Dung Power
What you need
- A tin can of 10 to 15 litres, with no hole in it anywhere except the mouth
- 3 to 5 kg of fresh, wet cow dung
- A rubber cork that fits the can's mouth tightly, with one hole bored through it
- A funnel
- String
- A rubber tube — the kind used for a blood transfusion is the right size
- A bucket or wide container for mixing
- 3 litres of water
- A hypodermic needle that fits the end of the tube
The manual states these. What it does not state is not here.
How it runs
The teaching sequence as the manual gives it.
-
01
Set up outdoors in the school compound, or in a laboratory with the windows open. You need a clean tin can of 10 to 15 litres with no holes in it except the mouth. -
02
Find a rubber cork that fits the mouth tightly. Bore one hole through the cork, just wide enough for the tube to pass through. A blood transfusion tube is the right size. -
03
Ask students to collect 3 to 5 kg of fresh, wet cow dung. Put it in the container, add 3 litres of water, and stir it well with a stick until it is an even slurry. -
04
Pour the slurry into the tin can through the funnel. Push the tube through the hole in the cork and fit the hypodermic needle onto the tube's outer end. Close the can tightly with the cork. -
05
Tie the tube shut with the string so that no gas escapes through the needle. Leave the can standing, undisturbed, for 24 hours. -
06
Keep the windows open the whole time, so any gas that leaks goes out of the room. The next day, loosen the string. Students should be able to smell the gas. -
07
Now the flame. The teacher does this step, not a student, and the class stands well back. Bring a lit matchstick close to the opening of the needle, from the side and never over it. The gas burns with a small flame. That flame is methane, made by bacteria out of dung, in a day.
Safety
- THIS ACTIVITY MUST BE DONE WITH EXTREME CAUTION. THE GAS IS METHANE AND IT IS FLAMMABLE. DO IT OUTDOORS, OR IN A ROOM WITH THE WINDOWS OPEN THROUGHOUT. THE TEACHER LIGHTS THE MATCH, NOT A STUDENT, AND THE CLASS STANDS WELL BACK. NEVER BRING A FLAME NEAR THE CAN ITSELF — ONLY NEAR THE NEEDLE. NEVER HEAT THE CAN.
Talking about it
Discussion points, worked examples and the handouts the manual prints with this session.
Points for discussion
Talk about what this gas is and what it can do — cooking, lighting, running a small engine. Then ask the harder question. The dung was going to be there anyway, so what else that the school throws out is already fuel? Wet waste from the canteen is the obvious candidate.
Ending it
How the manual closes this session, and where it can go next.
If it goes well
Dung from buffaloes, goats and other animals works too. Across rural India, gobar gas plants run on exactly this — animal dung, and in some places human waste as well — and the gas comes out on a kitchen stove.
Stand the can in cold water for a while and gas production slows down. Bacteria work faster when it is warm. This is also why a compost pit behaves differently in May and in January.
Where this comes from
Bridge the Gap is a compilation. This is what the manual records for this session.
The manual prints no source for this session. It is published here as Swechha has used it, adapted over years of classroom work; if you recognise its origin, tell us and we will credit it.
Before you start sets out where the compendium as a whole comes from.
Next
Where to go from here.