NUCLEAR CONDENSATION OF CERTAIN ORGANIC VAPOURS. 
447 
obtain a durable piston for expansions up to v 2 /i\ = 2. The expansion apparatus as 
used is drawn in fig:. L 
O 
The glass piston A slides freely in B. By pulling the glass rod H, the rubber bung 
E is withdrawn from the mouth of the tube F, the air inside A flows suddenly into an 
exhausted globe G, the piston descends rapidly through the mercury M, and is 
suddenly brought to rest by the rubber bung L. Its ground edge remains in tight 
contact with the rubber, and so no mercury or gas escapes from B. As the action of 
the piston is very regular, as shown by the constant pressure after expansions, its 
dimensions may be worth mentioning. They are : height 13 2 cms., diameter 4 - 5 cms., 
weight 42 grammes. P is a mercury pressure gauge in communication with B. 
The reservoir is for emptying and adjusting the height of the mercury in B. This 
form of apparatus can be readily taken to pieces and cleaned, which was often 
necessary, since a number of liquids were used. 
To obtain a given expansion, the piston A was adjusted in position until the initial 
pressure was the necessary one for that expansion. 
The pressure in the 25-litre globe G, with which the tube F communicates, was 
