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All about Soap

270321-soapSoaps are cleaning agents that are usually made by reacting alkali (e.g., sodium hydroxide) with naturally occurring fat or fatty acids. The reaction produces sodium salts of these fatty acids, which improve the cleaning process by making water better able to lift away greasy stains from skin, hair, clothes, and just about anything else. As a substance that has helped clean bodies as well as possessions, soap has been remarkably useful.

 

History of Soap

The discovery of soap predates recorded history, going back perhaps as far as six thousand years. Excavations  of ancient Babylon uncovered cylinders with inscriptions for making soap around 2800 B.C.E. Later records from ancient Egypt (c. 1500 B.C.E. ) describe how animal and vegetable oils were combined with alkaline salts to make soap.

According to Roman legend, soap got its name from Mount Sapo, where animals were sacrificed. Rain would wash the fat from the sacrificed animals along with alkaline wooden ashes from the sacrificial fires into the Tiber River, where people found the mixture helped clean clothes. This recipe for making soap was relatively unchanged for centuries, with American colonists collecting and cooking down animal tallow (rendered fat) and then mixing it with an alkali potash solution obtained from the accumulated hardwood ashes of their winter fires. Similarly, Europeans made something known as castile soap using olive oil. Only since the mid-nineteenth century has the process become commercialized and soap become widely available at the local market.

Chemistry of Soap

The basic structure of all soaps is essentially the same, consisting of a long hydrophobic (water-fearing) hydrocarbon “tail” and a hydrophilic (waterloving) anionic “head”:

CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 COO or CH 3 (CH 2 ) n COO

The length of the hydrocarbon chain (“n”) varies with the type of fat or oil but is usually quite long. The anionic charge on the carboxylate head is usually balanced by either a positively charged potassium (K + ) or sodium (Na + ) cation. In making soap, triglycerides in fat or oils are heated in the presence of a strong alkali base such as sodium hydroxide, producing three molecules of soap for every molecule of glycerol. This process is called saponification and is illustrated in Figure 1.

Like synthetic detergents, soaps are “surface active” substances ( surfactants ) and as such make water better at cleaning surfaces. Water, although a good general solvent, is unfortunately also a substance with a very high surface tension. Because of this, water molecules generally prefer to stay together rather than to wet other surfaces. Surfactants work by reducing the surface tension of water, allowing the water molecules to better wet the surface and thus increase water’s ability to dissolve dirty, oily stains.

Figure 1.

Figure 1.

In studying how soap works, it is useful to consider a general rule of nature: “like dissolves like.” The nonpolar hydrophobic tails of soap are lipophilic (“oil-loving”) and so will embed into the grease and oils that help dirt and stains adhere to surfaces. The hydrophilic heads, however, remain surrounded by the water molecules to which they are attracted. As more and more soap molecules embed into a greasy stain, they eventually surround and isolate little particles of the grease and form structures called micelles that are lifted into solution. In a micelle, the tails of the soap molecules are oriented toward and into the grease, while the heads face outward into the water, resulting in an emulsion of soapy grease particles suspended in the water.

With agitation, the micelles are dispersed into the water and removed from the previously dirty surface. In essence, soap molecules partially dissolve the greasy stain to form the emulsion that is kept suspended in water until it can be rinsed away (see Figure 2).

As good as soaps are, they are not perfect. For example, they do not work well in hard water containing calcium and magnesium ions, because the calcium and magnesium salts of soap are insoluble; they tend to bind to the calcium and magnesium ions, eventually precipitating and falling out of solution. In doing so, soaps actually dirty the surfaces they were designed to clean. Thus soaps have been largely replaced in modern cleaning solutions by synthetic detergents that have a sulfonate (R-SO 3 ) group instead of the carboxylate head (R-COO ). Sulfonate detergents tend not to precipitate with calcium or magnesium ions and are generally more soluble in water.

Uses of Soap

Although the popularity of soap has declined due to superior detergents, one of the major uses of animal tallow is still for making soap, just as it was in years past. Beyond its cleaning ability, soap has been used in other applications. For example, certain soaps can be mixed with gasoline to produce gelatinous napalm, a substance that combusts more slowly than pure gasoline when ignited or exploded in warfare. Soaps are also used in “canned heat,” a commercialized mixture of soap and alcohol that can be ignited and used to cook foods or provide warmth. Overall, soap is a remarkably useful substance, just as it has been for thousands of years.

David A. Dobberpuhl

Figure 2. How soap works: The hydrophobic tails of soap molecules embed in grease and oil, breaking it up into particles called micelles that lift off the surface and disperse into water.

Figure 2. How soap works: The hydrophobic tails of soap molecules embed in grease and oil, breaking it up into particles called micelles that lift off the surface and disperse into water.
These Facts May Surprise You
  • Soap was first used as a medicinal agent.
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  • The Egyptians regularly bathed, using a soap made by combining animal fats with wood ash.
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  • Real soap is created by combining a strong alkali (lye) with oils and fats.
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  • Real soap made with natural ingredients often has a healing effect on acne, eczema, psoriasis and other skin conditions.
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  • The soapmaking process, called “saponification,” separates the oils’ fatty acid bonds and combines them with molecules in the lye to form a salt. This salt is what we refer to as “soap.” (Yes, some salts are soft.)
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  • Most commercial soaps are not true soap, but are a combination of chemical detergents, artificial lathering agents and toxic chemicals.
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  • After a perfectly balanced saponification process finishes, the soap no longer contains lye or fat. Both are “consumed” during the saponification process.
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  • The best soapmakers add extra oils to their recipes. Doing so means some of the oils do not saponify and remain in the soap. This is called “superfatting” and creates a very moisturizing, nourishing bar of soap.
    Natural Handmade Soap.
  • Glycerin, a natural moisturizer, is a natural product created during the soapmaking process. Commercial soap manufacturers remove the glycerin, replacing it with artificial detergents and other chemicals. This creates a soap that is very drying to the skin. Real, homemade soap retains the glycerin.
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  • A single bar of commercial bar soap may contain over 20 toxic ingredients, many of which have been connected to cancer, endocrine issues, skin problems and more.
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  • The lather, hardness and moisturizing qualities of a soap are dependent on the various oils used in the recipe.
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  • A simple, moisturizing soap can be made using nothing more than olive oil, lard and lye. This soap can be made using common kitchen equipment. Nothing special is needed!

 

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One thought on “All about Soap

  1. I would be interested in-Bubble Bath Fizz-Shower Gel-Scented soap or Body Wash[[I rlaley like fruit scented]]-Maybe some home spa treatmentssuch as things to fix your nails,face masks,etc, Yeahh!And also cheap make up with good qualityI like the things you listed too.:>

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