Most recent answer: 08/03/2018 Q: I put a bottle of water in the freezer every night before bed. In the morning, I take it out and drink it. Sometimes its frozen solid, sometimes it stays liquid, depending on when I put it in there. But heres the kicker, sometimes I will pull the bottle out, it will be liquid, but as soon as I open it, it starts to turn into ice, from the top down (it takes a few seconds for the entire bottle to freeze. Is there an explanation for this?

- Greg (age 26)

Army, Iraq

A:



In the absence of impurities in the water and imperfections in the bottle, the water can get "stuck" in its liquid state as it cools off, even below its freezing point. We say this supercooled state is "metastable." The water will stay liquid until something comes along to nucleate crystal growth. A speck of dust, or a flake of frost from the screw-cap falling into the bottle are enough to get the freezing going, and the crystals will build on each other and spread through the water in the bottle.



Water releases 80 calories per gram when turning from a liquid to a solid. We suspect your freezer is only a few degrees Celsius below zero(perhaps ten or fifteen?), and the specific heat of water is one calorie per degree per gram. This means that your water, as it freezes, warms up the rest of the water until the process stops at 0 degrees Celsius, freezing perhaps ten or twenty percent of the water. This ice may be distributed throughout the bottle, though, as the crystallization process happens very quickly and heat flows slowly.



We suspect you have slush in your bottle rather than hard ice when this is done. You can compare with another bottle which froze hard in your freezer overnight how hard it is to squeeze the bottle and how long it takes to melt. The ice will also take up more room than the water it used to be, and some water may spill out the top.



There can also be some small effects of pressure and of dissolved gases on the freezing temperature. Is your water under pressure?



Tom and Mike

We suspect that what's happening here is that the water in the bottles which did not freeze overnight was "supercooled." Water normally freezes when it is cooled below 0 degrees Celsius, forming ice crystals. Ice crystals form more easily when they grow on existing ice crystals -- the water molecules like to pack themselves in place on a crystal that's already gotten started. It doesn't take much to start the crystallization process going -- a little piece of dust or other impurity in the water, or even a scratch on the bottle are sometimes all it takes to get ice crystals growing. The process of starting off a crystal is called "nucleation."In the absence of impurities in the water and imperfections in the bottle, the water can get "stuck" in its liquid state as it cools off, even below its freezing point. We say this supercooled state is "metastable." The water will stay liquid until something comes along to nucleate crystal growth. A speck of dust, or a flake of frost from the screw-cap falling into the bottle are enough to get the freezing going, and the crystals will build on each other and spread through the water in the bottle.Water releases 80 calories per gram when turning from a liquid to a solid. We suspect your freezer is only a few degrees Celsius below zero(perhaps ten or fifteen?), and the specific heat of water is one calorie per degree per gram. This means that your water, as it freezes, warms up the rest of the water until the process stops at 0 degrees Celsius, freezing perhaps ten or twenty percent of the water. This ice may be distributed throughout the bottle, though, as the crystallization process happens very quickly and heat flows slowly.We suspect you have slush in your bottle rather than hard ice when this is done. You can compare with another bottle which froze hard in your freezer overnight how hard it is to squeeze the bottle and how long it takes to melt. The ice will also take up more room than the water it used to be, and some water may spill out the top.There can also be some small effects of pressure and of dissolved gases on the freezing temperature. Is your water under pressure?Tom and Mike (published on 10/22/2007)

Follow-Up #1: Supercooled water in the freezer

Q: Water in my moms freezer or fridge,doesnt matter which one, can be in there for days and it wont freeze solid. In fact it looks perfectly clear until you do one of 3 things. You shake it, you drop it or you open it. It then turns to slush. I want to do a science fair project on this because its amazing to me, but Im not sure what my hypothesize would be. I was thinking that maybe oxygen had to be present to freeze, but you are saying that it all begins just with the change that causes the cystals to grow?

- Jordan Canevari 11

Okeechobee,Florida, usa

A:



Mike W.



Right. Youve actually done the experiment to show that oxygen is not the key. Shaking or dropping the bottle doesnt add oxygen to it, but does trigger the slush formation.Mike W. (published on 10/22/2007)

Follow-Up #2: supercooled water

Q: How super cooled can water get without freezing? also i would just like to comment that i was searching for this answer because the same thing was happening to me here in iraq.

- Greg (age 24)

Navy, Iraq

A:



Mike W.



According to Wikipedia water can be supercooled to a little below -40°C, at least briefly. I suspect that in practice it will be hard to go below about -20°C, just because ordinary bottles, bubbles, dust, etc. can nucleate freezing. The number of people who have written about observing this is now pretty large, so it seems easier to get large supercooling than I'd guessed.Mike W. (published on 07/02/2008)

Follow-Up #3: supercooling observed

Q: Thanks for the explanation! I observed this for the first time the other day, then reproduced it just to make sure it wasn't a fluke. Amazing and perplexing to watch the first time.

- Eric Ford (age 37)

Mesa, Arizona, USA

A:

Thanks for the info, (published on 08/15/2008)

Follow-Up #4: pressure and supercooling

Q: How is the freezing temperature of water affected by pressure? This phenomenon happened to me as well but I assumed supercooling was caused by the water in my water bottle being under a slight vacuum (the bottle was 'sucked in' when I put it in the freezer) and when I opened it the pressure change to atmospheric caused the phase change. Surprisingly I could not find a lot of data on the internet about this. My thermodynamic book has many property tables on superheated water vapor but little to say on the solid-liquid properties of water.

- garrett (age 26)

houston, tx

A: liquid , which (somewhat unusually) has smaller volume. Since your bottle's pressure seemed to slightly rise when opened, that effect would actually tend to reduce freezing. However, it's a very small effect and in this case is swamped by the nucleation phenomenon.



Mike W.



Liquid water and ice have only slightly different volumes, so the freezing point isn't very sensitive to pressure. To the extent that it is, higher pressure favors the, which (somewhat unusually) has smaller volume. Since your bottle's pressure seemed to slightlywhen opened, that effect would actually tend to reduce freezing. However, it's a very small effect and in this case is swamped by the nucleation phenomenon.Mike W. (published on 10/06/2008)

Follow-Up #5: bubbles in supercooled water

Q: I also put my water bottle at work in the freezer occasionally to cool the water faster to drink. The "supercooled water" happened to me today too. I took the water out and walked back to my desk. The water was completely clear and did not look frozen at all, but I noticed small bubbles floating through the water much more slowly than normal. When I opened the bottle to take a drink at my desk, it pretty quickly became opaque and started freezing. Needless to say I was amazed. Before the supercooled water freezes, does is it somehow thicker or denser than normal water? The bubbles floating very slowly was really weird.

- David (age 29)

Laguna Niguel, CA

A:



It's just possible that the bubbles themselves started nucleating some freezing, so perhaps they were dragging little ice crystals along, but that's just a wild guess.



Mike W.



Not only was that guess wild, it was kind of stupid. See the "viscosity" follow-up below, for a much more plausible answer from one of our readers.



This sounds like a really interesting observation. I'm posting it just to see if anybody has any thoughts.It's just possible that the bubbles themselves started nucleating some freezing, so perhaps they were dragging little ice crystals along, but that's just a wild guess.Mike W.Not only was that guess wild, it was kind of stupid. See the "viscosity" follow-up below, for a much more plausible answer from one of our readers. (published on 10/14/2008)

Follow-Up #6: desalinated water freezing

Q: FYI the bottled water provided to troops in Iraq is produced from Kuwaiti desalinization plants. Not from ground water as is common in the US. Might the desalinization process produce unusually pure water with no dissolved salts or mineral which is therefore be prone to super cooling?

