Protected By Science My hand is like a red-hot poker to the liquid nitrogen, but an insulating layer of nitrogen gas forms- a phenomenon known as the Leiden-frost effect- keeping my hand safe and warm for a fraction of a second. Mike Walker
When I first saw this photograph of a manís hand submerged in liquid nitrogen at somewhere below -320į F, my immediate thought was, ďThat guy must be crazy! One second in that stuff, and youíre shopping for new skin!Ē My shock was tempered only slightly by the fact that it was my hand, and weíd taken the picture just a minute earlier.
I hadnít realized that my hand was quite so deep into the liquid. Amazingly, I barely felt the cold at all. My skin didnít get hurt for the same reason that water droplets dance on a hot skillet. An insulating layer of steam forms almost instantly between the water and the metal, keeping the droplets relatively cool as they float for several seconds without actually touching the hot surface. To liquid nitrogen, flesh is like that skilletóa surface hundreds of degrees above its boiling point. So the moment my hand touched the liquid, it created a protective layer of evaporated nitrogen gas, just as the skillet created a layer of steam. That gave me just enough time to put my hand in and pull it out again. Any longer than that, and frostbite would have set in.
Hot Water: Droplets on a very hot skillet take longer to evaporate than they would on a less-hot surface where no insulating gas layer forms. Mike Walker
The phenomenon is called the Leidenfrost effect (after Johann Gottlob Leidenfrost, the doctor who first studied it in 1756). Iíd known about it for years, but when it came time to test it in real life, I have to admit that I used my left hand, the one Iíd miss less.
I drew the line at another classic example of the effect. According to the books, itís possible to stick a damp finger directly into molten lead without getting burned, if you do it fast enough. After some consideration, and remembering the times Iíve been burned by molten lead, I decided that it probably wouldnít make a very good picture anyway.
ACHTUNG! Do not try this. If liquid nitrogen soaks into your clothes, you will not be protected by the Leidenfrost effect, and you can get frostbite very quickly.
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