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Figure 2. Both of these flames are burning ethylene gas...Click to Enlarge Image

In common lore, soot exemplifies all things black, dark and dirty. But without it, fire would not have its warm, yellow glow: Clouds of tiny soot particles within the flame radiate heat, enhancing its brightness. But soot's ability to act as an insulator can feed fire's heat back into itself, exacerbating large blazes in industrial accidents. It helps furnaces efficiently transfer energy to heating pipes, but it wastes vehicle fuel and escapes through tailpipes. Quantifying these effects requires a better understanding of soot's optical properties. Christopher Shaddix and Timothy Williams have attempted to find out just how "black" soot is. They collected soot from controlled fires, examined particles under microscopes and flowed soot-laden gases in front of lasers to measure how much light was extinguished. They have come up with solutions for how much light the particles absorb or scatter and have developed an index of refraction for soot. This could help in the understanding of soot's role in engines or the atmosphere and in gauging the temperature of fires in accidents.

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