soap plant, any of various plants having cleansing properties. A few are of commercial importance, but most soap plants are used locally, as in early times, for toilet and laundry purposes. The soapbark (now often included in hair tonics) and the soapberry have been particularly valued for shampooing, and the California soap plant, the soapbark, and the soapwort for washing delicate fabrics. Soap plants contain no alkali and are considered mild and beneficial for cleansing purposes, with the exception of the soapberry, which is thought to harm some textile materials. The lather-producing substance is saponin, often poisonous if taken internally. This poisonous quality has been utilized by indigenous peoples, who have caught fish by first stupefying them with bits of the plants thrown into pools. There are many plants that are saponaceous, but only a few are known to contain appreciable amounts of saponin. The dried inner bark of the soapbark tree (Quillaja saponaria) of the rue family, native to the Andes, has been collected also for commercial use in fire-extinguishing solutions and as an emulsifying agent for medicines and tars. New World and Old World species of soapberry (genus Sapindus) provide saponin from the fruits. Since antiquity, S. mukorossi has been used in E Asia and the Himalayas as a detergent for shawls and silks and by jewelers for cleaning silver. The soapwort, or bouncing Bet (Saponaria officinalis), of the pink family is the best-known soap plant in America; it is indigenous to W Asia and Europe but was cultivated in colonial gardens of North America and is now widely naturalized. The lather is obtained from all parts of the plant. The California soap plant or soaproot (Chlorogalum pomeridianum) of the lily family is collected in the W United States for its bulb. Other soap plants used locally include an acacia (Acacia concinna), whose pods are used like the soapberry, and, among American plants, species of yucca and agave (see amaryllis), the red buckeye (Aesculus pavia), the California pigweed (Chenopodium californicum), the senega snakeroot (Polygala senega), and species of Zygadenus and Ceanothus. The Spanish name amole is sometimes given to American soap plants, particularly those of the Southwest, where they are most abundant and are still in common use.

soap, a cleansing agent. It cleanses by lowering the surface tension of water, by emulsifying grease, and by absorbing dirt into the foam.

Ancient peoples are believed to have employed wood ashes and water for washing and to have relieved the resulting irritation with grease or oil. In the 1st cent. A.D., Pliny described a soap of tallow and wood ashes used by Germanic tribes to brighten their hair. A soap factory and bars of scented soap were excavated at Pompeii. Soap fell into disuse after the fall of Rome but was revived in Italy probably in the 8th cent. and reached France c.1200; Marseilles became noted as a soapmaking center. Although soap was known in England in the 14th cent., the first English patent to a soapmaker was issued in the 17th cent. The industry was handicapped in England from 1712 to 1853 by a heavy tax on soap. In the American colonies soap factories appeared at an early date, and many housewives made soap from waste fats and lye (obtained by leaching wood ashes).

The manufacture of soap was stimulated by Chevreul's discovery of oleic and stearic acids in the early 19th cent. and by Leblanc's method (1791) of preparing soda from salt. Chemically, soaps are metallic salts of fatty acids. The manufacture of soap is based on a chemical reaction (saponification) in which an alkali acts upon a fat to form a metal salt (soap) and an alcohol (glycerol). A number of methods may be employed to make soap, but all are based on the same principle of operation. Fats and oils (often blended) are heated in a large vessel, then enough alkali to react with all the fat is stirred in. Salt is added, and the soap then forms a light curd that floats to the surface. Glycerol, a valuable byproduct, can be distilled from the liquid residue.

To produce a purer soap, the curds are washed with salt solution, water is later added, and the solution is allowed to settle; the upper of the two layers thus formed is the pure soap, called settled soap. It is thoroughly churned, poured into huge frames, cut with wires, shaped, and stamped. Hard-milled soap is run over chilled rollers and is scraped off as chips which are rolled into ribbons, cut, and shaped. Soap is marketed also as chips, flakes, and beads and in powdered form. Soap powders, as distinguished from powdered soap, contain builders that assist in rough cleaning. Soaps differ according to the lathering properties of the fat or oils and according to the alkali employed. When sodium hydroxide is used as the alkali, hard soaps are formed; potassium hydroxide yields soft soaps.

Aluminum, calcium, magnesium, lead, or other metals are used in place of sodium or potassium for soaps used in industry as paint driers, ointments, and lubricating greases and in waterproofing. Fillers are added to many soaps to increase lathering, cleansing, and water-softening properties; the sodium salt of rosin is commonly used in yellow laundry soap to increase lathering. Soap substitutes include saponin-containing plants such as soapwort and shagbark and the modern soapless detergents (usually sulfonated alcohols), which may be used in hard water and even in saltwater without forming curds.

Broadcast serial drama, characterized by a permanent cast of actors, a continuing story, tangled interpersonal situations, and a melodramatic or sentimental style. Its name derived from the soap and detergent manufacturers who originally often sponsored such programs on radio. Soap operas began in the early 1930s as 15-minute radio episodes and continued on television from the early 1950s as 30-minute and later hour-long episodes. Usually broadcast during the day and aimed at housewives, they initially focused on middle-class family life, but by the 1970s their content had expanded to include a wider variety of characters and situations and a greater degree of sexual explicitness. In the 1980s similar series began to be aired in prime-time evening hours (e.g., Dallas and Dynasty). Seealso Carlton E. Morse; Irna Phillips.

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Any of a group of organic compounds that are salts of fatty acids, usually stearic acid (with 18 carbon atoms) or palmitic acid (with 16 carbon atoms). The source may be any vegetable oil or animal fat. Soaps are emulsifying agents commonly used for cleaning; they have long been made from lye and fat. Detergents are entirely synthetic and may or may not be soaps. Soaps of metals heavier than sodium are not very soluble; the curdy precipitate made by soap in hard water is the calcium or magnesium salt of the fatty acid in the soap. Heavy-metal soaps are used in lubricating greases, as gel thickeners, and in paints. Napalm is an aluminum soap.

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