Re: What can I mix with water to make it stay frozen longer?
Ok, it has been a few years since chemistry class, but here goes.<br /><br />There is a concept called something like "latent heat of something or other" at any rate, for a solid to change state to a liquid, it takes a certain amount of heat to change a certain amount of ice (solid) to water (liquid). As this process continues, it uses heat (leaking in to the cooler) to change the ice to water, thus keeping the contents of your cooler cold. The rate at which the ice melts will be determined by the amount of heat leaking in, and the surface area of ice exposed to it. (Thus small cube ice will keep the cooler colder for short periods, but will melt quicker due to the increased suface area.)<br /><br />Once the ice has all melted, then this process is lost, and it takes, by definition, 1 cal of heat to change 1 ml of water 1 deg Cent.<br /><br />The process of changing state from solid to liquid is what allows you to keep the contents of the cooler cold. Once it turns to liquid, the contents, including the water, will all raise temp at the same rate. There may be better products out there, like the ice packs you buy at the sports store--I have no idea--but as far as water is concerned, pure water is best, and anything added to it will lessen its performance.<br /><br />As a sidelight, do you know why the anti-freeze in your car is mixed water and anti-freeze? It is because the water mixed with the anti-freeze will lower the temperature at which the anti- freeze will freeze --much in the same way that anything mixed with water will lower its freezing point. Pure anti freeze will freeze at a higher temperature that when mixed with water (at the right ratio, of course--something like 30% water and 70% anti-freeze) At some point in this graph, the anti-freeze no longer inhibits the water freezing, but rather the water inhibits the anti-freeze freezing.
