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The Science of Fire

Everybody loves fire, but what is fire, scientifically speaking? Everyday Einstein looks at the science of fire. Plus—a fun fire experiment you can do at home!

By
Lee Falin, PhD
Episode #008

An Eternal Flame

Once the rapid oxidation has started, energy is released from the reaction in the form of heat, light, and other radiation. This is what normal people would call a flame. The shape, size, color, and makeup of a flame depends upon many complicated factors. For the most part, flame color can be thought of as an indication of flame temperature and fuel composition. For example, red flames are cooler in temperature than blue and white flames.

A fun experiment you can do at home is called a “flame test." A flame test is used to identify the composition of unknown metals. When metal ions get hot, they start to emit light of a predictable color called an emission spectrum. For example, copper makes a blue-green flame whereas calcium is usually dark-red.  

An easy way to perform a flame test is to coat a small piece of wire with some metal salts. The most common metal salt in normal people’s homes is Sodium Chloride, or table salt. Hold the coated metal loop over a flame (the flame from a propane torch works best), and you should see it turn bright yellow, indicating that sodium is present. If you have other metal salts, such as calcium chloride or copper chloride, you can see other colors as well.

You may have heard that burning driftwood causes blue and purple flames; this is because of the metal salts absorbed by the wood. As a precaution however, driftwood fires give of large amounts of dioxin, which are carcinogenic. So be careful around driftwood fires. Don’t try to start one up in your kitchen.

Conclusion

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Fire image courtesy of Shutterstock

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About the Author

Lee Falin, PhD
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