o4 ACETATES. 
the cup or concavity of an animal’s joint,—par- 
ticularly that in the thigh of the horse. Both of 
them borrow the name from the vinegar saucer 
or original acetabulum of the ancients. 
ACETATES. Salts formed by the union of the 
acetic acid with an earthy, alkaline, or metallic 
base. These salts are nearly all soluble in water. 
The acetates, especially those of alumina, iron, 
and lead, are chiefly employed in dyeing and 
colour-painting: some of them, as the acetate of 
ammonia, lead, potash, and tin, are used in medi- 
cine. The acetate of potash exists in the juice 
of many plants, and when they are incinerated 
passes into carbonate of potash. 
ACETIC ACID. A very common vegetable 
acid,—largely employed in the arts, in domestic 
economy, and in medicine,—the same which, 
when in an impure and very diluted condition, 
is popularly called vinegar. Acetic acid exists, 
combinedly with potash, in sumach, ladies’ bed- 
straw, the elder tree, and a great many other 
plants; it occurs in urine, animal sweat, and 
fresh milk; it is often generated in stomachs of 
weak tone, or such as are afflicted with dyspep- 
sia; it is excreted by seeds during the process 
of their germination ; it is copiously yielded by 
some animal substances, and by almost all vege- 
table substances, when subjected in close vessels 
to a red heat; and it is the result of the sponta- 
neous fermentation of decomposing mixtures of 
either animal or vegetable matters with liquid. 
This acid, therefore, performs a very important 
part in the constant series of changes which go 
on in both the animal and the vegetable econom- 
ics of afarm. “It is distinguished from oxalic 
acid,” says Sir H. Davy, “by its peculiar odour ; 
and from the other vegetable acids, by forming 
soluble salts with the alkalies and earths.” An 
opinion was long entertained, that the vinous 
fermentation uniformly precedes the decompo- 
sitions which evolve acetic acid. But remark- 
able and well known instances to the contrary, 
are the souring of dough, starch, and cabba- 
ges, each without any trace of the vinous fer- 
mentation,—the first making sour bread, the 
second making the sour waters of the starch 
manufacturers, and the third making the sour 
krout of the domestic economy of the Germans. 
See article Acnrous Fermentation. The varie- 
ties of diluted and impure acetic acid known to 
merchants and farmers are four,—wine-vinegar, 
malt-vinegar, sugar-vinegar, and wood-vinegar ; 
but these will be more appropriately noticed 
under the words Prroztienzous Acip and VINE- 
GAR: which see. The acetic acids should never 
be kept in painted vessels, since white lead—the 
basis of all pigments—is readily dissolved by these 
acids, and forms the poisonous compound known 
as sugar of lead. Neither should they be allowed 
to cool in copper vessels; nor should they ever 
be kept in common earthen vessels glazed with 
oxide of lead or litharge. Salt glazed stoneware, 
good English pottery, or glazed iron form the 
ACETOUS FERMENTATION. 
safest materials for vessels employed in presery- 
ing, or boiling acetic acid, and its various pre- 
parations.—Ure’s Dictionary.—Thomson’s Chem- 
istry.—J ohnston’s Agricultural Chemistry.—Davy’s 
Elements of Agricultural Chemistry. 
ACETOUS ACID. A liquid possessing a me- 
dium character, in the degree of its oxygenize- | 
ment, between pure acetic acid and the most 
common vinegar. 
ACETOUS FERMENTATION. A change 
which many organic substances undergo spon- 
taneously, under particular circumstances, be- 
coming wholly or in part dilute acetic acid. It 
has been known from ancient times that the 
expressed juice of fruits, after becoming vinous 
by a species of fermentation, was subject to an- 
other change, by which it became sour to the 
taste, which conversion is now known to chem- 
ists as the acetous fermentation. Although there 
are many points which remain to be cleared up 
in some of the practical details of the acetous 
fermentation, yet we are enabled to lay down one 
principle as its cause in nearly all the processes 
of making vinegar, viz. that it depends on the 
absorption of oxygen from the atmosphere, the 
organic matter acting as a medium of conveying 
the oxygen from the air to the alcoholic fluid. 
Wine and beer only become acid when they con- 
tain organic substances capable of absorbing 
oxygen, for when the ferment by long-continued 
vinous fermentation is deposited, and the clear 
wine racked-off, it is little liable to become ace- 
tous; and beer subjected to very slow fermenta- 
tion at a low temperature, likewise deposits its 
altered nitrogenous ferment in an insoluble state, 
and is not subject to the acetous change at com- 
mon temperatures. Some vegetable substances 
are capable of undergoing the acetous fermenta- 
tion without a perceptible previous formation of 
alcohol; and some indeed which are not known 
to be capable of the vinous fermentation. Thus 
sugar, by the addition of certain ferments, may 
pass directly into acetic acid without an inter- 
mediate absolute change. The conditions most 
favourable to acetous fermentation—or in other 
words, to the absorption of oxygen by alcohol— 
are as extended a surface as possible, the free 
yet not unlimited access of air, and a proper 
temperature. In the quick process, the temper- 
ature should be from 100° to 105°; but, as such 
a temperature, in the ordinary process, would 
create too great a loss by evaporation, in such 
cases it should be from 70° to 80°. When the 
fermentation has ceased, the vinegar should be 
racked-off, or filtered from the lees, which would 
tend to produce the putrefactive fermentation. 
What is called the mother-of-vinegar, a slippery, 
gelatinous, coherent kind of vegetation, has no 
effect whatever in promoting acetous fermenta- 
tion, and being formed out of the acid, constantly 
tends to weaken it by its presence. Hence its 
formation should be avoided by excluding the 
See article VinEGAR. 
access of the air. 
