Soap is both a salt of a fatty acid and the term for a variety of
cleansing and lubricating products produced from it. Household uses
for soaps include washing, bathing, and other types of housekeeping,
where soaps act as surfactants, emulsifying oils to enable them to
be carried away by water. In industry, they are used as thickeners,
components of some lubricants, and precursors to catalysts.
1 Kinds of soaps
1.1 Non-toilet soaps
1.1.1 Production of metallic soaps
1.2 Toilet soaps
1.2.1 Production of toilet soaps
126.96.36.199 Ancient Middle East
188.8.131.52 Roman Empire
184.108.40.206 Ancient China
220.127.116.11 Islamic Middle East
18.104.22.168 Medieval Europe
22.214.171.124 15th–19th centuries
126.96.36.199 Liquid soap
1.2.3 Soap-making for hobbyists
2 See also
4 Further reading
5 External links
Kinds of soaps
Since they are salt of fatty acids, soaps have the general formula
(RCO2−)nMn+ (R = alkyl). The major classification of soaps is
determined by the identity of Mn+. When M = Na or K, the soaps are
called toilet soaps, used for handwashing. Many metals dications
(Mg2+, Ca2+, and others give metallic soap. When M = Li, the result is
lithium soap (e.g., lithium stearate), which is used in high
Soaps are key components of most lubricating greases and thickeners.
Greases are usually emulsions of calcium soap or lithium soap and
mineral oil. Many other metallic soaps are also useful, including
those of aluminium, sodium, and mixtures thereof. 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
Metal soaps are also included in modern artists' oil paints
formulations as a rheology modifier.
Production of metallic soaps
Most heavy metal soaps are prepared by neutralization of purified
2 RCO2H + CaO → (RCO2)2Ca + H2O
In a domestic setting, "soap" usually refers to what is technically
called a toilet soap, used for household and personal cleaning. When
used for cleaning, soap solubilizes particles and grime, which can
then be separated from the article being cleaned. The insoluble
oil/fat molecules become associated inside micelles, tiny spheres
formed from soap molecules with polar hydrophilic (water-attracting)
groups on the outside and encasing a lipophilic (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.
Structure of a micelle, a cell-like structure formed by the
aggregation of soap subunits (such as sodium stearate): The exterior
of the micelle is hydrophilic (attracted to water) and the interior is
lipophilic (attracted to oils).
Production of toilet soaps
The production of toilet soaps usually entails saponification of fats
(triglycerides). Triglycerides are vegetable or animal oils and fats.
An alkaline solution, often called lye or sodium hydroxide), induces
saponification whereby the triglyceride fats first hydrolyze into
salts of fatty acids.
Glycerol (glycerin) is liberated. The glycerin
can remain in the soap product as a softening agent, although it is
The type of alkali metal used determines the kind of soap product.
Sodium soaps, prepared from sodium hydroxide, are firm, whereas
potassium soaps, derived from potassium hydroxide, are softer or often
liquid. Historically, potassium hydroxide was extracted from the ashes
of bracken or other plants. Lithium soaps also tend to be hard. These
are used exclusively in greases.
For making toilet soaps, triglycerides (oils and fats) are derived
from coconut, olive, or palm oils, as well as tallow. Triglyceride
is the chemical name for the triesters of fatty acids and glycerin.
Tallow, i.e., rendered beef fat, is the most available triglyceride
from animals. Each species offers quite different fatty acid content,
resulting in soaps of distinct feel. The seed oils give softer but
Soap made from pure olive oil, sometimes called Castile
Marseille soap, is reputed for its particular mildness. 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
Palm kernel oil
Ancient Middle East
Box for Amigo del Obrero (Worker's Friend) soap from the 20th century,
part of the
Museo del Objeto del Objeto
Museo del Objeto del Objeto collection
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.