- Evan (age 34)

previously Kuwait

A:



Thanks for the interesting info.



Mike W.



Yes, it's possible that the desalinated water lacks nuclei. For example, if it's prepared by reverse osmosis, that could filter out various impurity nuclei. It's not the dissolved salts, though, that matter. Little bits of dust are more important.Thanks for the interesting info.Mike W. (published on 08/23/2009)

Follow-Up #7: supercooled soda

Q: when at work i commonly place a 2-liter of room temp soda in the freezer at 2 hours 15 minutes when i come to break its liquid(rarely partly frozen but it does happen) when opened it turns to a delicious slush. wouldn't the impurity's in soda prevent a supercooled state.

- Jason (age 23)

florida

A:



Mike W.



Not necessarily. The sugar and flavorings are individual smallish molecules. The nuclei which start the freezing are larger particles, such as specks of dust.Mike W. (published on 11/03/2009)

Follow-Up #8: Iraqi supercooled water

Q: The same thing happened to me on MULTIPLE occasions and here is the kicker...It also happened in Iraq. Mosul Iraq to be more clear and we had a freezer full of water bottles. Pull one out and hit the tabl with it and it woukd fkash freeze ,Take another out and repeat. Opening the bottle, smacking it, shaking it..all these things would initiate the flash freeze. Ive never seen it happen stateside, only at a couple locations in iraq during 06,07.

- Matthew O'Farrell (age 26)

El Paso. TX

A:



Mike W.



I'm starting to strongly suspect that the bottled water supplied in Iraq was prepared by reverse osmosis, and that many of the little nuclei usually present were filtered out in the process.Mike W. (published on 11/03/2009)

Follow-Up #9: more data

Q: Not a question, just an observation that this doen't just happen to small bottles. I had a 5 gallon bottle of water sitting on the porch last winter. I walked past it and wondered why it hadn't frozen, even though the temperature had dropped well below freezing over night. I thought maybe it had but I just wasn't able to tell, so I grabbed the bottle neck and tilted it and at that point I could see the ice form from top to bottom. It became opaque, as the ice was slushy.

- Craig (age 60)

Greenville, NC, USA

A:



Mike W.



Good new data point.Mike W. (published on 11/03/2009)

Follow-Up #10: more ice data

Q: I've seen this several times. I live in northern Illinois, and our winters get a lot of cold draft out of Canada/Minnesota. I commonly leave filtered water in bottles on my deck to stay cold for the next day during the winter. Several things I've observed: Water purity is the #1 important factor to see this. Reverse osmosis = supercooled. Brita/Pur filtered = frozen. Container cleanliness is 2nd. Fresh from the bottling plant = supercooled. Reused/recycled plastic = frozen. Lastly, in order to start the freezing process, I've often noticed that only motion is needed. I think of it as motion allowing the water molecules to "realign" themselves, thus, allowing them to start forming ice crystals around whatever they want to. I've grabbed one on my way out to the car and observed it go from water to solid ice in the 6 second walk. I've also seen quite a bit of the slushy. Ambient tempurature is important in deciding this one, the colder, the slushier. As the water forms crystals, it warms up, and when in a sealed container, pressure builds as well (water expands when frozen). Boyle's Law plays on this one, helping to increase the temp, as well (as pressure goes up, so does the tempurature). At the very least, it's a cool parlor trick. "Hey, go grab me a bottle of water, they're on the porch." "Aren't they frozen?" "Nope." (from the porch) "WHOA!" (back in the house) "Hey, this was water out there." "Dude, it's -10° outside...are you nuts?"

- Dan (age 24)

Rockford, IL, USA

A:



On the theory issues: The water molecules are moving around very quickly on their own even before you pick up the bottle, thanks to thermal energy. However, they do so without any collective structure large enough to start the freezing. When you pick up the bottle, some larger scale disturbance (e.g. a small bubble) is introduced, and that can be enough to nucleate the ice.



Mike W.



Thanks, those are great data! It all fits with the idea of needing some special nuclei (usually bits of dust, etc.) to start the freezing.On the theory issues: The water molecules are moving around very quickly on their own even before you pick up the bottle, thanks to thermal energy. However, they do so without any collective structure large enough to start the freezing. When you pick up the bottle, some larger scale disturbance (e.g. a small bubble) is introduced, and that can be enough to nucleate the ice.Mike W. (published on 11/11/2009)

Follow-Up #11: gas in soda

Q: This sounds like a really neat phenomenon! I was just wondering, because a few people have described that pressurized carbonated drinks exhibit supercooling, if it could in fact have something to do with dissolved gasses. The presence of dissolved gas seems as if it would impede the formation of the crystal lattice, yet perhaps gasses are maintained in solution by the increased pressure of the bottle? Perhaps this could account for the reason why sometimes some, but not all of the solution is frozen. This might mean that the solution has found a nucleation site, and begun to freeze, however as more pressure evolved from the dissolution of gasses, the freezing was eventually stalled until ample force or a reduction of pressure catalyzed the mass dissolution and freezing in the soda. I have noticed that sodas tend to have a grainy flaky sort of ice, as well as an increase in pressure (they'll often explode) that might exceed just the contribution of ice's slightly larger volume. Both seem to support this dissolved gas hypothesis. Any truth to this?

- Dave (age 19)

NY

A: 2 dissolved in pressurized soda, so a lot of what you notice is right. However, the reason for the partial freezing is much simpler and applies to plain water as well. As the ice forms, the latent heat of freezing is released. (Ice is lower energy than water at the same temperature.) That warms everything up. For reasonable levels of supercooling, the material warms up to 0° C before it's all frozen.



Mike W.



There is a lot of COdissolved in pressurized soda, so a lot of what you notice is right. However, the reason for the partial freezing is much simpler and applies to plain water as well. As the ice forms, the latent heat of freezing is released. (Ice is lower energy than water at the same temperature.) That warms everything up. For reasonable levels of supercooling, the material warms up to 0° C before it's all frozen.Mike W. (published on 11/19/2009)

Follow-Up #12: Navy weighs in

Q: Okay... I'm glad I wasn't the only one looking for this answer. This questions has crossed my mind daily as the water bottles we keep in the cooler remain liquid until you unscrew the cap or tap the bottle.

- Chris (Navy) (age 26)

Afghanistan

A:



Mike W.



This seems to be reported much more by the military than by others. That tends to confirm that your bottled water is unusually free of particles, and thus more prone to supercooling.Mike W. (published on 10/29/2010)

Follow-Up #13: more supercooling data

Q: I have also observed this phenomenon and it is really fun to watch the flash freeze progress through the bottle after removing it from the freezer. I've been using 16.9 oz bottles of Crystal Geyser water and I can reliably reproduce it. According to http://www.crystalgeyserasw.com/faq/ - this water is passed through a 1 micron filter so it is pretty pure in terms of particulate matter but is not purified water as it spring water that contain dissolved solids. Just another data point :)

- Adam Houston (age 39)

Blythe, CA

A:



Mike W.



Yeah, that 1 μm filter removes the little particles that nucleate freezing. An 0.2 μm might do even better. Thanks for the data!Mike W. (published on 11/09/2010)

Follow-Up #14: supercooled Aquafina water

Q: I have this happen regularly here in Florida. I can get it to happen with Aquafina brand bottled water everytime. Other brands just freeze solid. I am glad to have finally found an explanation.

- Cody S (age 26)

Florida

A:



We're very lucky here in Urbana. The tap water is delicious, clean, costs about $0.005/gallon, and doesn't fill up the landfills with plastic.



