When fat is heated with a strong alkali, it is split up into fatty acid and glycerine, the alkali uniting with the acid and forming a soap, and the glycerine being set free. This reaction is called saponification and may be expressed by the following formula: sodium sodium palmatin + hydrate = palmitate + glycerine C3H5(C16H21O2)3 +3NaOH = 3NaC16H21O2 + C3H5(OH)3

The soap is soluble in water. This reaction is made use of in household cleaning when a strong alkali as soda, lye, borax, etc., is added to " cut the grease."

An excellent soap may be made in the household from fats left in cooking combined with a strong alkali, such as concentrated lye. All fats or drippings left from cooking should, therefore, be saved for soap making. Full directions for making soap are given with the lye purchased for soap making.