tralized with calcium,
potassium, or sodium, forming acid salts, or combined with various alcohols
in the form of esters, are widely distributed in plants. They occur in
largest proportions in the fleshy tissues of fruits and vegetables, where
they are largely responsible for the flavors which make these products
attractive as food for men and animals. But organic acids and their salts
are also found in the sap of all plants, and undoubtedly play an important
and definite part in the vital processes of metabolism and growth.

CHEMICAL CONSTITUTION

All organic acids contain one (or more) of the characteristic
O
//
acid group, --COOH, or --C, known as "carboxyl." This
\
OH
group is monovalent, and in the simplest organic acid, formic acid
(H_{2}CO_{2}), it is attached to a single hydrogen atom, thus, H.COOH. In
all other monobasic acids, it is attached to some other monovalent group,
usually an alkyl radical, i.e., a radical derived from an alcohol and
containing only carbon and hydrogen (as methyl, CH_{3}, ethyl, C_{2}H_{5},
butyl, C_{4}H_{9}, acryl, C_{2}H_{3}, etc.). Hence, the general formula for
all monobasic organic acids is R.COOH, the R representing any monovalent
radical. In the simplest dibasic acid, oxalic (H_{2}C_{2}O_{4}), two
carboxyl groups are united to each other, thus, HOOC.COOH; but in the
higher members of the series, the two characteristic acid groups are united
through one or more --CH_{2}-- groups, or their oxy-derivatives (as
HOOC.CH_{2}.COOH, malonic acid; HOOC.CH_{2}.CH_{2}.CH_{2}.COOH, glutaric
acid; HOOC.CHOH.CH_{2}.COOH, malic acid, etc.). Polybasic acids, containing
three or more carboxyl groups, linked together through one or more alkyl
carbon atoms, are also possible, and a few typical ones (as

COOH
|
HOOC.CH_{2}.COH.CH_{2}.COOH, citric acid)

are found in fruits and other plant tissues.

The H atom of the COOH group may be replaced by metals, in exactly the same
way as it is replaceable in inorganic acids, producing either neutral or
acid salts, depending upon whether all or only a part of the acid H atoms
are replaced by the basic element.

Thus, with sulfuric acid:

OH ONa
/ /
S