The rising water experiment illustrates the effects of the expansion and contraction of air in a system. Pour water onto a plate and place a candle upright in the middle of the water-filled plate. Light the candle and place an inverted jar over the lit candle. As the candle heats up, the air inside the jar expands and escapes from the bottom, causing the water to bubble and the pressure outside of the jar to rise. When the candle flame goes out and the air begins to cool, pressure inside the jar drops and a vacuum is formed. As a result, water from the plate rises in the jar. The change in pressure, and not consumption of oxygen in the jar, is responsible for the rise in water level.
This experiment is designed to clearly show that if you light a candle inside a jar, it is not the consumption of oxygen that makes the flame go out, but rather the change in pressure. Place a large inverted jar over a lit candle and a mouse. Seal the jar. After some time the candle's flame will go out, but the mouse will not die. This proves that it is not the consumption of oxygen that extinguishes the flame, otherwise the mouse would have suffocated.
The fire extinguisher experiment demonstrates the basic principle firefighters use to fight fires; specifically that by removing one of the elements that creates fire you can eliminate it. Light a candle inside one glass jar. In another glass jar combine two tablespoons of baking soda and 1/5-cup of vinegar. The mixture will foam; add it to the jar with the burning candle, being careful not to let the liquid touch the wick. The candle flame with extinguish. The vinegar-baking soda combination produces carbon dioxide, which cannot be combusted by the flame. When the carbon dioxide rises to the level of the candle flame it displaces the oxygen, thus removing it from the equation and making the production of fire impossible.
The air composition experiment uses candles and jars to demonstrate the different makeup of fresh air versus exhaled air. Light two candles and place two separate inverted jars over the lit candles. Use a straw to blow air into one of the jars and then seal both jars. The candle in the jar with the exhaled air will go out first. Exhaled air is made up of less oxygen then fresh air, therefore the jar with the air blown into it through the straw will have less oxygen for the fire to consume. Once the flame consumes all the available oxygen it can no longer stay lit.