Soap: History and Production Processes
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Published: Wed, 23 May 2018
Soap is integral to our society today, and we find it hard to imagine a time when people were kept sweet-smelling by the action of perfume rather than soap. However, the current widespread use of soap is only a very recent occurrence, despite the fact that it has been made for more than 2500 years. The first recorded manufacture of soap was in 600BC, when Pliny the Elder described its manufacture by the Phonecians from goats tallow and ash, and it was known among the British Celts and throughout the Roman Empire. However, these people used their soap medicinally, and it was not until the second century AD that it was used for cleaning, and not until the nineteenth century that it began to be commonly used in the Western world.
Early this century the first synthetic detergents were manufactured, and these have now taken the place of soap for many applications. Their manufacture is covered briefly in the second
A collection of decorative soaps used for human hygiene purposes. This type of soap is typically found inside hotels.
Soap is an anionic surfactant used in conjunction with water for washing and cleaning that historically comes in solid bars but also in the form of a thick liquid.
Soap, consisting of sodium (soda ash) or potassium (potash) salts of fatty acids is obtained by reacting fat with lye in a process known as saponification. The fats are hydrolyzed by the base, yielding alkali salts of fatty acids (crude soap) and glycerol.
Many cleaning agents today are technically not soaps, but detergents, which are less expensive and easier to manufacture.
The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in Ancient Babylon. A formula for soap consisting of water, alkali and cassia oil was written on a Babylonian clay tablet around 2200 BC. The Ebers papyrus (Egypt, 1550 BC) indicates that ancient Egyptians bathed regularly and combined animal and vegetable oils with alkaline salts to create a soap-like substance. Egyptian documents mention that a soap-like substance was used in the preparation of wool for weaving.
It had been reported that a factory producing soap-like substances was found in the ruins of Pompeii (AD 79). However, this has proven to be a misinterpretation of the survival of some soapy mineral substance, probably soapstone at the Fullonica where it was used for dressing recently cleansed textiles. Unfortunately this error has been repeated widely and can be found in otherwise reputable texts on soap history. The ancient Romans were generally ignorant of soap’s detergent properties, and made use of the strigil to scrape dirt and sweat from the body. The word “soap” (Latin sapo) appears first in a European language in Pliny the Elder’s Historia Naturalis, which discusses the manufacture of soap from tallow and ashes, but the only use he mentions for it is as a pomade for hair; he mentions rather disapprovingly that among the Gauls and Germans men are likelier to use it than women.
A story encountered in some places claims that soap takes its name from a supposed “Mount Sapo” where ancient Romans sacrificed animals. Rain would send a mix of animal tallow and wood ash down the mountain and into the clay soil on the banks of the Tiber. Eventually, women noticed that it was easier to clean clothes with this “soap”. The location of Mount Sapo is unknown, as is the source of the “ancient Roman legend” to which this tale is typically credited. In fact, the Latin word sapo simply means “soap”; it was borrowed from a Celtic or Germanic language, and is cognate with Latin sebum, “tallow”, which appears in Pliny the Elder’s account. Roman animal sacrifices usually burned only the bones and inedible entrails of the sacrificed animals; edible meat and fat from the sacrifices were taken by the humans rather than the gods. Animal sacrifices in the ancient world would not have included enough fat to make much soap. The legend about Mount Sapo is probably apocryphal.
Galen describes soap making using causticised lye and prescribes washing to carry away impurities from the body and clothes. The best soap was German according to Galen; soap from Gaul was second best. This is the first record of true soap as a detergent.
Zosimos of Panopolis c. 300AD describes both soap and soap making.
True soaps made from vegetable oils (such as olive oil), aromatic oils (such as thyme oil) and lye (al-Soda al-Kawia) were first produced by Muslim chemists in the medieval Islamic world. The formula for soap used since then hasn’t changed. From the beginning of the 7th century, soap was produced in Nablus (West Bank, Palestine), Kufa (Iraq) and Basra (Iraq). Soaps, as we know them today, are descendants of historical Arabian Soaps. Arabian Soap was perfumed and colored, some of the soaps were liquid and others were solid. They also had special soap for shaving. It was sold for 3 Dirhams (0.3 Dinars) a piece in 981 AD. The Persian chemist Al-Razi wrote a manuscript on recipes for true soap. A recently discovered manuscript from the 13th century details more recipes for soap making; e.g. take some sesame oil, a sprinkle of potash, alkali and some lime, mix them all together and boil. When cooked, they are poured into molds and left to set, leaving hard soap.
