Candle Aquarium

In a small glass box three candles of different length burn. Which one will go out first?

The tallest one!

How does it work?
When the candles burn, they produce carbon dioxide. Normally CO2 is heavier than air. We know this because every year winemakers suffocate in their cellars due to the accumulation of this gas. However, here the CO2 is hot because it is produced through combustion. It is therefore lighter than air and rises to the top of the box, suffocating the biggest candle first.