ich is familiar to
everyone under its common name "glycerine," is a colorless, viscid liquid
having a sweetish taste. It is a very heavy liquid (specific gravity 1.27)
which mixes with water in all proportions and when in concentrated form is
very hygroscopic.

Glycerine is made from fats and oils by commercial processes which clearly
prove that the constitution of fats is as described above. The fat is
boiled with a solution of caustic soda and is decomposed, the sodium of the
alkali taking the place of the glyceryl (C_{3}H_{5}) group, the latter
combining with three (OH) groups from the three molecules of alkali
necessary to decompose the fat. A sodium salt of the organic acid, or soap,
and glycerol are thus produced, and are separated by saturating the hot
solution with common salt, which causes the soap to separate out as a layer
on the surface of the liquid, which, on cooling, solidifies into a solid
cake, which is then cut and pressed into the familiar bars of commercial
soap. From the remaining solution, the glycerine is recovered by
evaporation and distillation under reduced pressure. Taking stearin, a
common fat, as the example, the reaction which takes place in the above
process may be expressed by the following equation:

C_{3}H_{5}(C_{17}H_{35}.COO)_{3} + 3NaOH = 3C_{17}H_{35}COONa +
Stearin Sodium stearate--a soap
C_{3}H_{5}(OH)_{3}.
Glycerol

This process, since it yields soap as one of its products, is called
"saponification." All fats, when saponified, yield soaps and either
glycerol or (more rarely) some of the other alcohols which are described
below.

Glycerine is also prepared from fats by hydrolysis with superheated steam.
Using olein, a glyceride which is present in olive oil and many common
fats, as the example in this case, the equation for the reaction is:

C_{3}H_{5}(C_{17}H_{33}.COO)_{3} + 3H_{2}O = 3C_{17}H_{33}.COOH +
Olein Steam Oleic acid
C_{3}H_{5}(OH)_{3}
Glycerol

In this case the free fatty acid, instead of a soap, is the product which
is obtained in addition to glycerol.

In the equations presented above, a single glyceride has been used as the
example in each case. In