Well, that's not exactly the physics, Bill. All the chamois did was serve as a container for the dry ice.

I have a CO2 extinguisher, filled with highly compressed CO2. When I open the valve, the CO2 comes out and expands rapidly (hark back to our discussion about air conditioning some months ago.) There is only a certain amount of ambient energy in the gas (it was at room temperature under great pressure.) It expands and gets really REALLY cold (a couple hundred degrees below zero. The gas sublimates into a solid (dry ice) and begins to evaporate furiously.

The chamois contains the crystals of dry ice and insulates it a bit so the evaporation is controlled a little bit. What makes it feel cold is the rapid evaporation that's taking place.

TEd


TEd