This is from a terrific site, Steve Spangler Science. I do many density demos and lessons and I am going to try this one this year.
“ProjectsFizz, Bubble, Erupt! Learn how to make an inexpensive science toy that will be a guaranteed hit with the kids! Ok, so everyone knows that oil and water don’t mix. Try adding a few drops of food coloring and a little Alka-Seltzer fizz to the solution and the bubbling concoction is guaranteed to provoke a few ooohs & ahhhs!”