Isotherms deviations from normal

The authors show that depending on the chosen adsorption isotherm, all experimental curves fall into one or deviate from each other. The degree of scattering of the received normalized curves is discussed as a measure for the correctness of the chosen isotherm. 

For systems formed of two associated liquids, there are no reliable methods of isotherms calculation. An empirical method has been proposed, which is based on the assumption that each associated component mixed with the other associated component that does not interact chemically with the first one introduces the rigorously defined contribution into deviation from the volume-fractional additivity. The extent of these deviations for the first representatives of the series of aliphatic carbonic acids and alcohols of normal structure, as well as for some phenols, are given elsewhere. ... 

In the case of adsorption on a uniform surface, Henry s law is to be expected at low surface coverage [11, 22]. Unless the operational temperature is relatively high, the Henry s law region is normally restricted to a very small part of the isotherm (e.g., below p/p° l X 10 ) and the deviations may be in either direction. From a fundamental standpoint, the virial analysis of low-coverage adsorption data is important since it is analogous to the treatment of imperfect gases and nonideal solutions [22]. 

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