In semi-modern times soap was made 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 (sodium hydroxide) was commonplace, potash, potassium hydroxide, was produced at home from the ashes of a hardwood fire.
Castile soap was later produced in Europe from the 16th century. Modern castile soap is still popular, being made exclusively from vegetable oil (as opposed to animal fat). Soap, for example, is based on hemp oil in addition to jojoba oil.
In modern times, the use of soap has become universal in industrialized nations due to a better understanding of the role of hygiene in reducing the population size of pathogenic microorganisms. 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.
Sometimes the absence of oxygen in cold and humid environment allows for corpses to naturally accumulate a soap-like coating, adipocere, as covering the Soap Lady on exhibit in the Mutter Museum.
How soap works
Soaps are useful for cleaning 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. Applied to a soiled surface, soapy water effectively holds particles in suspension so the whole of it can be rinsed off with clean water.
(fatty end) Â :CH3-(CH2)n – COONa: (water soluble end)
The hydrocarbon (“fatty”) portion dissolves dirt and oils, while the ionic end makes it soluble in water. Therefore, it allows water to remove normally-insoluble matter by emulsification.
The most popular soapmaking process today is the cold process method, where fats such as olive oil react with lye. Soapmakers sometimes use the melt and pour process, where a premade soap base is melted and poured in individual molds. While some people think that this is not really soap-making, the Hand Crafted Soap Makers Guild considers it a form of soap making or soap crafting. Some soapers also practice other processes, such as the historical hot process, and make special soaps such as clear soap (glycerin soap), which must be made through the melt-and-pour process.
Handmade soap differs from industrial soap in that, usually, an excess of fat is sometimes used to consume the alkali (superfatting), and in that the glycerin is not removed leaving a naturally moisturising soap and not pure detergent. Superfatted soap, soap which contains excess fat, is more skin-friendly than industrial soap; though, if not properly formulated, it can leave users with a “greasy” feel to their skin. Often, emollients such as jojoba oil or shea butter are added ‘at trace’ (the point at which the saponification process is sufficiently advanced that the soap has begun to thicken), after most of the oils have saponified, so that they remain unreacted in the finished soap. Superfatting can also be accomplished through a process called superfat discount, where, instead of putting in extra fats, the soap maker puts in less lye.
Reacting fat with sodium hydroxide will produce a hard soap.
Reacting fat with potassium hydroxide will produce a soap that is either soft or liquid. Historically, the alkali used was potassium hydroxide made from the deliberate burning of vegetation such as bracken, or from wood ashes.
Soap is derived from either vegetable or animal fats. Sodium tallowate, a common ingredient in many soaps, is derived from rendered beef fat. Soap can also be made of vegetable oils, such as palm oil, and the product is typically softer. If soap is made from pure olive oil it may be called Castile soap or Marseille soap. Castile is also sometimes applied to soaps with a mix of oils, but a high percentage of olive oil.
An array of oils and butters are used in the process such as olive, coconut, palm, cocoa butter, hemp oil and shea butter to provide different qualities. For example, olive oil provides mildness in soap; coconut oil provides lots of lather; while coconut and palm oils provide hardness. Sometimes castor oil can also be used as an ebullient. Most common, though, is a combination of coconut, palm, and olive oils.
In both cold-process and hot-process soapmaking, heat may be required for saponification.
Cold-process soapmaking takes place at a temperature sufficiently above room temperature to ensure the liquification of the fat being used, and requires that the lye and fat be kept warm after mixing to ensure that the soap is completely saponified.
Unlike cold-processed soap, hot-processed soap can be used right away because lye and fat saponify more quickly at the higher temperatures used in hot-process soapmaking.
Hot-process was used when the purity of lye was unreliable, and can use natural lye solutions such as potash. The main benefit of hot processing is that the exact concentration of the lye solution does not need to be known to perform the process with adequate success.
Cold-process requires exact measurement of lye to fat using saponification charts to ensure that the finished product is mild and skin-friendly. Saponification charts can also be used in hot-process soapmaking, but are not as necessary as in cold-process.
