What does soapy mean

      Soap are sodium or potassium salts of higher fatty acids, which are mainly used for body cleaning and less for surface cleaning. As a general cleaning agent, especially as a detergent for textiles, soaps have lost their importance because insoluble lime soaps are formed.

History of soap

The first indications of soap production can be found with the Sumerians. They recognized that vegetable ash (al-quali, the origin of the word alkaline) (contains potash) mixed with oils has special properties, and created the basis of a soap recipe. However, they overlooked the cleansing effect of the alkaline mixture and used it as a remedy for injuries. The Egyptian people as well as the Greeks took over the chemical instructions for the production, whereby the cleaning effect of the soap was first established by the Romans. In ancient Rome people originally washed with pumice stone; Even at the turn of the century, the use of soap was decried as emollient.

Arabs then boiled oil and lye together for the first time in the 7th century and thus created the soap in the form we know today. This knowledge quickly spread across Europe. France and Spain later belonged to the centers of soap manufacturing worldwide. Hygiene and personal hygiene were important issues. In the Middle Ages, visiting the bathhouse was very popular and the body cleansing was better than commonly assumed. It was not until the outbreak of plague and cholera that washing with water was stopped. Since the transmission routes were unknown, it was believed that the bath water opened the body to the pathogens. You couldn't tell that it was because of the dirty streets and rivulets in front of the houses and the rats. Dry cleaning was used and aristocratic circles only relied on apparent gloss and a deceptive facade. Instead of soap and water, they used powder and perfume. Pathogenic germs, lice and fleas could spread unhindered. Up until the 17th century, doctors in Europe were of the opinion that water and air were harmful to the body. Clothing served as protection from these harmful elements. The powdering also served the purpose of closing off the body from the outside. Lingerie soaked up body sweat and it was thought that this was how the body was cleaned.

In the 17th century, Louis XIV helped soap to flourish again by bringing the best soap makers to Versailles. It was also he who in 1688 issued the purity law for soap, which is still known today. Accordingly, a soap was considered to be of particularly high quality if it contained at least 72% pure oil. The French Nicolas Leblanc (1742-1806) first succeeded in artificially producing large quantities of soda in 1790. In 1865 Ernest Solvay developed a new process that replaced the Leblanc process. So there was enough soda to make soap and soap became an affordable product. The body could now be washed regularly with soap and freed from unpleasant odors.

The traditional soap production continues to this day in Marseille (Savon de Marseille).

Soap making

Soaps are usually made from vegetable or animal fats. The main raw materials used are coconut fat, olive oil, palm oil and animal fats such as tallow, lard or bone fat, which are produced during animal processing.

Soaps are a product of breaking down these fats. The chemical reaction is called → saponification. To do this, fats are boiled with a lye (such as caustic soda or potassium hydroxide, formerly also potash or soda). One calls this procedure Soapy water. The fats are broken down into glycerine and the salts of the fatty acids (the actual soap). This viscous emulsion will Soap glue called and mixed with table salt. The emulsion separates (salting out) into the floating ones Soap corecontaining mainly the sodium salts of fatty acid and in Lower lyewhich mainly contains excess lye, glycerine and the dissolved table salt. The soap core is separated from the lower lye and boiled with plenty of water and a little lye to remove the remaining impurities. Renewed salting out then leads to the Curd soap. The product is then dried and pressed into the appropriate shape. Soaps also vary by adding essential oils or coloring agents afterwards.

The consistency of a soap product depends on the chain length of the fatty acids released. Long-chain fatty acids such as stearic acid or palmitic acid tend to lead to a firmer consistency. The decisive factor, however, is whether potassium or sodium salts of the fatty acids are formed. If the soap core is obtained from the soap glue by adding sodium chloride, a solid soap tends to be formed, the Curd soap. If, on the other hand, potassium hydroxide solutions and potassium salts are used, potassium salts of the fatty acids are formed, which, in contrast to sodium salts, are soft to greasy and hygroscopic. You get Soft soaps.

