Soap

The history of soap

What is soap?

How is soap made?

How does soap work?

Characteristics and uses of soap

Resources

Soap is a cleansing agent created by the chemical reaction of a fatty acid with an alkali metal hydroxide. Chemically speaking, it is a salt composed of an alka-limetal, such as sodium or potassium, and a mixture of “fatty” carboxylic acids. The cleansing action of soap comes from its unique ability to surround oil particles, causing them to be dispersed in water and easily rinsed away. Soap has been used for centuries and continues to be widely used as a cleansing agent, mild antiseptic and ingestible antidote to some forms of poisoning.

The history of soap

It is unknown exactly when soap was discovered. Ancient writings suggest it was known to the Phoenicians as early as around 600 BC, and was used to some extent by the ancient Romans. During this time, soap was made by boiling tallow (animal fat) or vegetable oils with alkali containing wood ashes. This costly method of production coupled with negative social attitudes toward cleanliness made soap a luxury item affordable only to the rich until the late eighteenth century.

Methods of soapmaking improved when two scientific discoveries were made in the late eighteenth and early nineteenth centuries. In 1790, the French chemist Nicholas Leblanc (1742-1806) invented a process for creating caustic soda (sodium hydroxide) from common table salt (sodium chloride). His invention made inexpensive soap manufacture possible by enabling chemists to develop a procedure whereby natural fats and oils can react with caustic soda. The method was further refined when another French chemist, Michel Eugene Chevreul (1786-1889), discovered the nature of fats and oils in 1823. As soap production became less expensive and attitudes toward cleanliness changed, soapmaking became an important industry.

What is soap?

Soap is a salt of an alkali metal, such as sodium or potassium, with a mixture of “fatty” carboxylic acids. It is the result of a chemical reaction, called saponification, between triglycerides and a base such as sodium hydroxide. During this reaction, the triglycerides are broken down into their component fatty acids, and neutralized into salts by the base. In addition to soap, this chemical reaction produces glycerin.

Soap has the general chemical formula RCOOX. The X represents an alkali metal, an element in the first column on the periodic table of elements. The R represents a hydrocarbon chain composed of a line of anywhere from 8 to 22 carbon atoms bonded together and surrounded by hydrogen atoms. An example of a soap molecule is sodium palmitate (C16).

How is soap made?

Before the end of World War II, soap was manufactured by a “full-boiled” process. This process required mixing fats and oils in large, open kettles, with caustic soda (NaOH) in the presence of steam. With the addition of tons of salt, the soap was made to precipitate out and float to the top. Here, it was skimmed off and made into flakes or bars. This process required large amounts of energy and over six days to complete one batch.

After World War II, a continuous process of soap manufacture became popular. In the continuous process of soap manufacture, fats and oils react directly with caustic soda. The saponification reaction is accelerated by being run at high temperatures (248°F; 120°C) and pressures (2 atm). Glycerin is washed out of the system and soap is obtained after centrifugation and neutralization. This process has several advantages over the “full-boiled” process. It is more energy efficient, time efficient, allows greater control of soap composition and concentration, and the important by-product, glycerin, is readily recovered.

Both manufacturing methods yield pure soap. Certain chemicals can be added to this pure soap to improve its physical characteristics. The foam in soap is enhanced by additives such as fatty acids. Glycerin is added to reduce the harshness of soap on the skin. Other additives include fragrances and dyes.

How does soap work?

Because soap is a salt, it partially separates into its component ions in water. The active ion of the soap molecule is the RCOO^-. The two ends of this ion behave in different fashions. The carboxylate end (-COO^-) is hydrophilic (water-loving), and is said to be the “head” of the ion. The hydrocarbon portion is lipophilic (oil-loving) and is called the “tail” of the molecule. This unusual molecular structure is responsible for the unique surface and solubility characteristics of soaps and other surfactants (agents affecting the surface of a material).

In a mixture of soap and water, soap molecules are uniformly dispersed. This system is not a true solution, however, because the hydrocarbon portions of the soap’s ions are attracted to each other and form spherical aggregates known as micelles. The molecules tails that are incompatible with water are in the interior of these micelles, while the hydrophilic heads remain on the outside to interact with water. When oil is added to this system, it is taken into these micelles as tiny particles. Then it can be rinsed away.

Characteristics and uses of soap

Soaps are excellent cleansing agents and have good biodegradability. A serious drawback which reduces their general use, is the tendency for the carboxylate ion to react with Ca+ and Mg+ ions in hard water. The result is a water insoluble salt which can be deposited on clothes and other surfaces. These hard water plaques whiten fabric colors and also create rings found in sinks and bath tubs. Another problem with using soaps is their ineffectiveness under acidic conditions. In these cases, soap salts do not dissociate into their component ions, and this renders them ineffective as cleansing agents.