Mike W.



My guess then is that Aquafina uses some different filtering method. Either they run the water through some filter to catch little particles or they use reverse osmosis to remove salts and as an incidental result remove larger particles.We're very lucky here in Urbana. The tap water is delicious, clean, costs about $0.005/gallon, and doesn't fill up the landfills with plastic.Mike W. (published on 03/10/2011)

Follow-Up #15: supercooling under pressure

Q: Hi I found this website while trying to research the behavior of supercooled water. I'm currently conducting an experiment with tap water here in Austin(many impurities) and found that it will super cool under pressures >=170kPa. This is just a rough estimate and I'm still trying to figure out what the exact pressure threshold to get the supercooling effect. I tried to do some research as to why this might occur if the crystallization process is stimulated by impurities but haven't had any luck. Also, one of my trials resulted in a sample of supercooled tap water around -5 deg C but didn't freeze when the water was disturbed or when the pressure was released which had worked for my other trials.

- James (age 22)

Austin, TX

A: I'd be surprised if you found a sharp pressure threshold for super cooling. Usually even tap water will supercool a bit under atmospheric pressure. If you do find that the amount of supercooling you can get does depend a lot on pressure, here's a possible reason.



Maybe the main nuclei are little bubbles. If you pressurize the water, you can shrink or eliminate them. Then you'll just be left with dust, etc. for nuclei. So you might find that the amount of supercooling you can get drops for the first bit of pressurization, then levels off for further pressurization. The reason that atmospheric pressure would be special is that the air dissolved in the water has had a chance to reach equilibrium with the atmosphere, so increasing pressure leads little bubbles to dissolve.



Since you find that taking the pressure off usually leads to freezing, I guess the bubbles have shrunk under pressure but not completely gone away. Maybe the one time that releasing the pressure didn't cause freezing, you'd actually managed to fully remove the bubbles.



Slightly depressurizing the water for a while, then letting it come back to atmospheric pressure without shaking it should remove bubbles. That too should increase supercooling.



You can see I'm doing a lot of guessing, but these are all testable ideas. One tool that might help would be a laser pointer. In a dark room, you can see how much the water scatters light. That scattering mostly comes from bubbles, dust, etc.



Mike W.

(published on 05/07/2011)

Follow-Up #16: supercooled slush and latent heat

Q: I was wondering how cold I could get tap water to supercool so I put a temperature probe in the water as it was cooling. To my surprise the temperature went back up to 0 deg Celcius almost instantly. My question is why does this happen regardless of the how cold the supercold water gets if ice can be below 0 deg Celcius?

- Becky (age 20)

San Antonio, TX

A: Great observation and great question.



When the freezing starts, the water molecules joining the ice lose energy. That's the whole reason they join the ice, the bonds between them in the ice are lower energy than the looser bonds in the liquid. That lost intermolecular bond energy (called latent heat) has to go somewhere. It heads straight into the vibrations of the nearby molecules, heating them up. That keeps happening until the water is back up to 0°C, at which point the freezing stops.



We've discussed this a little on some previous answers. The latent heat is big enough that for practical supercooling it will stop the freezing well before 100% of the water has frozen. That's why you end up with a slush.



(For purists, yes we should be talking about enthalpy rather than energy, but there's not much difference here.)



Mike W.

(published on 05/10/2011)

Follow-Up #17: supercool slurpies

Q: Most of the questions have been about water or soda pop but I have noticed this supercooled slush with other drinks... I've been doing this for years but mostly recently this has been happening with my low calorie Gatorade...my kids absolutely love it because it is so magical...tastes good too... We don't open the bottle to get the slush we just shake it up after a few hours in the freezer... My question is...do the contents of the bottle determine if the slush is able to form or can this happen to any liquid? Do you need to have pressure? Thanks for all your time,hope this helps with your research...

- Angel (age 32)

Idaho

A:

You don't need pressure.



As for whether it can happen with any liquid, the answer is basically yes. However, the ability to supercool is bound to vary among different liquids.



I think the liquids you're interested in here are almost all solutions of things in water. The big factor that varies among them is the presence of little bits of dust etc. that serve as freezing nuclei and prevent things from supercooling very much. It sounds like most soft drinks are filtered in a way that gets rid of the freezing nuclei. The sugar, artificial sweeteners, etc. are present as individual small molecules. It doesn't sound like they play all that much of a role.



Mike W.



You don't need pressure.As for whether it can happen with any liquid, the answer is basically yes. However, the ability to supercool is bound to vary among different liquids.I think the liquids you're interested in here are almost all solutions of things in water. The big factor that varies among them is the presence of little bits of dust etc. that serve as freezing nuclei and prevent things from supercooling very much. It sounds like most soft drinks are filtered in a way that gets rid of the freezing nuclei. The sugar, artificial sweeteners, etc. are present as individual small molecules. It doesn't sound like they play all that much of a role.Mike W. (published on 07/06/2011)

Follow-Up #18: thumping supercooled water

Q: My google query on this topic led me here, and I was quite surprised to see so many other Military here in the Middle-East referring to the same phenomena. I, too, was initially under the impression that this occured as soon as i opened the bottle--that some kind of pressure differential that was the catilyst. So, just to confirm all the points made above, i grabbed a 'super-cooled' bottle of water out of the fridge (made from ground water, fyi), took a quick glance to confirm it was still in a liquid state, then thumped it against the palm of my hand. Sure enough, as i observed, i saw the ice crystals racing down the contents of the water until the whole bottle was semi-opaque with slushy ice. Excellent, thank you for the answer to this particular (but interesting) puzzle!

- Philip

Iraq

A:



Mike W.



Thanks for letting us know about this clean experiment.Mike W. (published on 07/12/2011)

Follow-Up #19: Supercooled water project

Q: I, too, have placed my water bottle in my freezer for a few hours and had the same phenomenon occur. When I remove the bottle, sometimes, it is still liquid, but when I invert the bottle or shake it, ice crystals propagate throughout the bottle (usually from the top down). I've shown this phenomenon to my 10 year old daughter a few times and we have wondered about the physics of the process. I'm glad to have found your page since it seems to explain why this takes place. I think we will try some experiments regarding the use of purified water vs. tap water and new bottles vs. older scratched ones. This would be a nifty science project. Thanks!

- Margareth (age 46)

Gainesville, FL, United States of America

A:



If you could get your hands on some little proteins from Antarctic fish, you could actually suppress freezing- these fish use the proteins to live in a supercooled state. They may be available since some ice-cream makers use them to get a smooth texture.



Mike W.



This does sound like it will make a nice project. You might also try bits of sand, teflon, etc. to see if any of them promote freezing and thus suppress supercooling. (I know teflon promotes boiling, but don't know what it does to freezing.) It would also be interesting to know if you could trigger the freezing with loud sounds.If you could get your hands on some little proteins from Antarctic fish, you could actually suppress freezing- these fish use the proteins to live in a supercooled state. They may be available since some ice-cream makers use them to get a smooth texture.Mike W. (published on 09/12/2011)

Follow-Up #20: pesticide impurities in slushy ice-water?

Q: My observations in traveling around the world. I have found that I get slush more often in water in third world countries. I came to the following conclusion on my own, so I may be completely off about it. When I freeze bottled water, some water forms slush, while other water goes straight to ice. Since one of the biggest problems in third world countries is that they cannot get the pesticide runoff completely out of the water, I have decided that water that freezes to ice intead of slush is what I will drink. I found the results to be very consistent with the time that I left the water in the freezer and which products turned to slush or ice. So I made the decision that I would drink the water products that consistently turned to ice instead of slush since my thought is that there are more impurities in the slush water than the ice. And, most likely, impurities in third world distilled water is runoff pesticides. How does my reasoning hold up???

