The Ice Water Bottle

water is clean, plastic is clean, no nucleating sites = super cooling, a common phenomenon.

Google it or wiki it

I've seen this happen with the squeezable freezer pops (the long plastic tubes) when I was a kid, blew my socks off back then.

One would think that the heat of fusion would keep some of the water from freezing. I believe it is 144 btu/lb. A freezer usually operates around 0 degrees F. So the most one could supercool water would be about 30 btu/lb. I would think that only about 1/5 of the water would freeze. I don't know what the specific heat and heat of fusion for supercooled water is though, so my estimate could be off.

I don't remember the numbers, but you are essentially correct. The supercooled liquid can be several degrees below freezing; when agitation or the introduction of a seed crystal initiates freezing, the heat released by crystal formation brings the temperature up until the result is a mixture of solid and liquid. If the water was pure (distilled), the final temperature is exactly 0 degrees celsius, and remains so until outside heat melts the ice. This is a great way to calibrate zero on thermometers.

Thank you guys for the explanation the seed crystal is a clear explation to me, no maggic at all

Ciro

I would like more specific information so i can do this for school science project.

I did it many times when I was teaching physics. There are a few details for it to work reliably. 1. The water needs to be fairly pure, but not necessarily distilled. 2. The container needs to be transparent so the students can see the action, and smooth inside (scratches or points are places where freezing can initiate). Since glass is not a particularly good conductor of heat, a thinner walled container is probably better. The tabletop or other surface needs to be pretty free of vibrations (if the room has a wooden or otherwise flexible floor, you must keep people from walking near) while it it cooling.

Here is the procedure:

1. Pre-cool the container (a new 500ml beaker is good) nearly full of the pure water to near freezing in a refrigerator or ice-water bath. Also pre-cool an accurate glass or electronic thermometer (not necessary, but may speed things up slightly). Ideal would be a large-digit electronic thermometer that everyone can see (I never had one).

2. Away from the water container (to prevent contamination) prepare a significantly larger diameter container of salt and ice, with enough mixture to reach close but not all the way, to the top of the water container. I found it instructive to place a second thermometer in this mixture, to show it's temperature.

3. Place the water container in the salt-ice-water mixture carefully (don't splash salt water into pure water), and place the thermometer in the pure water if it isn't already there.

4. Have the students do some reading or writing, while you wait without touching the assembly for the temperature to drop. It must reach at least a couple of degrees below 0°C; -4 to -5 would be better. It seems like I had to wait around half an hour, but its been a long time... The colder it gets, the greater is the danger that that freezing will start spontaneously from vibration or a bit of dust falling into the water, or whatever. Practice a few times with no one around to see your initial fizzles!

5. When the desired temperature is reached, get a few tiny pieces of pure ice (not from the salt-ice mix) handy, like on a paper towel. Geeennnntttlllyyy remove the water container from the salt-ice mix, and geeennnntttlllyyy swirl it just a bit to show that it is still liquid.

6. You can do several things to initiate freezing. I prefer to use a pair of plastic tweezers (plastic doesn't melt the ice as fast as metal, so I can use a smaller seed) to drop a seed of ice into the water. You can also stir it with the thermometer, tap the thermometer on the side or bottom, snap the side with your finger, etc. If you have gotten it down to -5 or colder, it may well start to freeze just from the motion of lifting it out of the salt-ice mix.

Crystals will grow outward from the point of initiation. Depending on conditions, the growth may continue from a fraction of a second to several seconds. The result is normally a feathered mix of extremely thin crystals in water. I think its beautiful! Note the reading of the thermometer: if it doesn't say 0°C (or 32°F), then either the water is impure or the thermometer isn't calibrated correctly!

Of course you could do all of this with a freezer instead of the salt-ice mix, but then it would not be constantly visible, so some might think you did some 'magic' while it was hidden. I've never tried it, but it might be interesting to try using a Peltier effect cooling system, like one removed from an electric portable cooler.

Good luck and have fun!

Dick