causes of difference. The acetous acid, or vinegar, is produced by
exposing wine to a gentle heat, with the addition of some ferment: This
is usually the ley, or mother, which has separated from other vinegar
during fermentation, or some similar matter. The spiritous part of the
wine, which consists of charcoal and hydrogen, is oxygenated, and
converted into vinegar: This operation can only take place with free
access of air, and is always attended by a diminution of the air
employed in consequence of the absorption of oxygen; wherefore, it ought
always to be carried on in vessels only half filled with the vinous
liquor submitted to the acetous fermentation. The acid formed during
this process is very volatile, is mixed with a large proportion of
water, and with many foreign substances; and, to obtain it pure, it is
distilled in stone or glass vessels by a gentle fire. The acid which
passes over in distillation is somewhat changed by the process, and is
not exactly of the same nature with what remains in the alembic, but
seems less oxygenated: This circumstance has not been formerly observed
by chemists.
Distillation is not sufficient for depriving this acid of all its
unnecessary water; and, for this purpose, the best way is by exposing it
to a degree of cold from 4 to 6 below the freezing point, from 19 to
23 of Fahrenheit; by this means the aqueous part becomes frozen, and
leaves the acid in a liquid state, and considerably concentrated. In the
usual temperature of the air, this acid can only exist in the gasseous
form, and can only be retained by combination with a large proportion of
water. There are other chemical processes for obtaining the acetous
acid, which consist in oxygenating the tartarous, oxalic, or malic
acids, by means of nitric acid; but there is reason to believe the
proportions of the elements of the radical are changed during this
process. Mr Hassenfratz is at present engaged in repeating the
experiments by which these conversions are said to be produced.
The combinations of acetous acid with the various salifiable bases are
very readily formed; but most of the resulting neutral salts are not
cristallizable, whereas those produced by the tartarous and oxalic acids
are, in general, hardly soluble. Tartarite and oxalat of lime are not
soluble in any sensible degree: The malats are a medium between the
oxalats and acetites, with respect to solubility, and the malic acid is
in the middle degree of saturation between the oxalic and acetous acids.
With this, as with all the acids, the metals require to be oxydated
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