Soap is an anionic surfactant used in conjunction with water for washing and cleaning, which historically comes either in solid bars or in the form of a viscous liquid.
Soap consists of sodium or potassium salts of fatty acids and is obtained by reacting common oils or fats with a strong alkaline solution (the base, popularly referred to as lye) in a process known as saponification. The fats are hydrolyzed by the base, yielding alkali salts of fatty acids (crude soap) and glycerol.
Today, soap is often replaced by other cleaning agents, such as synthetic detergents.
Overview
Soaps are useful for cleaning because soap molecules have both a hydrophilic end, which dissolves in water, as well as a hydrophobic end, which is able to dissolve nonpolar grease molecules. Although grease will normally adhere to skin or clothing, the soap molecules can form micelles which surround the grease particles and allow them to be dissolved in water. Applied to a soiled surface, soapy water effectively holds particles in colloidal suspension so it can be rinsed off with clean water. The hydrophobic portion (made up of a long hydrocarbon chain) dissolves dirt and oils, while the ionic end dissolves in water. Therefore, it allows water to remove normally-insoluble matter by emulsification. In other words, while normally oil and water do not mix, the addition of soap allows oils to dissolve in water, allowing them to be rinsed away.
History
Early history
The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in Ancient Babylon. A formula for soap consisting of water, alkali and cassia oil was written on a Babylonian clay tablet around 2200 BC.
The Ebers papyrus (Egypt, 1550 BC) indicates that ancient Egyptians bathed regularly and combined animal and vegetable oils with alkaline salts to create a soap-like substance. Egyptian documents mention that a soap-like substance was used in the preparation of wool for weaving.
Roman history
It had been reported that a factory producing soap-like substances was found in the ruins of Pompeii (AD 79). However, this has proven to be a misinterpretation of the survival of some soapy mineral substance, probably soapstone at the Fullonica where it was used for dressing recently cleansed textiles. Unfortunately this error has been repeated widely and can be found in otherwise reputable texts on soap history. The ancient Romans were generally ignorant of soap's detergent properties, and made use of the strigil to scrape dirt and sweat from the body. The word "soap" (Latin sapo ) appears first in a European language in Pliny the Elder's Historia Naturalis , which discusses the manufacture of soap from tallow and ashes, but the only use he mentions for it is as a pomade for hair; he mentions rather disapprovingly that among the Gauls and Germans men are likelier to use it than women.
Another popular belief encountered in some places claims that soap takes its name from a supposed "Mount Sapo" where ancient Romans sacrificed animals. Rain would send a mix of animal tallow and wood ash down the mountain and into the clay soil on the banks of the Tiber, producing a sudsy substance that could be used to clean clothes. The location of Mount Sapo is unknown, as is the source of the "ancient Roman legend" to which this tale is typically credited. In fact, the Latin word sapo simply means "soap"; it was borrowed from a Celtic or Germanic language, and is cognate with Latin sebum , "tallow", which appears in Pliny the Elder's account. Roman animal sacrifices usually burned only the bones and inedible entrails of the sacrificed animals; edible meat and fat from the sacrifices were taken by the humans rather than the gods. Animal sacrifices in the ancient world would not have included enough fat to make much soap. The legend about Mount Sapo is probably apocryphal.
Zosimos of Panopolis c. 300 AD describes soap and soapmaking. Galen describes soap-making using lye and prescribes washing to carry away impurities from the body and clothes. According to Galen, the best was German and ones from Gaul was second best. This is a reference to true soap in antiquity.
Medieval history
Soap-makers in Naples were members of a guild in the late sixth century, and in the 8th century, soap-making was well-known in Italy and Spain. The Carolingian capitulary De Villis , dating to around 800, and sometimes attributed to Charlemagne, mentions soap as being one of the products the stewards of estates are to tally. Soap-making is mentioned both as "women's work" and the produce of "good workmen" alongside other necessities such as the produce of carpenters, blacksmiths and bakers.
Soaps made from vegetable oils (such as olive oil), aromatic oils (such as thyme oil) and lye ( al-Soda al-Kawia ) were first produced by chemists. From the beginning of the 7th century, soap was produced in Nablus (West Bank), Kufa (Iraq) and Basra (Iraq). Soap was perfumed and colored, some of the soaps were liquid and others were solid. They also had special soap for shaving. It was sold for 3 Dirhams (0.3 Dinars) a piece in 981 AD. The Persian chemist Al-Razi wrote a manuscript on recipes for true soap. A recently discovered manuscript from the 13th century details more recipes for soap making; e.g. take some sesame oil, a sprinkle of potash, alkali and some lime, mix them all together and boil. When cooked, they are poured into molds and left to set, leaving hard soap.
Modern history
Finer soaps were later produced in Europe from the 16th century, using vegetable oils (such as olive oil) as opposed to animal fats. Many of these soaps are still produced, both industrially and by small scale artisans. Castile soap is a popular example of the vegetable-only soaps derived by the oldest "white soap" of Italy.
In modern times, the use of soap has become universal in industrialized nations due to a better understanding of the role of hygiene in reducing the population size of pathogenic microorganisms. Industrially manufactured bar soaps first became available in the late eighteenth century, as advertising campaigns in Europe and the United States promoted popular awareness of the relationship between cleanliness and health.
Commercial production
Until the Industrial Revolution, soap-making was done on a small scale and the product was rough. Andrew Pears started making a high-quality, transparent soap in 1789 in London. His son-in-law, Thomas J. Barratt, opened a factory in Isleworth in 1862. William Gossage produced low-price good quality soap from the 1850s. Robert Spear Hudson began manufacturing a soap powder in 1837, initially by grinding the soap with a mortar and pestle. William Hesketh Lever and his brother, James, bought a small soap works in Warrington in 1885 and founded what is still one of the largest soap businesses, now called Unilever. These soap businesses were among the first to employ large scale advertising campaigns.
Soapmaking
The most popular soapmaking process today is the cold process method, where fats such as olive oil react with lye, while some soapers use the historical hot process.
Handmade soap differs from industrial soap in that, usually, an excess of fat is sometimes used to consume the alkali ( superfatting ), and in that the glycerin is not removed, leaving a naturally moisturising soap and not pure detergent. Superfatted soap, soap which contains excess fat, is more skin-friendly than industrial soap, though if too much fat is added, it can leave users with a "greasy" feel to their skin. Often, emollients such as jojoba oil or shea butter are added 'at trace' (the point at which the saponification process is sufficiently advanced that the soap has begun to thicken), after most of the oils have saponified, so that they remain unreacted in the finished soap. Superfatting can also be accomplished through a process called superfat discount, where, instead of putting in extra fats, the soap maker puts in less lye.
Lye
Reacting fat with NaOH will produce a stable soap that will usually become firmer as it cures.
Reacting fat with potassium hydroxide will produce a soap that is either soft or liquid. Historically, the alkali used was potassium hydroxide made from the ashes of bracken or from wood ashes.
Fat
Soap is derived from either vegetable or animal fats. Sodi
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