Measuring Oxygen in the air? | English

This old experiment has a lot of misconceptions about it regarding the physical phenomenon that is at play here. In this video, we’ll learn the real scientific reason behind the candle and rising water experiment and debunk some popular myths about it.


In this simple experiment, you have a candle on a base (this can be any dish, plate, or flat container). Now you fill the dish with some colored water, do not burn the candle. If you take a glass and cover the candle by placing it upside down in the water, you’ll notice that water level is lowered as the glass touches the water. This is because the air in the glass is trapped inside the space between the glass and water surface. This indirectly shows that air has volume.
Now Light one candle on fire, and place the glass on the candle. The candle slowly extinguishes as combustion will consume all the oxygen in the air. As the candle is fully extinguished, the water level rises upwards. There is a common misconception that water level rises as the oxygen is consumed during combustion. But the actual rise in the level does not correspond to level of oxygen in the air at all! The rise is level of water must have other scientific explanation.
To check this, we now burn all three candles and place a glass above them. All of them will get extinguished and water level will rise much higher. This does not mean that more oxygen is being consumed as the amount of oxygen in the air is still constant. The air inside the glass gets heated due to burning candles which results in expansion of air. Expansion of the air causes the increase in volume which tries to escape by formation of bubbles on the surface of water. After the candle is extinguished, the air cools down, contracts and results in low pressure zone. Outside air is at higher pressure which pushes the water inside the glass towards the low pressure zone. This causes the actual rise in water level.
Combustion does not only consume Oxygen but also results in production of carbon dioxide which is a gas as well. This gas will also occupy volume inside the glass thus there is no reduction in volume because of combustion. The rise in water level is due to initial expansion of air, escaping of some air in the form of bubbles and eventually formation of low pressure zone in the glass as air cools down.
Hope you now understand this experiment and the interpretation of its results in a more scientific way. For more exciting experiments about math’s and science subscribe to or YouTube channel.
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Team: Ashok Rupner, Chaitanya Mungi, Neha Apte, Sajeda Sayyad_Shaikh, Pinki Saha, Students of NCL School Pune, Dr. B N Das