This article is about a common cleaning mixture. For other uses of the word Soap, see Soap (disambiguation).

Soap is a surfactant cleaning mixture used for personal or minor cleaning. It usually comes in solid moulded form. In the developed world, synthetic detergents have superseded soap as a laundry aid.

Many soaps are mixtures of sodium or potassium 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 potash made from the deliberate burning of vegetation such as bracken, or from wood ashes.

Soap in bar form is often used in the washing areas of a house and can be made of other, more environmentally-healthy materials as well, such as natural vegetable oils or olive oil. "Sodium Tallowate", a common ingredient in many, is in fact rendered animal fat.

Purification and finishing

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.

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.

Use

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 grease 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.

(water soluble end)

CH3-(CH2)n - COONa

(fatty part)

The hydrocarbon ("fatty") portion dissolves dirt and oils, while the ionic end makes it soluble in water. Thus, it allows water to remove normally-insoluble matter.

The history and process of soap making

The ancient world was generally innocent of soap; the Romans built baths, but did not use soap in them. According to Pliny the Elder, soap was invented by the ancient Gauls. They did not use it for washing, though; they used it as a pomade to keep their hair shiny.

Historically, soap was made in the home 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.

In modern times, the use of soap has become universal in industrialized nations due to a better understanding of the role of hygiene in eliminating disease vectors such as germs. 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 soap-maker, is still used by those who make soap as a hobby. The most popular soap-making processes today are the cold process and the melt and pour process. Some soapers also practice other processes, such as the hot process, and make special soaps such as glycerin soap.

Disadvantages

Nowadays soap has mostly been superseded by modern detergents. Washing agents do not contain soap for cleaning fabric, but to reduce foaming.

The disadvantages of soap are:

• Soap deprives the skin of oils
• Soap reacts basically, which results in damage to the fabric:
  R-CO₂-Na --H₂0--> R-CO₂^- + Na⁺ + H₂0 ----> R-COOH (=fatty acid) + OH^- (basically)
• Soap reacts with lime to form an insoluble deposit (soap scum):
  2R-COO^- + Ca²⁺ (lime) ----> Ca(R-COO)₂

See also

• Saponin
• A great downloadable guide to soap making from Quamut.com  (http://www.quamut.com/soap/index.php)