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In , a soap is a salt of a .. " IUPAC Gold Book – soap" Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. . . Accessed 2010-08-09 Household uses for soaps include , , and other types of , where soaps act as , oils to enable them to be carried away by water. In industry they are also used in textile spinning and are important components of some . Metal soaps are also included in modern artists' oil paints formulations as a modifier.

Soaps for cleaning are obtained by treating vegetable or animal oils and fats with a strong base, such as or potassium hydroxide in an solution. Fats and oils are composed of ; three molecules of attach to a single molecule of .Cavitch, Susan Miller. The Natural Soap Book. Storey Publishing, 1994 . The alkaline solution, which is often called (although the term "lye soap" refers almost exclusively to soaps made with ), induces .

In this reaction, the triglyceride fats first into free fatty acids, and then the latter combine with the alkali to form crude soap: an amalgam of various soap salts, excess fat or alkali, water, and liberated (glycerin). The glycerin, a useful byproduct, can remain in the soap product as a softening agent, or be isolated for other uses.

Soaps are key components of most lubricating greases, which are usually emulsions of or and mineral oil.see the main Grease (lubricant) article Many other metallic soaps are also useful, including those of aluminium, sodium, and mixtures of them. Such soaps are also used as thickeners to increase the viscosity of oils. In ancient times, lubricating greases were made by the addition of lime to olive oil.Thorsten Bartels et al. "Lubricants and Lubrication" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Weinheim.

Mechanism of cleansing soaps

Action of soap
When used for cleaning, soap allows insoluble particles to become soluble in water, so they can then be rinsed away. For example: oil/fat is insoluble in water, but when a couple of drops of dish soap are added to the mixture, the oil/fat dissolves in the water. The insoluble oil/fat molecules become associated inside , tiny spheres formed from soap molecules with polar (water-attracting) groups on the outside and encasing a (fat-attracting) pocket, which shields the oil/fat molecules from the water making it soluble. Anything that is soluble will be washed away with the water.

Effect of the alkali
The type of alkali metal used determines the kind of soap product. Sodium soaps, prepared from , are firm, whereas potassium soaps, derived from potassium hydroxide, are softer or often liquid. Historically, potassium hydroxide was extracted from the ashes of or other plants. Lithium soaps also tend to be hard—these are used exclusively in greases.

Effects of fats
Soaps are derivatives of . Traditionally they have been made from (oils and fats).David J. Anneken, Sabine Both, Ralf Christoph, Georg Fieg, Udo Steinberner, Alfred Westfechtel "Fatty Acids" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. Triglyceride is the chemical name for the tri of fatty acids and . , i.e., rendered beef fat, is the most available triglyceride from animals. Its saponified product is called sodium tallowate. Typical vegetable oils used in soap making are palm oil, coconut oil, olive oil, and laurel oil. Each species offers quite different fatty acid content and hence, results in soaps of distinct feel. The seed oils give softer but milder soaps. Soap made from pure is sometimes called or , and is reputed for being extra mild. The term "Castile" is also sometimes applied to soaps from a mixture of oils, but a high percentage of olive oil.

+ Fatty acid content of various fats used for soapmaking
+ ! !! Lauric acid!! Myristic acid!! Palmitic acid!! Stearic acid!! Oleic acid!! Linoleic acid!! Linolenic acid

History of soaps

Ancient Middle East
The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in ancient .
(2017). 9780751404791, Kluwer Academic Publishers. .
A formula for soap consisting of water, , and cassia oil was written on a Babylonian clay tablet around 2200 BC.

The (Egypt, 1550 BC) indicates the bathed regularly and combined animal and vegetable oils with alkaline salts to create a soap-like substance. Egyptian documents mention a soap-like substance was used in the preparation of for weaving.

