This was a super fun experiment, we used an entire box of antacids. We used some 35mm film canisters that I have had stored for awhile. You could use any little container that seals. The kids filled them about 3/4 full of water, dropped in an antacid tablet, snapped on the lid and ran. The tablet and water create CO2 which makes the lid pop off. It is soooo fun. I was so happy that I actually captured the POP on film, it happens so fast. We counted how long it took each one, though we didn't get past 5.