516 Scientific Proceedings, Royal Dublin Society. 



hypothesis is scarcely sufficient. An explanation may be suggested from 

 Nernst's law of distribution. Since the relation between acid in the liquid and 

 vapour phases will only remain constant provided the molecular state does 

 not change, it might be inferred that in the solution some alteration in the 

 state of molecular aggregation takes place on the addition of sulphuric acid. 

 Small quantities of other non-volatile acids, such as phosphoric, have a 

 similar effect. With a change in the state of molecular aggregation the rate 

 of distillation will alter. It is assumed that in the case of the addition of 

 any other volatile fatty acids the rate of distillation is not altered. On this 

 assumption rests the basis for the determination of all mixtures of acids. As 

 a fair agreement between the observed and calculated results has been 

 obtained, this hypothesis is stated to have been proved. However, according 

 to Upson, Plum, and Schott, 1 the Duclaux method is incapable of detecting 

 less than four per cent, variation, consequently the statement that the rate of 

 distillation of each acid is not affected by the presence of other volatile acids 

 can only be stated to have been proved approximately. 



During the course of a distillation following Stem's procedure, it is import- 

 ant that the variation in the volume should be as small as possible. This 

 precaution is necessary as experimental results show that even a small change 

 in the volume appreciably influences the distillation constants. Stein states 

 that " the speed of distillation is reduced with increased amount of liquid in 

 the distilling flask, and it appears that the rate of evaporation of the liquid 

 in the flask is inversely proportional to the volume. To prove this, further 

 experiments are wanting." In the present work confirmation of this hypo- 

 thesis has been obtained. In the first experiment 50 c.c. of - 08 N. solution 

 of acetic acid were distilled at constant volume. In the second experiment 

 100 c.c. of - 08 N. acetic acid was the volume used, no other conditions being 

 altered. A series of experiments of this type were carried out, taking a 

 different volume for each distillation. In a second series of experiments 

 150 c.c. of - 08 N. acetic acid were used for each experiment. Before the 

 distillation a definite amount of water was added to the flask. The total 

 quantity of acid used in each experiment was therefore the same, so that with 

 increase in volume there was a proportional decrease in concentration. From 

 the constants obtained by the distillation of 1,000 c.c. the values of the con- 

 stants when other volumes of solution have been employed were calculated, 

 on the assumption that the rate of distillation is inversely proportional to the 

 volume. The results are recorded in Tables 1 and 2. In figs. 1 and 2 the 

 relation between the distillation constants and the volume of the solution is 



1 J. Amer. Chera. Soc, 1917, 39, 731. 