Washing effect of the soap

Soaps are a mixture of different, longer-chain alkali salts of fatty acids and count among the surfactants, more precisely among the anionic surfactants. The soap molecules owe their properties to the fact that they consist of a long, water-repellent (hydrophobic) hydrocarbon chain and a water-attracting (hydrophilic) part, the so-called carboxylate group (-COO-) consist. Soaps do not dissolve properly in water, but form so-called micelles. In pure water, the micelles (Fig. 1) are very small and cannot be seen. Inside these tiny "droplets" are the long, non-polar hydrocarbon chains, while the polar ends protrude into the water. The charges on the ends prevent the micelles from clumping together.

Soaps lower the surface tension (more generally: interfacial tension) of water, as they also arrange themselves on the water surface (Fig. 2). This effect allows the water to come into contact with surfaces much more intensively, which means that the actual cleaning effect of the soap and water can only develop in inaccessible places.

The "loosening of grease" (oil, dust, dirt) from the surface to be cleaned and the removal of this via the washing water is the actual cleaning effect of the soaps. The long hydrocarbon groups of the soap molecules dissolve easily in small fat droplets (Fig. 3). However, the polar ends protrude into the surrounding water. The fat droplet is then completely enveloped by the soap molecules and detached from the surface to be cleaned. The large number of fat and oil droplets coated with soap molecules form a so-called → emulsion in the water, which can be removed at the end of the washing process by rinsing with fresh water.

In some areas, tap water contains an increased amount of calcium and magnesium ions. They make this water "hard", block the polar ends of the soap and thus destroy the washing effect. Lime soaps that are insoluble in water are formed.

Moisturizing soaps

In advertising and sales one often reads about so-called "moisturizing" soaps. The so-called refatting is scientifically questionable. When saponifying cold soaps, more fats are sometimes deliberately added so that not all fats saponify, but all of the lye has reacted with the fats. With curd soaps (fine soaps), additional fats are sometimes added artificially. After the skin has been degreased by the normal washing process, these fats are supposed to be "regreased", i.e. given back to the skin. But since the soap locks in fats and combines them with the water, these fats are already completely bound in the soap and are washed away with the washing water. The alleged "moisturizing" subjective feeling comes from the fact that a soap with added fat is milder, since the soap can no longer be one hundred percent active in washing. The more fat the soap has already bound, the less aggressive it is on the natural body fats of the skin.

Types of soap


Glue soap

Glue soaps (Soap glue) are homogeneous masses in which the glycerine is not separated after saponification and thus remains in the product. Cold-boiled soaps are occasionally offered as glue soaps. The fats and the lye are saponified at 40 degrees and the mass is poured into a container immediately afterwards. There are many homemade glue soaps on offer.

Curd soap

Curd soaps are solid soaps and usually consist of the sodium salts of fatty acids. They are obtained by salting out the soap glue, which separates the glycerine. Curd soaps are most common body soaps, including fine soaps. In the trade, cheaper, unscented soaps are called "curd soaps", which are used especially for washing or felting.

Soft soap

Soft soaps are liquid or semi-solid soaps that are made from inexpensive fats or oils by saponifying with potassium hydroxide. They are therefore a mixture of potassium salts of higher fatty acids. They are also called "liquid soap" or historically "barrel soap". The liquids can easily be added to water and used for cleaning purposes, e.g. in the household. The formation of lime soaps is particularly disadvantageous here, since relatively small amounts of soap are mixed with relatively much and possibly hard water.

Fine soap

Fine soap, or also Toilet soap is mainly used for washing hands and consists of curd soaps of very pure, odorless fats with nourishing additives such as lanolin, as well as perfumes and dyes. Sometimes glue soaps are also offered as fine soaps.

Glycerine soap

Glycerine soap is a soap that is high in glycerine. It is cloudy to glassy and transparent. It is also easy to melt (like many waxes) and is therefore also used as a craft soap.

Paper soap

Paper soap is wafer-thinly cut soap. They are portioned so that the pieces dissolve quickly.

Shaving soap

Shaving soap is made with a high proportion of stearic acid so that the foam is creamy and remains stable. In addition, saponification is not only done with caustic soda, but also with potassium hydroxide. This makes the shaving soap smoother and easier to lather.

Gall soap

Another soap is that Gall soapthat is produced when soap is mixed with beef bile. Its main purpose is to remove organic dirt.

