Exploding Flour Tin

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Purpose -

A fantastic way to show the following concepts -

· the variable nature of a flammable substance in different conditions

· the increasing rate of reaction with a greater surface area

· the forces created by holding a reaction under pressure

Nature - 

Demonstration

Materials - 

Tin with a metal sealing lid (e.g. baby formula tin), hammer, metal punch, 2 m of vinyl tubing, small plastic funnel, candle stub, tripod, taper, matches, flour, spoon or spatula

Method - 

· Punch a hole in the bottom of the tin, a bit off of centre.  The hole needs to be the right size for the vinyl tube to fit snugly through.

· Force the vinyl tube through the hole so that about 3 cm is inside the tin.

· Jam the funnel snugly on the end of the tube inside the tin.

· Set the tin on the tripod and place the candle stub in the tin next to the funnel.

· Load a couple of spoons of flour into the funnel.

· Light the taper, and use it to light the candle stub.

· Quickly seal the top of the tin and (before the candle has time to go out) blow on the other end of the tube.

The flour should fill the tin and a loud bang be produced sending the lid up to the ceiling!

Safety -

Keep clear of the lid as it flies upwards and a flame erupts from the tin

Explanation -

Flour is an unusual substance because it requires a lot of air, and a great deal of surface area before it will ignite.  Once it has both of these though, it is quite explosive.

Notes -

It is best to complete steps 1 to 3 before class and leave the apparatus set up for quick use in future.

I usually make a small pile of flour on the bench first, and try to light it to show the low flammability of flour before going on to steps 4 to 8.  This is good fun to act really casual about so that when it does go off, it comes as a surprise to the class. 

A variation of this is to set up the hose and funnel to blow across a candle flame outside of the tin so you can see a flame-thrower effect.

Occasionally flour silos will explode under similar, though larger, circumstances