Bold Bubbles: The strange journey and superpowers of soap

According to Roman legend, thousands of years ago women washing in the river Tiber used bubbly globs flowing down a mountain to clean their clothing.

Whether they knew it or not, the bubbles were inadvertently created by the temple priests on Mount Sapo. Ashes from fires combined with animal fat and river water created a bubbly substance that lifted dirt from skin and clothing.

Soap.

Humans have been using soap for at least 5,000 years, but it isn’t an obvious sort of formula. Soap requires three ingredients: An alkaline (like lye), water, and fat.

The fat part is easy and lots of things work well, from olive oil to tallow, which is beef fat.

But lye is a different story. Lye has to be made with white ash from a hardwood fire. Lye makers literally had to go out to a place where hardwoods burned down to ash. They scooped up the white ashes and put them in a barrel. Then, they waited for rain, best for making lye. Buckets full of rainwater were poured into the ash barrel to soak the ash. The lye water formed at the bottom of the barrel. They then caught and stored the caustic lye water that leeched out from the bottom.

Strangely, somewhere along the line, someone decided to make lye and combine it with fat and more water.

Today we might think of soap as gentle, but it is actually fierce to dirt, bacteria, and viruses.

Soap molecules are pin-shaped crowbars. Their tails love fat but hate water. Their heads love water. So when soap molecules find a piece of dirt or virus, the tails pierce the fatty membrane, while the heads pull away toward the water, thus prying open the dirt or virus and destroying it. Fancy science for some glop that once rolled down a hill.

Today soap smells nice and has lots of different forms from hand soap to detergent. Yet, the recipe really hasn’t changed much from the recipe used by Romans or ancient Egyptians. It’s still ancient science.