In the reign of (556–539 BC), a recipe for soap consisted of uhulu ashes, cypress oil and sesame seed "for washing the stones for the servant girls".Noted in

Roman Empire
The word sapo, Latin for soap, first appears in Pliny the Elder's Historia Naturalis, which discusses the manufacture of soap from and ashes, but the only use he mentions for it is as a for hair; he mentions rather disapprovingly that the men of the and were more likely to use it than their female counterparts.Pliny the Elder, Natural History, XXVIII.191. See also , Epigrammata, VIII, 33, 20. Aretaeus of Cappadocia, writing in the first century AD, observes among "Celts, which are men called Gauls, those alkaline substances that are made into balls ... called soap".Aretaeus, The Extant Works of Aretaeus, the Cappadocian, ed. and tr. Francis Adams (London) 1856: 238 and 496, noted in Michael W. Dols, "Leprosy in medieval Arabic medicine" Journal of the History of Medicine 1979:316 note 9; the Gauls with whom the Cappadocian would have been familiar are those of Anatolian Galatia. The Romans' preferred method of cleaning the body was to massage oil into the skin and then scrape away both the oil and any dirt with a . The Gauls used soap made from .

A popular belief claims soap takes its name from a supposed , where animal sacrifices were supposed to have taken place; tallow from these sacrifices would then have mixed with ashes from fires associated with these sacrifices and with water to produce soap, but there is no evidence of a Mount Sapo in the Roman world and no evidence for the story. The word sapo simply means "soap"; it was likely borrowed from an early Germanic language and is with Latin sebum, "tallow", which appears in Pliny the Elder's account. soap. Retrieved on 2011-11-20. Roman animal 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.

Zosimos of Panopolis, circa 300 AD, describes soap and soapmaking. describes soap-making using lye and prescribes washing to carry away impurities from the body and clothes. The use of soap for personal cleanliness became increasingly common in the 2nd century A.D. According to Galen, the best soaps were Germanic, and soaps from Gaul were second best. This is a reference to true soap in antiquity.

(1999). 9780801859540, JHU Press.

Ancient China
A detergent similar to soap was manufactured in ancient China from the seeds of Gleditsia sinensis.
(2017). 9780191609619, Oxford University Press. .
Another traditional detergent is a mixture of pig pancreas and plant ash called "Zhu yi zi". True soap, made of animal fat, did not appear in China until the modern era.
(2017). 9780195176650, Oxford University Press. .
Soap-like detergents were not as popular as ointments and creams.

Islamic Middle East
Hard toilet soap with a pleasant smell was produced in the during the Islamic Golden Age, when soap-making became an established industry. Recipes for soap-making are described by Muhammad ibn Zakariya al-Razi (854–925), who also gave a recipe for producing from . In the Middle East, soap was produced from the interaction of and with . In , soap was produced using olive oil together with alkali and lime. Soap was exported from Syria, to other parts of the and to Europe.Ahmad Y. al-Hassan (2001), Science and Technology in Islam: Technology and applied sciences, pages 73-74,

A 12th-century Islamic document describes the process of soap production.BBC Science and Islam Part 2, Jim Al-Khalili. BBC Productions. Accessed 30 January 2012. It mentions the key ingredient, , which later becomes crucial to modern chemistry, derived from al-qaly or "ashes".

By the 13th century, the manufacture of soap in the Islamic world had become virtually industrialized, with sources in , , , and .

Medieval Europe
Soapmakers in were members of a in the late sixth century (then under the control of the Eastern Roman Empire),footnote 48, p. 104, Understanding the Middle Ages: the transformation of ideas and attitudes in the Medieval world, Harald Kleinschmidt, illustrated, revised, reprint edition, Boydell & Brewer, 2000, . and in the eighth century, soap-making was well known in Italy and Spain.Anionic and Related Lime Soap Dispersants, Raymond G. Bistline, Jr., in Anionic Surfactants: Organic Chemistry, Helmut Stache, ed., Volume 56 of Surfactant science series, CRC Press, 1996, chapter 11, p. 632, . The De Villis, dating to around 800, representing the royal will of , mentions soap as being one of the products the stewards of royal estates are to tally. The lands of were a leading soapmaker by 800, and soapmaking began in the Kingdom of England about 1200. Retrieved on 2015-10-31. Soapmaking is mentioned both as "women's work" and as the produce of "good workmen" alongside other necessities, such as the produce of carpenters, blacksmiths, and bakers.

In Europe, soap in the 9th century was produced from animal fats and had an unpleasant smell. Hard toilet soap with a pleasant smell was later imported from the Middle East.

