Oils are reacted with a strong alkali ("lye" became the nickname for the alkali, or caustic), and the result of the reaction is soap and glycerine. Early soap makers used caustic potash, or potassium hydroxide, for the alkali because it could be made from the ashes of hardwood fires. That tended to make a soft soap, and it was used for laundry mostly. Now we use caustic soda, or sodium hydroxide, for bar soap because it allows the bar to harden more.

To let you know just how old the art of soap making really is, there is evidence that a soap-like substance was made in ancient Babylon, according to the inscriptions found on some of the clay pots excavated there. The estimated dates are about 2800 BC, making them about 48 centuries old! The inscriptions on the urns indicate that ashes were mixed with animal fats, so what they had was soap, even if it was a little crude. It is thought that the resulting substance was used on their hair rather than being used for cleaning.

A legend that comes from the days of the Roman Empire also helps to illustrate how soap is made. The story goes that the people who washed their clothes in the rivers and streams of old Italy found that their clothes got cleaner if they would go just down from the places used for burnt offerings. This makes sense, because in a burnt offering, you have all the ingredients for soap. The fire makes ashes, which contains potash, and when the rains came, caustic potash would be produced. The fat from the animal offered in the sacrifice would drip down into the ashes. Mix the two together, and you get soap. The soap would run down into the stream, and it would help to get the dirt out of your toga. A stretch of the imagination perhaps, but then most legends are.

In any case, soap making is a very old art. Here is how you do it: You mix vegetable oils or animal fats together with a water solution of a strong alkali, such as caustic soda. That's it. Then you let Mother Nature take over. The chemical reaction that ensues does the rest.