A small pan containing a candle and a pile of lycopodium powder is set up behind a metal jack-o-lantern cut-out. When you blow through a hose leading to the pan, a large fireball erupts. Great Halloween demo! And it demonstrates how the rate of reaction of solids increases with finer division of the substance.
This demo is usually presented in a unit on rates of reaction, but it makes a great Halloween demo. Check out the photo of the result of a grain mill explosion. Allow about 5 minutes for this demo.
The rate of reaction of a solid material depends on its degree of division and on how intimately it is mixed with other reactants. Lycopodium powder (the spores of the clubfoot moss) is very finely divided, but it does not react with the oxygen in the air until it is intimately mixed with air by blowing it into a suspension. This increases the area of contact between the reactants, allowing the combustion reaction to proceed explosively. Huge explosions sometimes occur in grain mills because of the presence of finely divided flour or grain dust in the air.
For info on grain mill explosions:http://www.buffalohistoryworks.com/grain/function/form.htm
- metal cutout jack o' lantern apparatus with rubber hose attached
- Pyrex Petri dish and cover
- lycopodium powder
- box of kitchen matches
- Place a couple of spoonfuls of lycopodium powder in the Petri dish.
- Light a match and extinguish it in the lycopodium powder.Immerse the match flame in the powder quickly or the powder will catch on fire. If it does, cover the Petri dish with its cover to extinguish the flame. Do not try to blow it out! It will erupt in a fireball if you blow on it!
- Place a couple of spoonfuls of lycopodium powder in the tray attached to the jack-o-lantern. Heap the powder around the outlet nozzle that the hose is attached to.
- Light the candle and place it in the center of the tray.
- Move as far as possible away from the apparatus and blow vigorously through the hose. A fireball will erupt.
- If the candle is still burning, remove it from the apparatus and blow it out. Do not try to blow it out while it is still in the apparatus! It will erupt in a fireball if you do!
- Remove all flammable materials from the area of the demonstration.
- Be sure that a fire extinguisher is readily available.
- DO NOT try to blow out burning lycopodium powder. It will erupt in a fireball if you blow on it.
- Do not let your face get close to the apparatus when you blow through the tubing.
- If the candle is still burning after the fireball erupts, DO NOT attempt to blow it out while it is in the apparatus! You will raise a cloud of lycopodium dust that could explode in your face. Remove the candle from the apparatus to extinguish it.
- Wear goggles.