15th–19th centuries

In France, by the second half of the 15th century, the semi-industrialized professional manufacture of soap was concentrated in a few centers of , Hyères, and —which supplied the rest of France. In Marseilles, by 1525, production was concentrated in at least two factories, and soap production at Marseille tended to eclipse the other Provençal centers.Barthélemy, L. (1883) "La savonnerie marseillaise", noted by Nef 1936:660 note 99. English manufacture tended to concentrate in London.Nef 1936:653, 660.

Finer soaps were later produced in Europe from the 16th century, using vegetable oils (such as ) as opposed to animal fats. Many of these soaps are still produced, both industrially and by small-scale artisans. is a popular example of the vegetable-only soaps derived from the oldest "white soap" of Italy.

In modern times, the use of soap has become commonplace in industrialized nations due to a better understanding of the role of in reducing the population size of . Industrially manufactured bar soaps became available in the late 18th century, as advertising campaigns in Europe and America promoted popular awareness of the relationship between cleanliness and health.

(1990). 9780415013062, Taylor & Francis. .

Until the Industrial Revolution, soapmaking was conducted on a small scale and the product was rough. In 1780 established a chemical works at , for the manufacture of alkali from the sulfates of and soda, to which he afterwards added a soap manufactory. The method of extraction proceeded on a discovery of Keir's. started making a high-quality, transparent soap in 1807 in . His son-in-law, Thomas J. Barratt, opened a factory in in 1862.

During the (February 1665 – August 1714) a soap tax was introduced in England, which meant that until the mid-1800's, soap was a luxury, used regularly only by the well-to-do. The soap manufacturing process was closely supervised by revenue officials who made sure that soapmakers' equipment was kept under lock and key when not being supervised. Moreover, soap could not be produced by small makers because of a law which stipulated that soap boilers must manufacture a minimum quantity of one imperial ton at each boiling, which placed the process beyond reach of the average person. The soap trade was boosted and deregulated when the tax was repealed in 1853.

(1864). 9780243121328, Forgotten Books.

produced low-priced, 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. American manufacturer Benjamin T. Babbitt introduced marketing innovations that included sale of bar soap and distribution of . William Hesketh Lever and his brother, James, bought a small soap works in in 1886 and founded what is still one of the largest soap businesses, formerly called Lever Brothers and now called . These soap businesses were among the first to employ large-scale campaigns.

Liquid soap
Liquid soap was not invented until the nineteenth century; in 1865, William Shepphard patented a liquid version of soap. In 1898, B.J. Johnson developed a soap derived from palm and olive oils; his company, the B.J. Johnson Soap Company, introduced "Palmolive" brand soap that same year. This new brand of soap became popular rapidly, and to such a degree that B.J. Johnson Soap Company changed its name to Palmolive.

In the early 1900s, other companies began to develop their own liquid soaps. Such products as and Tide appeared on the market, making the process of cleaning things other than skin, such as clothing, floors, and bathrooms, much easier.

Liquid soap also works better for more traditional or non-machine washing methods, such as using a washboard.

Soap-making processes
The industrial production of soap involves continuous processes, such as continuous addition of fat and removal of product. Smaller-scale production involves the traditional . The three variations are the cold process, wherein the reaction takes place substantially at room temperature; the semi-boiled or "hot process," wherein the reaction takes place near the boiling point; and the fully boiled process, wherein the reactants are boiled at least once and the is recovered. There are several types of semi-boiled hot process methods, the most common being DBHP (Double Boiler Hot Process) and CPHP (Crock Pot Hot Process).Garzena, Patrizia, and Tadiello, Marina (2013). The Natural Soapmaking Handbook. Online information and Table of Contents. / Most soapmakers, however, continue to prefer the cold process method. The cold process and hot process (semi-boiled) are the simplest, and are typically used by small artisans and hobbyists producing handmade decorative soaps. The glycerol remains in the soap and the reaction continues for many days after the soap is poured into molds. The glycerol is left during the hot-process method, but at the high temperature employed, the reaction is practically completed in the kettle, before the soap is poured into molds. This simple and quick process is employed in small factories all over the world.

