1- In your container of choice, we used a tall thin glass vase, add two parts Vegetable oil, to one part water. You can see from the first image, which Caitlin thought was awesome, that water and oil really do not mix. Be sure you leave room at the top of your container for the bubbling action.
2- Add 2-3 drops, of your favorite color of food coloring. Caitlin added three drops, of all four colors, lol.
3- Observe what has already happened. Check out the pictures.
4- Add Alka Seltzer tabs one at a time. You can see that it immediately starts to work. The Alka Seltzer, oil, and water, all react in a way that makes a rolling bubbling show. Caitlin added a total of 4 tablets. One tablet created big fat bubbles, that kind of rolled and lifted slowly. The more tablets you add the faster, and smaller the bubbles will go up.
All in all, and easy and fun, Chemistry experiment. I got the original idea, here.