|MadSci Network: Chemistry|
Dear Mark, Dry ice is made by compressing gaseous carbon dioxide to between 900 and 1,000 pounds per square inch. The compressed gas is cooled to remove the heat generated during compression. It turns to liquid CO2 during this step. The cooled liquid carbon dioxide is then sprayed into an enclosed expansion chamber where it expands to atmospheric pressure. At this point it is about -70 deg. F. Some of the expanding CO2 is flash cooled during the process to about -110 deg. F. This portion solidifies into 'snow' which is removed from the chamber and mechanically compressed into standard 50-pound blocks which measure 10 inches on a side. This part of the process is much like making snowballs out of regular water snow. I hope this helps. The McGraw Hill Encyclopedia of Science and Technology, 5th Edition, 1982.
Try the links in the MadSci Library for more information on Chemistry.