Handmade soap from the cold process also differs from industrially made soap in that an excess of fat is used, beyond that needed to consume the (in a cold-pour process, this excess fat is called "superfatting"), and the glycerol left in acts as a moisturizing agent. However, the glycerine also makes the soap softer and less resistant to becoming "mushy" if left wet. Since it is better to add too much oil and have left-over fat, than to add too much and have left-over lye, soap produced from the hot process also contains left-over glycerol and its concomitant pros and cons. Further addition of glycerol and processing of this soap produces . Superfatted soap is more skin-friendly than one without extra fat. However, if too much fat is added, it can leave a "greasy" feel to the skin. Sometimes, an additive, such as oil or , is added "at trace" (i.e., the point at which the process is sufficiently advanced that the soap has begun to thicken in the cold process method) in the belief that nearly all the lye will be spent and it will escape saponification and remain intact. In the case of hot-process soap, an emollient may be added after the initial oils have saponified so they remain unreacted in the finished soap. Superfatting can also be accomplished through a process known as "lye discount" in which the soap maker uses less alkali than required instead of adding extra fats.

Cold process

Even in the cold soap making process, some heat is usually required; the temperature is usually raised to a point sufficient to ensure complete melting of the fat being used. The batch may also be kept warm for some time after mixing to ensure the is completely used up. This soap is safe to use after about 12–48 hours, but is not at its peak quality for use for several weeks.

Cold-process soapmaking requires exact measurements of lye and fat amounts and computing their ratio, using saponification charts to ensure the finished product does not contain any excess hydroxide or too much free unreacted fat. Saponification charts should also be used in hot processes, but are not necessary for the "fully boiled hot-process" soaping.

Historically, lye used in the cold process was made from scratch using rainwater and ashes. Soapmakers considered the lye solution ready for use when an egg would float in it. Homemade lye making for this process was unpredictable and therefore eventually led to the isolation of sodium hydroxide by English chemist Sir Humphry Davy in the early 1800s.

A cold-process soapmaker first looks up the saponification value for each unique fat on an oil specification sheet. Oil specification sheets contain laboratory test results for each fat, including the precise saponification value of the fat. The saponification value for a specific fat varies by season and by specimen species. This value is used to calculate the exact amount of sodium hydroxide to react with the fat to form soap. The saponification value must be converted into an equivalent sodium hydroxide value for use in cold process soapmaking. Excess unreacted lye in the soap results in a very high pH and can burn or irritate skin, whereas not enough lye leaves the soap greasy. Most soap makers formulate their recipes with a 2–5% deficit of lye, to account for the unknown deviation of saponification value between their oil batch and laboratory averages.

The lye is dissolved in water. Then, the oils are heated, or melted if they are solid at room temperature. Once the oils are liquefied and the lye is fully dissolved in water, they are combined. This lye-fat mixture is mixed until the two phases (oils and water) are fully emulsified. is most easily identified visually when the soap exhibits some level of "trace," which is the thickening of the mixture. Many modern-day amateur soapmakers use a stick blender to speed up this process. Varying levels of trace can occur at each stage of the saponification process. Depending on how additives affect trace, they may be added at light trace, medium trace, or heavy trace. After much stirring, the mixture turns to the consistency of a thin pudding. "Trace" corresponds roughly to viscosity. and can be added with the initial soaping oils, but solid additives such as botanicals, herbs, oatmeal, or other additives are most commonly added at light trace, just as the mixture starts to thicken.

The batch is then poured into molds, kept warm with towels or blankets, and left to continue saponification for 12 to 48 hours. (Milk soaps or other soaps with sugars added are the exception. They typically do not require insulation, as the presence of sugar increases the speed of the reaction and thus the production of heat.) During this time, it is normal for the soap to go through a "gel phase," wherein the opaque soap will turn somewhat transparent for several hours, before once again turning opaque.

After the insulation period, the soap is firm enough to be removed from the mold and cut into bars. At this time, it is safe to use the soap, since saponification is in essence complete. However, cold-process soaps are typically cured and hardened on a drying rack for 2–6 weeks before use. During this cure period, trace amounts of residual lye are consumed by saponification and excess water evaporates.

During the curing process, some molecules in the outer layer of the solid soap react with the carbon dioxide of the air and produce a dusty sheet of . This reaction is more intense if the mass is exposed to wind or low temperatures.