- Stuart Long (age 50)

Raleigh, North Carolina, USA

A:





Let's say that, doing that, you're still having trouble getting certain water to freeze solid in a certain time. That may be because:

1. There are a lot of solutes in the water

or

2. The freezer isn't very cold.



The important solutes under normal conditions are standard mineral salts. One thing that almost certainly is not involved is pesticides. The reason is that even highly dangerous levels of pesticides involve rather low molecular concentrations. You'll never notice their effects on the water freezing, because those effects are negligible compared to the effects of small variations in salt levels.



It's possible that in some of the countries you visit the freezers aren't as cold as they should be.



Mike W.





It's not quite clear under what conditions you're getting slush or solid ice. It's more or less impossible to get solid ice immediately after supercooled water freezes, because the latent heat is so big that even highly supercooled water will warm up to 0°C before fully freezing.To get solid ice you have to leave the water in a freezer for some time after the freezing starts.Let's say that, doing that, you're still having trouble getting certain water to freeze solid in a certain time. That may be because:1. There are a lot of solutes in the wateror2. The freezer isn't very cold.The important solutes under normal conditions are standard mineral salts. One thing that almost certainly is not involved is pesticides. The reason is that even highly dangerous levels of pesticides involve rather low molecular concentrations. You'll never notice their effects on the water freezing, because those effects are negligible compared to the effects of small variations in salt levels.It's possible that in some of the countries you visit the freezers aren't as cold as they should be.Mike W. (published on 11/08/2011)

Follow-Up #21: possible supercooling?

Q: I'm so glad I stumbled upon your site with the information about super cooled liquids. I have a newish refrigerator made by GE that has been giving me fits in that nearly everything put into it will freeze no matter what temperature the dial is set to. I thought I would also let you know that liquids in the normal sense such as water and Pepsi are not the only things to exhibit super cooling. I've also noticed it frequently in fruit juices, sport drinks, apple sauce, and even yogurt. It is really quite annoying to grab a drink or my lunch and find it has turned to slush.

- Eric (age 29)

Denton, TX , USA

A:



Some of the items you mentioned (e.g. applesauce) should be hard to supercool much, because they contain particles that would nucleate the freezing. When you say that they turn to slush, I'd guess you must mean that they're already slush when you remove them from the fridge. The reason they form slush rather than solid ice would be a little different than the reason that supercooled liquids turn to slush as they're removed from the fridge.



The supercooled liquid releases heat as it starts to freeze. That heat keeps it from staying cold enough to freeze completely. What's probably going on with your liquids is that, as they partially freeze, the sugar concentration in the remaining liquid goes up. As a result the freezing point of the remaining liquid goes down, below even the temperature that your malfunctioning fridge is reaching.



Mike W.



Eric- It sounds to me as if perhaps the thermostat on your new refrigerator is busted.Some of the items you mentioned (e.g. applesauce) should be hard to supercool much, because they contain particles that would nucleate the freezing. When you say that they turn to slush, I'd guess you must mean that they'reslush when you remove them from the fridge. The reason they form slush rather than solid ice would be a little different than the reason that supercooled liquids turn to slushthey're removed from the fridge.The supercooled liquid releases heat as it starts to freeze. That heat keeps it from staying cold enough to freeze completely. What's probably going on with your liquids is that, as they partially freeze, the sugar concentration in the remaining liquid goes up. As a result the freezing point of the remaining liquid goes down, below even the temperature that your malfunctioning fridge is reaching.Mike W. (published on 11/09/2011)

Follow-Up #22: more supercooling data

Q: Mike, Thank you for running this post. I noticed this exact issue a while back with water from our work fridge and have been curious about it for a while. A coworker of mine found this and at last our questions are answered. Just to add to your list of findings, I can very reliably recreate this with Ozarka 16.9 oz "eco friendly" bottles sourced from water here in Texas.

- Deryl

Dallas, Tx

A:



Thanks for your data and for your kind remarks.



Mike W



Deryl-Thanks for your data and for your kind remarks.Mike W (published on 12/28/2011)

Follow-Up #23: supercooled water cooler

Q: I have a water cooler in my house and every once in a while the water will come out of the spout as a liquid and turns to ice (slush) when it's in the cup. Do you know why this would happen? It is not something I cannot duplicate this on demand as I a have not figured out the condition which makes it happen. It occurs whether it is hot or cold in the house. It also doesn't seem to matter how long between use of the cooler. I will add, however, that I have only seen it happen in plastic cups - but that may because I use them more often.

- Kelly (age 49)

Phoenix, AZ US

A:



Mike W.



It sounds like your cooler is set to too low a temperature. It's cooling the water below the freezing point:"supercooling" it. I've marked your question as a follow-up to our older discussions of supercooling.Mike W. (published on 03/31/2012)

Follow-Up #24: our staff

Q: Mike, I appreciated this thread too - provided me with an answer to my question too. More amazing to me is the fact this thread started before Nov 2006 and it is now Mar 2012 - over five years later and you are still engaged - awesome! But what became of Tom? Thanks! David

- David Harper (age 53)

Manassas, VA

A:



Mike W.



Tom moved north to Fermilab, where he continues to work on fundamental high-energy physics.Mike W. (published on 03/16/2012)

Follow-Up #25: supercooled margaritas

Q: Would the supercooling phenomenon work the same if alcohol is mixed in? Tried freezing margarita mix with alcohol in a freezer mug - mug froze but 'rita mix was liquid until I took it out and stirred it. Then it slushed up!

- Pat (age 58)

San Jose, CA USA

A:



When you say "the mug froze" I'm guessing you mean that there was ice on its outside.



Mike W.



The basic supercooling effect should be the same even with some alcohol in the solution. I'd expect the resulting slush to be a little thinner than it would be if everything were the same except without the alcohol. The reason is that as the ice forms it excludes the alcohol, lowering the freezing point of the remaining liquid. That means that not quite as much ice will form at the point where the temperature of the solution reaches the freezing point.When you say "the mug froze" I'm guessing you mean that there was ice on its outside.Mike W. (published on 06/03/2012)

Follow-Up #26: nucleating supercooled water

Q: Mostly just a further observation but a small question as well. I keep tap water in 1 Liter bottles in a counter-top refrigerator in the office. When I open one I do not get immediate "slushing" - but if I add "Crystal-light" drink mix it happens almost immediately -especially if I reclose the bottle and shake it a little. The question is, which is more of a factor in the forming of the slush - the "impurities" of the drink mix; or the disturbance of the water in shaking - or is it about equal. Really cool phenomenon to share in a children's sermon by the way!

- Dana (age 58)

Aurora, Indiana, USA

A:



Mike W.



Thanks for the observation. I can only give an educated guess on your question. It sounds from your description like the powder is the most effective at nucleating the ice formation. Shaking helps spread it around through the bottle. That's particularly important if the water is only mildly supercooled. As it starts to freeze, say at the top, the released latent heat warms it up. That region reaches the melting point, so it won't freeze any more even with plenty of nuclei present. Shaking it up a bit gets the nuclei to the other parts, which are still cold enough to freeze.Mike W. (published on 06/11/2012)

Follow-Up #27: surprise supercooling

Q: not really a question, but very excited -- i think this hapened to me when i left a botte of SmartWater in my car overnight when we had zub-zero temps the winter before last in Chicago. SmartWater's bottling plant had filled this batch of bottles so that there was not *one* air bubble in it... i got in my car in the AM and, to my surprise, found the water crystal clear and totally liquid! it must have been an airtight seal on the cap. i went into my office building with the bottle and when i arrived at my floor in the elevator, i opened it immediately to take a drink and, in a flash, it turned to extremely heavy slush. i was so shocked that i told a bunch of people immediately and, they thought i was nuts. though i'm not a scientist, i did have great biology and earthscience teachers -- so i theorized about this "supercooling" in my own layman's language. i've looked for validation ever since, and have now found it! thank you! it's so appreciated.

