ON EVAPORATION AND DISSOCIATION. 
83 
copper sulphate induces a change, the liquid exhibiting the iodoform reaction. We 
have little doubt, therefore, that the specimen of ether used by Regnault contained 
alcohol; and it is known from Professor Guthrie’s researches that the presence of a 
minute amount of an impurity has a great influence on vapour-pressures. A further 
argument in support of this view will be given when we consider the heats of 
vaporisation. It should here be pointed out, moreover, that Regnault’s observations 
below 0° agree nearly as well with our formula as with his own, whereas our observa¬ 
tions are in very close accordance with our calculated results. 
II. Compressibilities .—The isothermals of the liquid state, showing decrease in 
volume w T ith increase of pressure, were, for the purpose of smoothing, plotted on a 
sheet of curve-paper, and isobars were drawn representing the relations of volume to 
temperature. The discrepancies of individual observations were thus eliminated, and 
from the isobars the numbers were retransferred to the isotherms. It will be seen on 
inspection of the curves (Plate 6) that the smoothed curves agree well with the 
observations. The Table which follows shows these results, and includes some of the 
isotherms corresponding to the gaseous state. The volumes are those of 1 gramme. 
M 2 
