A video on Reddit went viral recently that shows a man who puts his hand in molten metal and does not get injured. In the video, it can be seen that he removes his safety glove, and puts his hand in the red-hot liquid. After that, he walks away like it was no big deal for him at all.
The question is, how was he able to do that with having his arm burning seriously? He is definitely not any kind of a reverse terminator who is resistant to molten metal. The answer to this mystery is pretty cool.
There is a phenomenon called the Leidenfrost Effect. This effect causes water droplets to dance around on an extremely hot bed instead of evaporating. When liquid is dropped on a hot plate, the bottom layer of the drop evaporates and leaves a protective layer of gas between the hot plate and the rest of the water droplet. This prevents the contact between the two and slows down the heat transfer.
It is the same effect that is protecting the man in the video who is swiping his hand through the molten metal. For a very short time, the moisture on his hand boils and then forms a protective layer on the skin. The layer stops him to touch the liquid metal directly, thus allowing him to swipe his hand through the metal without being burned at all. However, if he held his hand there for even a fraction of second more, he will get seriously burned. Therefore, it is advised to not to try this at home.
This effect can also be seen with liquid nitrogen. When liquid nitrogen boils at -196 degree C, it evaporates as soon as it meets a warm surface. This also creates a layer of gas between itself and the surface. Using this effect people create many videos on the internet where they were pouring liquid nitrogen on their hands, however, if you insert your hand for a long time, it can all go badly wrong.