gray matter

A battery that runs on air? Why, that’s almost as good as a car that runs on water! Those cars are fantasy, but batteries that run on air are actually quite common, especially among older people. Tiny zinc-air batteries are widely used in hearing aids, where they have replaced toxic mercury-based batteries in providing a small but steady stream of power. They supply more energy for their size than any other battery, because they draw some of their power straight from the air.

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If you were a coal miner in the early 1800s, the light you used was an open-flame oil lamp—even though mines were sometimes filled with “fire-damp,” a volatile mixture of air and methane gas. Explosions were inevitable, and at times threw bodies from mine shafts like grapeshot from a cannon. Humphry Davy became a national hero when, in 1815, he found a remedy: Surround the lamp flame with mosquito screen.

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The explosive C4, a favorite for everything from demolition to terrorism to action movies, is in fact one of the safest explosives. How can an explosive be safe? If it’s hard to set off by accident. C4 is so stable that you can light it with a match (it burns but does not explode) or shoot it (it splatters but does not explode). To go bang, it requires a detonator that produces both heat and shock.

At the other end of the spectrum are mixtures that ignite simply from being scratched or knocked. There are obvious challenges in mixing, storing, and handling these substances so that they explode only when intended, yet they’re surprisingly common.

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I remember seeing a demonstration of a seemingly magic process at an engineering open house decades ago, in which a soft metal bit carved detailed shapes into far harder metals. It's called electrochemical machining (ECM), and it's so simple in principle that you can do it at home with a drill press, a battery charger and a pump for a garden fountain.

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What you consider solid, liquid or gas depends entirely on where you live. For example, men from cold, cold Mars might build their houses out of ice. Women from Venus, where the average temperature is about 870°F, could bathe in liquid zinc.

We think mercury is a liquid metal, but it’s all relative. At one temperature, the mercury atoms arrange themselves into a solid crystal; at another, they flow freely around each other as a liquid. Children from Pluto (like mine, for example) could happily cast their toy soldiers out of mercury, because on that frigid planet it is a solid, malleable metal a lot like tin. Here on temperate Earth, you need a stove to cast tin, but a tank of liquid nitrogen to make mercury figurines.

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Arthur C. Clarke wrote that "any sufficiently advanced technology is indistinguishable from magic," but he was wrong. It's easy to tell the difference -- technology works. For example, "remote-viewing" mentalists claim they can see events far away, yet they fail every test. In fact, remote viewing is simple: It’s called TV.

Another example that recently circulated online was a fake video of someone charging his iPhone by jamming the end of a USB cable into an onion. How do I know it was fake? First, you need contacts made of two different metals, and second, you can't get enough voltage out of a single vegetable. What makes the ruse so disappointing is that it is possible to charge an iPhone this way, if you do it right.

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I recently committed myself to the goal, before the weekend was out, of creating a device entirely from bacon and using it to cut a steel pan in half. My initial attempts were failures, but I knew success was within reach when I was able to ignite and melt the pan using seven beef sticks and a cucumber.

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Living in the Midwest, where heating homes with propane is common, I periodically see reports in the local paper that yet another unoccupied house has exploded. They often note that the roof was found in the basement, while the walls were spread some distance into the neighboring fields.

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