If you're outside on a hot day and your drink is hot (in our case, it was palettes and palettes full of bottled water), get a wash rag or a skivvy shirt wet, wrap it around your drink container, and let it sit out in the sun. In a little while, voila, cold drink.
Apropos of nothing.
The bag was canvas and leaked slightly--enough to keep the outside moist so that the contents would chill from the wind as the vehicle drove along. The water was nice and cold, just right for a hot summer's day.
Oddly, I don't see them any more. Perhaps there are enough roadhouses along the highways that anyone can pull in and buy a chilled soft drink when they want.
The British Royal Society offered a 1,000 pound prize recently for an explanation, so far this is the winner, though it's not complete:
If the water is purified, ie. steam distilled, the warm vs cold effect disappears?
Ice needs to form a particular crystalline structure when it freezes. This is what makes ice float in water. The molecules in warm water are moving faster and therefore have a greater chance to wander into this correct formation. The cold water molecules are moving more slowly and simply take more time to find the correct alignment.
There wasn't really any proof to this theory, but it was followed with a bunch of anecdotal evidence, like Canadian's washing their cars with cold water, etc.
The law is correct for when you can assume a constant Te, for example an object within a fluid flow (like an airplane wing during flight). The problem is, for stagnant situations, convection plays a huge role in heat transfer within the air. Controlling convection is really really hard, and even harder in a scientific setting that needs to be reproducible. Also, when dealing with transition temperatures, various things need to be taken care of, such as supercooling. This can literally stop working if your beaker is slightly dirty. So the problem is there isn't a way to universally control the conditions for this experiment. However, I did find that the winner of the RSC paper had a suitable explanation that involves the presence of supercooling for the colder sample of water. Essentially, if the colder sample supercools, it will take slightly more time to freeze, because while it should have frozen, the ice does not have a nucleation site. On the other hand, the warmer sample does not supercool, and freezes upon reaching 0 C. This experiment only works if the temperature difference is slight, probably within 15-30 C. Quite ingenious really!
Edit: After reading the rest of the comments, air bubble/filtered water/de-ionized water all have great effects on ice nucleation and supercooling, which for me supports the winner's paper.
This isn't "unexplained" unless you never took a college level physics course, which is pretty typical of the people who edit WikiPedia pages.
1. Prepare a glass with a little ice
2. Prepare a glass with a lot of ice
3. Pour the same amount of cocktail into each glass (make sure it's identical)
5. Simultaneously strain both glasses into measuring cups
6. See how much liquid came out of each glass
Sadly, most of the worst pseudo-science is too, which makes it largely useless as an indicator.