Just found an awesomely scientific take on granite as a ice alternative. (Credit to FlyFish at http://chowhound.chow.com/topics/302440)
"No. Here's why:
Let's assume that the stone "ice" cubes are made of granite and are 1-inch square (I'm going to work the rest of this explanation in SI [metric] units because it's easier and those are the units I use every day - a cubic inch is equivalent to about 16 cubic centimeters [cc]). Let's assume further that you have one of them, which has been kept in your freezer at minus 15 degrees C (more or less zero F) and you want to use it to cool a 100cc glass of water at room temperature (which we'll define as 20 degrees C). Let's also make the simplifying assumption that adding the cube to the drink doesn't change the overall mass of the system - it remains at 100 cc (which, for water, is also 100 milliliters and 100 grams).
The specific heat, which is a measure of how much heat a particular material can hold per unit mass, of granite is about 0.2 (water is defined as 1.0), which means that 0.2 calorie of heat is required to raise the temperature of 1 gram of granite by 1 degree C, and the specific gravity of granite is about 2.6 (again, water is defined as 1). If we multiply all that together, that means that the granite ice cube requires 8.5 calories of heat to warm up by 1 degree C. When you put it in your drink, it absorbs that heat from the 100 cc of water, so how much does the water cool down? Well, there's 35 C degrees difference between the granite and the water, so the granite will absorb 35 X 8.5, or about 300 calories, which will cool the water by about 3 degrees C (one calorie of heat removed from 100 cc of water will cool it by .01 degree, so .01 X 300 = 3 degrees).
Now let's work the same problem with water ice, instead of granite, all other conditions being the same. The water has a specific gravity and specific heat of 1.0, so the 16 cc ice cube will absorb 16 calories of heat per degree C of warm-up, which means (all things being equal, which they're not, as I'll explain in a second) it will decrease the temperature of the glass of water by 16 X 35 calories, or about 5.6 degrees C, nearly double the granite.
But here's the kicker, and this is the big difference: as it absorbs heat, the water ice not only warms up, it also melts, and as water goes from solid ice at 0 degrees C to water at 0 degrees C, there is additional energy required and it's substantial - 80 calories per cc, so in addition to the 16 X 35 calories needed to warm it up, there's an additional 16 X 80 calories required to melt it, for a total of 16 X 115 calories, which is sufficient to cool the glass of water by a whopping 18.4 degrees C (as compared, remember, to only 3 degrees C for the granite).
So, it's really the heat of fusion that makes ice such a good cooler of things, and that only kicks in as the ice melts. Melting granite would also release it's latent heat of fusion (and I don't offhand know how many calories per gram that might be), of course, but that occurs at a temperature that's of less interest for cooling drinks."
By FlyFish on Aug 3, 2005 09:57 AM