In the hot-process method, lye and fat are boiled together at 80-100 Â°C until saponification occurs, which the soapmaker can determine by taste (the bright, distinctive taste of lye disappears once all the lye is saponified) or by eye (the experienced eye can tell when gel stage and full saponification have occurred). After saponification has occurred, the soap is sometimes precipitated from the solution by adding salt, and the excess liquid drained off. The hot, soft soap is then spooned into a mold.
A cold-process soapmaker first looks up the saponification value of the fats being used on a saponification chart, which is then used to calculate the appropriate amount of lye. Excess unreacted lye in the soap will result in a very high pH and can burn or irritate skin. Not enough lye, and the soap is greasy. Most soap makers formulate their recipes with a 4-10% discount of lye so that all of the lye is reacted and that excess fat is left for skin conditioning benefits.
The lye is dissolved in water. Then oils are heated, or melted if they are solid at room temperature. Once both substances have cooled to approximately 100-110Â°F (37-43Â°C), and are no more than 10Â°F (~5.5Â°C) apart, they may be combined. This lye-fat mixture is stirred until “trace” (modern-day amateur soapmakers often use a stick blender to speed this process). There are varying levels of trace. Depending on how your additives will affect trace, they may be added at light trace, medium trace or heavy trace. After much stirring, the mixture turns to the consistency of a thin pudding.
Essential oils, fragrance oils, botanicals, herbs, oatmeal or other additives are added at light trace, just as the mixture starts to thicken.
The batch is then poured into molds, kept warm with towels or blankets, and left to continue saponification for 18 to 48 hours. Milk soaps are the exception. They do not require insulation. Insulation may cause the milk to burn. During this time, it is normal for the soap to go through a “gel phase” where the opaque soap will turn somewhat transparent for several hours before turning opaque again. The soap will continue to give off heat for many hours after trace.
After the insulation period the soap is firm enough to be removed from the mold and cut into bars. At this time, it is safe to use the soap since saponification is complete. However, cold-process soaps are typically cured and hardened on a drying rack for 2-6 weeks (depending on initial water content) before use. If using caustic soda it is recommended that the soap is left to cure for at least 4 weeks.
Purification and finishing
The common process of purifying soap involves removal of sodium chloride, sodium hydroxide, and glycerol. These components are removed by boiling the crude soap curds in water and re-precipitating the soap with salt.
Most of the water is then removed from the soap. This was traditionally done on a chill roll which produced the soap flakes commonly used in the 1940s and 1950s. This process was superseded by spray dryers and then by vacuum dryers.
The dry soap (approximately 6-12% moisture) is then compacted into small pellets. These pellets are now ready for soap finishing, the process of converting raw soap pellets into a salable product, usually bars.
Soap pellets are combined with fragrances and other materials and blended to homogeneity in an amalgamator (mixer). The mass is then discharged from the mixer into a refiner which, by means of an auger, forces the soap through a fine wire screen. From the refiner the soap passes over a roller mill (French milling or hard milling) in a manner similar to calendering paper or plastic or to making chocolate liquor. The soap is then passed through one or more additional refiners to further plasticize the soap mass. Immediately before extrusion it passes through a vacuum chamber to remove any entrapped air. It is then extruded into a long log or blank, cut to convenient lengths, passed through a metal detector and then stamped into shape in refrigerated tools. The pressed bars are packaged in many ways.
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. This process is called exfoliation. Many newer materials are used for exfoliating soaps which are effective but do not have the sharp edges and poor size distribution of pumice.
Commercial soap production
Until the Industrial Revolution, soap-making was done on a small scale and the product was rough. Andrew Pears started making a high-quality, transparent soap in 1789 in London. With his grandson, Francis Pears, they opened a factory in Isleworth in 1862. William Gossage produced low-price good quality soap from the 1850s. Robert Spear Hudson began manufacturing a soap powder in 1837, initially by grinding the soap with a mortar and pestle. William Hesketh Lever and his brother, James, bought a small soap works in Warrington in 1885 and founded what is still one of the largest soap businesses, now called Unilever. These soap businesses were among the first to employ large scale advertising campaigns.
