Kitchen Science: Boil Water Into Ice

Even water has a triple point, right?

Apply a vacuum to the container in which they have placed the water, as the pressure drops in the container, the vapor pressure of the water increases to the point where it reaches / exceeds the "atmospheric" pressure. As the water boils, it loses thermal energy to evaporation, dropping the temperature of the remaining water until ice forms.

I think.

Extending what Justin says, there is eventually a certain pressure below which eventually water in a liquid state can't exist, and it has to evaporate, so I guess alternating from boiling to ice isn't that hard.

That's a fancy hot plate and the video is time-reversed.

I wish they knew how to operate a video camera and light the subject because I'd like to observe under better conditions the forms being made there while it resided in that kind of dynamic equilibrium..beautiful.

lol, did this little thing in highschool physics. Around a vacumm of 0 atmospheres, 0 pascals, a real vacumm, there's "Standard Time and Pressure", which is a point at which all three states of matter may be present at once in terms of water, vapor and ice. It's the same reason your blood would boil if you were ejected from a spacecraft :D

The triple point of water is at 273.16 K, 611.73 Pa. This temperature is only .01 C above the sea-level ice point, and the pressure is very close to the mean surface pressure on Mars. So if you abruptly reduce the pressure, the water will boil until its temperature drops enough to freeze the remaining liquid. You can make dry ice this way by spraying liquid carbon dioxide into bag that's porous enough to let the gas out, but solid enough to catch the flakes of CO2 snow.

Another puzzle: It's also possible to cause hot water to suddenly boil by applying ice to the vessel.

@Saph: You really have no idea what you are talking about, do you? Standard TEMPERATURE and pressure [STP] means just that: about 20 degrees Celsius and 1 ATM pressure. What you are talking about is the triple point of a certain material, at which all three aggregation forms can exist: solid, liquid and gaseous.

If you look at a temperature/pressure diagram of water you will see how this is possible.

I heard once a long time ago that really rich ancient Egyptians would, like, evaporate water really fast somehow, like with the sun or something, and some of it would freeze. I dunno, I wasn't there.

Simple application of high vacuum. The water evaporates, as pressure drops [technically, it's not boiling]. This cools it enough that eventually the remainder freezes, at well above zero degrees Celsius I might add.

The interesting question is: What happens to the ice formed, when the air is let back into the vacuum chamber? Would it just melt, or would it sublimate into water vapour?

@Silicon Shaman: The water doesn't evaporate :) It boils, the difference being that boiling takes place in the whole mass of a substance [as seen in the video] whilst evaporation is a process at the surface of the liquid.
As for the second question, they did let the air back in and the water was still frozen. That is because, as the water boils, it 'sucks' energy from the remaining water, thus lowering its temperature until it solidifies, at .01 degrees Celsius [as previously mentioned]. Then it stays frozen.

Re: Egyptians and ice

I'd heard that some rich folk on the outskirts of the desert would hire people to dig shallow pits in the desert, line them with straw (for insulation) and pour water into them. They would freeze overnight. I've never heard anything about Egyptians making ice by somehow evaporating water really quickly.