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In this activity, candles of varying heights are placed and lit inside an open top glass walled container. An empty aquarium, terrarium, or clear glass vase can be used. Then sodium bicarbonate, or baking soda, and diluted acetic acid, or vinegar, are added to the bottom of the reaction vessel. This reaction creates carbon dioxide, which is non-combustible, and heavier than other gasses in the atmosphere, so it remains at the bottom of the vessel. As the CO2 quantity rises, the candles will be extinguished in order from shortest to tallest.