Many of the organic acids resemble closely in their composition starch
and sugar, and may to a certain extent act on the system in the same way.
In the classification adopted in the Food Collection, they are classed
under _medicinal or auxiliary food_.
_Acetic Acid or Vinegar_ is obtained either from the oxidation of alcohol
in fermented liquors, or from the distillation of wood. Common vinegar
is obtained from the oxidation of the fermented wort of malt. A series
of preparations illustrating the processes undergone in the formation of
vinegar from malt has been presented to the collection by Messrs. Beaufoy
and Co.
_Citric Acid_ is contained in many fruits, but exists in greatest
abundance and purity in the fruits of the orange, the lemon, the citron,
the shaddock, the pommeloe, the lime, and others. All these fruits
contain citric acid, and varying proportions of sugar. Citric acid can
be separated from the juice of these plants in a crystalline form.
_Tartaric Acid_ is found in the juice of the fruits of the vine tribe,
more especially of the common vine. This acid gives the acidity to the
fruit of the grape, and is the acid present in wines.
_Malic Acid_ is contained in the fruits of the natural order Rosaceæ. It
has the same general properties as the other acids, and is contained
alone in apples and pears; whilst in cherries, plums, &c. it is mixed
with other acids.
_Oxalic Acid_ is contained in the wood sorrel, also in the common sorrel,
and various species of rhubarb. Species of the latter genus are
extensively cultivated in this country, and the stalks of their large
leaves cut up and made into pies, puddings, &c. They are ready for use
early in the spring, and are an excellent substitute for fruit in pies
and tarts at that season of the year. Although oxalic acid is a _poison_
when taken in considerable quantities, as ordinarily consumed it probably
acts in the same way on the system as other acids.
For examples of Acids, Pickles of various kinds, &c., see Case 23.