Kids, have you ever wondered how those trick birthday candles work the ones that keep re-lighting themselves after they are blown out? All you need for this month¹s experiment is a regular birthday candle, a "trick" birthday candle, matches, and an adult partner to light the candles for you.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
To understand trick candles, you need to first understand how normal candles work. The key difference lies in the moment after the candle is blown out. In a normal candle, a smoldering ember in the wick causes a ribbon of paraffin wax smoke to rise from the wick. While the ember is plenty hot enough to vaporize paraffin, it is not hot enough to ignite the paraffin vapors coming off.
The key to a trick candle, then, is to add something to the wick that the ember is hot enough to ignite. After this material is ignited, the wick becomes hot enough to light the paraffin vapors. The most common wick additive is a metal called magnesium. Magnesium happens to burn (which means to combine with oxygen to make light and heat) really quickly at a fairly low temperature (low for fires anyway, at 800oF/430oC). Aluminum and iron metals both burn pretty well too, but they need higher temperatures.
Inside a burning wick, magnesium is shielded from oxygen and cooled by melted paraffin. But once the flame goes out, the ember ignites magnesium dust. If you watch the ember closely (and carefully!) you¹ll see tiny flecks of magnesium flicking off. Just one of these is needed to provide the heat that can re-light the paraffin vapors, and the candle flame comes back to life. You won¹t see this happening to the wick of a normal birthday candle. Check out these interesting weblinks for more information: www.howstuffworks.com/question267.htm describes how regular candles work, and www.delphion.com/details?pn=JP58049830A2 has the original 1983 Japanese patent on trick candles.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
June 2001
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Reference: Marshall Brain¹s "How Stuff Works" website (with video) at www.howstuffworks.com/question420.htm.
