light Karo syrup

honey

dish soap (blue or green)

water

oil

rubbing alcohol

tall clear glass or vase

food coloring

Add food coloring to the water and rubbing alcohol; use colors that will stand out in your rainbow.  Beginning with the Karo syrup, gently pour equal parts of each liquid into your cylinder.  Each will form a layer that does not mix!  The Karo syrup is the most dense liquid; the rubbing alcohol is the least.

Extensions: 

Try pouring the liquids in a different order; some will sink, some will float to the top!

Try making colorful play bottles by pouring oil and colored water into old water bottles.  Add glitter to make the bottle look really cool!  Screw on the lid tightly and shake.  The oil and water will eventually mix, then separate again over time.

Liquids have different densities.  Less dense liquids will float on top of more dense liquids.  For example, both water and vinegar are more dense than oil.  That's why when you make salad dressing the oil floats on top.  To mix them together, you have to stir or shake them with enough force to form an emulsion!