Youne— Vapour-pressure of a pure Liquid at constant Temp. 99 
II. Series in which signs of decomposition were observed at 
the higher temperatures. 
III. Series in which the removal of air appears not to have 
been successful. 
TV. Acetic acid, which exhibits molecular association in both 
the liquid and gaseous states. 
For each substance (except acetic acid) the number (JV) of 
vapour-pressure determinations is given, together with the mean 
percentage difference (A) between the pressures corresponding to 
the lowest and highest volume-ratios (Viig./Voap.). As the errors 
are likely to be smaller at low temperatures than at high, the 
data up to 180° and above 180° are given separately. 
[Group I. 
