Reilly and Hickinbottom — Volatile Fatty Acids. 531 



between weight of distillate and different constants both for single acids and 

 mixtures.) It is obvious therefore that although a consideration of the 

 logarithmic and other constants will give an accurate idea of the composition 

 of the vapour at any given time, it cannot be employed with certainty to 

 decide the composition of the solution distilled. The method suggested by 



6. 



i * 



40. 60 ?0. 100. no 



Weight (in grams) of distillate. 

 Fig. 6. 



««©. 



aoo. 



Dyer of taking the point at which the logarithmic curve of the mixture 

 becomes parallel to that of the less volatile component is therefore open to a 

 very wide error, and can only be approximate. The theory of mixtures may 

 be considered thus : — Let a and b be the amounts of acid present in flask 

 initially, and x n , y„ the amounts distilled over in n fractions. 



4n2 



