Science | Science Experiment of the Week 10 | 304 - Observation of a Candle

Chemical History, Burning Wax, Flammable Gas - Some of the marvels involved in the burning of a candle.

This Week's Experiment - #304 Observation of a Candle

These experiments are from Robert Krampf - The Happy Scientist

With the holiday season, I am once again rereading Michael Faraday's Chemical History of a Candle. You can find the entire book online at http://www.bartleby.com/30/7.html. This week we will take a few minutes to look at some of the marvels involved in the burning of a candle. You will need:

a candle
a candlestick or holder
a lighter or matches
metal tweezers or needle nosed pliers
an adult (as this experiment uses fire)

Place the candle in the holder. Light the wick. Watch carefully for a minute or so. What do you see? You probably noticed that the wick does not burn up. If you removed it from the candle and lit it, the wick would be consumed by the fire very quickly. Why does the wax make it last so much longer? To find out, use the tweezers to pinch the wick, just below the flame. What happens? The flame goes out. Why? The candle flame melts the wax, which soaks up into the wick, just as water soaks up into a paper towel. As this melted wax gets closer to the flame, it breaks down into a variety of chemicals, producing a very flammable gas. It is this gas that you see burning. When you pinch the wick, the melted wax cannot rise up to the flame. The fire runs out of fuel and goes out.

You may also have noticed that the melted wax forms a nice pool around the wick. How does the candle form the cup shape to hold the liquid wax? The flame heats the air. This air expands and rises. Air from below the flame moves up to take its place, where it will also be heated and rise. This forms a steady flow of air up the sides of the candle. The flow of air cools the outside of the candle, keeping the edges solid as the center melts. That forms the bowl to hold the melted wax. This only works well if there are no breezes blowing across the candle. Wind blowing from one side cools that side while disturbing the rising air which would cool the other side. The side towards the breeze forms a high wall of unmelted wax. On the side away from the breeze, the rising air is disrupted. This lets the wax melt all the way to the side of the candle. The melted wax can then run out, dripping down the side of the candle.

The upwards flow of air has an impact on the flame itself. Most of the flame is yellow, indicating that it contains many particles of carbon burning in a low oxygen environment. If there were plenty of oxygen, the carbon would all burn and the flame would be blue. The very base of the flame is getting plenty of oxygen, due to the upwards flow of air. If you look closely, you will see a small blue area of flame at the very lowest part.

This is only be beginning of the science involved in burning a candle. To learn more, read some of Faraday's lecture. It is fascinating science and amazing how well Faraday could explain it. In the mean time, have a wonderful holiday season.

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