 
heat, was supported horizontally on two stands. At one 
end of the tube was placed an electric lamp, the height 
and position of both being so ar- 
Fie.2. ranged that the axis of the tube, 
and that of the beam issuing from 
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 distinc- 
tion, I call this tube the experi- 
mental tube. It was connected with 
an air-pump, and also with a series 
of drying and other tubes used 
for the purification 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 two glass tubes: one of these 
tubes (a) ended immediately below 
the cork, while the other (b) de- 
scended 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 vulcanized india-rubber 
were invariably employed. 
The little flask, thus formed, being partially filled with 
the liquid whose vapor was to be examined, was introduced 
into the path of the purified current of air. The experi- 
mental 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 b, and escaped by 
the small orifice at the lower end of b into the liquid. 
Through this it bubbled, loading itself with vapor, after 
which the mixed air and vapor, passing from the flask by 
the tube a, entered the experimental tube, where they 
were subjected to the action of light. 
