Nearly everyone has probably wondered at one point or another: but, what exactly IS soap and why in the world does it make me clean? Proceed, gentle reader, as we take you on a soapy journey of wondrous discovery.
First, let's start with some...
No one really knows when soap was first invented and used. According to Michael Willcox ("Soap", 2000) we have evidence of soap being produced in Ancient Babylon as early as 2800 BCE. Ancient Egyptians are also reputed to have bathed in a soap-like substance and there's a funky story floating around about Roman women noticing that their clothes got cleaner in the bubbly water running down from Mount Sapo, headquarters of animal sacrifices. While the latter theory is probably not particularly accurate, suffice it to say that soap has been around for quite a while.
There's further evidence of true soap being produced in the medieval Islamic world and the advent of castile soap in Europe around the 16th century. However, soap was not refined and mass-produced until the Industrial Revolution...you can guess the road it took from there.
So, what is soap actually made of? Well, to put it simply, soap is the salt of a fatty acid. Not quite clear? Let's first look at how soap is made.
We get soap by mixing oils and a strong alkili, such as lye (sodium hydroxide). The chemical reaction that must take place in order to produce soap is called saponification - essentially, the alkili and water are used to hydrolize the oil and convert it into free glycerin (that great moisturizing stuff you find in handmade soaps) and soap (a fatty acid salt).
LYE, you gasp? Isn't that the stuff that will burn my face off??? Well, technically, yes. But this is why we're not giving you pure sodium hydroxide crystals to use as an exfoliant. A properly formulated soap will not contain any lye after the saponification process is complete. In fact, most soap-makers "superfat" their soaps, meaning they add extra oil that remains unreacted in the finished product so that 1) there's no free lye floating around, and 2) you get lots of extra moisture.
Now, in order to understand how exactly this works, let's examine what happens during saponification.
Your typical oil molecule is a triglyceride, consisting of three fatty acid chains and a type of alcohol called glycerol, or glycerin. To better illustrate this process, Bunny Butt Apothecary is proud to bring you...dun dun DUN...SOAPIMATION!
Our example uses a fat molecule containing palmitic acid, which is a common component of plant oils. Those squiggly lines you see on the left are a short-hand way of representing long hydrocarbon chains - in this case the chemical formula is [C15H31CO]3[C3H5O3]. So, we have our tree fatty acid "tails" that are attached to our glycerin. During the process of soap-making, the glycerin splits away from its fatty appendages and lye enters the equation. The sodium hydroxide splits up into...well...sodium and hydroxide and the sodium bonds to the fatty acid chains to produce that "salt of a fatty acid" we mentioned earlier. So, as you can see, once the sodium hydroxide is introduced, we basically wind up with two different molecules: soap and glycerin.
Now, this is all well and good, you say, but how does this "fatty salt" you speak of actually clean me? Well, a soap molecule has a polar (hydrophilic) end and a non-polar (hydrophobic) tail - that's the squiggly hydrocarbon chain we were talking about before. In English? This means that one end of the soap molecule likes to stick to water and the other end is more fond of things like grease or oil. To better illustrate this, we introduce you to Bob, the particle of gunk.
As you can see, Bob has been suspended in the water by all the soap molecules that are sticking to him as well as to the water molecules around him. This will allow us to easily detach Bob from wherever he has chosen to take up residence and rinse him away along with the soapy water. Cool, huh?