Several people have mentioned that water gives off heat as it freezes. If I remember my physics accurately it is quite a lot of heat. 1 calorie is the amount of heat it takes to raise one cc of liquid water 1 degree F. It takes 80 calories to change from ice to water and vice versa. In other words the amount of heat it would take to raise the temperature 80 degrees is what is absorbed by melting ice or given off by freezing water. Just imagine the tremendous number of calories that are being absorbed presently by the melting ice caps at the North Pole. Once that ice is gone imagine how hot it could get without something out there to absorb the excess. Bob Pries, zone 5-6 having a rather warm November day. And we our normal hard frost is about 20 days overdue. --- Jonathan Knisely <yale@email.med.yale.edu> wrote: > I tend to favor Jim McKenney's explanation. > > What I have observed, and what I have read, is that > there may be a difference > among plants in their ability to tolerate > subfreezing temperatures based upon > the presence of 'antifreeze-like' soluble compounds > that can prevent the > nucleation of ice crystals in plant cells. > Differences between kale and > lettuce might be partially explained by something > like this. I don't believe > that the cells would 'want' to deplete themselves of > water--what would they do > when the temperature got higher at midday? > > I wonder whether the anecdotal benefit of dousing > frosted plants (that are not > frozen) with water is because of the significant > heat capacity of water as it > undergoes a phase change from liquid to solid. The > splash of water would > prevent the nucleation of intracellular ice--all > that 'outside' water would > need to freeze before the intracellular water (with > those special solutes) > would freeze. > > Jonathan Knisely > Coastal Connecticut, USDA 6a > _______________________________________________ > pbs mailing list > pbs@lists.ibiblio.org > http://www.pacificbulbsociety.org/list.php > http://pacificbulbsociety.org/pbswiki/ >