As any child of the television age knows, among the most important decisions one faces in life is which kinds of soaps and detergents to use. The consequences of not having clothes that are cleaner than clean and brighter than bright, or of using the wrong brand of cleanser on your pearly skin, are too horrible to contemplate.
But what are all those commercials selling us? What are soaps and detergents?
Soap has a straightforward definition (although it’s not one they push in advertising): it’s a natural cleansing agent produced by the reaction of an alkali with animal fat or vegetable oil. A detergent is a synthetic chemical that acts as a soap. Most detergents are synthesized from hydrocarbons (found in oil, if you want to be crude about it).
Whether you’re washing with soap or detergent, the process is the same. Both contain “surfactants” (short for “surface-active agents”). Surfactant molecules have one end which is “hydrophilic,” or attracted to water, and another end which is “hydrophobic,” or not attracted to water: instead, it’s attracted to substances such as oils.
Just like what used to be called hydrophobia makes dogs foam at the mouth, the hydrophobia of one end of the surfactant molecule makes soapy water foam. That’s because it interferes with the usual bonding of the water molecules to each other. One effect of this is to make it possible for water to form much thinner films than usual, which sometimes trap air, creating bubbles. The more important effect is to make it possible for water to slip into smaller spaces than usual, such as between a bit of grit and a strand of fibre. At the same time, the hydrophobic end of the surfactant molecule binds with the dirt itself. Agitation by hand or machine helps the surfactant pull the dirt free of the surface being cleaned, and once the dirt is suspended in water, the surfactant molecules cluster around it, the ends that are attracted to dirt pointing in and the ends that are attracted to water pointing out. This helps keep the dirt suspended until it’s rinsed away.
Soap doesn’t work well in hard water because it binds with the minerals in the water to form an insoluble curd (sounds disgusting, doesn’t it?). Overcoming this problem was a main impetus to the development of detergents.
Besides having synthesized surfactants in them that don’t bind with hardness minerals, modern detergents contain additional chemicals soaps lack, called builders, that further help control hardness minerals, maintain the proper level of alkalinity (which maintains the effectiveness of the surfactant), suspend soil particles and break down oily soils.
Detergents may also include chemicals to keep soil from being re-deposited, plus brighteners, bleaches, corrosion inhibitors, suds-control agents (in some detergents, the suds you see are like the coloring in colas: they’re only there because consumers expect them), perfumes and colorants. Since detergents are synthesized, they can be designed to serve a wider variety of uses than soap, from cleaning hair to cleaning ovens.
The earliest reference to soap comes from Mesopotamian clay tablets from around 3,000 B.C. Much later, the Romans spread their knowledge of soapmaking (such as it was: the standard method was to boil animal fat in wood ashes) around the world.
In the Middle Ages important centers of soapmaking developed in Spain, France, and England, but manufacturing remained crude until the Industrial Revolution, when inventions such as the steam engine and improved techniques enabled soapmaking to become competitive industry. The use of animal fat gave way to vegetable oils as exploration of the New World opened up sources of new oils such as palm and coconut.
The first detergent, a mixture of soap and sodium salts, was marketed by a German company in 1907 under the name of Pilser (not to be confused with Pilsner, or you’ll be sorry). The first detergents were introduced in the United States in the early 1930s. They performed better than soaps in hard water but didn’t clean all that well overall.
The next breakthrough, after the Second World War, was the first detergent with a builder: phosphate. It worked in hard water and had good all-around cleaning power.
Some early detergent surfactants weren’t easily broken down by bacteria, so concentrations of them sometimes built up to the point that streams would foam like dishwater. In response, the U.S. detergent industry changed in 1965 to new materials that are quickly broken down and eliminated from the environment.
However, detergents continued to be “built” with phosphate, which contains the element phosphorus. Phosphorus is an essential nutrient to water plants and algae, so increasing the level of phosphorus in the water leads to lakes choked with weeds and algae. (Anybody know a lake like that?)
Various places have banned the sale of detergents with phosphates, and detergent manufacturers are responding by reducing phosphate use. To get the same cleansing power in non-phosphate-built detergents, some manufacturers add extra surfactants, while others have added enzymes normally found in the digestive tract, which, as you might expect, are particularly good at removing food stains..
Soap is easy to manufacture at home: all it takes is lard, lye and a little know-how. You just melt lard in a low-heat oven, cool it down a bit, stir in lye solution, let it all harden, age it for three or four weeks, and presto! Soap. Colouring and perfumes can be added during the process, and it can be molded into pleasing or humorous shapes.
My idea is to market a bunch of little soaps molded into the likenesses of Placido Domingo, Luciano Pavarotti and Beverly Sills.
With the whole set, you can stage your own soap opera!