Acidum Acetosum, E. Acetum Vini. D.
QUALITIES. Too well known to require description.[324] CHYMICAL
COMPOSITION. Acetic acid largely diluted with water, vegetable gluten,
mucilage, sugar, extractive matter, and frequently malic and tartaric
acids, together with small proportions of sulphate of lime, sulphate of
potass, and alcohol. Its composition however varies according to the
fermented liquor from which it is obtained:[325] e. g. wine yields a
paler, purer, and stronger acid than fermented malt liquors or solutions
of sugar, hence the superiority of that prepared in France and Italy.
Vinegar is liable to spontaneous decomposition, or to become mouldy, and
consequently for the purposes of pharmacy it should be distilled; as
however the change depends upon the presence of gluten, it may if boiled
be kept for a much longer time, and if powdered _animal_[326] charcoal
be previously added, it will become quite colourless like distilled
vinegar, and that without being impaired in strength, whereas it always
becomes much weaker by distillation. It is a curious circumstance that
this is the only vegetable acid, except the _Prussic_, that rises in
distillation in combination with water.
ADULTERATIONS. Sulphuric acid, as it does not produce any turbid
appearance in vinegar, is generally the acid selected for sharpening it;
but it must be remembered, that the maker is allowed by law, to mix one
thousandth of its weight of Sulphuric acid[327] with it; so that the
_muriate of baryta_ when added to such vinegar may be expected to
produce 1⅕ grain of insoluble _sulphate_ in every fluid-ounce; if a more
considerable quantity of precipitate occurs, we may infer that an
excessive proportion of sulphuric acid is present; although some
allowance ought perhaps to be made for the presence of the sulphates of
potass and lime, which are always contained in vinegar. Of this vinegar
1000 grains should saturate 148 grains of crystallized sub-carbonate of
soda; a fluid-ounce of the same, 68–3/4 grains.[328] For the purpose of
making the vinegar appear stronger, acrid vegetables, as _grains of
Paradise_, _berries of Spurge Flax_, _Capsicum_, _Pellitory of Spain_,
&c. are sometimes infused in it, but by tasting it with attention, the
pungency of such substances may be easily detected. For the other
adulterations, see _Acidum Aceticum_.
The purest vinegar which I have ever examined is that manufactured from
malt, by Mr. Mackintosh of Glasgow. The strongest malt vinegar is termed
_proof vinegar_, and is called by the manufacturer No. 24; it is
estimated to contain 4·73 per cent. of real acetic acid.[329] Its
strength in relation to the other forms of acetic acid, will be seen by
referring to the MEDICINAL DYNAMETER, and to the table inserted under
the article ACIDUM ACETICUM FORTIUS. In the former Editions of this work
it was stated, that a Vinegar had of late years appeared in the market
produced from the distillation of wood, (_Pyroligneous Acid_.) This
article has now come into very general use; and the manufacturers have
at length succeeded in divesting it of that empyreumatic flavour which
had so long rendered it objectionable. See _Acidum Aceticum Fortius e
Ligno destillatum_.