  Supercooling of water can be easily studied with a simple apparatus suitable
for the student laboratory. We describe such an apparatus and its capabilities.
The parameters influencing supercooling include the initial temperature of the
water and the temperature and the type of chilling medium. We correlate the
occurrence of supercooling with the ability of the chilling medium to promptly
nucleate ice; if it nucleates promptly, the layer of ice crystals formed on the
boundary will initiate freezing of the bulk water without supercooling. If the
chilling medium is unable to nucleate ice promptly, ice nucleation is delayed
and the water supercools. Students can study and compare supercooling of
distilled and natural water. Even quite dirty river water may be supercooled by
as much as 5 C.