Although primarily used for their cleansing ability, soaps are also effective as mild antiseptics and ingestible antidotes for mineral acid or heavy metal poisoning. Special metallic soaps, made from soap and heavier metals, are used as additives in polishes, inks, paints, and lubricating oils.

See also Emulsion.

KEY TERMS

Carboxylic acid —A compound containing a carbon atom chemically bonded to two oxygen atoms.

Continuous process —A method of manufacturing soap which involves removing glycerin during the reaction between fats and oils and caustic soda.

Emulsifier —Chemical which has both water soluble and oil soluble portions and is capable of forming nearly homogenous mixtures of typically incompatible materials such as oil and water.

Fatty acid —A carboxylic acid which is attached to a chain of at least eight carbon atoms.

Full-boiled process —A method of manufacturing soap which involves boiling fats and oils with caustic soda.

Micelle —Particle formed when the molecules of an emulsifier surround oil droplets allowing them to be dispersed in water.

Saponification —A chemical reaction involving the breakdown of triglycerides to component fatty acids, and the conversion of these acids to soap.

Triglycerides —A molecule containing three fatty acids chemically bonded to a glycol molecule.

Resources

BOOKS

Boys, C.V. Soap Bubbles: Their Colors and Forces Which Mold Them. New York: Dover: 1959.

Fishbein, Morris, ed. Medical Uses of Soap. Philadelphia: J.B. Lippincott, 1945.

Garrett, H.E. Surface Active Chemicals. New York: Pergamon Press, 1972.

Levitt, Benjamin. Oil, Fat and Soap. New York: Chemical Publishing Co., 1951.

Perry Romanowski

Randy Schueller

Soap

Background

Soap is a combination of animal fat or plant oil and caustic soda. When dissolved in water, it breaks dirt away from surfaces. Through the ages soap has been used to cleanse, to cure skin sores, to dye hair, and as a salve or skin ointment. But today we generally use soap as a cleanser or perfume.

The exact origins of soap are unknown, though Roman sources claim it dates back to at least 600 b.c., when Phoenicians prepared it from goat's tallow and wood ash. Soap was also made by the Celts, ancient inhabitants of Britain. Soap was used widely throughout the Roman empire, primarily as a medicine. Mention of soap as a cleanser does not appear until the second century a.d. By the eighth century, soap was common in France, Italy, and Spain, but it was rarely used in the rest of Europe until as late as the 17th century.

Manufacture of soap began in England around the end of the 12th century. Soap-makers had to pay a heavy tax on all the soap they produced. The tax collector locked the lids on soap boiling pans every night to prevent illegal soap manufacture after hours. Because of the high tax, soap was a luxury item, and it did not come into common use in England until after the tax was repealed in 1853. In the 19th century, soap was affordable and popular throughout Europe.

Early soap manufacturers simply boiled a solution of wood ash and animal fat. A foam substance formed at the top of the pot. When cooled, it hardened into soap. Around 1790, French soapmaker Nicolas Leblanc developed a method of extracting caustic soda (sodium hydroxide) from common table salt (sodium chloride), replacing the wood ash element of soap. The French chemist Eugene-Michel Chevreul put the soap-forming process (called in English saponification) into concrete chemical terms in 1823. In saponification, the animal fat, which is chemically neutral, splits into fatty acids, which react with alkali carbonates to form soap, leaving glycerin as a byproduct. Soap was made with industrial processes by the end of the 19th century, though people in rural areas, such as the pioneers in the western United States, continued to make soap at home.

Raw Materials

Soap requires two major raw materials: fat and alkali. The alkali most commonly used today is sodium hydroxide. Potassium hydroxide can also be used. Potassium-based soap creates a more water-soluble product than sodium-based soap, and so it is called "soft soap." Soft soap, alone or in combination with sodium-based soap, is commonly used in shaving products.

Animal fat in the past was obtained directly from a slaughterhouse. Modern soapmakers use fat that has been processed into fatty acids. This eliminates many impurities, and it produces as a byproduct water instead of glycerin. Many vegetable fats, including olive oil, palm kernel oil, and coconut oil, are also used in soap making.

Additives are used to enhance the color, texture, and scent of soap. Fragrances and perfumes are added to the soap mixture to cover the odor of dirt and to leave behind a fresh-smelling scent. Abrasives to enhance the texture of soap include talc, silica, and marble pumice (volcanic ash). Soap made without dye is a dull grey or brown color, but modern manufacturers color soap to make it more enticing to the consumer.

