It was the Roman scholar, Pliny, who first wrote of adding salt to soap to harden it.
Theories are divided as to who first used soap - some credit the Celtics with being
the first to use it for bathing and the Romans for using it in cleaning textiles
A soap-like material found in clay cylinders during the excavation of ancient Babylon is
evidence that soapmaking was known as early as 2800 B.C. Inscriptions on the cylinders say
that fats were boiled with ashes, which is a method of making soap
The first known written mention of soap was on Sumerian clay tablets dating about 2500 BC.
They were found in the area of the Tigris and Euphrates river. The tablets spoke of the use of
soap in the washing of wool. Another Sumerian tablet, dating 2200 BC, describes a `soap'
[this author's `..'] formulation of water, alkali and cassia oil. The Ebers Papyrus, a medical
document from about 1500 BC, shows evidence that Egyptians bathed regularly and that they
combined animal and vegetable oils with alkaline salts to create a soap-like (sic) substance for
washing
Soap got its name, according to an ancient Roman legend, from Mount Sapo, where animals
were sacrificed. Rain washed a mixture of melted animal fat, or tallow, and wood ashes down
into the clay soil along the Tiber River. Women found that this clay mixture made their wash
cleaner with much less effort.
he location of Mount Sapo is unknown, as is the source of the "ancient Roman legend"
This certainly cannot be documented; but it is quite possible soap could have been discovered
even in prehistoric times. Early people cooking their meats over fires might have noticed after
a rainstorm there was a strange foam around the remains of the fire and its ashes.
The first definite and tangible proofs of soap making are found in the history of ancient Rome.
Pliny, the Roman historian, described soap being made from goat's tallow and causticized
wood ashes. The ruins at Pompeii revealed a soap factory complete with finished bars.
The women noticed the clothes became cleaner with far less effort at that particular location.
What was happening? The ashes and the grease of animals from the sacrificial fires of the
temples situated on the top of Sapo Hill mixed with the rain, making soap which ran down the
slope in the streams of rain water giving the women a wash day bonus
During World War II housewives saved used cooking fats to be used in making
soap; and its resulting by-product, glycerin, was used in making
explosives.
Small scale soap production didn't start until the Middle Ages, when, in the 1200's, the first
manufacturing factories were set up in France and in England, still using animal fat as the
main ingredientLittle is known of the use of soap in the Dark Ages which followed the fall of
Rome. Personal hygiene was probably not a high priority in regions where life was
precarious. Saponins
The manufacture of soap in Europe and the Mediterranean region had re-emerged by the end
of the first millennium. Early centres of production were Marseilles in France and Savona in
Italy
Through out the centuries, there have been other times when people were able to make soap
using a form of sodium alkali as is done presently. The Egyptians are thought to have
employed local soda deposits for their source of alkali as the Spaniards did during the 8th
century. Also people in various coastal regions burned seaweed producing sodium based
barillia for their alkali.
But by far the most common soap was made from potash and pearlash. Potash and pearlash
are forms of the potassium based alkali present in plant and wood material. Potash and
pearlash soaps were used by everyone from the reigning monarchs to the peasant or cottager,
who made their own soap from the waste fats and ashes they saved.
Most people who have made soap down thru the centuries had no idea what occurred. They
just made soap by trial and error, by having lots of luck, and believing in many superstitions
in how to make soap. When people learned that saponification was the reaction that made
soap, we will tell you later.
The First Soap
This certainly cannot be documented; but it is quite possible soap could have been discovered
even in prehistoric times. Early people cooking their meats over fires might have noticed after
a rainstorm there was a strange foam around the remains of the fire and its ashes. They might
have even noticed when water was put in a pot that had been used for cooking meats and then
got ashes in it, which often happens with outdoors cooking, also had this strange foamy
substance. This women, most likely who was doing the washing, might have also observed
the pot became cleaner or at least her hands became cleaner then usual.
It is recorded that the Babylonians were making soap around 2800 B.C. and that it was known
to the Phoenicians around 600 B.C. These early references to soap and soap making were for
the use of soap in the cleaning of textile fibers such as wool and cotton in preparation for
weaving into cloth.
