Soap
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Soap most commonly appears in bar form. This particular bar has seen some use and thus has lost its "bar" shape. |
Soap is a
surfactant used in conjunction with
water for washing and
cleaning. It usually comes in a solid
moulded form, termed
bars due to its historic and most typical shape. In this century, the use of thick
liquid soap has become increasingly widespread, especially from
soap dispensers in public
washrooms. Applied to a soiled surface, soapy water effectively holds particles in suspension so the whole of it can be rinsed off with clean water. In the developed world, synthetic
detergents have superseded soap as a
laundry aid.
Many soaps are mixtures of
sodium (
soda) or
potassium (
potash)
salts of
fatty acids which can be derived from oils or fats by reacting them with an
alkali (such as
sodium or
potassium hydroxide) at 80°–100 °C in a process known as
saponification. The fats are
hydrolyzed by the base, yielding
glycerol and crude soap. Historically, the alkali used was
potassium made from the deliberate burning of vegetation such as
bracken, or from wood ashes.
Soap is derived from either oils or fats.
Sodium Tallowate, a common ingredient in many soaps, is in fact derived from
rendered beef fat. Soap can also be made of vegetable oils, such as
olive oil. Soap made entirely from such oils, or nearly so, is called
castile soap. The use of the word "soap" has become such a household name that even cleaning solutions for the body that don't have soap in the ingredients are referred to as soap.
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A collection of decorative soaps used for human hygiene purposes. This type of soap is typically found inside hotels. |
The common process of purifying soap involves removal of
sodium chloride,
sodium hydroxide, and
glycerol. These impurities are removed by
boiling the crude soap
curds in water and re-precipitating the soap with salt.
Most of the water is then removed from the soap. This was traditionally done on a chill roll 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 This process was superseded by spray dryers and then by vacuum dryers.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 (approximately 6-12%
moisture) is then compacted into small pellets. These pellets are now ready for soap finishing. Soap finishing is the process of converting raw soap pellets into salable product, usually bars.
Soap pellets are combined with fragrances and other materials and blended to homogeneity in an amalgamator (mixer). The mass is then discharged from the mixer into a refiner which, by means of an auger, forces the soap through a fine wire screen. From the refiner the soap passes over a roller mill (French milling or hard milling) in a manner similar to
calendering paper or plastic or to making
chocolate liquor. The soap is then passed through one or more additional refiners to further plasticize the soap mass. Immediately before extrusion it passes through a vacuum chamber to remove any entrapped 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.
Sand or
pumice may be added to produce a
scouring soap. This process is most common in creating soaps used for human hygiene. The scouring agents serve to remove dead skin cells from the surface being cleaned. This process is called
exfoliation. Many newer materials are used for exfoliating soaps which are effective but do not have the sharp edges and poor size distribution of pumice.
Although the word
soap continues to be used informally in everyday speech and product labels, in practice nearly all kinds of "soap" in use today are actually synthetic
detergents, which are less expensive, more effective, and easier to manufacture. While effort has been made to reduce their negative effect upon the environment, the results have been mixed.
Soaps are useful for cleansing because soap
molecules attach readily to both
nonpolar molecules (such as or
oil) and polar molecules (such as
water). Although grease will normally adhere to skin or clothing, the soap molecules can attach to it as a "handle" and make it easier to rinse away. Allowing soap to sit on any surface (skin, clothes etc) over time can imbalance the moisture content on it and result in the dissolving of fabrics and dryness of skin.
:::(fatty end) :CH
3-(CH
2)
n - COONa: (water soluble end)
The hydrocarbon ("fatty") portion dissolves dirt and oils, while the ionic end makes it soluble in water. Therefore, it allows water to remove normally-insoluble matter by
emulsification.
Soap water can be used as a nature friendly way to get rid of an ant in your food problem. By pouring soap water on an ant trail it destroys the ant's sense of smell and the scent the ants were following to get to the food.
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1922 magazine advertisement for Palmolive Soap |
The earliest known evidence of soap use are
Babylonian clay cylinders dating from 2800 BC containing a soap-like substance. 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.
It is commonly reported that a soap factory with bars of scented soap was found in the ruins of
Pompeii (79 AD). However, this has proved 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 innocent of soap's detergent properties. The word "soap" 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. [
1]
The Arabs made the soap from vegetable oil as olive oil or some aromatic oils such as thyme oil. Sodium Lye (Al-Soda Al-Kawia) NaOH was used for the first time and the formula hasn't changed from the current soap sold in the market. From the beginning of the 7th century soap was produced in Nablus (Palestine), Kufa (Iraq) and Basra (Iraq). Arabian Soap was perfumed and coloured, some of the soaps were liquid and others were hard. They also had special soap for shaving. It was commercially sold for 3 Dirhams (0.3
Dinars) a piece in 981 AD.
