Liquefied compressed gases definitions

Cryogenic Liquid A cryogenic liquid is a refrigerated liquefied gas having a boiling point colder than -130 °F at one atmosphere, absolute. A material that meets this definition is subject to the same requirements tor compressed gases widrout regard to whether it meets the standard definition of a compressed gas. 

Aerosol technology may be defined as involving the development, preparation, manufacture, and testing of products that depend on the power of a liquefied or compressed gas to expel the contents from a container. This definition can be extended to include the physical, chemical, and toxicological properties of both the finished aerosol system and the propellants. 

Let us clarify the nature of the fluid phases (liquid and gas) and of the critical point hy describing two different ways that a gas can he liquefied. A sample at point IVin the phase diagram of Figure 13-18b is in the vapor (gas) phase, below its critical temperature. Suppose we compress the sample at constant T from point IV to point Z. We can identify a definite pressure (the intersection of line IVZ with the vapor pressure curve AC) where the transition from gas to liquid takes place. If we go around the critical point by the path WXYZ, however, no such clear-cut transition takes place. By this second path, the density and other properties of the sample vary in a continuous manner there is no definite point at which we can say that the sample changes from gas to liquid. 

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