The Romans and Celtics
The first definite and tangible proofs of soap making are found in the history of ancient Rome.
Pliny, the Roman historian, described soap being made from goat's tallow and causticized
wood ashes. He also wrote of common salt being added to make the soap hard. The ruins at
Pompeii revealed a soap factory complete with finished bars.
While the Romans are well known for their public baths, generally soap was not used for
personal cleaning. To clean the body the Greeks and then the Romans would rub the body
with olive oil and sand. A scraper, called a strigil, was then used to scrape off the sand and
olive oil also removing dirt, grease, and dead cells from the skin leaving it clean. Afterwards
the skin was rubbed down with salves prepared from herbs.
Throughout history people were also known to take baths in herb waters and other additions
to the bathing medium thought to be beneficial. It is well known that Cleopatra, who
captivated the leaders of the Roman world, attributed her beauty to her baths in mare's milk.
During the early century of the common era soap was used by physicians in the treatment of
disease. Galen, a 2nd century physician, recommended bathing with soap would be beneficial
for some skin conditions. Soap for personal washing became popular during the later
centuries of the Roman era.
The Celtic peoples are also though by some historians to have discovered soap making and
were using it for bathing and washing. Maybe do to increased contact with the Celtics by the
Romans, using soap for personal washing care became popular.
It is also important to remember when writing a history of life styles there are no grand trends
that get disseminated throughout the globe via mass communications such as we have today.
Usage and knowledge of common skills and arts can vary from one locale to the next. When
they are starting to use soap in the public baths in 3rd century A.D. in the major cities, the
people in small villages are likely to be using the olive oil, sand, and strigil method. The
Celtics might have been washing their faces daily with soap long before the Romans even
went over the Italian Alps. Dates can be exact when dealing with events such as battles,
births, and deaths. But not usage of every day items. "The state of the art" varies depending
both on time and location.
There is an interesting legend surrounding the discovery of soap making. This legend accords
the discovery of soap to the Romans so it must be a Roman legend to confront the Celtic
claim to soap making. Probably both of these inventive peoples discovered soap making
independently. The legend says soap was first discovered by women washing clothes along
the Tiber River at the bottom of Sapo Hill. The women noticed the clothes became cleaner
with far less effort at that particular location. What was happening? The ashes and the grease
of animals from the sacrificial fires of the temples situated on the top of Sapo Hill mixed with
the rain, making soap which ran down the slope in the streams of rain water giving the women
a wash day bonus. You can see at a glance saponification, the chemical name for the soap
making reaction, bears the name of that hill in Rome long ago, which caused one Roman
washer women to comment to another, "My wash is cleaner than yours".
The European Dark Ages
After the fall of the Roman Empire in Western Europe, there was little soap making done or
use of it in the European Dark Ages. In the Byzantine Empire, the remains of the Roman
world in the eastern Mediterranean area, and in the expanding Arab world soap was made and
used. Around the 8th century soap making was revived in Italy and Spain. By the 13th
century, France also became a producer of soap for the European market. During the 14th
century, soap making was started in England. Soaps produced in the south of Europe, Italy,
Spain, and the southern ports of France (Marseilles and Castle soaps) were made from olive
oils. These soaps made using olive oils were of a higher quality than those made by the soap
producers of England and northern France. These northern soap makers, not being able to
obtain the olive oil, made their soaps with only animal fats. Tallow, the fat from cattle, was
the chief fat used. Northern European soap makers even resorted to making soap from fish
oils. Soaps made from the poor quality animals fats and oils, while adequate for laundry and
textile usage, were not desirable for bathing and washing. The soap from southern Europe
with their olive oils were superior. This resulted in a lively trade of exporting fine soaps from
southern Europe.
Wait a minute you say, people did not take baths in the Middle Ages. That is a popular
misconception. They did. There were public bath houses, called stews, where the patrons
bathe in large wooden tubs and were given bars of soap to use. Nobles and rich merchants had
their own private baths. It was during the later Medieval Times, when bathing fell out of
favor. Public baths were closed because the authorities of the time thought these baths
promoted the spread of the Plague. In general people of the Renaissance moved away from
the idea of keeping the body clean. They preferred to cover the body with heavy scents.
