448 
me. t. h. laby on the supersaturation and 
kept below 80 mm. of mercury. With this pressure the piston falls rapidly—so 
rapidly, in fact, that a number of pistons were broken. 
The*amount of the expansion in any experiment is measured by 
v -2 _ the initial gas pressure _ B — it— ^ 
i\ the final gas pressure B — 7r— s 2 ’ 
where B is the barometric pressure, it the saturated vapour pressure of the liquid at 
the temperature of the experiment (i.e., initially), and .q the initial and s 2 the final 
reading; of the gauge P. 
The Expansion Chambers. 
The expansion chamber, used to find the least expansion to produce condensation in 
dust-free air saturated with the various organic vapours, is drawn in fig. 2. It waa 
made so that only mercury and glass come in contact with the vapour. The test- 
tube T is fitted by the rubber cork B to the expansion apparatus E. Mercury and 
then the liquid to be used are admitted from M, until the liquid, which is always 
above the mercury, overflows into E and the lower part of the apparatus. When the 
apparatus is in use, the liquid L under examination lies above the mercury, as 
