APTER II.

CONSTITUTION OF OILS AND FATS, AND THEIR SAPONIFICATION.

_Researches of Chevreul and Berthelot--Mixed Glycerides--Modern
Theories of Saponification--Hydrolysis accelerated by (1) Heat
or Electricity, (2) Ferments; Castor-seed Ferment, Steapsin,
Emulsin, and (3) Chemical Reagents; Sulphuric Acid, Twitchell's
Reagent, Hydrochloric Acid, Lime, Magnesia, Zinc Oxide, Soda
and Potash._

The term oil is of very wide significance, being applied to substances
of vastly different natures, both organic and inorganic, but so far as
soap-making materials are concerned, it may be restricted almost
entirely to the products derived from animal and vegetable sources,
though many attempts have been made during the last few years to also
utilise mineral oils for the preparation of soap. Fats readily become
oils on heating beyond their melting points, and may be regarded as
frozen oils.

Although Scheele in 1779 discovered that in the preparation of lead
plaster glycerol is liberated, soap at that time was regarded as a mere
mechanical mixture, and the constitution of oils and fats was not
properly understood. It was Chevreul who showed that the manufacture of
soap involved a definite chemical decomposition of the oil or fat into
fatty acid and glycerol, the fatty acid combining with soda, potash, or
other base, to form the soap, and the glycerol remaining free. The
reactions with stearin and palmitin (of which tallow chiefly consists)
and with olein (found largely in olive and cotton-seed oils) are as
follows:--

CH_{2}OOC_{18}H_{35} CH_{2}OH
| |
CHOOC_{18}H_{35} + 3NaOH = 3NaOOC_{18}H_{35} + CHOH
| |
CH_{2}OOC_{18}H_{35} CH_{2}OH

stearin sodium sodium glycerol
hydroxide stearate

CH_{2}OOC_{16}H_{31} CH_{2}OH
| |
CHOOC_{16}H_{31} + 3NaOH = 3NaOOC_{16}H_{31} + CHOH
| |
CH_{2}OOC_{16}H_{31} CH_{2}OH

palmitin sodium sodium glycerol
hydroxide palmitate