You gotta love it when science goes goth. Gallium, a silvery metal, can be made to pulse like a living heart when touched with an iron nail. Take a look at a robot's heartbeat, and find out how this metal heart works!
You don't hear about gallium much. In part, that's because it's not found in large quantities in nature. But that's also because it's not a very useful metal. It's too easily melted. One trick that chemistry teachers do is make spoons out of gallium that dissolve when put in hot tea. When it's put in hot sulfuric acid, it melts right down, too. But unlike tea, sulfuric acid keeps gallium together in one piece. As the gallium melts, its outer layer combines with the sulfuric acid to form gallium sulfate. Gallium sulfate has a strong cohesive property - all of its molecules will cling tenaciously to all its other molecules. This skin of gallium sulfate will cause the melted gallium to pull together into a ball, a little like a drop of liquid water beads up on a wax surface.
When the gallium is touched by a piece of iron, it will suddenly relax, spreading to a pool instead of a ball. When the iron is removed, the gallium springs back up into a ball again. Position the iron just right, and the gallium will stop touching it as it relaxes, and spring back up to touch the metal again, pulsing like a heart.
How does this happen? The gallium isn't the only thing being affected by the sulfuric acid. The metal is dissolving and giving off electrons. When those electrons come in contact with the gallium sulfate, they grab hold of the sulfur and the oxygen atoms, leaving the gallium on its own again. Since gallium doesn't have the same cohesive force as gallium sulfate, the entire ball relaxes. As soon as it's not in contact with the metal, the gallium sulfate skin forms again and makes the gallium contract again. And so it keeps pulsing until the sulfuric acid dissolves enough gallium, or iron, to stop the connection.
A cooler, but tougher, version of this experiment is done by adding potassium dichromate to the solution. This will also snatch the sulfate off the gallium, and cause the ball to relax only to contract again as more sulfate forms. The "heart" will appear to be beating entirely on its own. It is very difficult to get the proportion of sulfuric acid and potassium dichromate just right, though, and few people get more than a few pulses. With a nail, you get a rapid, steady pulse.
Via Periodic Table.