ACETIC ACID.
219
for sale.—(For farther information on this subject, consult Aikins’ Diet,of Chern., and Donovan’s Domestic Economy, in Lardner ’s Cabinet Cyclo-pedia). Green twigs, or fresh cuttings of the vine, recommended byBoerliaave, are sometimes employed, instead of rape, to flavour vinegar.
Formerly acetification was effected by placing the wash in barrels thebung-holes of which were loosely covered with tiles, and exposing it tothe air for several months. But the introduction of stoved chambers hasnearly superseded this method.
{b.) Theory of acetification. —The theory of the acetous fermentationis imperfectly understood. During the process oxygen of the air isabsorbed, and carbonic acid is usually evolved, while the alcohol of thewash gradually disappears, and acetic acid is produced. A remarkable dis-tinction between the acetous and vinous fermentation, is, that for theformer to be perfectly established, the presence of atmospheric air (or ofoxygen) is essential, while for the latter this is not necessary. It is usuallysupposed, that during the acetous fermentation the alcohol is convertedinto acetic acid. Two equivalents or 46 parts of alcohol, with four equi-valents or 32 parts of atmospheric oxygen, contain the elements of oneequivalent or 51 parts of acetic acid, and of three equivalents or 27 partsof water.
INGREDIENTS USED.4 eq. Atmospheric
Oxygen
32
2 eq. Alcohol ... 46 •
3 eq. Oxygen . ,
1 eq. Oxygen . ,
3 eq. Hydrogen .1 3 eq. Hydrogen .
4 eq. Carbon . .
2 eq. Oxygen . ,
24.
8
3.32416 -
RESULTS.
-3 eq. Water ... 27
Several circumstances favour this hypothesis; such as the simultaneousdisappearance of alcohol and production of acetic acid—'the strongestwines yielding the best vinegars : in other w'ords, the quantity of aceticacid being proportional to that of alcohol; and, lastly, the formation ofacetic acid by the slow' combustion of alcohol, as well as by allowing amixture of alcohol, water, and yeast, to trickle through beech shavings pre-viously soaked in vinegar,—a mode of generating acetic acid practised inGermany. (Mitscherlich , Lehrbuch der Chemie.) But, on the other hand,it is to be recollected, that many vegetable substances yield acetic acidduring their spontaneous decomposition, without the production of alco-hol. In alluding to these cases, Dr. Turner (Elem. of Chem.) observes—■“ all these processes, however, appear essentially different from the properacetous fermentation above described, being unattended with visiblemovement in the liquid, with absorption of oxygen, or disengagement ofcarbonic acid.”
The student will observe that the theory of acetification above givendoes not account for the appearance of carbonic acid during the process.The evolution of this substance is generally considered to be accidental,and not essential to the formation of acetic acid.
(c.) Properties of Vinegar. —Malt vinegar is of a yellowish or reddishcolour, an agreeable acid taste, and a peculiar but pleasant odour. Itssp. gr. varies from T0135 to T0251. (Thomson, System of Chemistry ).It is very liable to undergo decomposition when exposed to the air : itbecomes turbid, loses its acidity, acquires an unpleasant odour, and de-posits a slippery gelatinous substance called the mother of vinegar, which,