Soap, however, did remain a useful item for cleaning and washing clothes. Soap also was still
used for personal washing as well but by our standards far less frequently than was needed.
The fact that soap was a valuable item in the 17th and 18th centuries even though the idea of
bathing was not popular is shown by the efforts the settlers to the New World took to make it.
While maybe bathing the whole body was out of fashion keeping you and your surroundings
clean was not.
Soap in the American Colonies
At first the earliest settlers simply brought a plentiful supply of soap along with them. The
Talbot, a ship chartered by the Massachusetts Bay Company to carry persons and supplies
from England to its colonies at Naumbeak now known as Salem and Boston, listed among its
cargo 2 firkins of soap. A firkin is an old measurement which was a wooden, hooped barrel of
about nine gallon capacity. John Winthrop, who was to become the first governor of the
Massachusetts Bay Colony, when writing to his wife in 1630 from Boston included soap in a
list of necessities to be brought on her crossing to the New world.
After the colonists were settled and had been able to survive the first years of hardships, they
found it more advantageous to make soap themselves using the copious amount of wood
ashes, a natural result of their homesteading activities. With also a plentiful supply of animal
fat from the butchering of the animals they used for food, the colonists had on hand all the
ingredients for soap making. They did not have to rely on waiting for soap to be shipped from
England and waste their goods or few pieces of currency in trade for soap.
Soap with some work and luck could be made for free. Soap making was performed as a
yearly or semiannual event on the homesteads of the early settlers. As the butchering of
animals took place in the fall, soap was made at that time on many homesteads and farms to
utilize the large supply of tallow and lard that resulted. On the homes or farms where
butchering was not done, soap was generally made in the spring using the ashes from the
winter fires and the waste cooking grease, that had accumulated throughout the year.
The hardest part was in determining if the lye was of the correct strength, as we have
said. In order to learn this, the soap maker floated either a potato or an egg in the lye. If
the object floated with a specified amount of its surface above the lye solution, the lye was
declared fit for soap making. Most of the colonists felt that lye of the correct strength would
float a potato or an egg with an area the size of a ninepence (about the size of a modern
quarter) above the surface. To make a weak lye stronger, the solution could either be boiled
down more or the lye solution could be poured through a new batch of ashes. To make a
solution weaker, water was added.
The difficulties in making soap the colonists endured arose from the lack of knowledge of the
chemical processes involved and the inability to obtain lye's of known and dependable
strengths. There were many superstitions which the colonist believe caused success or failure.
For making good soap, the tide and the phases of the moon among other things were taken in
account. A Pennsylvania Dutch recipe carefully warned that a sassafrasas stick was the only
kind of implement suitable for stirring the soap and the stirring must be done always in the
same direction.
In later colonial times, when the trade of soap making was well established in the cities and
towns, many of these trades people became very astute observers of the process and were able
to produce their soap with dependable high quality. However, many house holders,
particularly in rural areas, made their own potash soap until the middle of the 19th century.
There the difficulties and the related folklore still existed around the soap making process.
From the diary of Elizabeth Ranch Norton, a niece of President John Adams, written in 1799,
we learn how an exasperating job soap making could be. On one occasion Mrs. Norton had to
make three batches of soap before she was able to make one barrel of soap fit for her family's
needs.
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.
A soap factory with bars of scented soap was found in the ruins of Pompeii (79 AD).
However, 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 commerciallyproduced 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
TRAVAIL DU SAVON
*
Soap has two main functions: 1. Decrease water's surface tension
2. Bind to dirt, oil and bacteria
It can do these things because one part of the soap molecule is hydrophilic (water-binding) and the
other is hydrophobic (water-repellent). The hydrophilic part allows the hydrophobic fatty acids to come
into contact with other hydrophobic substances, such as the dirt on the surface that is being cleaned.