Medical soap and antibacterial soap

The so-called Doctor soaps are soaps with supposedly skin-friendly composition. “Doctor's soap” is not necessarily a disinfectant. Often, pure glycerine soaps are also offered as doctor soaps. Some soaps contain bacteria-inhibiting additives, such as B. Farnesol or Triclosan. Research from the University of Michigan has shown that special produced for home use antibacterial soaps No better way of removing germs than conventional soap. With these soaps, there is a risk that the additives will weaken. Soaps which are used in the medical sector and which contain significantly higher concentrations of antibacterial agents were not examined.[1]

Petrol soap

Petrol soap is a petrol-based stain remover for removing organic soiling and for pretreating soiling with lubricating oil and grease on textiles.

Modern liquid soaps

Liquid soaps are used for hand washing, but more so than shower gel, shampoo and bubble baths. Although they emerged from soft soaps, they have completely different ingredients and different properties.

Metal soaps

Metal soaps are soaps made from alkaline earth, light and heavy metals such as magnesium, aluminum or cadmium. While they are poorly soluble in water, they dissolve well in organic solvents such as benzene. They mostly have colloidal and surface-active properties. The soaps of alkali metals are not counted among the metal soaps.[2]

Advantages and disadvantages of soaps

The use of soap as a detergent is low, especially in industrialized countries, and surfactants compete with them. Soap in detergents is not supposed to clean the laundry, but to prevent excessive foaming.

The disadvantages of the soap are:

  • Soap not only removes existing dirt, it also removes part of the skin's natural greasy film. This can lead to cracked, rough skin, especially if you wash too often. Soaps with a high glycerine content (which e.g. remains in the finished product during cold saponification) offer protection.
  • Soap has an alkaline reaction in water, which can damage the fabric:
    R-COO- + H2O ----> R-COOH + OH-
  • Soap and hard water form a whitish precipitate on solid surfaces, the lime soap:
    2R-COO- + Approx2+ (Lime) ----> (R-COO)2Approx

Advantages of soap over synthetic surfactants are:

  • good biodegradability
  • Pure soaps (e.g. olive oil soaps) are suitable for allergy sufferers, as soap made from natural fats is tolerated by most people. Synthetic surfactants can, however, act as allergens.

Physiology of washing with soap

  • When washing, soap removes sebum, powder and cream residues from the pores. This normalizes skin breathing.
  • Soap attacks the fatty layer on the skin and more or less loosens it.
  • The soapy alkali acts on the acid mantle of the skin. However, this effect is balanced again 30 minutes after washing.
  • Soap solution causes the skin to swell. This swelling effect is irrelevant in healthy skin, but can lead to drying out and cracking in the sick state.
  • Soaps can cause irritation if they contain higher levels of short-chain, saturated fatty acids. However, allergic skin reactions are more likely to be triggered by the perfume oils and additives used than by the actual soap.

Soap and education

In the upbringing of children, especially in the American cultural area, the soap found an understandably unpopular use among children until the recent past: In order to wean the children from using swear words and fecal words, their mouths were punished with soap, usually applied to a rag washed out. This is intended to clarify the "dirtiness" of certain terms. The nauseating taste should condition children to avoid using these words. This was actually more of a phrase than anything else.


  • Foam and fragrance from NZZ Format, http://www-x.nzz.ch/format/broadcasts/broad_431.html
  • Oriental soap. In Aleppo, Tripoli and Beirut. Documentation, 45 min., A film by Birgitta Ashoff, production: SR, first broadcast: January 17, 2007
  • Fight Club by David Fincher, "Tyler sold his soap to department stores at $ 20 a bar. Lord knows what they charged. It was beautiful. We were selling rich women their own fat asses back to them.". Imdb: http://www.imdb.com/title/tt0137523/.


  1. n-tv.de, Antibacterial Soap - No Better Than Others, August 24, 2007
  2. Where. Ostwald, R. Riedel: Contributions to the colloid chemistry of metallic soaps, in: Colloid & Polymer Science, 1934, 69, 2, pp.185-199

Categories: Chemical group | Detergents | Surfactant