Supercritical Fluid

If carbon dioxide is heated under high pressure, the liquid density decreases but the gas density increases.  When the pressure is above 72.8atm and the temperature above 304.2K, the densities of the gas and liquid are equal.  A meniscus between the two states does not exist and hence we have a supercritical fluid. 

A supercritical fluid can fill a container like a gas but can act as a solvent, and can be used in the extraction of caffeine.  Carbon dioxide is passed over beans and dissolves between 97 and 99% of the caffeine into solution.  This method is non-toxic.