- ingrid g. (age 50)

chicago, il usa

A:

Thanks for the story. You can tell your coworkers that nature itself is the nutty one. Mike W. (published on 07/01/2012)

Follow-Up #28: Thank you for the thanks

Q: I just wanted to say thanks! Never thought I would find do much about this topic. Lately, I have been freezing bottles of aquafina. Several times I've reached in to grab a bottle...that had a solidly frozen bottle laying right against it...and ass soon add I grab it the water starts to turn to slush, top to bottom. At first when it started to happen i never saw it and thought i was mistaken thinking the water was frozen before I grabbed it. Today i saw it and googled it. Its a cool process!

- draya (age 52)

A:



We appreciate it when we get a note like yours. It makes our efforts worthwhile.



LeeH and MikeW





Hello Draya,We appreciate it when we get a note like yours. It makes our efforts worthwhile.LeeH and MikeW (published on 08/09/2012)

Follow-Up #29: slush from supercooled water

Q: I'm so excited to find this page. I never personally experienced the phenomenon until very recently, so I suspect it's related to the change in my bottled water company filtering. After I read other questions about supercooling, I can't wait to taste some soda slush. Oh, about the slush, due to the combination of living in tropical country, and the filtering I mentioned previously, when I first watched the phenomenon in internet, I never realize the ice produced is slush, in fact the first time I knew the existence of slush is when I held my first own supercooled water bottle. I thought I did it wrong until I read the questions here mentioning the ice is indeed supposed to be like that.

- Martheen (age 25)

Jakarta, Indonesia

A:



It's fun that we can use theoretical arguments to confidently conclude things like that the product must be slush, not solid ice, and then see the result in a simple home experiment.



Mike W.



Martheen- Thanks for the information.It's fun that we can use theoretical arguments to confidently conclude things like that the product must be slush, not solid ice, and then see the result in a simple home experiment.Mike W. (published on 11/07/2012)

Follow-Up #30: supercooled water viscosity

Q: Apparently no one has addressed Follow-Up #5 and the presence of sluggish little bubbles in the cold water. The answer is that as the liquid water cools, both its viscosity ("thickness") and density increase. So the little bubbles do appear to be moving through a thicker liquid because they are. At the point at which the water freezes into a crystalline structure, however, its density decreases to less than that of the liquid water. That's why ice floats in liquid water. Follow-Up #4 stated that "Liquid water and ice have only "slightly" different volumes . . .", but ice is actually about 9 percent less dense (ice volume is greater) than liquid water at 0 deg C; wouldn't that be more than "slightly"? And don't ice skates work as well as they do because the concentration of pressure on a small area of ice causes the ice to melt temporarily and lubricate the interface? Last observation: With reference to Follow-Up #25, the viscosity (thickness) of a 50/50 water and isopropyl alcohol mixture is actually higher than either the water or alcohol alone. I think ethyl alcohol behaves the same way, but I don't have the data at hand. Strange things happen when different molecules interact.

- Rodney F. (age 66)

Sacramento, CA, USA

A:



On the effect of pressure in melting ice, I've heard that the old story we always told about the pressure from the skates melting a layer doesn't hold up. The effect just isn't big enough.



On the water-alcohol solution, our point concerned the thermodynamics of freezing, which is simpler than the viscosity effects you discuss. For such solutions the melting point always turns into a melting range. Rather than having a single freezing point below which ice is the stable phase, as the temperature is lowered the stable state has an increasing fraction of ice.



Mike W.



You make an excellent point about the viscosity of the supercooled water. Extrapolating from the viscosity vs. temperature of stable liquid water, the supercooled water might have close to twice the viscosity of water at 0°C. Since we're so used to seeing bubbles in normal water, that might well be enough different for David to have noticed it. I feel rather stupid for not having thought of that obvious explanation!On the effect of pressure in melting ice, I've heard that the old story we always told about the pressure from the skates melting a layer doesn't hold up. The effect just isn't big enough.On the water-alcohol solution, our point concerned the thermodynamics of freezing, which is simpler than the viscosity effects you discuss. For such solutions the melting point always turns into a melting range. Rather than having a single freezing point below which ice is the stable phase, as the temperature is lowered the stable state has an increasing fraction of ice.Mike W. (published on 12/14/2012)

Follow-Up #31: freezing supercooled foam!

Q: My scienve teacher friend led me to this Q&A page. I had a 2 liter of soda in left in the car last night, only about 2/3 full. When I opened it up this morning all the fizz froze. Is that normal with super cooling soda? The bottom layer of liquid remained liquid but all the bubbles froze as it started to fizz upon opening. Coolest science effect I've ever seen, by the way. Even better than mentos in soda.

- Adelina P (age 26)

SAlina, UT, USA

A:



Now to try to understand it, here's some thoughts.



The reason that ordinary supercooled water only forms a slush is that the latent heat it releases warms it up as it starts to freeze. If it starts at -20°C, about as cold as you're likely to be able to supercool it, the latent heat will warm it to 0°C when about 1/4 is frozen. So in order to get all the bubbles to freeze, they must have someplace else to dump that latent heat energy. I can think of two effects that would help.



1. There's a lot of cold gas nearby. The liquid in the bubble is very thin- maybe only about 10-4 cm. If the bubbles are around 10-1 cm in size, there's roughly 1000 times the volume of gas as of liquid. (This estimate could easily be off by a factor of 10.) That means that the net heat capacity (heat energy absorbed per increase in temperature) of the gas in those bubbles can be nearly as big as that of the liquid. That still doesn't sound like quite enough to soak up enough energy to let the whole bubble freeze.



2.When you open the bottle, the bubbles expand, doing work. This is described in standard thermodynamics books as the cooling on adiabatic expansion. You could probably get gas cooling of around -60° C in this process, if I calculate right. That would let the gas soak up some more heat before reaching 0°C.



Combining those two effects would be just about enough to explain what you saw. Maybe other effects are involved as well. Perhaps, for example, only some of the fizz freezes, the rest falling back into the liquid. When you look, you see only frozen fizz. That's called "post-selection", an effect well known to distort many statistical studies.



Mike W.



p.s. Can you try repeating this? Was that soda with sugar? Anything else we should know before trying it?



We'd never heard of this before. It does sound amazing. Maybe we can make a lecture demo or student lab out of it. I will refrain from making any jokes about "supercool".Now to try to understand it, here's some thoughts.The reason that ordinary supercooled water only forms a slush is that the latent heat it releases warms it up as it starts to freeze. If it starts at -20°C, about as cold as you're likely to be able to supercool it, the latent heat will warm it to 0°C when about 1/4 is frozen. So in order to get all the bubbles to freeze, they must have someplace else to dump that latent heat energy. I can think of two effects that would help.1. There's a lot of cold gas nearby. The liquid in the bubble is very thin- maybe only about 10cm. If the bubbles are around 10cm in size, there's roughly 1000 times the volume of gas as of liquid. (This estimate could easily be off by a factor of 10.) That means that the net heat capacity (heat energy absorbed per increase in temperature) of the gas in those bubbles can be nearly as big as that of the liquid. That still doesn't sound like quite enough to soak up enough energy to let the whole bubble freeze.2.When you open the bottle, the bubbles expand, doing work. This is described in standard thermodynamics books as the cooling on adiabatic expansion. You could probably get gas cooling of around -60° C in this process, if I calculate right. That would let the gas soak up some more heat before reaching 0°C.Combining those two effects would be just about enough to explain what you saw. Maybe other effects are involved as well. Perhaps, for example, only some of the fizz freezes, the rest falling back into the liquid. When you look, you see only frozen fizz. That's called "post-selection", an effect well known to distort many statistical studies.Mike W.p.s. Can you try repeating this? Was that soda with sugar? Anything else we should know before trying it? (published on 12/26/2012)

Follow-Up #32: supercool experiments

Q: Hello, I'm am very interested in this experiment, and I was thinking about trying this at home. Is there a particular rate of cooling that has to be achieved to supercool distilled water? And also, does it have to be a plastic container. Would a glass beaker work? Presuming it had no scratches or blemishes.

