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Why not fill the gap with a liquid that evaporates slowly, some kind of alcohol? For something to evaporate it must draw heat from something else and if you make the wall of the next to the jar thinner than the one next to the bath it should draw heat from the jar ......... sheesh it's just after 8am and this is too much thinking. Hope it makes some sense.

I KNOW that there is some element that will cool water down quite a bit when mixed, could be some sort of salt, but not regular cooking salt (NaCl).

Here's my suggestion (dunno if it'll do the trick sufficiently):

KrazyKraut posted the following in this thread about hot/cold packs...

theres a chemical inside that gets cold and stays cold

if u mean the instant ones
the ones where u hit and get cold
the secret is when i hit it u crack open a chemical pouch
that mixes wid the chemical that was around the pouch
than u r suppose to shake it
that further mixes the chemicals
to get it really cold

Now, get as many of these packs as you need (drop by the nurse or the P.E. teacher, maybe?), the clue is they will be room temperature when you bring them in (and thus according to the rules), and your "drink" will even be colder after 16 minutes than at the start, without any insulation at all . Just be sure to make a "Speedguide.net" sticker and put it on the can.

Should at least get you the smart-ass award or something !

Cheers,
Ronald

i believe what people are referring to is ammonium nitrate, NH4NO3. ammonium nitrate and water will yield a endothemic reaction.

should you choose to go this route, i would suggest just buying a cold pack, cut it open, take the powder (ammonium nitrate) out. becareful not to mix it with water and keep it in a sealed container until use.

you can also get this material in some gardening stores.

Lol.. I'll go ask the teacher tomorrow @ school...
"Am I allowed to add ammonium nitrate to my water?

Although I'm pretty sure its a definite NO, I'll give it a whirl.

You can use air as the insulator very easily. all you need it a small sheet of bubble pack and some tape to hold it onto the can. the "big cell" bubble packing would probally work better (more air between the warm water and the can).

Originally posted by brembo
Find a schematic a thermos on google. Use a design similar. Air is one of the best insulators out there. The lack of air(vacuum) is even better.

Bingo. The first thing that came to mind was a vacuum.

I would go to a party store and buy a few mylar ballons. Then I would layer it and styrofoam around the can.

Mylar is a awesome insulator, one of the main things that protects astronauts.

Mylar:
The trade name of DuPont for their product used as thermal blanketing. It is a very thin material that has a shiny appearance. It is often used as an insulator in satellites, as well as for things on Earth like juice box packaging and emergency first-aid blankets.

http://quest.arc.nasa.gov/space/teacher ... 5emu1.html

You guys no un natural products>> STYE FOAM BUBBLE WRAP ETC


wrap it in whale blubber or seal skin, or polar bear bum fur

Not sure if you figured this out yet but, If you wrap black electerail tape around the can, Then coat the can with a nice layer of candle wax it will stay cool quite awhile.

You know, you could probably try duct tape as well.. 1,75 cm thick duct tape around it would probably keep it cool for a while (that would be the ghetto-version)