That’s the water in the baked potato. 
Wait, are you saying that ice continues to expand as it’s cooled below 0 C? So the same quantity of water has a larger volume at -75 C than it does at -1 C? I don’t think that’s true, but I’m not positive about that. Cooling the sphere in dry ice would cause the water to freeze FASTER than just putting it in an ordinary freezer, but I don’t think the pressure would be any higher.
I am not saying solid ice expands as it cools further and further below zero.
I am saying that if you constrain (i.e. hold constant) the volume of a body of liquid water as you cool it further and further below 0C, the liquid water will exert greater and greater pressure against its containment; the liquid water is trying to expand to achieve the volume it needs in order to become solid ice. Assuming a constant-volume container (a cast-iron sphere is a good approximation of this), the pressure of the liquid water at -75C will be much greater than at -1C. The phase diagram for water shows you what’s happening. at 101 kPa and 0C, you’re at the boundary between liquid and solid. As you lower the temperature, the water remains in its liquid phase, provided the pressure is high enough. And that elevated pressure is what the cast-iron sphere provides, at least up to its strength limit. Cooling this cast-iron sphere in your kitchen freezer (to -15C) won’t make the liquid water generate enough pressure to crack it. But if you cool it to the temperature of dry ice, it does generate enough pressure; as soon as the cast-iron sphere cracks, the liquid water expands and becomes solid ice.
That’s awesome! Mythbusted by a six-year-old!
Ok, I understand what you’re saying now. Your last clause is the key though. Even fairly high pressures don’t reduce the freezing point all that much. Even at 100,000 kPa, the freezing point drops only to about -9 C (cite), well within the range of a typical household freezer. I’m not sure how to calculate the actual pressure that would be produced in this situation.
Presumably by “this situation”, you mean cooling a bomb full of water down to -77C. I don’t know either, but based on the pictures I saw so many years ago, the pressure was more than a thick-walled cast-iron sphere could withstand.
There’s a better phase diagram here. The nearly-vertical line rising up from (273K, 1 bar) is what we’ve been talking about, and shows that enormous pressures result in small decreases in the freezing temperature. Once the pressure gets high enough, it’s going to become solid ice even at freaky high temperatures; it’ll just have a different crystalline structure.
At temps below -20C, it looks like you’ll have solid ice regardless of pressure, but the density for each of those solid phases is still substantially less than for liquid water.
The table further down that page shows the change in molar specific volume (inverse of density) for each of the phase changes; each of those solid phases is less dense than the liquid phase.
For more interesting reading, check out this Gizmodo article:
What Happens When Water Freezes in a Box So Strong It Can’t Expand?
The link I gave earlier gives a coefficient of thermal expansion of ice as ~ 50 x 10[sup]-6[/sup] deg[sup]-1[/sup]. That’s a little higher than gold. But it’s positive, so colder=smaller.
OTOH, it’s not a constant. Once you get sort of close to Absolute Zero it goes negative. Then it’s expanding as you get colder.
That really got interesting. I never read that article or any other about the inch thick cannon balls but there it is, the very thing I was asking about in my OP.
So from Machine Elf’s link, we learn that the highest attainable pressure of freezing water is over 43, 500 psi, at which point it becomes Ice II. That’s the chamber pressure of a modern rifle cartridge. So if the container does split, watch out.
Dennis
Actually, the beer wasn’t kept liquid by the pressure, but merely by the absence of a suitable crystallization nucleus—the freezing process needs a kind of ‘starter’, and if you cool a liquid carefully enough, it will go below its freezing temperature, but remain liquid, entering a ‘supercooled’ state.
Any physical disturbance then is likely to induce rapid freezing, such as you observed. The process releases heat; that’s how those sodium acetate heating pads with the disk you click work.
This property of water is one of the fortunate properties that helps life. Ponds & lakes would freeze solid much easier if this didn’t happen. As it is as water gets colder it sinks to the bottom, mixing the water, till that temperature is reaches at which time the coldest water stays near the top, and will freeze over, insulting the water below.
I suspect that this is a situation where “common” is the operative word, along with engineering practicality in an industrial environment.
Those two attributes of water were very specifically identified in navy nuclear power school as key stand-out features. I suspect that a scientist in a laboratory would have very different opinions of the awesomeness of water alongside its competition.
I believe the beer didn’t freeze because of the alcoholic contents. Alcohol has a lower freezing point than water. It’s why we use alcohol in anti-freeze/coolant for our cars.
It did freeze, once I popped the cap off. Half Man Half Wit’s explanation - that I had achieved a supercooled liquid state - is plausible, with newly-formed CO2 bubbles (when I relieved the pressure) perhaps serving as the nuclei that started the freezing process.
See How to Instantly Freeze A Beer (includes video demo) they claim that it’s the act of striking the bottle on the counter than generates bubbles, but I’m pretty sure the bubbles happen as soon as you open the bottle. I wish they had also done a “control” bottle, i.e. one that they had opened without striking on the counter.
This is interesting. Seeing that it has 5% alcoholic content I can see how that happened. I remember the therapist told me to mix alcohol with water in a bag to have super cold packs without freezing for my back aches.
Water doe certainly have some interesting properties which can often be useful, and it’s also extremely common, at least on this planet, and very safe for the lifeforms native to this planet. So if you want a big tank of something to soak up heat, for instance, you’re likely to use water instead of (say) ammonia (which has an even better heat capacity), just because it’s really cheap and easy.
This did not go unnoticed, sir. 
Ammonia does not have a higher heat capacity at the temperatures water is liquid, even if we switch to your non-standard but requested mole based numbers.
@ 1 bara and 17 C:
Water: 75.4 kJ(kmol *K)
Ammonia: 36.9 kJ(kmol *K)
You need to move up to 50-100 bara for the isoberic heat capacity for Ammonia to be higher. So I am guessing you are looking at or calculating isochoric heat capacity which as it would be gaseous and under pressure is a bit of a trivia point when I was mentioning common materials. Unless you consider 1000psi to be a common I guess.
Yes, he fact that water expands below 4C is why we get crusty solid surfaces on bodies of water. But, in summer the surface layer stays warn and does no mix with the lower levels, since it above 4C and hence warmer means less dense than lower levels.
IIRC it is around 0F /-17C that ice stops expanding as it gets colder and starts contracting. I heard once that the reason warmer ice is slippery is because the pressure can cause the fine surface layer to melt (expanded ice to less expanded liquid) providing lubrication. Once ice is cold enough that compression does not bring on melting then ice is no longer slippery.
That explanation has been around for a long time, but according to Wikipedia, it’s incorrect:
This claim in the first paragraph is backed up with cites, although I’ll admit I haven’t looked at them.