When the grime adheres to the soap's fatty acids, it becomes encapsulated in droplets of water. Dirt,
oil and bacteria are easily scrubbed off and washed away in this suspended state
Detergent contains sodium laurel sulfate, which cleans dishes by removing
fats and proteins. It acts the same way in the DNA extraction protocol,
pulling apart the fats (lipids) and proteins that make up the membranes
surrounding the cell and nucleus. Once these membranes are broken
apart, the DNA is released from the cell.
Soap molecules and grease molecules are made of two parts:

Heads, which like water

Tails, which hate water.
Both soap and grease molecules organize themselves in bubbles (spheres)
with heads outside to face the water and tails inside to hide from the
water
When soap comes close to grease, it captures it, forming a greasy soapy
ball
Nearly all compounds fall into one of two categories: hydrophilic ('water-loving') and
hydrophobic ('water-hating'). Water and anything that will mix with water are hydrophilic. Oil
and anything that will mix with oil are hydrophobic. But if you've ever tried mixing oil with
water, you've probably noticed that it doesn't work very well. Hydrophilic and hydrophobic
compounds just don't mix. (Ok, there's more to the chemistry than just this, but this is the
short version.)
This is why it's so hard to clean grease off of dirty dishes. The grease won't mix with the
water in your sink, so it won't come off. This is where soap comes in. Soap molecules are
kind of special in that they have a hydrophilic part and a hydrophobic part. So one end of the
soap molecule can mix with water and the other end can mix with oil.
When you mix soap into the water in your sink, the soap molecules arrange themselves into
tiny clusters (called 'micelles'). The water-loving (hydrophilic) part of the soap molecules
points outwards, forming the outer surface of the micelle. The oil-loving (hydrophobic) parts
group together on the inside, where they don't come into contact with the water at all.
Now you add the greasy dishes. The hydrophobic oil molecules on the dishes still don't mix
with the water. Instead, it gets trapped in the center of the soap micelles, where all of the
molecules around it are hydrophobic too. Then you can rinse away the soapy-water, taking all
of the trapped oil molecules with it.
If you want a neat way of seeing this at home, try taking a clear glass of water and adding a
thin layer of oil. You should be able to see them separate pretty clearly. Now add a squirt of
liquid dishsoap and stir it up. The oil doesn't separate at all any more! It's all trapped in little
clusters of soap molecules, which can dissolve in water just fine.
-Tamara
Soap molecules: love and hate
Soap molecules (also called surfactant (*) molecules) are said to be amphiphilic which means
`loving both'. Their crucial characteristic is that they are made of two very different parts : a
polar hydrophilic (*) (meaning `water loving') head and one or two long, hydrophobic (*)
(meaning `water hating') tails.
The polar (*) heads carry a small electrical charge, which makes them soluble in water but not
very soluble in oil. The long, uncharged tails are much less soluble in water but more soluble
in oil which is also non-polar (*). The molecules are typically about 100nm (*) (10-9m) long.
When they are mixed with water such molecules will tend to gather themselves together and
form small spherical micelles (*) as shown below.
When arranged as a micelle only the polar hydrophillic heads are in contact with the water, all
the hydrophobic tails are shielded from the water.
If surfactant molecules are added to an oil/water mixture they will tend to sit at the interface
with the hydrophillic heads in the water and the hydrophobic tails in the oil. In this way they
can create a layer of molecules, a monolayer (*), as shown below.
The monolayer is just one molecule thick - it has almost no thickness and we can think of it as
a 2 dimensional surface, or membrane.
So, how does this help us understand why surfactants allow oil and water to mix? Well, the
answer is that the surfactant molecules actually go between the water and oil. Imagine putting
a little oil inside a big micelle. The hydrophillic heads would still be in water and the
hydrophobic tails would now be in oil - everyone is `happy'. It turns out that there are actually
a large number of different ways that surfactant, or amphiphile, molecules can be arranged in
oil and water mixtures.
Amphiphiles as surfactants What are these molecules used for and how
do they work? How are surfacants used to help clean up oil spills?
