Is there a liquid that can float on a gas?

Answer

Dear Nelson,

No, the distance between gas molecules is usually much greater than in a liquid. The difference in density between gases and liquids is, on average, much greater than between liquids and solids, so there is no example where the density reverses (as with ice and liquid water, allowing ice to indeed float on water).

There is a gas with a density six times greater than air: sulfur hexafluoride.

This is sometimes used for demonstrations: you can float a container of aluminum on a container full of (invisible) sulfur hexafluoride. This is even a solid, but the solid is only a thin layer filled with air. (So ​​it works like a ship: you can make a ship out of a material that doesn’t float on water itself.) You could also put a little bit of water in the container and in a sense there would be “a liquid on a gas” float, but if you poured the water directly on the gas it would sink in, so it’s a bit of cheating! 😉

Just look at this video.

Regards,
Sylvia

PS: If you inhale the gas sulfur hexafluoride and then talk, your voice sounds much heavier than usual. The opposite is the case with helium: helium has a lower helium than air and your voice sounds higher than normal. There is also a video of that.