CHAPTER 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:—

CH2OOC18H35CH2OH
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CHOOC18H35+3NaOH=3NaOOC18H35+CHOH
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CH2OOC18H35CH2OH
stearinsodium hydroxidesodium stearateglycerol
CH2OOC16H31CH2OH
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CHOOC16H31+3NaOH=3NaOOC16H31+CHOH
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CH2OOC16H31CH2OH
palmitinsodium hydroxidesodium palmitateglycerol

CH2OOC18H33CH2OH
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CHOOC18H33+3NaOH=3NaOOC18H33+CHOH
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CH2OOC18H33CH2OH
oleinsodium hydroxidesodium oleateglycerol