128 Scientific Proceedings, Royal Dublin Society. 



In the t'oUowing table the qualitative elfect of the addition of acids is 

 shown, the distillation being carried out at constant volume. 



The solutions had the following compositions : — 



1. 100 c.c. of dilute acetic acid + 50 c.c. water. 



2. „ „ „ + 50 c.c. of phosphoric acid. 



3. „ „ „ + 50 c.c. of sulphuric acid 



4. „ „ „ +50 c.c. of oxalic acid solution. 



These results are not comparable, but they show that acids otlier than 

 sulphuric acid considerably influence the distillation constant. 



The addition of a neutral salt to a solution of a weak acid, such as acetic, 

 will have a small influence on the degree of dissociation. If a salt of the acid 

 is added, an ion is introduced into the solution which is common to both 

 electrolytes.' A considerable suppression of the ionisation of the acid will 

 occur if the salt added is ionised to any great extent. Sodium acetate when 

 added to acetic acid considerably reduces the dissociation of the a.cetic acid. 

 It might be expected that the distillation constant of acetic acid in presence 

 of sodium acetate would be approximate to that for the undissociated acid. 



' In a recent paper, published since the present work had been completed, M'Bain and 

 Kam (Trans. Chem. Soc. , 1919, 115, 1332) have recorded an investigation into the efifect 

 of the addition of certain salts to acetic acid. They determined the ratio of acetic acid in 

 the vapour to that in the liquid phases for the pure aqueous solutions, and solutions 

 containing dissolved salts. They suppose that the addition of a salt enhances the 

 chemical potential of the acid, and as a consequence there is an increase in the vapour 

 tension of the acid. They also found that there was a considerable variation in the 

 eft'ect when different salts were employed. [Cf. Reilly and Hickinbottom, Brit. Assoc. 

 Ann. Report, 1919, p. 170.] 



