Watch What Happens When Molten Salt Is Poured Into Water

March 11, 2016 | Joanne Kennell

Molten salt exploding in a fish tank of water
Photo credit: screen capture from video posted by TheBackyardScientist

Can you say, “kaboom?”

Have you ever heard of molten salt before?  It turns out, molten salt, which is salt in a liquid state after being heated to more than 1,474 degrees Fahrenheit (801 degrees Celsius), can conduct electricity and be used as a solvent, according to  It also reacts quite interestingly with water.

The experiment, conducted by The Backyard Scientist, was inspired by a video he saw entitled What We Made, which shows molten salt triggering small explosions in water.  "I had to try this for myself. I was extremely curious why it exploded," he explained on Reddit.

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Now, combining salt and water seems innocent enough, so what exactly happens that causes the molten salt to explode?  It is not entirely clear, but there are a couple possible explanations.

First is something called the Leidenfrost Effect.  To put it simply, if you heat a substance (like salt) way beyond the temperature of water’s boiling point, the Leidenfrost Effect can occur and result in what is called a steam explosion.  If the temperature of the salt is extremely hot, a thin layer of vapor will form on the surface, insulating the salt from the water.  

Once the salt is poured into the water, the vapor around the salt becomes superheated, causing an increase in pressure.  According to Reddit user midnight-cheeseater, “at the surface of the water, this high pressure steam can easily escape. But as the blob of molten salt sinks deeper, the pressurised steam is confined by the water around it. This causes the pressure to rise even further, even quicker, until it overcomes the water pressure holding it back and you get an explosion."

The second explanation, according to Reddit user Ontologian, is that water was folded into the salt and turned to steam, and the steam them compressed the salt and forced it into the water, breaking the Leidenfrost effect.  This resulted in a “rapid heat transfer […] and ultimately a significantly greater steam production rate. At the same time the water closest to the center would most likely be compressed from the salt being forced into the water causing a compounding pressure wave which acted like a container and thus the explosion.”

However, there is a lot of debate on the reasons why.  We will just have to wait for The Backyard Scientist to give a more definitive explanation.

Do not try this experiment at home, The Backyard Scientist was lucky he was not injured during the explosion.  "First two times nothing happened, just a little splattering," he wrote in the video's description. "On the third try... BAM!"



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