- William (age 14)

UK

A:



The container probably is more important. We've heard from more people with highly supercooled water in plastic bottles. Maybe that means that glass bottles are more likely to trigger ice formation, especially on those scratches that you mention, or maybe it just means that plastic bottles are more common. The most important factor that I know about is to not have little bits of dust in the water. It's not necessary that the water be distilled, but it does help a lot if it's well-filtered. By that I mean with a particle filter, not a chemical filter. The water purified by reverse-osmosis has accidentally had particles removed as part of the chemical purification process.



Mike W.

In principle there are limits on the cooling rate. For example, if you were to cool very slowly, say taking a billion years to cool the water down, the odds would go up that it would find a way to crystallize before you were done. If you tried to cool very quickly, say with some dry ice, you might accidentally form a very cold spot that would trigger ice formation. In practice for the types of supercooling we hear about, the cooling rate doesn't seem to be a big issue.The container probably is more important. We've heard from more people with highly supercooled water in plastic bottles. Maybe that means that glass bottles are more likely to trigger ice formation, especially on those scratches that you mention, or maybe it just means that plastic bottles are more common. The most important factor that I know about is to not have little bits of dust in the water. It's not necessary that the water be distilled, but it does help a lot if it's well-filtered. By that I mean with a particle filter, not a chemical filter. The water purified by reverse-osmosis has accidentally had particles removed as part of the chemical purification process.Mike W. (published on 01/03/2013)

Follow-Up #33: shaking triggers ice formation

Q: So just another point to this. If you have a freezer that vibrates or rattles a lot it is more likely to freeze solid. This is because of the many reasons you said before. just thought i would share in case anyone is having trouble getting this to work.

- apa (age 19)

north dakota

A:



Mike W.



Thanks for that useful point.Mike W. (published on 01/20/2013)

Follow-Up #34: supercooled water and slush?

Q: I observed this a few years back. I left a water bottle in my truck. It was a cold morning; about 10 degrees F (-12C). I expected my water to be frozen as usual, but it wasn't. I picked it up and it froze solid. Not slush. It even formed cracks in the ice as it froze. It was pretty cool to watch.

- Ryan (age 34)

CT

A:



We're a bit puzzled.



Mike W.



This is a mystery. The latent heat of freezing for water is about 80 cal/gm, enough to heat water 80°C. So after 12/80 or 15% of your water froze, the temperature should have risen to 0° C and freezing should have slowed dramatically, requiring gradual heat leakage to the outside. Now maybe your bottle got a lot colder at night than the morning air, maybe -20°C, but that would still leave only about 25% quick-forming ice. Maybe the cold bottle itself would pull a little more heat out of the water, but I still don't see how to get to 100%.We're a bit puzzled.Mike W. (published on 01/24/2013)

Follow-Up #35: solid ice from supercooled water?

Q: I can't believe it has taken this long for someone to chime in that their water bottles froze solid "hard as rock". I only had to squeeze the bottles to get them to freeze completely solid in 1 to 2 seconds. I did this about six times in a freezer while I was on vacation, so I wouldn't be able to repeat it now.

- George (age 56)

21075 USA

A:



Mike W.



We're still puzzled. More information about the temperature, etc. might help. How did you check for solidity?Mike W. (published on 04/08/2013)

Follow-Up #36: frozen supercooled water

Q: Nothing specific is known about the temperature. The bottles were in a tray on the freezer door. If I were to do it again I might saw one in half with a hack saw. People did the usual knock on a table like a hammer. At the time it was more of a magic show than a science experiment. Some of the bottles formed real milky looking ice and some were clearer. The one that froze the fastest seemed the milkiest.

- George (age 56)

21075 USA

A:



Mike W.



This sounds quite interesting. We still don't understand it. It would be great if you could do that experiment where you saw the bottle open.Mike W. (published on 04/09/2013)

Follow-Up #37: supercooling in Estes Park

Q: My son and I did an experiment to test methods of cooling water quickly. One bottle of water was in a mixture of salt, water and ice. It quickly cooled to 25 degrees F. The cap was off the bottle and we inserted and removed an instant read thermometer every 5 minutes for 50 minutes. Once the temperature stabilized for 20 minutes, my son took a drink and the water was still liquid. Then, just to see what would happen, we put the bottle outside in a snow bank, the water instantly turned to slush and the temperature rose to 30 degrees. We were able to repeat this result with another bottle. Since we must have introduce particles during the supercooling period and while drinking, what happened?

- Candice (age 42)

Estes Park, CO

A:



So for our other readers, two parts of this are easy to understand. Initially, the water a bit below 32°F is supercooled, meaning it doesn't freeze until something disrupts a little region to get the ice formation started. Finally, something does get the ice formation started ("nucleated") and the latent heat released by the freezing raises the temperature to almost 32°F.



The mystery is the step in between. Why didn't opening the bottle and taking a sip disrupt some little region enough to nucleate the freezing? I'll just make a guess. 25° F isn't way below 32°F, so just moving the bottle around may not be enough to nucleate freezing. When your son took a drink, the part near his mouth was warmed and picked up some salt, both of which would tend to keep it from freezing. Then when the bottle went in the snowbank, some little bits of something that got in could settle down into the cold part and nucleate the freezing.



Mike W.



Nice question. I love that you repeated the experiment to test for reproducibility.So for our other readers, two parts of this are easy to understand. Initially, the water a bit below 32°F is supercooled, meaning it doesn't freeze until something disrupts a little region to get the ice formation started. Finally, something does get the ice formation started ("nucleated") and the latent heat released by the freezing raises the temperature to almost 32°F.The mystery is the step in between. Why didn't opening the bottle and taking a sip disrupt some little region enough to nucleate the freezing? I'll just make a guess. 25° F isn't way below 32°F, so just moving the bottle around may not be enough to nucleate freezing. When your son took a drink, the part near his mouth was warmed and picked up some salt, both of which would tend to keep it from freezing. Then when the bottle went in the snowbank, some little bits of something that got in could settle down into the cold part and nucleate the freezing.Mike W. (published on 04/23/2013)

Follow-Up #38: experience with supercooled water

Q: I'm so glad I found this question/answer! I was also wondering why this was taking place. My work colleagues and I have been amazed by it for months. Since it depends on the purity of the water and bottle, I find it interesting that I get different results from the same case of water. I would say that about 4 bottles freeze completely solid by the time I drink them, which is normally within 24 hours of placing them in the work mini-fridge. About the same number do not freeze when I remove them. But a majority of the bottles will freeze, top to bottom, as I walk back to my desk from the break room. When the bottles freezes after removal, it is a slushy opaque ice that doesn't quite make it to the bottom of the water (about 90% down). When the water freezes while in the freezer, it becomes a solid brick from top to bottom and is completely clear, with a few pockets of air frozen in place. After looking at the label I see that I'm using purified drinking water, which is "processed by advanced filtration, ozone and reverse osmosis technologies." Just thought I would share my observations!