We know that amphiphilic molecules possess a special molecular structure -contain both a water loving polar part (hydrophilic) and a water hating nonpolar part (hydrophobic). This property turns out to be very important in
determining the special structures formed by amphiphilic molecules. The
formation of these special structures is responsible for the use of amphiphiles
in a large number of applications ranging from oil recovery to efficient
delivery of drugs at a desired site in the body to their use in soaps and
detergents.
Amphiphiles are a special class of surface active molecules called surfactants . They are
called surface active because they have the unique properties of getting adsorbed at various
interfaces(e.g air-water, oil-water etc) and altering the properties of the interface. The
hydrophilic part of an amphiphilic molecule (usually called the head) is a polar molecule
whereas the hydrophobic part (called the tail) is a hydrocarbon chain 8-16 Carbon atoms in
length.
Let us first try to understand how (or why?) special structures are formed.
When placed in a solvent (say water -an ionic solvent) the hydrophilic head and the
hydrophobic tail behave differently. The hydrophobic parts tend to arrange themselves as
close as possible to each other (in order to minimize contact with water) whereas the
hydrophilic part try to separate from each other as far as possible. This can be explained by


hydrophilic interaction induced repulsion and
hydrophobic interaction induced attraction .
Depending upon the relative strength of these forces different structures tend to form . If the
interaction between the polar heads is strong relative to the interaction between the non-polar
parts than the molecules tend to form micelles (from the Latin 'micella' - meaning small bit) .
If the interaction between the polar heads is not strong relative to the non-polar part then the
molecules tend to form spherical, double-layered shells called vesicles. The formation of these
structures can also be understood by realizing that they are the lowest energy configuration
possible (i.e. energetically favorable) at different concentrations and given system parameters.
If the surfactants were placed in oil (or any other non-polar liquid) then the
corresponding inverted structures form.Can you explain why ?
The stability of the micelles formed also depends upon whether the
concentration of molecules is greater than or less than a critical micelle
concentration. On changing the concentration of the amphiphilic molecules the resultant
structures formed changes. For example the lamellar phase forms at high concentrations (this
is also known as the smectic phase of lyotropic liquid crystals.) .
The property of amphiphilic molecules that invariably plays a role in all applications is their
ability to reduce the interfacial tension of the interfaces.
A simple consequence of the property of lowering the interface tension is their ability to act as
emulsifiers - that is the phenomenon of otherwise immiscible fluids becoming miscible.
The surface activity of the molecules encourages their migration to the surface (interface) of
the two fluids (say oil and water). By lowering the interfacial tension the energy required for
the two fluids to mix (by creating more surfaces) is reduced .Consequently the interface that
separated the two fluids gets broken up into many many smaller closed interfaces - such that
the two fluid have effectively mixed - they are now miscible.
Pages: [1] [2]
To understand what is needed to achieve effective cleaning, it is helpful to have a basic
knowledge of soap and detergent chemistry.
Water, the liquid commonly used for cleaning, has a property called surface
tension. In the body of the water, each molecule is surrounded and attracted by
other water molecules. However, at the surface, those molecules are surrounded
by other water molecules only on the water side. A tension is created as the
water molecules at the surface are pulled into the body of the water. This tension
causes water to bead up on surfaces (glass, fabric), which slows wetting of the
surface and inhibits the cleaning process. You can see surface tension at work by placing a
drop of water onto a counter top. The drop will hold its shape and will not spread.
In the cleaning process, surface tension must be reduced so water can spread
and wet surfaces. Chemicals that are able to do this effectively are called surface
active agents, or surfactants. They are said to make water "wetter."
Surfactants perform other important functions in
cleaning, such as loosening, emulsifying (dispersing in
water) and holding soil in suspension until it can be rinsed away.
Surfactants can also provide alkalinity, which is useful in removing
acidic soils.
Surfactants are classified by their ionic (electrical charge)
properties in water: anionic (negative charge), nonionic (no charge),
cationic (positive charge) and amphoteric (either positive or
negative charge).
Soap is an anionic surfactant. Other anionic as well as nonionic surfactants are the main
ingredients in today's detergents. Now let's look closer at the chemistry of surfactants.
