Detergent and soap. A detergent is a substance that cleans soiled surfaces. Soap is a type of detergent. But detergent usually refers only to synthetic detergents, which have a different chemical makeup than soap.
Soap and detergent products are produced in the form of bars, flakes, granules (grains), liquids, and tablets. People use soap to wash their bodies. They shampoo their hair and brush their teeth with soaps and detergents. Doctors clean sores and wounds with soap to kill germs that cause infection.
Detergents and soaps have many household and industrial uses. People use these products to wash dishes and laundry, to scrub floors, and to clean windows. Industries use detergents and soaps as cleaners, lubricants, softeners, and polishers. Some motor oils contain detergents that break down soot, dust, and other particles that can harm engine parts. Tire manufacturers apply soap to hot tires to prevent them from sticking to the molds used in vulcanizing (hardening) rubber. In addition, soap is used to polish jewelry and to soften leather.
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.
The chemical industry produces a wide variety of synthetic surfactants, each with a different chemical makeup. There are three main types of synthetic surfactants: those that become positively charged when exposed to water; those that become negatively charged; and those that remain neutral. Nearly all the surfactants used in detergents and soaps become positively charged in water.
Most detergents contain a synthetic surfactant plus other chemicals that may improve a detergent's cleaning ability or make it easier to use. All soaps consist of basically the same kind of surfactant. Detergents and soaps may also contain such ingredients as perfumes, coloring agents, and germicides (germ-killing agents).
Detergents have certain advantages over soaps. For 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 does not dissolve, and so it is difficult to remove from fabrics and other surfaces. It also causes "bathtub ring." Detergents do not leave such deposits, and they also penetrate soiled areas better than soap does. In addition, detergents dissolve more readily in cold water.
