Cathy Jo Jones, age 8, of Lahoma, Okla.) for her question:
WHAT IS SOAP MADE OF?
Each person in the United States uses an average of about 30 pounds of soaps and detergents each year. We use these products in bars, flakes, granules, liquids and tables. And we use both soaps and detergents each day to wash our bodies and shampoo our hair as well as to wash our dishes and clothes, scrub our floors, walls and windows. Soap is important in our daily lives.
Detergent is a substance that cleans soiled surfaces, and soap is a type of detergent. But the word detergent usually refers to synthetic detergents, which have a different chemical makeup than soap.
Soap and detergents contain a cleaning agent called a surfactant or surface active agent. Surfactants are made up of molecules that attach themselves to dirt particles. The molecules pull these particles out of the material and hold them in the wash water until they are rinsed away.
Chief ingredients of soap are fats and chemicals called alkalis. Manufacturers use either animal fats or such vegetable oils as coconut oil and olive oil. Most use sodium hydroxide, which is often called lye or caustic soda, as the alkali.
Either the kettle method or continuous processing method is used to make soap.
Until the 1940s, all soap was made using the kettle method. Today only a few use this method. Steel tanks that stand three stories tall are filled with more than 100,000 pounds of fats and alkalis. Steam from coils in the tanks heats the ingredients for several hours. The heat triggers a chemical reaction called hydrolysis which causes a creamy soap to form within the mixture. Later, in a mixer called a crutcher, the soap is mixed with perfumes, colors, germ killers and substances that help remove dirt. The soap is then hardened into bars or made into flakes or granules.
The continuous processing method of making soap takes only a few hours while several days are required in the kettle method. A stainless steel tube called a hydrolyzer, which measures about three feet in diameter and is about 80 feet high, is used to make soap. Water heated to 500 degrees Fahrenheit and under great pressure is pumped into the top of the hydrolyzer as hot fat is pumped in at the bottom. Under these conditions, the fat splits into fatty acids and glycerol.
Fatty acids rise to the top of the hydrolyzer when the continuous processing method of soapmaking is used. At the top, the material is removed, purified and then mixed with alkali to make soap. It is then mixed with other ingredients in a crutcher and made into bars, granules or flakes.