Why Does Dry Ice Not Melt?

Sublimation of Dry Ice

If all matter can exist as a solid, liquid or gas then why does dry ice not liquefy? Actually, this is a trick question. Under laboratory conditions, dry ice or frozen carbon dioxide turns to a liquid when air pressure is 870 pounds per square inch. At normal air pressure, dry ice will go directly from a solid to a gas through the process of sublimation. Likewise, at sea level, water normally boils at 212 degrees Fahrenheit but at a higher elevation, water can boil at a much lower temperature. The same also holds true for freezing temperatures. In the absence of high salinity (salt), water freezes at 32 degrees Fahrenheit. Salt actually reduces the freezing temperature of water hence it is commonly used to melt ice.