by Theodore Zuckerman

Initial Simplistic Summary

To make soap manufacturers start with fats, and sodium hyroxide or another alkalai. Water and heat are used in the processing. According to soap-making terminology, the alkalai is used to saponify the fats. But I think it better reflects reality to say that the 2 substances, the fats, and the alkalai, interact with each other, with the result of their interaction being soap and glycerine. The fats that soap manufacturers use can come from plants or animals. Sodium hydroxide is usually a byproduct in the production of chlorine from salt.¹

You can use potassium hydroxide instead of sodium hydroxide, or a substance such as wood ashes (or relatively simple derivatives therof) -- containing potassium carbonate. However wood ashes are generally used only in home soapmaking, and not in commercial production.

After describing a bit about how soap is made, I will describe more about where the fats used in soapmaking come from, and I will try to find out more about where sodium hydroxide comes from, too.

"When caustic soda is added to fat, glycerin separates out, leaving sodium oleate, ...which is soap.^"2

This appears to be the traditional "definition" of soap.

The traditional chemistry

Sodium hydroxide consists of sodium and hydroxide -- chemically united. Sodium hydroxide is the alkalai that has traditionally been used to make soap, ever since it became widely available, starting around 1791. It has been called caustic soda and lye.

A fat consists of glycerine, and 3 fatty acids -- chemically united.

Adding sodium hydroxide (or potassium hydroxide) to a fat results in the glycerine and the fatty acids of the fat separating from each other, and the sodium and the hydroxide of the sodium hydroxide separating from each other. At the same time, the hydroxide and the glycerine combine, to form complete , stable, glycerine molecules. Also, at the same time, the sodium (or the potassium) and the fatty acids combine, forming "soap." According to this chemistry, soap is a synonym for a "sodium salt" or "potassium salt" of a fatty acid. The whole process of the salting out of soap, from fats, along with the production of glycerine, by adding an alkalai to the fats, gets labeled as being saponification. Water and heat may be needed to get the chemical reaction to take place.

Modern commercial soapmaking

However, according to the Encyclopedia Britannica: "if industrially produced fatty acids are used in place of natural fats and oils, the reaction with caustic soda yields soap and water instead of soap and glycerin." ³

And, in fact, modern commercial soap, in the "industrialized " nations of the world, is most often made using the "continuous process" or "hydrolyzer process" of soap-making, wherin natural fats are first separated into their component fatty acids and glycerin, the fatty acids are then separated from each other, and then sodium hydroxide (caustic soda) is added to single fatty acids, causing water to separate out, leaving soap. Each of the different soaps made from each of the different fatty acids are then blended -- to achieve soaps with desirable properties.

How are the fatty acids first separated from the glycerine? From Britannica: "by means of water at high temperature and pressure in the presence of a catalyst, zinc soap. The splitting reaction is carried on continuously, usually in a vertical column 50 feet (15 metres) or more in height. Molten fat and water are introduced continuously into opposite ends of the column; fatty acids and glycerin are simultaneously withdrawn. Next, the fatty acids are distilled under vacuum to effect purification."^Link.

The use of zinc soap suggests that a very small amount of animal fats, made into "zinc soap," (catalysts are used in small amounts) may possibly be used in the process of separating fatty acids from vegetable fats, to produce "vegetable oil soaps."

Note that with this "continuous process" of producing soap "the by-product glycerin is purified and concentrated as the fatty acid is being produced."^Link.

Until the "continuous process" began being used in the 1930's, the "kettle process," or "boiling process" enabled by development of the Leblanc process in 1791, for creating sodium hyroxide, was used. Before 1791, wood ashes were used instead of sodium hydroxide, and soap was made in smaller batches.

In the 1950's synthetic detergents began greatly replacing simpler soaps as cleaning agents. I will get to synthetic detergents later.

According to Brady and Clauser: "About half of all soap is made with tallow [beef fat ], 25 percent with coconut oil, and the remainder with palm oil, greases, fish oils, olive oil, soybean oil, or mixtures. A typical soap contains 80 percent mixed oils and 20 coconut oil, with not over 0.2 free alkali."⁴

McGraw Hill says "tallow and coconut oil are the most common fatty materials used for soapmaking."⁵

But can I get soap made from vegetable oils only?

Yes.

Some brands of vegetable oil soap, by the way, are Kiss My Face Olive Oil soap, which the package labeling says is entirely from olive oil, and Dr. Bronner's liquid soaps, with package labeling that, if I recall correctly, claims it lists every ingredient, and that all are non-animal. 

More about soap fats

Soap can be made from any fat. Many kinds of soaps, with wide ranges of properties, can be made from vegetable fats, without the use of animal fats. I believe the reason for the use of animal fats is simply availability, and that if suddenly animal fats became unavailable, there would be no problem finding suitable vegetable substitutes for every home and industrial soap need.

From Brady and Clauser: "high grade soft soap for industrial use is made with coconut or palm kernal oil, with caustic potash..." (Caustic potash is a synonym for potassium hydroxide.) 

Again from Brady and Clauser: "The lauric acid of coconut oil gives the coconut-oil soaps their characteristic of profuse lathering, but .... Palm oil produces a crumbly soap. It does not lather freely, but is mild to the skin. Olive oil is slow-lathering, but has good cleansing powers. It is often used in textile soaps." 

And from Brady and Clauser: "Blending of various oils is necessary to obtain a balance of desired characteristics." 

