Water actually does start to freeze at 4 deg C.
Every compound actually has a 'freezing range' of a few degrees. What I find interesting here is that the hot water stays at this temperature for far less time than the cold water. I would call this a 'critical point' in the transition of liquid to solid. I liked the idea of dissolved gasses in the water affecting this. It appears that dissolved oxygen and nitrogen appear to interfere with water crystal formation. As dissolved salts do, but to a lesser extent.
Back to my point. The dissolved gas molecules interfere with ice crystal formation. Therefore the lattice energy (lattice energy is the amount of energy released when a liquid freezes) is higher because the water molecules have to 'kick out' the gasses from their crystal lattice in order to freeze effectively.
Evaporation is a very minor effect when both liquids are at 4 deg C IMO. Convection currents (warm water rising to the surface) are a lot harder to explain however. Convection currents make liquid temperatures non-uniform and therefore an average temperature has to be guessed at. Making the experiment inaccurate.
One of the factors that make liquids so hard to study is that convection is very hard to quantify. This is also true with gasses in some cases. Which is why atmospheric weather conditions are so hard to predict.
Anyway, just some thoughts on the subject. <img src="/ubbthreads/images/graemlins/alien.gif" alt="" /> Chill homes. <img src="/ubbthreads/images/graemlins/silly.gif" alt="" />
