The one stop source for all your CO2 information.
CO2 Properties
Carbon Dioxide can exist in three states; Gas, Liquid & Solid.

Gaseous Carbon Dioxide
CO2 gas is heavier than air with a specific gravity of 1.53 at 70 dF
At normal tempatures and pressures, CO2 is colorless with a slighty pungent odor at high concentrations. If compressed and cooled to proper tempatures the gas liquifies.  Solid CO2, dry ice sublimates back to the natural gaseous state.

Liquid Carbon Dioxide
Liquid CO2 is produced by compressing and cooling CO2 gas. This liquid is a clear transparent fluid. Liquid CO2 cannot exsist as a liquid at atmospheric pressure. It must be pressurized above 60.4 psi  to remain as a liquid. At this pressure, Triple Point, CO2 can exsist as liquid, gas and solid. Below this pressure it will flash to a gas and solid. CO2 above a temperature of 87.9 dF Critical Point cannot exsist as a liquid.
Normally liquid CO2 is delivered and maintaned at 0 dF and 300 psi.

Solid Carbon Dioxide
Solid CO2 is commonly refered to as Dry Ice. It is produced by allowing liquid CO2 to expand to atmospheric pressure which forms dry ice snow. This snow is then compressed to form blocks and pellets. Dry ice at atmospheric pressure is -109 dF.