Friday, March 1, 2013

There's Solid Nitrogen and Then There's SOLID Nitrogen ...

Oh, the fun you can have with a vacuum chamber! You can even make nitrogen molt. In this video, the medium of the fun is liquid nitrogen:

When the pressure drops and gas is pumped out, the nitrogen starts to evaporate to fill the void. Because the atoms escaping as gas have so much more freedom/so many more configurations, they are in a sense "hotter" and the atoms left behind must cool down as a result. (This evaporative cooling is the same reason sweat on a hot day will cool you down.) The cooled nitrogen drops quickly below its freezing point and the atoms lock into place. You have a glassy puddle of frozen nitrogen.

But it's still not done. The atoms are frozen but they froze too quickly -- they are still disordered and puddly. After a moment (about 1:20 in the video), the bonds start to rearrange into a better crystal, and the rearrangement propagates along the nitrogen ice, shedding nitrogen snowflakes as the crystal pops into place. It reminds me of a snake shedding its skin for some reason.

Not sure what this has to do with cooking, but good basic science can always find its true application later. Enjoy the show.

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