Fixed oils and fats are substances of either vegetable or animal origin, and consist of various organic acids of high molecular weight belonging chiefly to the stearic, oleic, linolic or ricinoleic acid series combined with glyceryl; they yield by saponification with caustic alkalies the alcohol glycerol (glycerin), the alkali combining with the organic acids to form soaps.

Waxes are solid or, occasionally, liquid substances resembling the fats and oils but differing in yielding monatomic alcohols instead of glycerol by saponification, which is readily effected by boiling alcoholic solutions of caustic alkalies, but not by aqueous.