Apart from being just holy, cow – dung (and urine), has served Indian villages for a long time, in terms of its usefulness. It is used as a fertilizer, as a fuel (for cooking!!), for maintaining mud floors, as mosquito repellent, as an antiseptic and some people are even using it as a soft drinks (using cow-urine)!!! Unfortunately in this article I will only talk of a rather uninteresting usefulness of the cow-dung. I will talk of using cow-dung to produce electricity. Here goes its recipe:
Take a lump of cow-dung (approximately 500gm) in a container. Then mix adequate water to make it creamy/buttery (say about 150 mL of water). Now add some salt (4 spoons) and mix it well with the cow-dung. Now take some tamarind (250gm will do it) and mix it well with the previous mixture.
Take some old batteries and take out the carbon rods. Collect 4-6 of them.
Now collect some old cans (pepsi or cocacola) which are made of aluminium. Other Aluminium containers can equally be used. Instead of aluminium you can also use zinc (which would be better in terms of producing electricity), which can be obtained from old batteries (the shell of a AA battery is made of zinc).
Now put some mixture in the aluminium cans. Insert one carbon rod into the mixture in each of the aluminium container. Make sure that the carbon rod do not touch the aluminium can.
Now connect a wire to the can and another to the carbon rod. Here the carbon rod is the Cathode (Positive teminal) and the aluminium container is the Anode (Negetive terminal).
The mechanism of this cowdung battery is simple. Cow-dung is acidic (contains uric acid) and so is tamarind (tartaric acid). Aluminium has three electrons in its valent shell, and in the acidic conditions it leaves them in itself and comes out into the mixture as Al3+. Dissociated Chlorine ions (as the salt, NaCl, disociates into Chlorine and Sodium ion) combines with Aluminium ions and forms Aluminium chloride (AlCl3). So gradually the electron density in the aluminium metal container increases.
On the other hand the H+ ions, which disociated from the tartaric, uric and other organic acids that are present in mixture, collects one electron each from the carbon rod. Thus the electron density gradually falls in the carbon rod. The nutral H atoms later combine to produce H2 gas.
The difference in the electron density between the carbon rod and the zinc results in an EMF, which is responsible for the electricity in these batteries.
Make 4 of these batteries and connect them in the parallel configuration. Then connect a LED to light it up!
When we made it, each cell typically produced roughly 1.3V.
This video may help you more.