Originally published in Popular Science Magazine, reproduced with permission of the magazine and the author (that would be me).

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Playing With Poison

Mercury used to be lots of fun--before we knew that it could kill you. Here's how several pounds of it made the first electric motor spin

There are great things to come in the future, jet cars and all that. But the past held a few wonders tooa^\200'for example, jars of mercury available at the corner apothecary. Just 50 years ago, people treated the shiny liquid metal like a toy. Sadly, Ia^\200\231ll never experience the strange sensation of sticking my entire arm into a barrel of mercury, as kids once did during factory tours. Today mercury is considered a horrific poison, so bad that schools are evacuated for a broken thermometer.

Of course, mercury didna^\200\231t become more poisonous; we just learned more about it, including the fact that breathing its vapors can lead to brain damage. The Mad Hatter of Alice in Wonderland fame was mad (crazy) because of the mercury compounds used in hatmaking.

But mercury can do more than amuse you and destroy your brain. As one of the few liquid metals, ita^\200\231s also the best liquid electrical conductor. So with big ventilation fans, latex gloves, and catch basins under everything, I used a 60-pound pool of it to re-create the first electric motor, invented in 1821 by Michael Faraday in his basement lab in London.

The motor works by running an electric current through a wire that hangs next to a magnet. This setup generates an electromagnetic force that drives the wire in circles. But to get current through the wire, you need a connection at both ends, so Faraday used mercury, which allows the loose end to move freely. (Back to the present: None of the supplies I used can ever enter a kitchen again.)

Although Faradaya^\200\231s motor is essentially useless, ita^\200\231s the simplest possible design for a device that turns electricity into rotary motion, a wonderful proof-of- concept both that electric motors are possible and that mercury is still neat stuff.

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In this simple electric motor, current running through the wire into 60 pounds of mercury causes the wire to revolve around a magnet.

The Nonlethal Version

If you don't have a banana hook and a big bowl of mercury, you can make a motor that operates on the same principle by hanging a screw from an AA battery with a strong neodymium magnet. Touch the wire gently to the magnet to make it spin. Get a kit for this motor at scitoys.com.

Photo Credits:
Mike Walker
Mike Walker