Measuring the Oxygen in the Air?

In this experiment, a burning candle is placed in a plate filled with water. When a transparent glass is inverted onto the candle, the candle extinguishes after some time and the water level inside the glass rises. When the same experiment is repeated with two burning candles, the water level rises more than in the first case. When repeated with three candles, water rises more compared to the other two. This is not an experiment of measuring oxygen level because the amount of oxygen supplied was the same in all three cases, which is whatever was available in the volume of air trapped in the glass. While placing, some gas escapes the glass as air expands due to heat. When glass is inverted onto the plate, the seal between the plate and glass rim is not airtight. Hence, as the candle burns, air escapes in the form of small bubbles through the glass rim. When oxygen inside is depleted to a level below the required level for combustion, hot air inside the glass cools and pressure drops, and it sucks the water in. When using two candles, due to more heat, more air escapes during covering, and more air escapes when covered. This process happens most effectively when 3 candles are used. 

Learning Objective:
To understand the composition of air by measuring the oxygen content through combustion and observing the resulting changes in air pressure and volume.

Keywords:
Oxygen content, Air composition, Combustion, Air pressure, Gas behavior