The Manufacturing
Process

The kettle method of making soap is still used today by small soap manufacturing companies. This process takes from four to eleven days to complete, and the quality of each batch is inconsistent due to the variety of oils used. Around 1940, engineers and scientists developed a more efficient manufacturing process, called the continuous process. This procedure is employed by large soap manufacturing companies all around the world today. Exactly as the name states, in the continuous process soap is produced continuously, rather than one batch at a time. Technicians have more control of the production in the continuous process, and the steps are much quicker than in the kettle method—it takes only about six hours to complete a batch of soap.

The Kettle Process

Boiling

• 1 Fats and alkali are melted in a kettle, which is a steel tank that can stand three stories high and hold several thousand pounds of material. Steam coils within the kettle heat the batch and bring it to a boil. After boiling, the mass thickens as the fat reacts with the alkali, producing soap and glycerin.

Salting

• 2 The soap and glycerin must now be separated. The mixture is treated with salt, causing the soap to rise to the top and the glycerin to settle to the bottom. The glycerin is extracted from the bottom of the kettle.

Strong change

• 3 To remove the small amounts of fat that have not saponified, a strong caustic solution is added to the kettle. This step in the process is called "strong change." The mass is brought to a boil again, and the last of the fat turns to soap. The batch may be given another salt treatment at this time, or the manufacturer may proceed to the next step.

Pitching

• 4 The next step is called "pitching." The soap in the kettle is boiled again with added water. The mass eventually separates into two layers. The top layer is called "neat soap," which is about 70% soap and 30% water. The lower layer, called "nigre," contains most of the impurities in the soap such as dirt and salt, as well as most of the water. The neat soap is taken off the top. The soap is then cooled. The finishing process is the same as for soap made by the continuous process.

The Continuous Process

Splitting

• 1 The first step of the continuous process splits natural fat into fatty acids and glycerin. The equipment used is a vertical stainless steel column with the diameter of a barrel called a hydrolizer. It may be as tall as 80 feet (24 m). Pumps and meters attached to the column allow precise measurements and control of the process. Molten fat is pumped into one end of the column, while at the other end water at high temperature (266°F [130°C]) and pressure is introduced. This splits the fat into its two components. The fatty acid and glycerin are pumped out continuously as more fat and water enter. The fatty acids are then distilled for purification.

Mixing

• 2 The purified fatty acids are next mixed with a precise amount of alkali to form soap. Other ingredients such as abrasives and fragrance are also mixed in. The hot liquid soap may be then whipped to incorporate air.

Cooling and finishing

• 3 The soap may be poured into molds and allowed to harden into a large slab. It may also be cooled in a special freezer. The slab is cut into smaller pieces of bar size, which are then stamped and wrapped. The entire continuous process, from splitting to finishing, can be accomplished in several hours.

Milling

• 4 Most toiletry soap undergoes additional processing called milling. The milled bar lathers up better and has a finer consistency than non-milled soap. The cooled soap is fed through several sets of heavy rollers (mills), which crush and knead it. Perfumes can best be incorporated at this time because their volatile oils do not evaporate in the cold mixture. After the soap emerges from the mills, it is pressed into a smooth cylinder and extruded. The extruded soap is cut into bar size, stamped and wrapped.

Byproducts

Glycerin is a very useful byproduct of soap manufacture. It is used to make hand lotion, drugs, and nitroglycerin, the main component of explosives such as dynamite.

Where To Learn More

Books

Cavitch, Susan M. The Natural Soap Book: Making Herbal and Vegetable-Based Soaps. Storey Communications, 1995.

Maine, Sandy. The Soap Book: Simple Herbal Recipes. Interweave Press, 1995.

Spitz, Luis, ed. Soap Technologies in the 1990s. American Oil Chemists Society, 1990.

Other

About Soap. Procter & Gamble, 1990. (513) 983-1100.

—Sheila Dow

Soap

Soap is a cleansing agent created by the chemical reaction of a fatty acid with an alkali metal hydroxide. Chemically speaking, it is a salt composed of an alkalimetal, such as sodium or potassium, and a mixture of "fatty" carboxylic acids . The cleansing action of soap comes from its unique ability to surround oil particles, causing them to be dispersed in water and easily rinsed away. Soap has been used for centuries and continues to be widely used as a cleansing agent, mild antiseptic and ingestible antidote to some forms of poisoning.

