PRODUCTS OF ACETOUS FERMENTATION. 43 



per cent, of water shows the same specific gravity as the anhy- 

 drous acid. From this point on, the specific gravities of the 

 mixtures decrease with the increase in the content of water. 



This peculiar behavior of the mixtures renders the accurate 

 determination of the content of acid in a concentrated mixture 

 by means of the aerometer impossible. There are a number 

 of determinations of specific gravities of acetic acid with varying 

 contents of water (by Mohr, von der Toorn, Oudemans, etc.), 

 but they differ considerably from each other, like the tables at the 

 end of this volume, so that, while the specific gravity test answers 

 very well for the determination of the amount of anhydrous acid 

 in dilute solutions, it is very fallacious when the acid increases in 

 strength, and an accurate determination can only be effected by 

 chemical methods. 



Highly concentrated acetic acid has recently found considerable 

 application in photography and surgery, and frequently occurs in 

 commerce in the form of so-called vinegar essence. The acetic 

 acid occurring under this name is generally prepared from wood 

 vinegar and is only fit for the preparation of table vinegar when 

 a chemical examination shows no trace of tar products, which are 

 formed in abundance, besides acetic acid, in the dry distillation of 

 wood. 



In regard to the composition of acetic acid, it may be men- 

 tioned that one atom of hydrogen can be readily replaced by 

 univalent metals or univalent compound radicals which may be 

 expressed by 



H lo 



c 2 H 3 or 



TT ~j 



wherebv the acetic acid is considered 'as water tr > O in which 



M J 

 one atom of hydrogen is replaced by the compound radical 



C 2 H 3 O = acetyl 



If the one atom of hydrogen standing by itself be replaced by 

 a univalent metal a neutral acetate is formed, for instance : 



Na ) Q 

 C 2 H 3 OJ C 

 or sodium acetate. 



If this atom of hydrogen is replaced by a uuivalent compound 