- Mike C (age 36)

Harrod, OH

A:



Mike W.



Thanks for sharing that data. It's interesting how closely it fits what one expects theoretically. That part about reverse osmosis is particularly telling- it removes larger particles as well as salts.Mike W. (published on 04/28/2013)

Follow-Up #39: supercooled beer

Q: Last time a friend of mine showed me a trick with a beer bottle. It had been in a freezer for a couple of hours and then he tapped it against the table, it was instantly frozen solid. Is it the same priciple as with water? (excuse if my english isn't that good.)

- maxime (age 19)

Belgium

A:

1. If you read the earlier parts of this thread, you can see that because of the latent heat, it's basically impossible to supercool water enough for it to freeze solid. It should turn to partly-frozen slush.

2. That limitation is even stronger for beer, because as part of it freezes the alcohol concentrates in the remainder, keeping it from freezing.



So I bet you got partly frozen beer.



Mike W.



Even excellent Belgian beer is mostly water, so the basic principle is the same. (With some American beers the difference from water is even more subtle.) The part about becoming "frozen solid" seems very strange, however.1. If you read the earlier parts of this thread, you can see that because of the latent heat, it's basically impossible to supercool water enough for it to freeze solid. It should turn to partly-frozen slush.2. That limitation is even stronger for beer, because as part of it freezes the alcohol concentrates in the remainder, keeping it from freezing.So I bet you got partly frozen beer.Mike W. (published on 04/29/2013)

Follow-Up #40: ice water turning to slush

Q: I placed a bottle of water, unopened, in the freezer. After a short time I went to get it out(worried it might freeze)and when I picked it up by the bottle neck/lid a white cloud appeared inside the bottle and traveled down the length of the bottle to bottom.In just a few seconds the ENTIRE bottle was solid white and felt frozen solid.This was NOT condensation, it was inside the bottle. I opened it and the water was frozen...but more slushy or soft ice than not. I have NEVER before observed this,nor have my co-workers.Any ideas?

- Jason (age 41)

Sadler,TX,USA

A:



Mike W.



Welcome to the club! This is a well-understood effect, caused by supercooling, as described in this thread.Mike W. (published on 05/12/2013)

Follow-Up #41: popsicle making

Q: I watched an episode of "How It's Made" where they showed making popsicles. In it they mentioned "supercooled" water as the way they freeze the molded popsicles. They mentioned adding something to the water to keep it from freezing. My question is, "What can you add to water to make it reach subzero temperatures, and still be consumable, without letting it freeze or 'slush'?"

- Johnah Crain (age 22)

Edna, Texas

A: I'm not sure what the procedure is. Adding any solute (e.g. sugar) to water will lower its true freezing point below 0°C. I think you're talking about trying to actually supercool it, to keep it from forming big ice crystals even when it's cold enough to start freezing despite the sugar. One possible way to promote supercooling is by adding some of the special antifreeze that antarctic fish have in their blood. It's a sort of very small protein. () The concentration is too low to lower the true freezing point much but it binds to ice crystals as they just start to form, greatly slowing the formation of big crystals. That's how the fish can make it through the winter below the true freezing point of their blood. Some ice creams and popsicles are made using these materials, since they help keep big crystals from forming. Mike W.

(published on 07/24/2013)

Follow-Up #42: supercooled water science projects

Q: There have been several posts from people wanting to use this phenomenon as a science fair project. My daughter has been excited about doing exactly that ever since we saw a bottle of Perrier freeze before our eyes one very cold day in Bryce Canyon. We thought somehow the pressure of carbonation at altitude had kept the water from freezing but now I understand what happened thanks to your blog. My question is, have you seen how could this be a science fair project? What would be the variable and how would you measure the effect? Thanks, Rob

- Rob Young (age 45)

Irvine, CA

A: This won't be the easiest sort of science fair project, because it takes some care to make the supercooled water reproducibly. Still, there are several interesting questions that could be explored. One, mentioned above, would to see what sorts of things are best at triggering the freezing. How cold does the water have to be for say a little piece of some rock to trigger the freezing? How cold for some reproducible little tap on the water to do it? and so forth. You could even try something where the size of the disturbance could be varied in a controllable way, maybe via little taps from different size pendulums. How does the maximum temperature at which the tap works vary with the size of the tap? It's probably beyond the scope of what your daughter could do for the science fair, but pursuing this type of experiment far enough could lead to something systematic on the whole topic of how nucleation of the ordered phase occurs. Which reminds me that I've got to quit answering these and get back to helping with a research paper on that very topic, although in a different system. mike W.

(published on 09/29/2013)

Follow-Up #43: supercooled spring water?

Q: I was just wondering- Will spring water (i.e. the dollar store brand) supercool? It says on the label- "Bottled at the spring source." No filtration. Thanks.

- lily (age 19)

USA

A: Any water can supercool a little bit, but your guess that the unfiltered spring water may not supercool much sounds reasonable to me. Still, the label might not be right or that spring may naturally not have many good nucleation particles in it, so the only real way to tell is by experiment. Mike W.

(published on 10/18/2013)

Follow-Up #44: freezing supercooled saltwater

Q: Follow up to #42. My daughter decided to vary the amount of salt in the water and measure its effects. After supercooling 3 bottles with no salt, 1/4 teaspoon salt, and 1/2 teaspoon, we poured the water onto a chilled and iced sieve and observed the nucleation of instant ice while the excess water drained off. Then we weighed the sieve to determine how much ice was created. With no salt, the ice formed in a clear formation with spikey crystals around the edges. Weights ranged from 1.4 to 4.6 oz (from a 12 oz bottle). With 1/4 teaspoon the ice formed a soupy slush, which made the entire solution very thick. The water didn't drain as much, and the results were usually between 0.5 and 2.0 oz heavier than the no salt solution. With 1/2 teaspoon we also saw a soupy slush, but the results were inconsistent, sometimes they weighed more than the 1/4 teaspoon measurement, and sometimes less. How can we explain the data which does not consistently demonstrate a pattern with a positive slope? The salt seems to be forming a gelatinous material vs. the ice crystals. Does this mean the NaCl is bonding to the water, resulting in more of the water altered into slush and therefore less drains off? I would have expected that due to the lower freezing point of salt water that we would have measured less ice. Do you have any insight as to what is happening? Thanks very much.

- Rob Y (age 45)

CA

A: My first reaction is that it's hard to get highly reproducible results with supercooling, as we said in #42. For background, let's try to calculate about how much that salt should lower the freezing point. 1/2 tsp is ~2.8 gm. The weight of a mole of NaCl is ~58 gm. So that batch had ~0.05 moles NaCl. 12 oz is ~ 1/3 liter. So you had up to ~0.15 M salt solution. That would give a freezing point depression of only around 0.5°C, not enough to make a huge difference in the net amount frozen, assuming that you've gotten the water and the sieve much more than 0.5°C below 0°C. Yet this salt seems to have made a big difference in the freezing pattern, although maybe not in the total amount frozen. The different pattern will leave different amounts of liquid stuck to the surfaces, messing up the weight comparison, as you noticed. That small amount of salt doesn't change the viscosity of water much at all, so I think it's the different crystal pattern that accounts for the different amount of water stuck. Why does the salt change the pattern of crystal growth so much? Here's a guess. As crystals start to form, they exclude the salt. That makes a layer of extra-salty water around them, suppressing further crystal growth. (The released latent heat of crystallization has a similar effect, but it diffuses away faster.) That promotes the formation of many little crystals rather than fewer bigger ones. That's how you get that slush. Mike W.

