Science

There are, however, other oscillating chemical reactions. None of them result in mechanical action, but the cyclical color changes of, for instance, the Briggs-Rauscher reaction (shown above) are pretty cool in and of themselves. The prototype chemical oscillator is the Belousov-Zhabotinsky reaction (Wikipedia) which was only discovered in the 1950s. For years, no respectable journal would print reports of oscillating chemical reactions because many editors could not reconcile their understandings of thermodynamics with the notion of an oscillating reaction. Guess who had to eat crow?

This classic chemistry demo involves the use of toxic metallic mercury, so it’s one of those that is best to just watch on YouTube instead of trying yourself. The pulsing action is caused by surface tension effects–metallic mercury is oxidized at the surface of the drop to form a film of mercury (I) sulfate, which lowers the drop’s surface tension and causes it to flatten under its own weight. The flattening brings the drop into contact with the tip of a carefully-positioned iron nail, which reduces the mercury (I) sulfate back to metallic mercury, which in turn increases the drop’s surface tension and causes it to contract away from the nail. Thanks to YouTuber sciencevidds for sharing it with us. [via Boing and then some more Boing]