This beaker contains water tinted blue with food coloring and vegetable oil. The beaker is on a hot plate so the water is boiling, which simply enhances the visual effect of the two fluids separating.
The cool thing with density experiments is that you can do many of them at home. Try different fluids. If water and oil separate, what about milk and oil? Orange juice and oil? Liquid soap and oil? If something floats in water, does it also float in oil? What about sinking?
The possibilities are limitless. Just open your cupboard and open up your mind! Be careful with baking soda! It will react with vinegar and make a mess!