ACETIC ACID. 



783 



of oxygen, with the formation of 1 atom of anhydrous acetic acid, 

 and 3 atoms of water : 



C 4 H 6 O 2 and 4O=C 4 H 3 O 3 and 3HO. 

 or C 4 H 5 + HO and 4O=HO,C 4 H 3 O 3 , + 2HO. 



Hence, when alcohol is converted into acetic acid, 2 atoms of 

 oxygen are directly absorbed, and 2 atoms of oxygen convert 2 

 atoms of hydrogen into water. The atom of water of the alco- 

 hol and the 2 atoms of water produced, are all retained, and 

 form a remarkable terhydrate of acetic acid. 



Pure alcohol, diluted with water and exposed to air, does not 

 acidify ; the presence of some foreign organic matters, which 

 exist in wine and beer, is necessary to act as a ferment, and to 

 place the alcohol in a condition to absorb oxygen. This fer- 

 ment is no doubt an oxidable azotised matter. Some kinds of 

 beer, in which the ferment has been completely exhausted and 

 precipitated by a preceding highly-protracted vinous fermenta- 

 tion, such as the Bavarian beer, are not liable to become sour or 

 undergo the acetous fermentation. The rapid process of acidi- 

 fying alcohoi, introduced into Germany by MM. Wageman and 

 Schuzenbach, is the most interesting, in a scientific point of view. 



Strong alcohol is diluted with 4 or 6 parts of water, and about 

 1- 1000th of yeast, must of beer, vinegar or honey added to it. 

 To acidify this liquid, it is heated to 75 or 80, and made to 

 trickle through a cask, filled with beech- 

 wood shavings, (Fig. 95), and pierced 

 with holes at top and bottom to allow a 

 circulation of air through it. From the 

 great surface exposed by the liquid, the 

 absorption of oxygen is most rapid, and 

 the temperature rises to 100 or 104. 

 When the liquid has been passed three 

 or four times through the barrel, at the 

 high temperature, all the alcohol it con- 

 tains is changed into vinegar; an opera- 

 tion which may be completed in twenty- 

 four or thirty-six hours. The addition of 

 certain aromatic substances, such as the 

 essential oils, or a mere trace of wood vinegar, entirely prevents 

 the acidification of the alcohol. 



Wood vinegar, or pyroligneous acid is prepared on a large 



FIG. 



