DIY Amazing Density Tower from Things Found in Your Kitchen by stevespanglerscience: Make objects float in the middle of a liquid with this amazing trick. The idea is cool, but you need a tall glass (a vase?) and lots of each liquid to make it look good.
Cool Experiments: Exploring the Density of Liquids. Put water in a clear cup, and add oil. Add a few drops of food coloring. The food coloring floats until you add a pinch of salt, then it sinks through the oil like a lava lamp.