We really love the good old erupting volcano using baking soda and vinegar but since our sand box is snowed in I wanted to try an indoor, mini version. I poured baking soda into a tin baking tub. Then we put vinegar in little cups with a little food coloring. Using pipettes (droppers), we dropped the vinegar into the baking soda causing little eruptions. It was super fun and exciting and we ended up using an entire box of baking soda. My son kept yelling "look, I'm making carbon dioxide". It also makes a super, slimy mixture that is fun to stir and mix.