ABSTRACT
Matter generally assumes one of three forms (or phases): gas, liquid, or solid. Gases are essentially shapeless and formless, and naturally or artificially exist or co-exist with the other two phases, such as in sponge, cork, aerogel, cake, for example. In fact, gas molecules are capable of penetrating into a liquid or solid phase to create mixtures. Table 1.1 presents a summary of typical gas/liquid and gas/solid mixtures.
