Queen Elizabeth I of England said that she bathed once a month, “whether she needed it or not.” And it is that personal hygiene was something that left a lot to be desired since the Middle Ages, when the Church became the light and guide of the Western world. The meat had to be mortified as much as possible, therefore the care of the body was something sinful . What sinner would think of exposing his body, shamelessly naked, in view of the rest? In this way, the culture of Roman spas, where bathing was a social activity, disappeared. Thus, the Black Death, which landed in the port of Messina in October 1347, had a powerful ally in the lack of hygiene in Europe at the time.
And it would not be for lack of raw material. Water has always been there and the use of soap for personal hygiene and cleaning clothes dates back as far as 5,000 years ago . We have evidence of the existence of something similar to soap in Babylonian clay cylinders from 2800 BC. C. The inscriptions on these cylinders say that fats were boiled with the ashes of plants, which is a method of making soap. The Egyptians, who used to bathe regularly, have left us in the Ebers papyrus – a medical text from 1500 BC. C.- their soapy recipe: animal and vegetable oils and alkaline salts, which they used both to wash themselves and to treat different skin diseases. In Greece and Rome, soap did not even come close to their bodies. For personal hygiene they used pieces of clay, sand, pumice stone and ashes, leaving clothes at the mercy of soda -known in the Roman world as natrium- , ashes, wine feces… white used ammonia, which the Greek artisans obtained from the fermentation of urine. For this reason, behind the door of his businesses he had some jars that were available to customers who wanted to use them.
the first soap
It was not until the 7th century that what we might call soap craftsmanship was institutionalized in Europe. The master soapmakers, as the pyrotechnics would later do, carefully hid the secret of the mixture: vegetable and animal oils, ashes of certain plants and, of course, the substances that gave it the appropriate fragrance. Italy, France and Spain were the first countries to enter the soap business : having olive oil had to be of some use… The manufacturing process was simple. The artisans boiled olive oil with a potash obtained from treating ashes with lime in a cauldron. Little by little, using the ubiquitous principle of trial, trial and error, the technique was perfected. But there was a small detail that did not worry anyone: why the soap cleans. It was not until well into the 19th century, and thanks to the spectacular progress that organic chemistry experienced during that century due to something as material as fashion and the development of new synthetic dyes.
The chemistry of soap
Fatty acids are obtained from vegetable and animal oils and fats. They are made up of two parts: what is called a carboxyl group, which is a molecule made up of one hydrogen, two oxygen and one carbon atom, attached to a hydrocarbon, which is essentially a chain of carbons each attached to two hydrogens. In fats and oils, fatty acids are found forming a triglyceride: three of them united by a glycerin molecule .
On the other hand, a base or alkali is nothing more than a soluble salt of an alkali metal, such as sodium and potassium: the most common are sodium hydroxide -an atom of sodium, another of oxygen and another of hydrogen-, or caustic soda, and potassium hydroxide -identical but changing the sodium for potassium-, or caustic potash. Bases have the property that when reacting with an acid they neutralize it, and that is what is sought when obtaining soap.
The method used to obtain soap is called saponification: heating fats with the ashes of alkaline plants, which produces soap, water and glycerin. Depending on what base is used, we will have one type of soap or another . If we use soda we obtain sodium soaps, which are “hard”. If potash is used, other softer ones are obtained, which we can find in liquid soaps.
Why does soap clean?
What gives soap its peculiar ability to clean clothes is that its molecule behaves as if it had a dual personality: the end where the hydrocarbon is found flees from the water – it is hydrophobic – and tends to bind to fat, while the other it is hydrophilic, it loves water. Obviously the ‘pulling’ effect on the hydrophilic side must be greater in order to remove the dirt from the clothes, which we help when we rub the garment. In the end, a tiny drop of dirt is left surrounded by a soap wrapper , a process that is favored if hot water is used.
However, the effectiveness of soap is reduced if it is washed in hard water, which contains a large amount of mineral salts -mainly calcium and magnesium, but also iron and manganese-. This is so because these salts react with the soap to form an insoluble precipitate that gives the clothes a starched feel. That’s why we use fabric softener.
Soap’s long reign ended at the end of World War II . It was then that detergents became popular, whose operation is identical to that of soap. But in this case, the so-called surface active agent or surfactant is obtained by reacting certain petroleum derivatives -which constitute the hydrophobic part- with certain chemical substances such as sulfuric acid or sulfur trioxide and, later, with soda or potash to compose the hydrophilic part.