Watch: What Happens When You Drop an Iron Anvil in a Vat of Liquid Mercury
Science YouTuber CodyDon Reeder has nearly 2 million subscribers to his channel Cody’s Lab. In this video, he glugs mercury into a tub from a reused antifreeze jug, then reveals he’s standing in the tub of mercury and it’s cutting off his circulation.
I have a lot of questions about Reeder’s safety and work-life boundaries (later in the video, he jokes there’s “mercury in my glove, some good that did”), but the floating anvil is pure science. The 110-pound iron anvil is only half as dense as mercury, meaning not only does the anvil float—it’s genuinely difficult to even push down.
How does this compare with some less toxic experiments you could do?
My favorite one is that many bowling balls actually float. A bowling ball-shaped amount of water weighs 12 pounds, so any bowling ball lighter than that will be buoyant in water. At a typical bowling alley, you’ll find bowling balls for everyone from children to the strongest adults, so usually a range of 8 to 16 pounds. Almost half that range would be buoyant in water.
A slightly less glamorous version is how humans float in different kinds of water. The human body’s density is around 985 kilograms per cubic meter, and fresh water is 1,000 kilograms per cubic meter. This makes intuitive sense: The human body is mostly water, with a little bit of denser stuff than water, but other stuff less dense than water, like fat and trapped air. That means the average human floats just barely in average fresh water.
Sea and ocean water is denser than fresh water because salt is dissolved in the water. If you dissolved that level of salt in a bath at home, you’d be just as buoyant as you are on the ocean, give or take an adjustment for temperature. Cold water of any makeup is denser than hot. If you visit the Dead Sea, people speculate it’s impossible to sink because of how buoyant you are there. The reason? The much higher salt content—nearly ⅓ by percentage—means the seawater is a wild 1,200+ kilograms per cubic meter.
Even so, none of these ratios is even close to how mercury is twice as dense as the anvil in Reeder’s video. According to this chart, one substance that’s about half as dense as water is lithium, which would be just as buoyant as the anvil. But don’t try this at home: lithium reacts powerfully with water.