You may have already seen this viral video of a man casually putting his hand through a cascade of melted metal, like a kitten playing with the tap. One cannot help but wonder at first sight if it is not a hoax. And yet, this tour de force is real and hides a scientific explanation.
Discover our latest podcast
First of all, we strongly advise against attempting to replicate this experiment. The melting point of aluminium is 660° C and it is generally necessary to exceed 1000° C to see a metal heated to white as on the video. Add to that that even though science assures us that passing one's hand quickly through metal is possible, the resulting splashes can be extremely dangerous.
The Leidenfrost effect
The secret behind this spectacular performance is called the Leidenfrost effect. You may have seen it in your kitchen when you splash water on your hot stove or on a hot pan. Under the effect of the heat, water takes the shape of droplets that begin to bounce and move as if driven by a will of their own.
When a drop is placed in contact with a heated surface above 160° C, its base evaporates. A kind of small gas cushion develops underneath the drop: it allows it to travel around by levitating and has the added advantage of ensuring its longevity.
The air, being a poor conductor of heat, creates a protective barrier between the hot surface and the drop. Protected from quick evaporation, the drop is able to move freely during several seconds until it disappears completely.
The same effectcan be observed with liquid nitrogen. With a boiling point of -196 ° C, it vaporizes instantly when it encounters a surface at room temperature. And in the case of our viral video, it is the moisture on the human hand that is instantly vapourised, once again creating a thin layer of protective air that isolates it sufficiently, at least during the fraction of a second where the hand crosses the flow of molten metal.
