What Is Soap Made of?
Soap is not a very modern product, although we have rarely read of soap in olden times. As long ago as two thousand years, the Germans had an ointment which was made in practically the same way as we now make soap. A soap factory was engaged in making soap in France in 1000 A. D.
Even before soap was manufactured, people knew that ashes of some plants, when mixed with water, gave it a peculiar, smooth, slippery feeling, and added to the cleansing qualities of water. Although they did not know it, this was due to the soda of potash which was in the ashes. Pure soda and potash both have excellent qualities for cleaning, but are likely to injure the skin, and other things coming in contact with them.
Soap is made by boiling together oil or fat and “caustic” soda or potash. Caustic soda is a substance made from sodium carbonate by adding slaked lime to a solution of it. The slaked lime contains calcium in combination with hydrogen and oxygen, and is known in chemistry as calcium hydrate. When calcium hydrate is added to a solution of sodium carbonate, the sodium present combines with the oxygen and hydrogen to form a compound, variously called sodium hydrate, sodium hydroxide, or caustic soda. A similar compound of potassium is formed when the same kind of lime is mixed in a solution of potassium carbonate. In both cases the calcium is converted into calcium carbonate, which is not soluble in water and settles to the bottom; but the caustic soda or potash is dissolved.
The word “caustic” means to burn. Both will burn the skin if allowed to touch the skin for a short time.
The fats used for making soap consist of glycerine, in chemical combination with what are called fatty acids. When these fats are boiled with caustic soda, or caustic potash, the fat is decomposed; the fatty acid combines with the sodium or potassium to form soap and the glycerine is left uncombined.
In modern soap factories the manufacture is carried on in large iron vessels. Some fat and oil are put into the vessel and a little lye, which is really caustic soda or potash, is added and the mixture boiled. The fat and the lye combine very quickly and form a whitish fluid. More lye is now added and the boiling continued. This process is repeated until nearly all the oil or fat has combined with the lye. If yellow laundry soap is being made, some rosin is put in, and this gives the yellow color. If toilet soap is being made, common salt is put in instead of rosin. The addition of the salt has the effect of separating the water and the glycerine from the soap. The soap rises to the surface and is skimmed off. As soon as the separation is complete, and the soap is then cut or pressed into cakes after it has become hard.
Soaps referred to above are the ordinary hard soaps. In making soft soaps no salt is added to separate the soap from the liquid. As the water and glycerine do not separate from the soap, the entire mixture remains of a soft consistency. Soft soap is also made with a lye, that is obtained from wood ashes. The ashes are placed in barrels and water poured upon them. The water drips down through the ashes in the barrel and dissolves the potash contained in them, making lye or caustic potash. This lye is then in liquid form and is mixed and boiled with grease or fat to make soap.
There are many different fats used in soap making. Palm oil is perhaps the most common, but tallow, olive oil, cotton seed oil, and many other fats are used. The hardness of the soap varies with the kind of fat and lye used. Palm oil or tallow soap is very hard, and other oils are sometimes mixed with it to soften it.
These are the main facts connected with the making of soaps. There may appear to be different kinds all of which look and smell differently. The difference in them is largely due to the presence of different perfumes and coloring matters.