SOAPS
Soaps are water-soluble sodium or potassium salts of fatty acids. Soaps are made from fats
and oils, or their fatty acids, by treating them chemically with a strong alkali.
First let's examine the composition of fats, oils and alkalis; then we'll review the soapmaking
process.
Fats and Oils
The fats and oils used in soapmaking come from animal or plant sources. Each fat or oil is
made up of a distinctive mixture of several different triglycerides.
In a triglyceride molecule, three fatty acid molecules are attached to one molecule of
glycerine. There are many types of triglycerides; each type consists of its own particular
combination of fatty acids.
Fatty acids are the components of fats and oils that are used in making soap. They are weak
acids composed of two parts:
A carboxylic acid group consisting of one hydrogen (H) atom, two oxygen (O) atoms, and one
carbon (C) atom, plus a hydrocarbon chain attached to the carboxylic acid group. Generally, it
is made up of a long straight chain of carbon (C) atoms each carrying two hydrogen (H)
atoms.
Alkali
An alkali is a soluble salt of an alkali metal like sodium or potassium. Originally, the alkalis
used in soapmaking were obtained from the ashes of plants, but they are now made
commercially. Today, the term alkali describes a substance that chemically is a base (the
opposite of an acid) and that reacts with and neutralizes an acid.
The common alkalis used in soapmaking are sodium hydroxide (NaOH), also
called caustic soda; and potassium hydroxide (KOH), also called caustic
potash.
How Soaps are Made
Saponification of fats and oils is the most widely used soapmaking process. This method
involves heating fats and oils and reacting them with a liquid alkali to produce soap and water
(neat soap) plus glycerine.
The other major soapmaking process is the neutralization of fatty acids with an alkali. Fats
and oils are hydrolyzed (split) with a high-pressure steam to yield crude fatty acids and
glycerine. The fatty acids are then purified by distillation and neutralized with an alkali to
produce soap and water (neat soap).
When the alkali is sodium hydroxide, a sodium soap is formed. Sodium soaps are "hard"
soaps. When the alkali is potassium hydroxide, a potassium soap is formed. Potassium soaps
are softer and are found in some liquid hand soaps and shaving creams.
The carboxylate end of the soap molecule is attracted to water.
It is called the hydrophilic (water-loving) end. The
hydrocarbon chain is attracted to oil and grease and repelled
by water. It is known as the hydrophobic (water-hating) end.
How Water Hardness Affects Cleaning Action
Although soap is a good cleaning agent, its effectiveness is reduced
when used in hard water. Hardness in water is caused by the presence
of mineral salts - mostly those of calcium (Ca) and magnesium (Mg),
but sometimes also iron (Fe) and manganese (Mn). The mineral salts
react with soap to form an insoluble precipitate known as soap film or
scum.
Soap film does not rinse away easily. It tends to remain behind and
produces visible deposits on clothing and makes fabrics feel stiff. It
also attaches to the insides of bathtubs, sinks and washing machines.
Some soap is used up by reacting with hard water minerals to form the
film. This reduces the amount of soap available for cleaning. Even
when clothes are washed in soft water, some hardness minerals are introduced by the soil on
clothes. Soap molecules are not very versatile and cannot be adapted to today's variety of
fibers, washing temperatures and water conditions.
These nonionic surfactants can be reacted further with sulfur-containing acids to form another
type of anionic surfactant.
HOW SOAPS AND DETERGENTS WORK
These types of energy interact and should be in proper balance. Let's look at how they work
together.
Let's assume we have oily, greasy soil on clothing. Water alone will not remove this soil. One
important reason is that oil and grease present in soil repel the water molecules.
Now let's add soap or detergent. The surfactant's water-hating end is repelled by water but
attracted to the oil in the soil. At the same time, the water-loving end is attracted to the water
molecules.
These opposing forces loosen the soil and suspend it in the water. Warm or hot water helps
dissolve grease and oil in soil. Washing machine agitation or hand rubbing helps pull the soil
free.
Having understood how interfacial tension is reduced and that different structures are formed
at different concentrations let us explain some applications of these structures. We will deal
with