Ebers papyrus (Egypt, 1550 BC) indicates the ancient Egyptians
bathed regularly and combined animal and vegetable oils with alkaline
salts to create a soap-like substance. Egyptian documents mention a
similar substance was used in the preparation of wool for
In the reign of
Nabonidus (556–539 BC), a recipe for soap consisted
of uhulu [ashes], cypress [oil] and sesame [seed oil] "for washing the
stones for the servant girls".
The word sapo, Latin for soap, likely was borrowed from an early
Germanic language and is cognate with Latin sebum, "tallow". It first
appears in Pliny the Elder's account. 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 the men of the Gauls and Germans were more likely
to use it than their female counterparts. 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". 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 strigil. The Gauls used soap made from animal fat.
Zosimos of Panopolis, circa 300 AD, describes soap and soapmaking.
Galen 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.
A detergent similar to soap was manufactured in ancient China from the
seeds of Gleditsia sinensis. 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.
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 Middle East
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
glycerine from olive oil. In the Middle East, soap was produced from
the interaction of fatty oils and fats with alkali. In Syria, soap was
produced using olive oil together with alkali and lime.
exported from Syria, to other parts of the
Muslim world and to
A 12th-century Islamic document describes the process of soap
production. It mentions the key ingredient, alkali, 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 Nablus, Fes,
Damascus, and Aleppo.
Naples were members of a guild in the late sixth century
(then under the control of the Eastern Roman Empire), and in the
eighth century, soap-making was well known in Italy and Spain. The
Carolingian capitulary De Villis, dating to around 800, representing
the royal will of Charlemagne, mentions soap as being one of the
products the stewards of royal estates are to tally. The lands of
Medieval Spain were a leading soapmaker by 800, and soapmaking began
Kingdom of England
Kingdom of England about 1200. 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
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.
Advertisement for Pears' Soap, 1889
A 1922 magazine advertisement for Palmolive Soap
Manufacturing process of soaps/detergents
In France, by the second half of the 15th century, the
semi-industrialized professional manufacture of soap was concentrated
in a few centers of Provence—Toulon, Hyères, and Marseille—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. English
manufacture tended to concentrate in London.
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
Castile soap 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
hygiene in reducing the population size of pathogenic microorganisms.
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
Until the Industrial Revolution, soapmaking was conducted on a small
scale and the product was rough. In 1780
James Keir established a
chemical works at Tipton, for the manufacture of alkali from the
sulfates of potash and soda, to which he afterwards added a soap
manufactory. The method of extraction proceeded on a discovery of
Andrew Pears started making a high-quality, transparent soap
in 1807 in London. His son-in-law, Thomas J. Barratt, opened a
Isleworth in 1862.
Restoration era (February 1665 – August 1714) a soap tax
was introduced in England, which meant that until the mid-1800s, 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
William Gossage 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
Benjamin T. Babbitt
Benjamin T. Babbitt introduced marketing innovations that
included sale of bar soap and distribution of product samples. William
Hesketh Lever and his brother, James, bought a small soap works in
Warrington in 1886 and founded what is still one of the largest soap
businesses, formerly called Lever Brothers and now called Unilever.
These soap businesses were among the first to employ large-scale
See also: Detergent
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
In the early 1900s, other companies began to develop their own liquid
soaps. Such products as
Pine-Sol 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 for hobbyists
A variety of methods are available for hobbyists to make soap.
Most soapmakers use processes where the glycerol remains in the
product, and the saponification 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 alkali (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. Addition of
glycerol and processing of this soap produces glycerin soap.
Superfatted soap is more skin-friendly than one without extra fat,
although it can leave a "greasy" feel. Sometimes, an emollient is
added, such as jojoba oil or shea butter.
pumice may be added to produce a scouring soap. The scouring agents
serve to remove dead cells from the skin surface being cleaned. This
process is called exfoliation.
The lye is dissolved in water.
To make antibacterial soap, compounds such as triclosan or
triclocarban can be added. There is some concern that use of
antibacterial soaps and other products might encourage antibiotic
resistance in microorganisms.
Azul e branco soap – a bar of blue-white soap
Handmade soaps sold at a shop in Hyères, France
African black soap
List of cleaning products
Soap made from human corpses
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