The Neatest Little Paper Ever Read ®

Issue 974

TIDBITS® WASHES WITH

SOAP

by Janet Spencer

Come along with Tidbits as we scrub up!

HOW DOES SOAP WORK?

• Oil and water don’t mix. They repel each other like opposite ends of a magnet. Your skin secretes oil called sebum. Splash water on your skin, and the oil repels the water and nothing gets very clean. That’s where soap comes in. But before we discuss why soap works, let us discuss what soap is.

• Basically speaking, soap is oil plus alkali. For centuries, that meant fat plus lye. Colonists and pioneers saved fat scraps from their butcher blocks and dinner tables. They also saved the ashes from their fireplace, which they placed in a barrel with a spigot at the bottom. Water, poured over the ashes and left to soak, would form lye which was then drained off from the bottom. The fat scraps would be rendered in a vat over a fire, then the lye would be added. After much stirring and cooking, a chemical reaction would take place and soap was the result. Too much lye, and the soap would be harsh on the skin. Too much fat, and the soap would be greasy.

• The newly formed soap would then be poured into boxes to harden and cure for several months. But why does a combination of fat and ash carry off dirt? Let us get out our microscopes.

• Water is a molecule composed of hydrogen and oxygen. The hydrogen end of the molecule has a positive charge, and the oxygen end is negatively charged. Oil, however, has neither a positive or negative charge, but carries a uniform electrical distribution. That’s why water and oil repel each other. Soap is actually a compound called sodium stearate. Sodium stearate has the properties of both oil and water: partly polar, partly non-polar. That is how it brings oil and water together.

• A molecule of soap is shaped like a snake, with the head being the water-loving sodium compound, and the tail being the water-hating stearates. Add soap to water, and the tail end tries to get away from the water. Add something greasy to the water, and the tail end of the soap molecules rush to cling to the compatible polar charge of the grease molecules. The grease molecule bonds with the stearate tail, and floats away led by the water-loving sodium head.

SOAP HISTORY

• Around 1000 B.C., Romans performed animal sacrifices to the gods on Mount Sapo. The fat from the animals mixed with the ashes of the sacrificial fires. This mix of fat and alkali flowed down to the Tiber River and accumulated in the clay soils. Women washing clothing there found the clay seemed helped get things cleaner.

FAST FACT

• Individually wrapped cakes of soap were first manufactured in New York in 1830 by a soapmaking company called Colgate, now known for its toothpaste. Previously the merchant merely hacked a chunk off a huge block of soap.

 

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