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Infobox on Soap
Example of Soap
Origin -
Stowage factor (in m3/t) 1,42/1,56 m3/t (boxes)
Humidity / moisture -
Ventilation -
Risk factors See text



In chemistry, soap is a salt of a fatty acid. Soaps are mainly used as surfactants for washing, bathing, and cleaning, but they are also used in textile spinning and are important components of lubricants. Soaps for cleansing are obtained by treating vegetable or animal oils and fats with a strongly alkaline solution. Fats and oils are composed of triglycerides; three molecules of fatty acids are attached to a single molecule of glycerol. The alkaline solution, which is often called lye (although the term "lye soap" refers almost exclusively to soaps made with sodium hydroxide), brings about a chemical reaction known as saponification. In this reaction, the triglyceride fats are first hydrolyzed into free fatty acids, and then these combine with the alkali to form crude soap, an amalgam of various soap salts, excess fat or alkali, water, and liberated glycerol (glycerin). The glycerin is a useful by-product, which can be left in the soap product as a softening agent, or isolated for other uses.

Soaps are key components of most lubricating greases, which are usually emulsions of calcium soap or lithium soaps and mineral oil. These calcium- and lithium-based greases are widely used. Many other metallic soaps are also useful, including those of aluminium, sodium, and mixtures of them. Such soaps are also used as thickeners to increase the viscosity of oils. In ancient times, lubricating greases were made by the addition of lime to olive oil.

When used for cleaning, soap allows otherwise insoluble particles to become soluble in water and then be rinsed away. For example: oil/fat is insoluble in water, but when a couple of drops of dish soap are added to the mixture the oil/fat apparently disappears. The insoluble oil/fat molecules become associated inside micelles, tiny spheres formed from soap molecules with polar hydrophilic (water-loving) groups on the outside and encasing a lipophilic (fat-loving) pocket, which shields the oil/fat molecules from the water making it soluble. Anything that is soluble will be washed away with the water. Synthetic detergents operate by similar mechanisms to soap.

The type of alkali metal used determines the kind of soap product. Sodium soaps, prepared from sodium hydroxide, are firm, whereas potassium soaps, derived from potassium hydroxide, are softer or often liquid. Historically, potassium hydroxide was extracted from the ashes of bracken or other plants. Lithium soaps also tend to be hard—these are used exclusively in greases.

Soaps are derivatives of fatty acids. Traditionally they have been made from triglycerides (oils and fats). Triglyceride is the chemical name for the triesters of fatty acids and glycerin. Tallow, i.e., rendered beef fat, is the most available triglyceride from animals. Its saponified product is called sodium tallowate. Typical vegetable oils used in soap making are palm oil, coconut oil, olive oil, and laurel oil. Each species offers quite different fatty acid content and, hence, results in soaps of distinct feel. The seed oils give softer but milder soaps. Soap made from pure olive oil is sometimes called Castile soap or Marseille soap, and is reputed for being extra mild. The term "Castile" is also sometimes applied to soaps from a mixture of oils, but a high percentage of olive oil.

Shipment / Storage / Risk factors

Soap is shipped in cartons or kegs. Soap, even under normal conditions, is subject to loss in weight due to water evaporation. This does not result in reduced efficiency, the active washing material remaining unaltered. Dampness or contact with water deforms cakes of soap and will damage packing, making it necessary for the soap to be recast. Although the commercial value of the soap may be affected, the soap does not lose its ‘specie’ and can still be used. Temperatures above normal hasten drying, and subsequent cooling may lead to sweating, a condition also brought about by damp conditions. Sweating makes the soap clammy and sticky and such deterioration can effect the saleability. Soap in disintegrated form, such as chips, flakes or powders in bulk, may become self-heated if stored under hot humid conditions, particularly if stacked and ventilation is bad. Soap powders, in boxes or cartons, are highly susceptible to damage by exposure to dampness and/or heat. Brand names can cause problems in disposal of damaged goods.