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  • Thanks to Brilliant for supporting this episode of SciShow. Go to Brilliant.org/SciShow to

  • learn more.

  • [ ♪INTRO ]

  • During long, cold winters in medieval Europe, there was something weird going on with church

  • organs.

  • Across the continent, some of these instruments were getting what people at the time called

  • tin leprosyortin pest.”

  • The organs grew gray, sickly-looking circles that spread over time and made the pipes hard

  • and brittle. Eventually, many of them fell apart.

  • But tin pest isn't actually a sicknessor, as people once thoughtthe work of the

  • devil. It's actually just some pretty simple chemistry.

  • It all comes down to the fact that a lot of organ pipes, even now, are made with tin,

  • since it can produce bright, resonant tones. And it's pretty and shiny.

  • At least, sometimes.

  • The thing is, tin exists in two different forms, or phases, depending on the temperature.

  • It's a lot like how water can be liquid at room temperature and solid when it gets

  • cold.

  • Except, instead of going from liquid to solid, tin goes from one type of solid to another.

  • Above 13.2 degrees Celsius, tin is a white, shiny, strong metal. That's the form of

  • tin that people use to make organ pipes.

  • But below that temperature, tin becomes dull, gray, and easy to break. That's the form

  • those pipes were transforming into during those long, cold winters.

  • The reason these two forms are so different, even though they're both tin, is because

  • of the way the atoms arrange themselves in each phase.

  • In white tin, atoms are arranged in what's called a tetragonal, or rectangular, structure.

  • But in gray tin, atoms are farther apart, arranged in more of a cube shape that's

  • less sturdy.

  • These two forms are called allotropes. And you might be more familiar with this phenomenon

  • than you think.

  • A similar thing happens with carbon, which can either take the form of graphite, like

  • in your pencil, or a crystal-clear diamond, all depending on how its atoms are arranged.

  • When it comes to tin, though, the process of turning from white to gray doesn't happen

  • overnight.

  • In fact, it can take months or years of cold temperatures for it to noticeably transform.

  • This is because it doesn't happen as soon as temperatures drop to 13 degrees Celsius.

  • Just below the transition temperature, there's not enough difference between the energy of

  • white tin and the energy of gray tin to motivate a transformationunless something acts

  • as a catalyst. But that energy difference increases as temperature drops.

  • Around -30 degrees Celsius, that energy difference becomes significant, and transformation can

  • happen much more easily.

  • But! If it gets much colder than that, another factor comes into play that makes a transformation

  • less likely.

  • See, white tin has to expand by about a quarter to transition to the gray form, and it takes

  • a lot of energy to get the process started.

  • Except, as the temperature drops, the molecules in tin vibrate slower, so they don't have

  • the energy to overcome the barrier that it takes to start the phase change.

  • That means that right around -30 degrees, there's sort of a sweet spot where the transition

  • is most likely to happen.

  • But even at an ideal temperature, tin takes a long time to transform. It's not like

  • water, which quickly turns into ice as soon as it's cold enough.

  • That's because both phases of tin are solid, so its atoms are locked up in tight lattices,

  • and it takes a long time for them to rearrange themselves.

  • That's why old tin organs weren't just collapsing constantly. It took a long cold

  • winter for those tin pipes to start transforming.

  • But once gray tin appears, it can spread really quickly, like a rash.

  • The expansion of the tin makes little cracks in the metal, and that creates more exposed

  • edges, where atoms are free to move around and rearrange themselves.

  • And before long, the atoms of the white tin reorganize into the structure of gray tin.

  • Luckily, now that we know what causes it, the tin pest is easy to prevent. Just adding

  • small amounts of other metals, like lead, can keep tin atoms from moving around and

  • changing form.

  • And since a lot of organ pipes are made of metal blends, many have been able to withstand

  • the test of time.

  • It turns out a lot of mysteries aren't so mysterious once you've figured out a little

  • bit of the science behind them. And you can build your science skills with the courses

  • on Brilliant.org.

  • Brilliant's course on everyday physics is all about the unexpected ways you interact

  • with physics in your day-to-day life.

  • By the end, you'll learn how traffic jams, bridges, and even axe-throwing are founded

  • in physics.

  • And there are dozens of courses to choose from in science, engineering, and mathall

  • designed by educators at leading universities, like MIT, Caltech, and Duke.

  • The courses are hands-on, with interactive quizzes and guided problems with explanations,

  • and they'll help you hone your scientific thinking.

  • If you're one of the first 200 people to sign up at Brilliant.org/SciShow, you'll

  • save 20% on an annual premium subscription. And as always, thanks for watching SciShow.

  • [ ♪ OUTRO ]

Thanks to Brilliant for supporting this episode of SciShow. Go to Brilliant.org/SciShow to

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襲擊中世紀教會機關的 "疾病" (The "Disease" That Struck Medieval Church Organs)

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    林宜悉 發佈於 2021 年 01 月 14 日
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