Our modern technological solution (since the 1940s) to the soap scum problem is to use SYNTHETIC DETERGENTS which don’t precipitate the mineral salts found in hard water. Some of these synthetic detergents are chemically related to soaps, as they are derived from the same fatty acids used to make soaps. SODIUM LAURYL SULFATE (derived from the fatty acid lauric acid by a series of chemical reactions) is such a detergent. It can be found in _many_ common household products. Sodium lauryl sulfate belongs to a class of detergents referred to as “anionic.” These compounds are especially effective at cleaning fabrics that absorb water readily, such as those made of NATURAL FIBERS, such as COTTON, WOOL AND SILK.
“ORVUS” is a commercial name for sodium lauryl sulfate. It is available at feed stores, which sell it as a shampoo for the manes and tails of show animals. Sodium lauryl sulfate is also packaged as a quilt soap and can be found at suppliers of quilting products.
Sodium lauryl sulfate is a common ingredient of SHAMPOOS, and some persons like to use shampoo for handwashing natural fibers. However, you should be aware that shampoos may contain additional compounds which could cause undesirable results if used for laundering fabric.
Read product labels! In the USA, ingredients are listed on labels in order of decreasing quantities. If you use a shampoo for washing natural fibers, you want to find ingredients that contain the chemical prefix “laur” (from lauric acid). Myristic acid, palmitic acid, and stearic acid are also produced from fats by the action of lye, and are considered excellent soaps. Like lauric acid, they are converted into anionic detergents; therefore, you might also find the forms “myris,” “palm,” and “stear” among the ingredients.
The usual granular laundry detergents are sodium salts of fatty derivatives of aromatic sulfonic acids. They are of the anionic class, with similar cleaning properties to those of sodium lauryl sulfate. Manufacturers have now solved the problems with biodegradability which originally plagued these types of synthetic detergents.
Another class of detergents is referred to as “nonanionic.” These are especially good for cleaning synthetic fabrics, such as polyesters. Most are liquids and produce little foam. You’ll find them (along with anionic detergents) in dishwashing liquids and liquid laundry detergents. The “cationic” detergents, as well as being cleaners, also happen to be effective germicides and are used in antiseptic soaps and mouthwashes. They’re also used in fabric softeners because their positive charges (cations) adhere to many fabrics that normally carry negative electrical charges (anions).
In conclusion, it needs to be emphasized that no one cleaning product is best for everything because of the chemical properties of the fabric being cleaned, and the chemical properties of the detergent.
Detergents, especially those made for use with water, often include different components such as:
Surfactants to ‘cut’ (dissolve) grease and to wet surfaces
Abrasive to scour
Substances to modify pH or to affect performance or stability of other ingredients, acids for descaling or caustics to break down organic compounds
Water softeners to counteract the effect of “hardness” ions on other ingredients
oxidants (oxidizers) for bleaching, disinfection, and breaking down organic compounds
Non-surfactant materials that keep dirt in suspension
Enzymes to digest proteins, fats, or carbohydrates in stains or to modify fabric feel
Ingredients that modify the foaming properties of the cleaning surfactants, to either stabilize or counteract foam
Ingredients to increase or decrease the viscosity of the solution, or to keep other ingredients in solution, in a detergent supplied as a water solution or gel
Ingredients that affect aesthetic properties of the item to be cleaned, or of the detergent itself before or during use, such as optical brighteners, fabric softeners, colors, perfumes, etc.
Ingredients such as corrosion inhibitors to counteract damage to equipment with which the detergent is used
Ingredients to reduce harm or produce benefits to skin, when the detergent is used by bare hand on inanimate objects or used to clean skin
Preservatives to prevent spoilage of other ingredients
Sometimes materials more complicated than mere mixtures of compounds are said to be detergent. For instance, certain foods such as celery are said to be detergent or detersive to teeth.
There are several factors that dictate what compositions of detergent should be used, including the material to be cleaned, the apparatus to be used, and tolerance for and type of dirt. For instance, all of the following are used to clean glass. The sheer range of different detergents that can be used demonstrates the importance of context in the selection of an appropriate glass-cleaning agent:
- a chromic acid solution-to get glass very clean for certain precision-demanding purposes such as analytical chemistry
- a high-foaming mixture of surfactants with low skin irritation-for hand-washing of dishware in a sink or dishpan
- any of various non-foaming compositions-for dishware in a dishwashing machine
- other surfactant-based compositions-for washing windows with a squeegee, followed by rinsing
- an ammonia-containing solution-for cleaning windows with no additional dilution and no rinsing
- ethanol or methanol in Windshield washer fluid-used for a vehicle in motion, with no additional dilution
- glass contact lens cleaning solutions, which must clean and disinfect without leaving any eye-harming material that would not be easily rinsed off.
