History of Soap

   
    Soap is a cleansing agent that has a very interesting, but rather sketchy, history dating back to more than 4000 years ago. First invented by the early inhabitants of the Mediterranean area, soap was not originally used for washing or cleaning, but as a method for dressing hair and administering medicine to wounds. The first soaps were made from fats and oils rendered from animals and mixed with the caustic run-off water from fireplace ashes. The chemical interaction of fat and the sodium hydroxide leached from the ashes (also called Iye) created a harsh, but effective, brown soap.

    To produce a purer soap, the curds are washed with salt solution, water is later added, and the solution is allowed to settle; the upper of the two layers thus formed is the pure soap, called settled soap. It is thoroughly churned, poured into huge frames, cut with wires, shaped, and stamped. Soap is sold also as chips, flakes, and beads and in powdered form. Soap powders, as distinguished from powdered soap, contain builders that assist in rough cleaning, such as detergents like Tide and Gain. Soaps differ according to the lathering properties of the fat or oils and according to the alkali employed. When sodium hydroxide is used as the alkali, hard soaps are formed; potassium hydroxide yields soft soaps.

How Does Soap Identify Dirt  

When you think about soap, you would think it has all the properties it needs to tell dirt from everything else.Hmmmmm!?!  How does soap really know what to clean?  Simple as it may sound, nearly everything we label as dirt  or dirty has/is either a oily substance or is stuck to oil. What gives soap the special ability to remove oil?

How Dirt Sticks

Anything we don't want attached to us (i.e.. dirt) can be stuck to us in one of two simple ways.

1. trapped in microscopic crevices. For instance the dirt you get on a dry dusty road.
2. or moisture makes it adhere. For instance the dirt you get from a muddy road.

But what if the dirt particles have a slightly oily coating? They will stick to your skin like wet mud. In addition, the dirt doesn't have to even bring its own oily coating. Your skin many times has enough oil on it to make dirt particles stick. But unlike the mud, this dirt is going to stay stuck because oil doesn't evaporate and dry up as water does. Nor will a spray of plain water dislodge it because it will simply roll off the dirt as water rolls off the oil. Assuming that the force of water isn't sufficient enough to dislodge the oil of course.

Removing Oil Substances

To unstick the oil adhering dirt is to seek out and destroy the sticky oil itself. A liquid can then be applied and the dirt will fall off and be swept away.

You could fill a sink with alcohol, kerosene, or gasoline as they are all good solvents for oil. In fact dry cleaners tumble our clothes in a barrel full of a solvent such as perchlorethylene an organic solvent that is a phenomenal dissolver of oil. The problem with these solvents is they are all toxic to greater degrees.

The answer is soap. But soap doesn't really dissolve oil like solvents do. It works by enticing the oil into the water so the oil and its dirt can be flushed away. It also disturbs the surface tension of water. In other words, it makes water lay flatter and not ball up like a rain drop. This allows the water to get into micro crevices even better and wash away the dirt.

But How Does Soap Work Then

Soap molecules are composed of long chains of carbon and hydrogen atoms. At one end of the chain is a configuration of atoms which likes to be in water (hydrophilic). The other end shuns water (hydrophobic) but attaches easily to grease. In washing, the "greasy" end of the soap molecule attaches itself to the grease on your dirty plate, letting water seep in underneath. The particle of grease is pried loose and surrounded by soap molecules, to be carried off by a flood of water.

In a soap-and-water solution the hydrophobic (greasy) ends of the soap molecule do not want to be in the liquid at all. Those that find their way to the surface squeeze their way between the surface water molecules, pushing their hydrophobic ends out of the water. This separates the water molecules from each other. Since the surface tension forces become smaller as the distance between water molecules increases, the intervening soap molecules decrease the surface tension. If an over-filled cup of water were lightly touched with a slightly soapy finger, the pile of water would immediately spill over the edge of the cup; the surface tension "skin" is no longer able to support the weight of the water because the soap molecules separated the water molecules, decreasing the attractive force between them.

                                                               

If you did not fully grasp that information you read above continue reading, if you understood the information it is time for you to move on to the experiment.  

Soap molecules are long and stringy just like oil molecules are. They have two very distinct ends. The head of this soap molecule string loves water and will attach to other water molecules. Its tail on the other hand loves oil and will search out and attach to other oil molecules. (See the picture above and below)  This gives us a very interesting situation where the head of the soap molecule will attach to other water molecules and the tail will find and attach to other oil molecules. The effect is that the soap molecule will latch onto the oil with its tail and be flushed away with other water molecules attached with its head. To make matters even better, soap molecules disrupt the surface tension of water by crowding around the water surface with their water loving heads which disrupts the waters ability to stay tightly coupled together in a sphere like a rain drop. So in a way it flattens waters ability to remain in this sphere configuration and makes the water molecules flatter thus wetting everything even the smallest crevices.

              

Are you really coming clean when wahsing your hands.  Let's see.