Bell's Demonstration

An Italian named Galvani was preparing to eat some frogs! He was hanging them from a copper hook on his porch. When the legs of the frogs touched the rail below, they jumped!  Since that time (almost 300 years ago),  when the muscles of an animal react to electricity, we call it the Galvanic effect.

Alexander Graham Bell used the demonstration below to show his grandson the Galvanic effects on an earthworm. Bell did many demonstrations for his grandchildren.  His life with these children is chronicled in the book Grampie, available at https://www.wakerobinpress.com/grampie.html#/

Materials Required

• Piece of aluminum foil

• Large coin

• Paper Towel

• Salt water

• Earthworms (Tiny ones work best--look under moist leaves or in rotting yard waste to find worms)

Procedure

1. Spread out a piece of aluminum foil on the table.

2. Prepare a piece of paper towel that is folded about 3 times the size of the coin

3. Wet the paper towel with salt water that is the most salty you can make it

4. Place a large coin on the wet, salty paper towel.

5. Put a little water on the top of the coin--just make it damp.

6. Place some tiny earthworms on the coin.

7. Observe carefully.

Here is a video. Watch what happens when one of the worms tests the environment beyond the coin:

8.  When finished with the exploration, return your worms (they will not have been harmed by this mild electrical shock) to where you found them...or, go fishing!

Discussion

The aluminum is one kind of metal and the coin is either zinc or copper or silver, depending on what coin you choose.  When we place two metals near one another and place an electrolyte (a liquid that electricity can pass through), it forms a electrochemical cell.  In the case above, the cell was measured at  0.6 Volts.  When the worm touches both sides of this cell, it completes a circuit--just like when you complete a circuit by placing a 9 volt battery on your tongue!

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