An interesting experiment is to mix the ordinary ammonium nitrate (a fertilizer) with room temp. water. Try to put in as much ammonium nitrate as it is possible to dissolve. You will see the temperature of the mixture DROP to below the freezing point (for pure water that is). Wow. I did that 12 years ago and was amazed. A really easy way to get cold water if no freezer is available. - Igor.