Wow. That title is a bit of a mouthful, eh? But the good news is this: this experiment has become a kid-science standard because it is actually quite easy to execute, is a great introduction to the concept of liquid density and, it looks pretty when you are done. An all around winner.
I've seen this experiment done with as many as seven or eight different liquids. You can certainly add in additional liquids (such as corn syrup) for more layers, but I decided that in the interest of being able to get the experiment done while the baby was napping (and with minimal mess) we'd just go with four. It goes like this...
What you will need:
dish soap (colored)
canola or vegetable oil
clean jars or glasses for mixing (we used 1/2 pint canning jars)
larger sized jar (we used a one pint canning jar)
What you will do:
Begin by filling the larger jar with about 1/4 cup of the dish soap. We happened to have some green dish soap on hand, so I used that and then didn't need food coloring in this first layer. The colors of each layer aren't important, but the order in which you pour the liquids really is. Also, pouring liquids slowly and through a funnel proved to incredibly useful and I'd definitely recommend that.
Mix 1/4 cup of water with food coloring of your choice. We used blue because we thought that it would work nicely against the green dish soap. Using the funnel, slowly pour the water into the jar on top of the dish soap.
Next pour 1/4 cup of vegetable oil into the jar on top of the water and soap. Pour this slowly and carefully so that you don't disturb the other layers any more than necessary. The vegetable oil is difficult to mix color into, so don't bother. Just leave it in its natural state.
You can see here that pouring the vegetable oil into the jar did disturb the layers a bit, but this is the beauty of this experiment. As long as the layers aren't totally mixed into each other by the force of the next liquid pouring from above, they should sort themselves out (which is both fun to watch and the entire point of all of this).
Finish up by mixing red food coloring into 1/4 cup of rubbing alcohol and then carefully pouring this solution into the jar. This will leave you with four layers in the jar. They will be a bit muddled from the pouring action, so set the jar aside in a well lit location where you can watch the layers begin to separate more cleanly.
What's at work:
Different liquids have different densities (mass per volume) and therefore, different weights. The heaviest liquids will sink, the lighter liquids will rise to the top. So, dish soap is heavier than water which is heavier than oil which is heavier than rubbing alcohol. And we all just learned something new- awesome!