VARIATION OF MOLECULAR SURFACE-ENERGY WITH TEMPERATURE. 673 
millims. rise iii the narrow capillary with which the other observations were made. 
But such observations demand abrupt change of curvature between 20° and — 90°. 
As we have no intermediate observations to guide us, the lines are not drawn. 
Plate 25 exhibits the variation of surface-energy with temperature. The close 
approach to parallelism of the straight lines is noteworthy; k, in the equation 
y (Mr)* = k{t — d) has nearly the same numerical value for all substances, except, of 
course, for those which associate. The steeper slope of the curves of acetic acid and 
of the alcohols is well marked, and also the reflex curvature; for at temperatures 
near the critical temj)eratures, the deviation, /cd (1 — begins to tell ; while at 
low temperatures the lines are curved owing to association of simple molecules to 
complex molecular groups. 
4 n 
mdcccxciii.—A. 