The history of soap

It is unknown exactly when soap was discovered. Ancient writings suggest it was known to the Phoenicians as early as around 600 b.c., and was used to some extent by the ancient Romans. During these times, soap was made by boiling tallow (animal fat ) or vegetable oils with alkali containing wood ashes. This costly method of production coupled with negative social attitudes toward cleanliness made soap a luxury item affordable only to the rich until the late eighteenth century.

Methods of soapmaking improved when two scientific discoveries were made in the late eighteenth and early nineteenth centuries. In 1790, the French chemist Nicholas Leblanc (1742-1806) invented a process for creating caustic soda (sodium hydroxide ) from common table salt (sodium chloride ). His invention made inexpensive soap manufacture possible by enabling chemists to develop a procedure whereby natural fats and oils can react with caustic soda . The method was further refined when another French chemist, Michel Eugène Chevreul (1786-1889), discovered the nature of fats and oils in 1823. As soap production became less expensive and attitudes toward cleanliness changed, soapmaking became an important industry.

What is soap?

Soap is a salt of an alkali metal, such as sodium or potassium, with a mixture of "fatty" carboxylic acids. It is the result of a chemical reaction, called saponification, between triglycerides and a base such as sodium hydroxide. During this reaction, the triglycerides are broken down into their component fatty acids , and neutralized into salts by the base. In addition to soap, this chemical reaction produces glycerin.

Soap has the general chemical formula RCOOX. The X represents an alkali metal, an element in the first column on the periodic table of elements. The R represents a hydrocarbon chain composed of a line of anywhere from 8-22 carbon atoms bonded together and surrounded by hydrogen atoms. An example of a soap molecule is sodium palmitate (C16).

How is soap made?

Before the end of World War II, soap was manufactured by a "full-boiled" process. This process required mixing fats and oils in large, open kettles, with caustic soda (NaOH) in the presence of steam. With the addition of tons of salt, the soap was made to precipitate out and float to the top. Here, it was skimmed off and made into flakes or bars. This process required large amounts of energy and over six days to complete one batch.

After World War II, a continuous process of soap manufacture became popular. In the continuous process of soap manufacture, fats and oils react directly with caustic soda. The saponification reaction is accelerated by being run at high temperatures (248°F; 120°C) and pressures (2 atm). Glycerin is washed out of the system and soap is obtained after centrifugation and neutralization . This process has several advantages over the "full-boiled" process. It is more energy efficient, time efficient, allows greater control of soap composition and concentration , and the important by-product, glycerin, is readily recovered.

Both manufacturing methods yield pure soap. Certain chemicals can be added to this pure soap to improve its physical characteristics. The foam in soap is enhanced by additives such as fatty acids. Glycerin is added to reduce the harshness of soap on the skin. Other additives include fragrances and dyes.

How does soap work?

Because soap is a salt, it partially separates into its component ions in water. The active ion of the soap molecule is the RCOO-. The two ends of this ion behave in different fashions. The carboxylate end (-COO-) is hydrophilic (water-loving), and is said to be the "head" of the ion. The hydrocarbon portion is lipophilic (oil-loving) and is called the "tail" of the molecule. This unusual molecular structure is responsible for the unique surface and solubility characteristics of soaps and other surfactants (agents affecting the surface of a material).

In a mixture of soap and water, soap molecules are uniformly dispersed. This system is not a true solution , however, because the hydrocarbon portions of the soap's ions are attracted to each other and form spherical aggregates known as micelles. The molecules tails that are incompatible with water are in the interior of these micelles, while the hydrophilic heads remain on the outside to interact with water. When oil is added to this system, it is taken into these micelles as tiny particles. Then it can be rinsed away.

Characteristics and uses of soap

Soaps are excellent cleansing agents and have good biodegradability. A serious drawback which reduces their general use, is the tendency for the carboxylate ion to react with Ca+ and Mg+ ions in hard water . The result is a water insoluble salt which can be deposited on clothes and other surfaces. These hard water plaques whiten fabric colors and also create rings found in sinks and bath tubs. Another problem with using soaps is their ineffectiveness under acidic conditions. In these cases, soap salts do not dissociate into their component ions, and this renders them ineffective as cleansing agents.

Although primarily used for their cleansing ability, soaps are also effective as mild antiseptics and ingestible antidotes for mineral acid or heavy metal poisoning. Special metallic soaps, made from soap and heavier metals, are used as additives in polishes, inks, paints, and lubricating oils.

See also Emulsion.

Resources

books

Boys, C.V. Soap Bubbles: Their Colors and Forces Which Mold Them. New York: Dover: 1959.

