Dry ice is colorless, odorless, and non-flammable. It is slightly acidic. The density of dry ice varies. In general, the common density of dry ice is 1.4 to 1.6g/cm3. Dry ice is sometimes called flake ice, and this name is a trademark registered by Gas Liquid UK Ltd. In the mass production of dry ice, the first step is to over-compress the carbon dioxide gas until the carbon dioxide liquefies. During the compression process, carbon dioxide begins to generate heat. If the excess heat is removed and the gas is kept at room temperature, the carbon dioxide will begin to liquefy at a pressure of about 61 kg per square inch.