504 
SECOND REPORT- 1832 . 
three portions. The lightest contains the gallic and acetic 
acids, if the latter be present in excess ; the next, an aethereal 
solution of tannin ; and the heaviest, the water and extractive 
matter. 
Acetic acid .—A most important improvement has recently 
been introduced into the manufacture of vinegar, which is al¬ 
ready extensively practised on the Continent. The introduction 
of this improvement is chiefly due, I believe, to Mitscherlich. 
It is founded upon the principle that alcohol, by absorbing 
oxygen, is changed into acetic acid and water. For, 
Two alcohol + four oxygen = one acetic acid + three water 
(6H + 4C + 2 0) +40 =(3H + 4C + 3 0)+3(H+0). 
This oxidation is promoted by the process of fermentation ; 
and when the fermentation has begun, is much accelerated by 
the presence of acetic acid. The oxidation is effected entirely 
at the expense of the oxygen of the air :—to accelerate the pro¬ 
cess, therefore, by producing as many points of contact as pos¬ 
sible between the liquid and the air, the following arrangement 
is adopted. A large cask is taken, placed upright with a stop¬ 
cock at the bottom, and a series of holes, half an inch in dia¬ 
meter, bored, one in each stave, a few inches above it. It is 
then nearly filled with chips or shavings of wood, previously 
steeped in strong vinegar till they are perfectly saturated. 
Within the upper end of the cask a shallow cylindrical vessel 
is placed, nearly in contact with the shavings, the bottom of 
which is perforated with many small holes, each partially 
stopped with a slender twig which passes an inch or two be¬ 
neath the perforated bottom of the cylinder. The alcohol, 
diluted with eight or nine parts of water, and mixed with the 
fermenting substance, is now poured into the cylinder, through 
the bottom of which it trickles, drop by drop, upon the shavings 
below, becomes oxidized in its passage, and runs out at the 
stop-cock beneath, already converted almost entirely into 
vinegar . The air rushes in by the holes beneath, and passes 
out above by eight glass tubes, cemented for that purpose into 
the bottom of the cylinder; and so rapidly is it deprived of its 
oxygen, that when it escapes above, it extinguishes a candle. 
During the process much heat also is developed ; so that from 
the temperature of 60° (that of the room), the interior of the 
cask rises as high as 86° F. In the proper regulation of this 
temperature, much of the difficulty consists. 
A second transmission of the acid, thus obtained, through 
another similar cask, finishes the process. The whole is con¬ 
cluded in a few hours ; four-and-twenty is considered amply 
sufficient to convert a given quantity of alcohol into vinegar. 