Sometimes the word detergent is used to distinguish a cleaning agent from soap. During the early development of non-soap surfactants as commercial cleaning products, the term syndet, short for synthetic detergent was promoted to indicate the distinction. The term never became popular and is incorrect, because most soap is itself synthesized (from glycerides). The term soapless soap also saw a brief vogue. There is no accurate term for detergents not made of soap other than soapless detergent or non-soap detergent.
Plain water, if used for cleaning, is a detergent. Probably the most widely-used detergents other than water are soaps or mixtures composed chiefly of soaps. However, not all soaps have significant detergency and, although the words “detergent” and “soap” are sometimes used interchangeably, not every detergent is a soap.
The term detergent is sometimes used to refer to any surfactant, even when it is not used for cleaning. This terminology should be avoided as long as the term surfactant itself is available.
The detergent effects of certain synthetic surfactants were noted in 1913 by A. Reychler, a Belgian chemist. The first commercially available detergent taking advantage of those observations was Nekal, sold in Germany in 1917, to alleviate World War I soap shortages. Detergents were mainly used in industry until World War II. By then new developments and the later conversion of USA aviation fuel plants to produce tetrapropylene, used in household detergents, caused a fast growth of household use, in the late 1940s. In the late 1960s biological detergents, containing enzymes, better suited to dissolved protein stains, such as egg stains, were introduced in the USA by Procter HYPERLINK “http://en.wikipedia.org/wiki/Procter_&_Gamble”&HYPERLINK “http://en.wikipedia.org/wiki/Procter_&_Gamble” Gamble.
Personal Cleansing Products include bar soaps, gels, liquid soaps and heavy duty hand cleaners. These products get their cleaning action from soap, other surfactants or a combination of the two. The choice of cleaning agent helps determine the product’s lathering characteristics, feel on the skin and rinsability.
Bar soaps or gels are formulated for cleaning the hands, face and body. Depending on the other ingredients, they may also moisturize the skin and/or kill or inhibit bacteria that can cause odor or disease. Specialty bars include transparent/translucent soaps, luxury soaps and medicated soaps.
Liquid soaps are formulated for cleaning the hands or body, and feature skin conditioners. Some contain antimicrobial agents that kill or inhibit bacteria that can cause odor or disease.
Heavy duty hand cleaners are available as bars, liquids, powders and pastes. Formulated for removing stubborn, greasy dirt, they may include an abrasive.
Laundry Detergents and Laundry Aids are available as liquids, powders, gels, sticks, sprays, pumps, sheets and bars. They are formulated to meet a variety of soil and stain removal, bleaching, fabric softening and conditioning, and disinfectant needs under varying water, temperature and use condiditons.
Laundry detergents are either general purpose or light duty. General purpose detergents are suitable for all washable fabrics. Liquids work best on oily soils and for pretreating soils and stains. Powders are especialy effective in lifting out clay and ground-in dirt. Light duty detergents are used for hand or machine washing lightly soiled items and delicate fabrics.
Laundry aids contribute to the effectiveness of laundry detergents and provide special functions.
Bleaches (chlorine and oxygen) whiten and brighten fabrics and help remove stubborn stains. They convert soils into colorless, soluble particles that can be removed by detergents and carried away in the wash water. Liquid chlorine bleach (usually in a sodium hypochlorite solution) can also disinfect and deodorize fabrics. Oxygen (color-safe) bleach is more gentle and works safely on almost all washable fabrics.
Bluings contain a blue dye or pigment taken up by fabrics in the wash or rinse. Bluing absorbs the yellow part of the light spectrum, counteracting the natural yellowing of many fabrics.
Boosters enhance the soil and stain removal, brightening, buffering and water softening performance of detergents. They are used in the wash in addition to the detergent.