So-called "hard" and "soft" soaps

Soaps have been divided into 2 classes: "soft" soaps -- made with potassium hydroxide; and "hard" soaps -- made with sodium hydroxide. But in actuality the initial product obtained by saponifying fats with one or the other of these chemicals is a rather gooey mass. To get a "bar" of hard soap, from sodium hydroxide saponified fats, further processing, beyond simple saponification, has to be done. 

Here is a link to info about hard and soft soaps, included with information about Nazi soapmaking from human fat. 

A water extract of pot ash, or potash, that is, wood ashes from fireplaces, collected in pots, apparently contains a large enough quantity of potassium carbonate to saponify fats, and in fact, such a water extract was used, without futher refining, by many people, historically, to make soap. Here is some information about how colonists in the United States made soap.

And apparently chemists got the idea for the name for the chemical potassium -- from the pot ash in which it they first discovered it.

Most modern soap is made with sodium hydroxide. Some soaps, for example liquid soaps, are often made with postassium hydroxide, as are industrially-used soaps. But most toilet soap is made with sodium hydroxide. Modern day sodium hydroxide comes from sodium chloride -- the common salt of table salt, and of the earth's oceans.

According to Brady and Clauser: "It is usually a by-product in the production of chlorine from salt."⁶

The LeBlanc process for making sodium carbonate (soda) was developed in 1791. Sodium carbonate could be used in place of ashes, to make soap, or could be converted to sodium hydroxide (caustic soda). The LeBlanc process made the time-consuming processes of saving wood ashes -- unnecessary. This resulted in a revolution in soapmaking, and in soap becoming abundant. In the LeBlanc process, sodium carbonate (soda) is produced. Sodium hydroxide (caustic soda) is produced from the sodium carbonate (soda), by reacting it with calcium hydroxide. Calcium hydroxide (slaked lime) is produced by mixing calcium oxide (quicklime) with water. Calcium oxide (plus carbon dioxide) is produced by heating calcium carbonate. Calcium carbonate is the main constituent of limestone, which is found in the earth. It is also the main constituent of sea shells. Limestone, slaked lime, and quicklime, are all sometimes referred to, simply as "lime."

From Comptons Encyclopedia (on-line):

The Leblanc process produces soda by first heating salt (sodium chloride) with sulfuric acid. The sodium in the salt and the hydrogen in the acid change places, producing hydrogen chloride, or hydrochloric acid, and sodium sulfate, or "salt cake." Additional steps yield a mixture of sodium carbonate and calcium sulfide. The two are separated by washing out the sodium carbonate with water.

Another manufacturing process, for producing sodium carbonate, the Solvay process, was named after its developer, a Belgian manufacturer. Put on a commercial basis in about 1863, it has largely superseded the Leblanc process. In the Solvay method strong ammonia-saturated salt brine is treated with carbon dioxide gas that is bubbled through the brine from below. This causes reactions that produce ammonium chloride, or sal ammoniac, and sodium bicarbonate (NaHCO3), or baking soda. The sodium bicarbonate forms a crystalline precipitate, which is filtered out. This is then heated, driving off hydrogen, carbon, and oxygen and leaving sodium carbonate (soda).

In an even newer process -- the electrolytic process -- an electric current is passed through a solution of sodium chloride, splitting the salt molecules into atoms of sodium and chlorine (see Electrochemistry ). The sodium atom displaces one of the hydrogen atoms of the water, forming caustic soda (NaOH).

It is not clear from Comptons Encyclopedia, in regard to the modern production of sodium hydroxide, how much is produced by the Solvay process, and how much is produced by the electrolytic process. But note that the Haber process for producing ammonia was developed around 1915. It produces ammonia, generally, from air, and natural gas.

Also, I ought to check out how the carbon dioxide, needed for the Solvay method, is generally produced.

Is glycerine a "by-product" of soapmaking, or is it soap that is a "by-product" of glycerine-making?

Beats me.

But what I do know, is this: when ashes, instead of pure potassium hydroxide, or pure sodium hydroxide, were used to make soap, much of the glycerine that was produced remained mixed in with the soap. But in modern soapmaking the glycerin and soap are separated. With the continuous process, the separation is even more readily facilitated, than with the kettle process. While the soap produced by these processes, goes into all kinds of cleaning agents, from cleaning agents for human skin, to cleaning agents for industrial purposes of various kinds; and while some of the glycerine may go back into the soap; glycerine also goes into -- explosives. It is used in producing glycerine-trinitrate, once more popularly called nitroglycerine. (Yes, this is the same nitroglycerine that heart patients take.) Mixed with other substances, that help control how fast it explodes, nitroglycerine is dynamite.

Where does the nitrogen for the nitroglycerine come from? The answer is that it comes from the same industrially-produced (by the Haber process) synthetic ammonia that is used in producing the sodium hydroxide (via the Solvey process) that is used in soap making, and that is used as a source of plant-food nitrogen.

That is, once fats are split into fatty acids and glycerine (using zinc soap made from previous batches of fatty acids), ammonia is used both to (1) create the sodium hydroxide that is used to produce soap from the fatty acids, and (2) to create explosives from the glycerine.

Also, nitrogen obtained from ammonia, when mixed with cellulose (from cotton or wood) -- produces another explosive: modern smokeless gun-powder, also called nitrocellulose, gun-cotton.

Summary. Nitrogen and fat and oil waste: dynamite. Nitrogen and cotton waste or sawdust: gunpowder.

In summary, homemade soap is made, from scratch, from animal or vegetable fats and wood ashes, or substances obtained from wood ashes.

Commercial soap is made, "from scratch," from animal or vegetable fats, and alkalai. Alkalai is made from salt, or from salt and ammonia. Ammonia is made from air and natural gas.