264 VEGETABLE FOOD. 
be substituted for any of the other substances in the group. The 
following paragraphs explain their action ; 
Organic Acids enter extensively into -the composition of various kinds 
of food. The acids most commonly used in diet are — Acetic acid, citric 
acid, tartaric acid, malic acic, oxalic acid. 
As articles of diet they probably all act in the same manner on the 
system. They all exert a solvent power over mineral substances, and 
assist in carrying the alkalies and alkaline earths into the blood. There 
is also reason to believe that in certain states of the system they favour 
the development of the gastric juice in the stomach, and assist, by their 
decomposition, in oxidising the materials of the blood. In all cases 
they act medicinally, or as auxiliaries, to the first class of foods. 
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. 
Vinegar is added to sauces and food to give them a flavour. It also 
preserves vegetable substances from decomposition, and is used in the 
manufacture of what are called " Pickles." 
Citric Acid is contained in many fruits, but it exists in greatest 
abundance and purity in the fruits of the Orange tribe (Aurantiacea } ). 
Citric acid is separated from the fruits of these plants in a crystalline form. 
Tartaric Acid is found in the juice of the fruits of the vine tribe 
( Vitacece), more especially of the common vine ( Vitis mnifera). This 
acid gives the acidity to the fruit of the grape, and is the acid present in 
wines. It forms with potass an insoluble salt, known by the name of 
cream of tartar. 
Malic Acid is contained in the fruits of the rose tribe (Rosacea). 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 (Oxalis acetosella, also 
in the common sorrel (Rumex acetosa), and various species of rhubarb 
(Rheum). Species of the latter genus are extensively cultivated in this 
country, and the petioles of their large leaves cut up and made into 
pies, puddings, &c. 
The basis of vinegar consists of acetic acid, which is composed of 
carbon, hydrogen, and oxygen ; the same elements that enter into the 
composition of alcohol. This compound is also procured from the dis- 
tillation of wood. The acetic acid thus procured is called pyroligneous 
acid. The quantity of acetic acid in vinegar is from four to five per 
cent. Malt vinegar contains, besides acetic acid, water, dextrin, and 
frequently sulphuric acid. Wine vinegar contains besides acetic acid, 
the constituents of the wine from which it is made, as tartaric acid, &c. 
Pure vinegar is transparent, but burnt sugar is added to give it a colour, 
on account of a popular prejudice in favour of coloured vinegar. 