Enzyme presoaks are used for soaking items before washing to remove difficult stains and soils. When added to the wash water, they increase cleaning power.
Fabric softeners, added to the final rinse or dryer, make fabrics softer and fluffier; decrease static cling, wrinkling and drying time; impart a pleasing fragrance and make ironing easier.
Prewash soil and stain removers are used to pretreat heavily soiled and stained garments, especially those made from synthetic fibers.
Starches, fabric finishes and sizings, used in the final rinse or after drying, give body to fabrics, make them more soil-resistant and make ironing easier.
Water softeners, added to the wash or rinse, inactivate hard water minerals. Since detergents are more effective in soft water, these products increase cleaning power.
Dishwashing Products include detergents for hand and machine dishwashing as well as some specialty products. They are available as liquids, gels, powders and solids.
Hand dishwashing detergents remove food soils, hold soil in suspension and provide long-lasting suds that indicate how much cleaning power is left in the wash water.
Automatic dishwasher detergents, in addition to removing food soils and holding them in suspension, tie up hardness minerals, emulsify grease and oil, suppress foam caused by protein soil and help water sheet off dish surfaces. They produce little or no suds that would interfere with the washing action of the machine.
Rinse agents are used in addition to the automatic dishwasher detergent to lower surface tension, thus improving draining of the water from dishes and utensils. Better draining minimizes spotting and filming and enhances drying.
Film removers remove build-up of hard water film and cloudiness from dishes and the interior of the dishwasher. They are used instead of an automatic dishwasher detergent in a separate cycle or together with the detergent.
Lime and rust removers remove deposits of lime and/or rust from the interior of the dishwasher. They are used when no dishes or other dishwasher products are present.
Household Cleaners are available as liquids, gels, powders, solids, sheets and pads for use on painted, plastic, metal, porcelain, glass and other surfaces, and on washable floor coverings. Because no single product can provide optimum performance on all surfaces and soils, a broad range of products has been formulated to clean efficiently and easily. While all-purpose cleaners are intended for more general use, others work best under highly specialized conditions.
All-purpose cleaners penetrate and loosen soil, soften water and prevent soil from redepositing on the cleaned surface. Some also disinfect.
Abrasive cleansers remove heavy accumulations of soil often found in small areas. The abrasive action is provided by small mineral or metal particles, fine steel wool, copper or nylon particles. Some also disinfect.
Specialty cleaners are designed for the soil conditions found on specific surfaces, such as glass, tile, metal, ovens, carpets and upholstery, toilet bowls and in drains.
Glass cleaners loosen and dissolve oily soils found on glass, and dry quickly without streaking.
Glass and multi-surface cleaners remove soils from a variety of smooth surfaces. They shine surfaces without streaking.
Tub, tile and sink cleaners remove normal soils found on bathroom surfaces as well as hard water deposits, soap scum, rust stains, and/or mildew and mold. Some also treat surfaces to retard soiling; some also disinfect.
Metal cleaners remove soils and polish metalware. Tarnish, the oxidation of metal, is the principal soil found on metalware. Some products also protect cleaned metalware against rapid retarnishing.
Oven cleaners remove burned-on grease and other food soils from oven walls. These cleaners are thick so the product will cling to vertical oven surfaces.
Rug shampoos and upholstery cleaners dissolve oily and greasy soils and hold them in suspension for removal. Some also treat surfaces to repel soil.
Toilet bowl cleaners prevent or remove stains caused by hard water and rust deposits, and maintain a clean and pleasant-smelling bowl. Some products also disinfect.
Drain openers unclog kitchen and bathroom drains. They work by producing heat to melt fats, breaking them down into simpler substances that can be rinsed away, or by oxidizing hair and other materials. Some use bacteria to prevent grease build-up which leads to drain clogging.
Both soaps and detergents share a critical chemical property- they are surfactants. In other words they reduce the surface tension of water. There are some differences between them, however. Soaps posses a number of qualities that make them preferable to detergents. First they are natural products and less harmful to the human skin and the environment. Soaps are biodegradable and do not create pollution in our rivers and streams.
On the other hand, soap will combine with the magnesium and calcium ions in hard water to create an insoluble residue that can clog drains and stick to clothing. The hardness of a water sample can be gauged by the amount of calcium carbonate that is present. S
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