Page 235 - Gas Adsorption Equilibria

4. Volumetric – Gravimetric Measurements 221

Starting with the ideal gas value of the compressibility factor (Z=1), eq. (4.70)
leads to certain mass fractions which inserted in an analytic
expression for and eq. (4.70) can be iterated to converge
(usually after ca. 5 steps) to the sorptive gas mass fractions
needed to calculate from eq. (4.69). Then from eqs. (4.63),
(4.64), (4.67), (4.69) we have for the Gibbs excess masses adsorbed

using again the convention

For sake of completeness we also mention the dispersion or uncertainty of
Gibbs excess masses as given by eq. (4.71). Gauss’ law of propagation
of uncertainty leads to the expression

Here the symbols indicate terms of order

The dispersions used in eq. (4.72) are related to the respective measurable
quantities as follows: