Chemistry and Physics. 223 
The only apparatus required in most cases is represented in 
the accompanying figure, which is drawn to scale, The bulb } 
has a capacity of about 100 cm.’ and is about 20 c.m., long, and 
the glass tube to which it is attached is about 60 ¢c.m. long and 
6mm. wide. The upper end of this tube is closed by a rubber 
stopper d, while to its side is united the very narrow delivery 
tube a, which conducts the expelled air to a ' 
pneumatic trough. By means of a wire guard 
the bulb is prevented. from touching the sides 
of the iron bath in which it is heated, and a 
small amount of asbestos at the bottom of 
the bulb serves to break the fall of the small 
to be obtained. For comparatively low tem- 
peratures the most convenient bath is the 
vapor of some high boiling liquid, whose ebul- 
lition is so regulated that the vapor condenses 
before reaching the open mouth of the long 
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constant (a condition which is indicated by 
the fact that bubbles of gas cease to escape 
rom the open mouth of the tube, while at the 
Same time there is no teridency in the water 
to recede) the necessary observations are Made in a very simple 
way. The stopper at d is removed, the small tube containing 
the — substance is dropped in, and the stopper instantly 
replaced. The few bubbles of air displaced by the stopper are of 