Fishbein, Morris, ed. Medical Uses of Soap. Philadelphia: J.B. Lippincott, 1945.

Garrett, H.E. Surface Active Chemicals. New York: Pergamon Press, 1972.

Levitt, Benjamin. Oil, Fat and Soap. New York: Chemical Publishing Co., 1951.

Perry Romanowski
Randy Schueller

KEY TERMS

Carboxylic acid

—A compound containing a carbon atom chemically bonded to two oxygen atoms.

Continuous process

—A method of manufacturing soap which involves removing glycerin during the reaction between fats and oils and caustic soda.

Emulsifier

—Chemical which has both water soluble and oil soluble portions and is capable of forming nearly homogenous mixtures of typically incompatible materials such as oil and water.

Fatty acid

—A carboxylic acid which is attached to a chain of at least eight carbon atoms.

Full-boiled process

—A method of manufacturing soap which involves boiling fats and oils with caustic soda.

Micelle

—Particle formed when the molecules of an emulsifier surround oil droplets allowing them to be dispersed in water.

Saponification

—A chemical reaction involving the breakdown of triglycerides to component fatty acids, and the conversion of these acids to soap.

Triglycerides

—A molecule containing three fatty acids chemically bonded to a glycol molecule.

Soap

Soaps 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":

CH₃CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂CH₂COO⁻ or CH₃(CH₂)_nCOO⁻

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.

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-SO₃⁻) 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

Bibliography

Brady, James E.; Russell, Joel W.; and Holum, John R. (2000). Chemistry: Matter and Its Changes, 3rd edition. New York: Wiley.

Internet Resources

"The History and Chemistry of Soaps and Detergents." The Soap and Detergent Association. Available from the SDA Kids Corner at <http://www.sdahq.org/>.

SOAP

It would appear that in the biblical period soap was derived almost exclusively from plants. Many such plants grow in Israel. They contain chiefly potash and soda, and their ash, dissolved in oil, was used until as late as a generation ago for making a liquid soap. Most of these plants grow in the salty regions of the Arabah, in the Negev, and on the seashore. These belong to the botanical genera Salicornia, Salsola, Mesembryanthemum, Saponaria. Statice, and Atriplex. In the Bible these washing materials are referred to as bor, borit, and sheleg. Borit is mentioned in apposition to neter ("soda") in the Bible as a material for cleansing stains (Jer. 2:22). The messenger of the covenant will purify the people on the day of the Lord as "with fuller's soap" (borit, Mal. 3:2). In other places in the Bible the term bor is used for material for the cleansing of hands and clothes (Job. 9:30), and metaphorically for cleanness of hands (Job. 22:30; ii Sam. 22:21). Bor and borit are connected with the word baroh ("clean"). According to the Tosefta, borit and ahal are perennial plants that disappear from the field at the end of the season (Shev. 5:6) and the Jerusalem Talmud (Shev. 7:2, 37b) characterizes them as "species of laundering plants." According to the Babylonian Talmud (Nid. 62a), "borit is identical with ahal," i.e., both are species of aloe. Ahal, in Akkadian uhulu, Syrian ahala, and Arabic gasul, are soap-producing plants containing soaping matter such as Salicornia, and in particular the genus Mesembryanthemum, called in modern Hebrew ahal. One species, M. crystalinum, grows on walls and rocks facing the Mediterranean Sea, and it is grown in some countries in order to extract the soda it contains. In the Arabah other species of Mesembryanthemum are widespread. These can be recognized by their finger-like thick leaves. After the rains they spread widely.

In rabbinical literature ashlag is mentioned together with washing materials (Shab. 9:5; Nid. 9:6). According to the Jerusalem Talmud (Shab. 9:5, 12b), a plant called oẓerot ru'aḥ ("wind collector") is meant. It seems that the reference is to the plant Vaccaria (Saponaria) segetalis which contains saponin. In fields of cereal it grows as a weed whose calyx expands when the fruit ripens as if it is "collecting wind." It is called ashlag also in Arabic. Perhaps the shaleg ("snow water") of Job 9:30 is actually ashlag, as suggested by the parallel with bor ("soap").

bibliography:

Loew, Flora, 1 (1926), 637–50; G. Dalman, Arbeit und Sitte in Palaestina, 2 (1932), 263; 5 (1937), 155; J. Feliks, Olam ha-Ẓome'aḥ ha-Mikra'i (1968²), 298–300. add. bibliography: Feliks, Ha-Tzome'aḥ, 35.

[Jehuda Feliks]