What is it?
How did it get here?
Why does it work?
Soap is made by the reaction of a fat with a strong base known as an alkali. The alkali widely used today in making bar soap is lye. Lye is also known as caustic soda or sodium hydroxide. The chemical reaction that produces soap is saponification.
A word about lye: Even though lye is used to make soap, there is no lye present in the finished product. The lye combines with the fats, oils and butters during saponification to produce a completely different substance - soap. Kind of like alchemy.
Soap, or something very much like it, has been around for thousands of years. It's mentioned in writings of Sumarians, Egyptians, Greeks and Romans. A soap factory, complete with finished bars, was found in the ruins of Pompeii.
According to ancient Roman legend, Soap got its name from Mount Sapo. Animal sacrifices were conducted on Mount Sapo. When it rained, a mixture of melted animal fat (tallow) and wood ashes washed down into the Tiber River. Women washing clothes along the river banks noticed this soapy mixture made the washing up a bit easier. Some historians contend that the Celtic peoples discovered soap making and used it for bathing and washing. The ancient Turks, Germans and Gauls are also credited with combining tallow and ashes to produce soap.
As you might suspect, bathing is closely tied to the history of soap, although personal hygiene wasn't necessarily the goal. Bathing was often a communal affair and getting clean was coincidental. Bathing gained early popularity in Europe when the first Roman baths were built there around 312 B.C. The Greek physician Galen recommended soap for cleansing and medicinal purposes during the second century AD. Alas, the fall of the Roman Empire in 467A.D. saw a decline in bathing and the use of soap throughout Europe. Many non-European cultures, including Japan and Iceland, continued bathing practices during Medieval times, but it took several centuries for bathing - and soap - to come back into fashion in Europe. A chart showing when bathing was "in" or "out" would doubtless look like a Six Flags roller coaster.
Soapmakers' guilds began to appear in Europe during the seventh century. Guilds attempted to control prices, develop fair labor practices, and evenly distribute work. Guild members took an oath to keep secrets of their trade just that - secret. In Venice, a guild member could be hung for revealing trade secrets. Craftsman were trained and promoted according to strict regulations.
The supply of olive oil from olive trees, along with an abundance of ash from barilla trees in Italy, Spain, and France made these Southern European countries early production centers for soap. The English began making soap during the 12th century.
There was a lot of saponifying going on, but most of the end product was used for laundry. Perfume was used to muffle offending personal odors. Henry IV came up with a clever way get noblemen into a bath at least once during their lives. In 1399, he instituted the Order of the Bath as a ritual of knighthood.
Time marched on, and soap gained popularity. The soap business was so good that in 1622, King James I granted a monopoly to a soapmaker for $100,000 a year. Soap was heavily taxed as a luxury item in several countries well in to the 19th century. When the high tax was removed, soap became available to ordinary people, and the world was a cleaner place.
Soapmaking in the colonies was considered "woman's work". It was an annual affair. Households saved grease and animal fat throughout the year for the big day. The fats had to be rendered to remove hair, dirt and other things you wouldn't want in your soap. The home-leaching process for lye makes me tired just thinking about it: they saved ashes; built a leaching pit out of a log with twigs, straw and such, trickled rain water over it...They tested the strength of the lye with a fresh egg. If it drifted slowly to the bottom, the lye was the proper strength. Too weak, and the egg floated; too strong and it sank.
In case you get a hankering to make your own lye soap using potash, read the following instructions on how to make lye and soap are from the November 28, 1861 edition of the DAILY CHRONICLE & SENTINEL:
The manner of making potash in the most perfect way is this: a quantity of vegetable matter is burnt into gray ashes, and the ashes boiled in water, so as to make a very strong lixivium or ley [lye]; after which, the ley [lye], being previously strained, is evaporated over a quick fire almost to dryness, the matter remaining is put into an iron crucible, melted, and then poured on an iron plate, where, when cool, it appears in the form of a solid lump of potash.
To Make Soap.--Take 18 pounds grease, 15 pounds potash or equivalent in ley [lye], pour on it 5 gallons water, boiling, stir it occasionally every day, after three days it will be fit for use, put it in a barrel. Increase quantities in proportion, if vessel or barrel will hold it.--Mobile Tribune.
Sounds like fun, doesn't it?
Beginning in the late 18th century, several scientific break-throughs led to the modern era of soap making. In 1791, French scientist Nicholas Leblan patented a process for making soda ash from common salt. Twenty years later another French chemist, Michel Eugene Chevreul, discovered the chemical nature and relationship of fats, glycerin and fatty acids. His studies established the basis for soap chemistry. This is why we know how much lye to use for different kinds of fats and oils. The old ways were pretty hit or miss, and gave "lye soap" its unpleasant image as a harsh way to come clean.
It starts getting pretty commercial from here, including how the large manufacturers actually extract the glycerin that occurs naturally in soap as a result of the chemical process, and sell it off for other uses.
So why does soap work? Soap works because during saponification process, a new molecule is created. The following from the Washington Post's "Dear Science" explains it better than I can.
Most of the stuff you try to clean off with soap - food baked onto dishes, dust caked into your skin - is infused with oil. It's hard to wash off with water because water molecules are more attracted to one another than they are to oil. Oil molecules are large and awkward, and they don't have poles - ends with different electric charges - so they're not very easy to bond with. When you try to wash a greasy pan with mere water, it will just run off without picking up the dirty, oily particles that cling to the surface.
But thousands of years ago, people figured out how to make a substance that overcame the deep antagonism between oil and water. If they took a fatty acid, like rendered fat from a cow or sheep, and mixed it with an alkaline substance, like water mixed with ashes, it would produce a thick, brown curd that was incredibly efficient at getting dirt to wash away. This recipe dates back to ancient Roman times.
A soap molecule is perfectly suited to mixing oil and water because it shares some qualities of each. The alkaline substance that helped create it gives it a polar "head" at one end. The electric charge at the head makes it "hydrophilic," or water loving, since the hydrogen atoms in water molecules have slight positive charges. When you turn on the faucet, the head of the soap molecule will readily bond with the nearest water molecule.
Meanwhile, the fatty acid component gives soap a long tail made of carbon and hydrogen atoms. Like oil, this tail is hydrophobic, so it latches onto the grease on the pan. Working together, the head and the tail lift the bits of oil up and suspend them in the water. As the faucet keeps running, the additional water will wash the suspended droplets of oil away.
So there you have it! Fun facts about soap. Now go wash your hands!