Leanne Stein, age 11, of Bessemer, Ala., for her question:
IS THERE A DIFFERENCE BETWEEN SOAP AND DETERGENT?
A detergent is a substance that cleans soiled surfaces. Soap is a type of detergent. But when we use the word "detergent," we usually refer only to synthetic detergents, which have a different chemical makeup than soap.
The chief ingredients of soap are fats and chemicals called alkalis. Manufacturers may use animal fats or such vegetable oils as coconut oil and olive oil. Most soap makers use sodium hydroxide, often called lye or caustic soda, as the alkali.
The manufacture of detergents involve several complicated chemical processes.
Both detergents and soaps contain a basic cleaning agent called a surfactant or surface active agent. Surfactants consist of molecules that attach themselves to dirt particles in soiled material. The molecules pull these particles out of the material and hold them in the wash water until they are rinsed away.
Most detergents contain a synthetic surfactant plus various other chemicals. These chemicals may improve a detergent's cleaning ability or make it easier to use.
All soaps consist of basically the same kind of surfactant.
Both detergents and soaps may also contain such ingredients as perfume and coloring agents.
Science has found that detergents have certain advantages over soaps. As an example, the most important feature of detergents is their ability to clean effectively in hard water. Hard water contains certain minerals and many soaps cannot be used to launder in it. Such soaps react with the minerals to form a substance called lime soap or soap curd. Lime soap doesn't dissolve and so it is difficult to remove from fabrics and other surfaces.
Lime soap also causes "bathrub ring." Detergents do not leave such deposits and they also penetrate solid areas better than soap does. In addition, detergents dissolve more readily in cold water.
History doesn't tell us exactly when or where people first made soap. But we know that the ancient Romans may have used a soap about 3,000 years ago.
People in France used a rough kind of soap about A.D. 100. And by about 700, soapmaking had become a craft in Italy. By 800, Spain was a leading soapmaker and soapmaking began in England about 1200.
At first soap was very expensive. Then in the late 1700s, a French scientist named Nicolas Leblanc found that lye could be made from ordinary table salt. Following Leblanc's discovery, soap began to be made and sold at prices that almost everyone could afford.
Many early settlers in North America made their own soap. They poured hot water over wood ashes to make an alkali called potash. Then they boiled the potash with animal fats in large iron kettles to make soap.
A German scientist named Fritz Gunther is usually credited with developing in 1916 the first synthetic surfacant for use in detergents. In 1933, the first household detergents based on synthetic surfactants were introduced in the United States.