Sir J. W. Lubbock on the Heat of Vapours. 25 



The solid and liquid acid still present two curves, but the 

 curve of the solid acid is constantly below that of the liquid acid. 



Fourth Series, February 3. 



The fourth series was made with acetic acid distilled a second 

 time over anhydrous phosphoric acid. The same fact was ob- 

 served as in the third series ; that is to say, two separate curves, 

 that of the liquid acid having the larger ordinates. 



I think that the anomalies presented by monohydrated acetic 

 acid may be explained by the presence of very small quantities 

 of foreign substances. The acid obtained by simple crystalliza- 

 tion probably contained a very small quantity of water in excess, 

 whilst the distilled acid contained a little acetone. As long as 

 the acid is liquid, the foreign matter is disseminated through its 

 whole mass, and does not exert any sensible influence upon the 

 tension of the vapour. But this is by no means the case when 

 the acid becomes solid ; then the foreign matter separates, in 

 combination with a smaller quantity of acetic acid, and its influ- 

 ence upon the tension of the vapour thus becomes much more 

 remarkable. 



III. On the Heat of Vapours. 

 By Sir J. W. Lubbock, Bart., F.R.S.* 



IN my Treatise on the Heat of Vapours, p. 2, I gave 

 lowing expression : 



the fol- 



l+aff = {l + a0) 



i-v 

 (p—-E) 



(/-T-E) 



* Communicated by the Author. 



