Joseph Thiebes portland, ore. | science | art | food | politics

29Sep/170

Boiling : Sublimation :: Evaporation : Infralimation

Liquids become gases by two processes: evaporation, which happens at the surface only and occurs at any temperature as long as there is room in the atmosphere for the liquid to go; and boiling, which happens all over the volume of liquid at once and occurs only at the boiling temperature for the liquid at a given pressure.

Solids can become gases in these two ways as well. A block of CO2 (dry ice) or water ice will gradually evaporate, even at cold temperatures. This evaporative process in solids is called sublimation and occurs at the surface of the solid, almost like rock being weathered by the wind, but on a molecular scale.
This is why your ice cubes gradually get smaller if you leave them in the freezer long enough. The molecules of water are swept away in the microscopic movement of air molecules, and end up being deposited somewhere else in your freezer as frost.

In the case of CO2, if you heat it uniformly, it will reach a temperature at which it will become gas all at once, similar to the way liquids do when they boil. In solids, this is also called sublimation.

This ambiguity is a little bit of a problem, for reasons described in the excellent and captivating video below. The producer of the video suggests that there should be two terms to describe the two processes, and that one of the processes could be named after his YouTube channel. I agree that two terms would be a useful disambiguation.

I think "sublimation" is a good word for the solid analog of boiling. From sub (up to) + limen (limit), thus "up to the limit."

For the solid analog of evaporation at the surface, I suggest "infralimation," from infra (below) + limen, thus "below the limit."