owever. Most
natural fats are mixtures of several different triglycerides in each of
which the three (OH) groups of the glycerol has been replaced by the
same organic acid radical, as in the example of stearin shown above. But
recent investigations have shown that some of the common animal fats,
and perhaps some plant oils, may be made up of mixed glycerides, i.e.,
those in which the different (OH) groups have been replaced by different
acid groups, as oleo-stearin, oleo-stearo-palmitin, etc.

THE ACIDS WHICH OCCUR IN NATURAL FATS

The acids which, when combined with glycerol, produce fats are of two
general types. The first of these are the so-called "fatty acids" having
the general formula C_{_n_}H_{2_n_+1}.COOH. These are the "saturated"
acids, i.e., they contain only single-bond linkages in the radical which is
united to the .COOH group; hence, they cannot take up hydrogen, oxygen,
etc., by direct addition. The second type are the "unsaturated" acids
belonging to several different groups, as discussed below, but all having
one or more double-linkages between the carbon atoms of the alkyl radical
which they contain. Because of these double linkages, they are all able to
take on oxygen, hydrogen, or the halogen elements, by direct addition. When
exposed to the air, for example, these "unsaturated" acids, or the oils
derived from them, take up oxygen, increasing in weight, and becoming solid
or hard and stiff. Hence, natural oils which contain considerable
proportions of glycerides of these "unsaturated" acids are known as "drying
oils" and are largely used in the manufacture of paints, varnishes,
linoleums, etc.; while oils which contain little of these glycerides are
known as "non-drying," and are used for food, for lubrication, or for other
technical purposes in which it is essential that they remain in unchanged
fluid condition when exposed to the air.

The following are some of the more important of the acids which occur as
glycerides in natural fats: Saturated Acids:

(_a_) Acetic, or stearic, acid series--general formula,
C_{_n_}H_{2_n_+1}.COOH.

(1) Formic acid, H.COOH, occurs free in nettles, ants, etc.

(2) Acetic acid, CH_{3}.COOH, occurs free in vinegar.

(3) Butyric acid, C_{3}H_{7}.COOH, in butter fat.

(4) Capric acid, C_{9}H_{19}.COOH, in butter fat and cocoanut
oil.

(5) Myristic acid