Joshua and I made an eruption (sans volcano) out of baking soda and vinegar. He was super excited about it!
I had never done this before so I think my proportions were off, but it was still cool.
What we did:
Emptied out a 20 ounce gatorade bottle. Filled it most of the way with hot water. Put in several teaspoons of baking soda. Poured in some vinegar and then watched it erupt.
Then we added more baking soda and more vinegar. And more baking soda and more vinegar. And more baking soda and more vinegar.
I bought two more boxes of baking soda the last time I went to the grocery store so we can do it again. And again. And again.