Place half of a lemon onto a plate, tray or bowl that will contain the mess when it erupts.
Using a craft stick, poke holes in the sections of the lemon to aid with the reaction.
Place drops of food coloring in the sections to add color.
Pour dish soap all over the top of the lemon (This will add foam and bubbles to the reaction).
Sprinkle baking soda on the top of the lemon and press it down with a craft stick to create the reaction.
The reaction may take a few minutes, and you can add more baking soda to continue it.
Science Behind It
The citric acid in the lemon reacts with the baking soda, which is sodium bicarbonate. The reaction, a double replacement acid-base neutralization, creates a compound that dissolves in water and carbon dioxide gas.
Erupting Lemon Video
Tips
You'll have to wait a few minutes for the reaction to work. If you want to, you can add more baking soda, as this will continue the reaction.