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Lycopodium powder is a fine yellow powder derived from the spores of Lycopodium clavatum (stag's horn club moss, running ground pine). When a lighted match is dropped into a pile of this powder, it does not burn. However, when the powder is dispersed into a fine mist near a candle flame, it ignites into a spectacular fireball. This results from an increasing the available surface area for combustion: when the powder is dispersed into a mist, the particles are surrounded by enough oxygen to support a combustion reaction.
This demonstration illustrates the basic principle behind a grain elevator explosion. Grain dust, like lycopodium powder, is not especially flammable, but when grain is dumped into a grain silo or elevator, some of the finer dust particles can remain suspended in air, surrounded by oxygen. The mixture can be ignited by a spark or flame, resulting in a devastating explosion. (For more information, see the following web sites: Kansas Grain Elevator Photographs and a National Materials Advisory Board report on grain elevator explosions.)
In the video clips below, a match is first dropped into a pile of lycopodium powder in a watch glass, whereupon the match is almost immediately extinguished. In the second part of the demo, the same powder is placed through a funnel into a rubber tube, with a glass pipette at the other end. When the powder is blown through the pipette past a candle flame, the powder bursts into a fireball.
Video Clip 1: REAL, 3.25 MB
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Video Clip 2: REAL, 535 KB
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!!! Hazards !!!
Lycopodium powder is flammable when dispersed into a fine mist. Usually, with this procedure, the flame burns out too quickly to light any other combustible materials, but caution should be exercised nonetheless.
Procedures
Explosions of Lycopodium and Other Powers: Bassam Z. Shakhashiri, Chemical Demonstrations: A Handbook for Teachers of Chemistry, Volume 1. Madison: The University of Wisconsin Press, 1983, p. 103-105.
References
Entry on Lycopodium clavatum from Flora, Fauna, Earth, and Sky...The Natural History of the Northwoods (link)
Entry on Lycopodium clavatum from Ulster Museum, Flora of Northern Ireland (link)
Martha Windholz (ed.), The Merck Index, 10th ed. Rahway: Merck & Co., Inc., 1983.