Hot process
Hot-processed soaps are created by encouraging the saponification reaction by adding heat to speed up the reaction. In contrast with cold-pour soap which is poured into molds and for the most part only then saponifies, hot-process soaping for the most part saponifies the oils completely and only then is poured into molds.

In the hot process, the hydroxide and the fat are heated and mixed together at 80–100 °C, a little below boiling point, until saponification is complete, which, before modern scientific equipment, the soapmaker determined by taste (the sharp, distinctive taste of the hydroxide disappears after it is saponified) or by eye; the experienced eye can tell when gel stage and full saponification has occurred. Beginners can find this information through research and classes. Tasting soap for readiness is not recommended, as sodium and potassium hydroxides, when not saponified, are highly caustic.

An advantage of the fully boiled hot process in soapmaking is the exact amount of hydroxide required need not be known with great accuracy. They originated when the purity of the alkali hydroxides were unreliable, as these processes can use even naturally found alkalis, such as wood ashes and potash deposits. In the fully boiled process, the mix is actually boiled (100+ °C), and, after saponification has occurred, the "neat soap" is precipitated from the solution by adding common salt, and the excess liquid is drained off. This excess liquid carries away with it much of the impurities and color compounds in the fat, to leave a purer, whiter soap, and with practically all the glycerine removed. The hot, soft soap is then pumped into a mold. The spent hydroxide solution is processed for recovery of glycerine.

Purification and finishing
In the fully boiled process on an industrial scale, the soap is further purified to remove any excess , , and other impurities, color compounds, etc. These components are removed by the crude soap in and then precipitating the soap with salt.

At this stage, the soap still contains too much water, which has to be removed. This was traditionally done on chill rolls, which produced the soap flakes commonly used in the 1940s and 1950s. This process was superseded by spray dryers and then by vacuum dryers.

The dry soap (about 6–12% moisture) is then compacted into small pellets or noodles. These pellets or noodles are then ready for soap finishing, the process of converting raw soap pellets into a saleable product, usually bars.

Soap pellets are combined with fragrances and other materials and blended to homogeneity in an (mixer). The mass is then discharged from the mixer into a refiner, which, by means of an auger, forces the soap through a fine screen. From the refiner, the soap passes over a roller mill (French milling or hard milling) in a manner similar to paper or plastic or to making . The soap is then passed through one or more additional refiners to further the soap mass. Immediately before extrusion, the mass is passed through a vacuum chamber to remove any trapped air. It is then extruded into a long log or blank, cut to convenient lengths, passed through a metal detector, and then stamped into shape in refrigerated tools. The pressed bars are packaged in many ways.

or may be added to produce a soap. The scouring agents serve to remove dead cells from the skin surface being cleaned. This process is called exfoliation. Many newer materials that are effective, yet do not have the sharp edges and poor particle size distribution of pumice, are used for exfoliating soaps.

To make soap, compounds such as or can be added. There is some concern that use of antibacterial soaps and other products might encourage antibiotic resistance in microorganisms.

Image:Azul e Branco.JPG|Azul e branco soap – a bar of blue-white soap Image:Soap P1140887.jpg|Handmade soaps sold at a shop in Hyères, Image:Savon de Marseille.jpg|Traditional

Many commercially available soap molds are made of silicone or various types of plastic, although many soapmaking hobbyists may use cardboard boxes lined with a plastic film. Wooden molds, unlined or lined with silicone sleeves, are also readily available to the general public. Soaps can be made in long bars that are cut into individual portions, or cast into individual molds.

See also

Further reading
  • Free ebook at .
  • Dunn, Kevin M. (2010). Scientific Soapmaking: The Chemistry of Cold Process. Clavicula Press. .
  • Garzena, Patrizia, and Marina Tadiello (2004). Soap Naturally: Ingredients, methods and recipes for natural handmade soap. Online information and Table of Contents. /
  • Garzena, Patrizia, and Marina Tadiello (2013). The Natural Soapmaking Handbook. Online information and Table of Contents. /
  • Mohr, Merilyn (1979). The Art of Soap Making. A Harrowsmith Contemporary Primer. Firefly Books. .
  • Thomssen, E. G., Ph. D. (1922). Soap-Making Manual. Free ebook at Project Gutenberg.

External links
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