There are a number of apocryphal tales about bathing and cleanliness. For example, Cleopatra is said to have bathed in goat's milk while Queen Elizabeth I only bathed once a month. Louis the XIV is reported to have bathed only once a year to avoid injuring his health.
While some of these stories may be true, our ancestors were not unhygienic.
Recipes for soap date back to ancient times and many other methods for removing dirt were employed. For example, the ancient Greeks coated their bodies in olive oil and then scraped the skin clean using a flat-bladed stick. It is still practiced today.
Soap is actually fairly easy to make and owes its origins to two very unlikely ingredients - the ashes of a fire and animal fat. Most people would be disinclined to spread either on their body by itself but chemical reactions can convert the fat into soap.
Historically, soap required "washing soda" which is sodium carbonate. It can be obtained by suspending ash from the combustion of grasses or seaweed in water. The sodium carbonate dissolves and the organic component of the ash can then be removed. Evaporating the water leaves the washing soda as a solid.
The process is labour intensive and time consuming so in the late 1700s, the French offered a prize equivalent to around $500,000 today to anyone who could come up with a better method of making it. The prize was claimed a French chemist, Nicholas LeBlanc.
His process involved combining sodium chloride with sulfuric acid at 800 C, generating sodium sulfate. The other product of the reaction was hydrochloric acid which was released in gaseous form. When combined with atmospheric moisture, it formed a particularly strong acid rain.
The second step in making soda was to combine the sodium sulfate with limestone and carbon. The carbonate in the limestone reacts with the sodium while the sulfate, carbon, and calcium from the limestone react to give calcium sulfide and carbon dioxide.
Calcium sulfide dissolves in acid or water releasing hydrogen sulfide, a toxic substance with the smell of rotten eggs.
Needless to say, the LeBlanc process was not an environmentally friendly industry and had a major impact on its locale. However, the demand for sodium carbonate was so high, whole regions of European countries were given over to its production. It is also a critical ingredient in the production of glass, paper and a number of other industrial products so the LeBlanc process flourished.
In the early 1800s, it was replaced by the much cleaner Solvay process and over time sodium carbonate was replaced by sodium hydroxide as the alkali of choice in most industries. Indeed, sodium hydroxide is still one of the major commodity chemicals produced by industry as it finds its way into everything from polymer production to baking bread.
A significant use for sodium hydroxide remains the production of soap although purists could still capture sodium carbonate from the ash generated by burning plants.
With either sodium hydroxide or sodium carbonate, the next step in making soap is to simply mix the alkali with fat. Fat is a triglyceride consisting of a head group or glycerol unit and three long chain fatty acid. The alkali cleaves the linkage holding the glycerol and acids together. The process is called saponification.
While soap can be made by mixing the two ingredients cold and letting them sit, generally it is easier and quicker to warm the mixture melting the fat. In this state, and with very precise measurement of the quantities of alkali and fat, a useable soap can be obtained.
Most soap makers take the process a step further and bring the alkali and fat to a boil in a large pot. The soap layer forms on the surface and can be skimmed off. It must be allowed to cure for a few days but essentially that is all that is required to make soap.
The glycerol gives rise to glycerin and this can be added back into the long chain fatty acid component to give a much smoother mixture with a creamy feel. Glycerin has a number of other industrial uses, including the synthesis of nitroglycerin.
However, it is the long chain fatty acids which are the cleaning component of any soap or detergent. In essence, these molecules consist of two regions - a water-loving or hydrophilic acid group and a water-fearing or hydrophobic hydrocarbon tail.
The long chain tail inserts itself into dirt or oils securing the molecule to the surface of any grime while the hydrophilic group is attracted to water. Essentially the fatty acid forms a molecular bridge between water-fearing dirt and the wash water used to sweep it away.
Whether you bath many times a day or just once a year, soap is a major part of our lives.
