A Misinterpreted Experiment
A common version of the candle-in-jar demonstration involves
placing the jar upside-down in a dish of water, its lip submerged
but elevated above the bottom.
Because the rim is held
above the bottom of the
dish, water is free to flow
into the jar. After lighting
the candle and replacing the jar, the water level in the jar climbs
as water enters. It continues to rise after the flame goes out. In
a typical classroom setup, the water rises 15–20% of the way up
the jar. This percentage (15–20%) is tantalizingly close to the
the proportion of air composed of oxygen.