(published on 11/30/2013)

Follow-Up #45: why does supercooling work?

Q: Hello, I understand that water can be "super cooled" to a temperature below freezing (for the ambient pressure) and still remain a liquid. There are videos of people doing this then smacking or seeding the cold water to make it freeze. How is this possible? I thought that water would be frozen by the time it dropped below the freezing temperature. I appreciate your input.

- Sandra (age 33)

Sacramento, CA, USA

A: I've moved your question to a thread on supercooling. You give us an excuse to explain the effect at a little more depth. The question is why would water stay a liquid even though it's cold enough so that the solid ice would be more stable than the liquid. Let's start with the basics: why are the liquid and solid separate phases to begin with? Why don't they mush together on the scale of molecules? The stable form of things is the one that minimizes the free energy (U-TS), a balance between lowering the energy (U) and raising the number of different possible micro-arrangements, measured by the entropy (S). At low temperature (T), lowering U is more important. So when water is cold, the molecules line up into the low-U crystal form, even though that lowers their S. At high T, S is more important, so they break loose and wander among more different arrangements. Imagine there is a little region with an ice crystal contacting a little region of liquid, near the freezing temperature. The molecules on the surface of the ice have lost entropy by lining up, but not lost much energy because on one side the liquid molecules aren't lined up with them. So molecules at that surface have higher free energy than ones in either the liquid or the solid. The molecules arrange to minimize the liquid/solid surface, separating the two phases. What happens if you start with pure liquid and cool it enough so the solid is more stable? Let's say a few molecules by accident happen to arrange in an ice-like pattern. Mostly, they're still at the ice surface. They have higher free energy than the liquid, not lower. So usually they will just roll back down in free energy to the liquid state. This sort of pure accidental arrangement takes a very long time to get an ice crystal started that's big enough to keep growing, unless the liquid is way below the freezing point. That's why you can supercool water until some special nucleation gets the freezing going. Mike W.

(published on 01/01/2014)

Follow-Up #46: supercooled wine

Q: A couple of questions:When a supercooled liquid finally solidifies is the heat released the same as the latent heat of fusion for that liquid if it solidified at zero degree C?Red wine super cools very easily (-20C) but wine has many chemicals in its composition and is not filtered to the degree of RO water. Thus there are zillions of nucleation points in the wine yet it "prefers" the super cooled state over the solid state? Wiered or explainable?

- Pato (age 61)

Darwin, NT, Auustralia

A: For starters, the freezing temperature of the wine is around -6°C thanks to the alcohol and other solutes.

See . So -20°C is not as much supercooled for wine as it would be for water. Still 14° or so supercooling seem large, especially for something with some sediment in it. The solute molecules themselves would not serve as nucleation centers. Other readers have written in of problems with wine freezing, so perhaps you have an unusual wine, maybe filtered. (See .)

So I'm not sure how weird your result is. As for the heat of fusion, it's about the same for supercooled liquids as for ones right at the freezing point. It shrinks below the true freezing point by an amount proportional to the difference between the heat capacities of the solid and liquid. That's not typically a big deal for ordinary supercooling. The latent heat of the alcohol solution, however, is a bit different from that for pure water. (see ) I doubt that difference matters much for what you're seeing. Mike W. posted without vetting until Lee returns

(published on 01/18/2015)

Follow-Up #47: experiments on supercooling

Q: If I or someone else were to try to experiment with this and record the data, i would think it would be hard to get constants since like you said dust or irregularities in the bottle can start nucleation. So if any, what are the steps one could take to keep constants and reduce variables in things like bottles and water.

- Finn McGinnis (age 13)

Nigeria

A: One direct possibility is to buy some particle filters and use these to remove particles from the water. Then you can reuse the same filtered water many times. For example, 0.22 micron cellulose acetate filters should remove most dust. I think you can buy these in small quantities and use them with a standard syringe. It would help to experiment with different types of bottles. Perhaps standard polyethylene would be good. It's a good idea to avoid glas because it can break as the water freezes. You could also buy a few brands of bottled water and see which supercool best. Some already seem to be filtered and in suitable bottles, because our readers report accidental supercooling. Mike W.

(published on 12/11/2016)

Follow-Up #48: minerals and supercooling

Q: I've observed this in my home as well but I guessed that it was because of the difference in minerals in the water. I drink Food Lion brand "Purified Water with minerals added for flavor". The bottle states that is is "purified by reverse osmosis" and lists the "ingredients: purified water, calcium chloride, sodium bicarbonate". This water will still be in a liquid state when I open the freezer door and see it on the shelf laying on its side. However, when I remove the bottle and turn it upright, it turns to a thick slush. I think I saw that one previous poster questioned the properties of the bottle. My water bottle is made with a very thin plastic and states "eco air bottle / 100% recyclable bottle and cap". But, although this bottle may be different from other bottles, it doesn't produce the same effect when refilling it with the city tap water from my sink and freezing it. I've never noticed this effect before with other brands of water and am unsure of their ingredients at the moment. Do you think these added minerals play a part in how it supercools to slush instead of freezing to a solid?

- Bethenia Dixon (age 33)

Newport, NC, USA

A: The minerals will slightly lower the freezing point but have very little effect on supercooling. The reverse osmosis process has the incidental effect of filtering out not just ions and molecules but also lager particles. That's what allows the supercooling to work so well, since it's those larger particles that trigger freezing. Mike W.

(published on 02/05/2017)

Follow-Up #49: acetate hot ice

Q: Thanks for all the information on supercooling! Are there any liquids that cannot be supercooled? I'm curious if the creation of "hot ice" from sodium acetate trihydrate is an example of supercooling or is it from supersaturation? Is the amount of latent heat released correlated to the normal freezing point?

- Laura Griffeth (age 38)

Rigby, ID, USA

A: I can't think of any ordinary liquids that can't be supercooled at least a little bit. The liquid-solid transition in 3-D is first-order, which means that even looking at a small region the structure of the liquid and solid look different. That makes it hard for the liquid to find its way over to the different solid state, since in between it has to go through some unlikely state that's not either one. (I guess you could say the liquid 3He can't be supercooled, however. That's because at atmospheric pressure the lowest-temperature phase is actually liquid, not solid, due to some quantum spin effects.) From what I've just read about "hot ice" on Wikipedia, it sounds like the hot ice heaters use supersaturated solutions. The physics behind supersaturation and supercooling are quite similar, however. Getting that first little acetate crystal started is hard, just like getting that first little ice crystal started is hard. What's different is that when the phase transition is done, water forms a crystal. The supersaturated solution forms crystals together with leftover liquid. I think there's a general correlation between the temperature of a phase transition and the latent heat. High temperature transitions tend to involve larger latent heat. It's not a rigid relation by any means, however. In general, phase transitions in any temperature range don't even have to be first-order (although liquid-solid is), which means that they don't even have to have any latent heat. Mike W.

(published on 02/23/2017)

Follow-Up #50: water didn't freeze

Q: I bought Arrowhead bottled water and put several of the bottles in my freezer. After 2-days all but one of the bottles froze. Today is the 7th day and that one bottle is still liquid and not frozen. What could be the cause? Is the water still good to drink?

- John NWOKO (age 65y)

Los Angeles

A: The most likely reason is that each of the other bottles had a fleck of something in it that triggered the freezing. The last bottle maybe didn't have that, so it stayed supercooled longer. Mike W.

(published on 08/03/2018)

Follow-up on this answer.