A story 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. Eventually, women noticed that it was easier to clean clothes with this "soap". The location of Mount Sapo is unknown, as is the source of the "ancient Roman legend" to which this tale is typically credited.[
2] 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 a
hoax.
Historically, soap was made by mixing
animal fats with
lye. Because of the
caustic lye, this was a dangerous procedure (perhaps more dangerous than any present-day home activities) which could result in serious
chemical burns or even
blindness. Before commercially-produced lye was commonplace, it was produced at home for soap making from the ashes of a wood fire.
Castile soap, made from
olive oil, was produced in Europe as early as the
16th century.
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. Manufactured bar soaps first became available in the late nineteenth century, and
advertising campaigns in Europe and the United States helped to increase popular awareness of the relationship between cleanliness and health. By the 1950s, soap had gained public acceptance as an instrument of
personal hygiene.
Some individuals continue to make soap in the home. The traditional name "
soaper", for a soapmaker, is still used by those who make soap as a
hobby. Those who make their own soaps are also known as soapcrafters.
The most popular soapmaking processes today is the
cold process method, where fats such as
olive oil react with
lye. Soapmakers sometimes use the
melt and pour process, where a premade soap base is melted and poured in individual molds. This is not really to be considered soap-
making though. Some
soapers also practice other processes, such as the historical
hot process, and make special soaps such as clear soap (aka
glycerin soap).
Handmade soap differs from industrial soap in that, usually, an excess of fat is used to consume the alkali (
superfatting), and in that the
glycerin is not removed. Superfatted soap, soap which contains excess fat, is more skin-friendly than industrial soap; though, if not properly formulated, 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.
Today, fat-based soaps have mostly been superseded by modern
detergents. Washing agents do not contain soap for cleaning fabric, but for reducing foam.
The disadvantages of commercial soaps are:
*Soap deprives the
skin of natural, beneficial oils.
*Some antibacterial soaps have chemicals killing bacteria that coexist on the skin's surface and are essential to skin health. More alarmingly, the rise of antibacterial soaps contributes to
antibiotic resistant bacteria.
*Soap-based products often contain the additive
sodium laureth sulfate, which research has found to be harsh on skin. This product however is also present in many non-soap cleaners for personal hygiene (shampoos, bathfoams, etc.).
*Soap can react mildly
basically with fabrics resulting in damage over the long term. This is usually due to excess
sodium hydroxide (
NaOH, an
alkali/
base) left from manufacture, but can also be caused by the very slight presence of NaOH from the
equilibrium reaction:
R-COO-Na + H
2O ↔ R-COO
- + Na
+ + H
2O ↔ R-COOH + NaOH
However, this
equilibrium strongly favors the left-hand side so the fraction of NaOH formed is minuscule
*Soap reacts with
lime to form an insoluble deposit (soap scum) in "
hard water":
2Na
+(R-COO)
-(aq) + Ca
2+(HCO
3-)2(aq) → 2Na+(HCO3)-(aq) + Ca(R-COO)2(s) - where R stands for an alkyl group (ppt)Commercially made bar soaps are formulated to mitigate all of these disadvantages:
*A wide variety of emollient materials, such as shea or cocoa butters, are substantive to the skin.
*Poorly finished soaps contain alkali (NaOH) and react mildly basically with skin and fabric; commercial products are finished to neutrality or to a weak acid content to prevent this and be more compatible with the skin's slightly acidic pH.
*Commercial products use chelating molecules (sequestrants), often EDTA derivatives to bind with any free or ions and prevent soap scum. These also help reduce fragrance loss, discolouration and rancidity.
*Soap dispenser
*Saponin
*Unsaponifiable
*Saponification
*Soaper
*Glycerin soap
*Soapmaking
*Stainless steel soap* Maine, Sandy (1995). The Soap Book: Simple Herbal Recipes. Interweave Press. ISBN 1883010144.
* Tarekh Al-Masoudi\the first book. [The Masoudi History-printed in 1989 Beirut-Lebanon]History
*Soap history by The Soap and Detergent Association
*The Discovery and Prehistory of Soap by R W Hedge at Butser Ancient Farm
*The History of Soap by C'etrange
*History of soap by the Pharmaceutical Journal
*Colonial Soap Making. Its History and Techniques. (The Soap Factory)
*Soap Naturally by Patrizia Garzena, contains a history of soap; rebuts the "Mount Sapo" legend.Soap making
*About Candle and Soap Making - Soap making projects, instructions, recipes, suppliers and more from About.com
*Glossary for the Modern Soap Maker. Soap making terminology defined.
*The Soap Making Home Page
*Handcrafted Soap Maker's Guild
*Soap Making Instructions & Recipes
*Instructions for Making Crock Pot Handmade SoapOther
*The Columbia Encyclopedia's soap entry (via Bartleby.com)
* How to Use Shaving Soap
* Fight Club - Novel & movie with soap making a central theme
* Documentary about Dr. Bronner, famous soapmaker and counterculture hero
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