A fun way to examine the principles of density and immiscible liquids (fluids that just won't mix) is by creating a homemade version of that classic mind-expanding device, the lava lite.
PSYCHEDELIC SCIENCE MATERIALS:
Glass jarWater with food coloring added
Vegetable oil
Shaker filled with salt
TO DO:
Fill a glass jar with about 3 inches of water and add food coloring until the shade matches the
tapestries in your pad. Add 1/3 cup of vegetable oil and wait until the layers settle. Watching carefully, shake salt into the jar while you count to five. The oil and salt should form a glob and sink to the bottom of the jar. As the salt dissolves in the water, the oil should float back to the top. Keep adding more salt to watch the action repeat. As you sprinkle on the salt, watch the globs of oil sink, rest on the bottom, then rise again.
WHAT'S GOING ON & WHY:
At first, the oil floats on the water because it's lighter--or, more accurately, it's less dense than the water. It also doesn't mix with water, so it won't dissolve. The salt, however, is denser than the water and does dissolve. When you shake it onto the oil, it clings and drags a glob to the bottom. In time, however, the salt starts to dissolve in the water. At a certain point, it can no longer hold down the oil blob, which then floats back up to the surface.
