Exploding Can

I saw Peter Cattermole from Winchester College use this apparatus in the mid 1980’s, he claimed the cocoa can had been in the science department as long as he had!

We use a catering size instant coffee can with an attached glass tube chimney. The dimensions are shown on the diagram; the hole sizes and tube diameter are fairly critical so you may need to experiment.  The glass tube fits inside a tin collar tube soldered to a hole in the side of the can.  We use gaffer tape to seal the glass tube in the collar.  I not sure that the flap over the gas entry hole in the end of the can is essential.

Methane (or natural gas) is passed into the can by means of a rubber tube inserted in the hole in the end of the can.  You need a good flow of gas to flush out all of the air.  Turn off the gas supply and remove the tubing.  

Light the gas at the top of the chimney; you get a lovely yellow flame indicating incomplete combustion, insufficient oxygen in the surrounding air diffusing into the reaction front to completely burn all the carbon.  However as the low density methane continues to rise up the chimney, air is drawn into the can to produce an air/methane mixture which burns at the chimney top.  The flame slowly changes, becoming small and blue as the reaction becomes faster as sufficient oxygen is available to oxidise all the carbon.  After developing the typical “blue cone flame” of the gas cooker, the flame reduces to a blue ring and “strikes-back” down the chimney; the rate of reaction being faster than the movement of the gas mixture up the tube.  The flame accelerates down the chimney and ignites the gas/air mixture in the can, which gently explodes, blowing the lid across the floor.  

The audience are usually surprised; a nice finale to a visually interesting experiment illustrating lots of chemistry.  Choose your words and level of explanation to the suit the audience.  We light the simpler version of this apparatus, a similar can standing on a tripod with a small hole in the lid and a larger gas entry hole in the base, before we start the experiment described.  This reaction is slower but the flame at the hole in the lid goes through the same sequence of changes and is small and blue after the first can has exploded.  The audience now knows what to expect and the second explosion is usually louder, firing the lid high into the air.

Safety Important Note These notes give an outline of demonstrations intended for suitably qualified people.  As such, some safety precautions are not listed. The demonstrator should make a full risk assessment before use and ensure that the demonstration is safe to carry out.

Newsletter Spring 1998 Contents

Centres > Satrosphere News | What is happening to Light on Science? | Inspire News | Herstmonceux News

Exhibits > BIG working group on exhibit development | What is Design? | Exhibit Aphorisms | "Here's Looking at Euclid" - exhibit idea | Roald Dahl and the Children's Gallery | Are hybrids best? - viewpoint

Demonstrations and shows > Shows at the Exploratory | Exploding Can Demonstration | Water to wine Demonstration | Nitrogen story - urban myth?

Millennium News > More Millennium Grants | Pantechniques rewarded | Millennium awards scheme | A listing of interactive projects funded by lottery grants

Research > Measuring the performance of interactive centres

Resources and conferences > Conferences and Future Events | Indian Science Congress Report | Managing Science Centres Book Review | Children's Museums Book information

BIG > BIG Moves - From the Chair | BIG AGM Report | BIG Annual Report 1997