Evaporation and Dissociation. 



197 



lies much higher, the pressures were in no case very great. 

 The behaviour of acetic acid, however, contrasted with that 

 of the alcohols, ether, and carbon dioxide is very striking. 

 The equation p = bt—a does not apply; in other words lines 

 of equal volume are not straight, but are curves of double 

 flexure. We shall consider the meaning of this peculiarity 

 after adducing data. 



1. Methyl Alcohol. — The data are at present in the hands 

 of the Royal Society. The values of b were, as before, deter- 

 mined by reading points on the isothermal curves at equal 

 volumes ; constructing isochors graphically, and having thus 

 obtained approximate values of 6, these were smoothed by 

 plotting them as abscissas, the ordinates being the reciprocals 

 of the volumes. The values of b given in the Table which 

 follows were those read from this curve. The values of a 

 were calculated from the equation a = bt—jp, the mean value 

 obtained from all the readings at each volume being taken 

 as correct. 



Table I. 



Vol. 



b. 



log b. 



a. 



c. c. per gram. 









7 



626-5 



2-79692 



263430 



8 



569-0 



2-75511 



235370 



9 



509-0 



2-70672 



206290 



10 



452-5 



2-65562 



179090 



11 



405-3 



2-60778 



156660 



12 



3650 



2-56229 



137810 



14 



2990 



2-47567 



107460 



16 



248-5 



2-39533 



84730 



18 



211-0 



2-32428 



68364 



20 



184-8 



2-26670 



57474 



25 



139-8 



214551 



39724 



30 



112-5 



205115 



29834 



40 



80-0 



1-90309 



18913 



50 



620 



1-79239 



13401 



70 



43-5 



1-63849 



8631 



100 



26-95 



1-43056 



4092 



135 



18-95 



1-27761 



2398 



170 



14-50 



106137 



1624 



200 



1200 



107918 



1187 



240 



9-65 



098453 



794 



280 



8-00 



0-90309 



455 



340 



6-30 



0-79934 



307 



400 



5-15 



0-71181 



159 



450 



4-57 



0-65992 



130 



The following Table gives the pressures read from the iso- 

 thermals from which these values of a and b were obtained; 

 and vve have added, for the sake of comparison, the pressures 

 recalculated by help of these values. 



