Simultaneous gravimetry and manometry

Gravimetry can also be associated with adsorption manometry, which is a simple and safe way to study co-adsorption of two gases, provided their molar masses are sufficiently different (Keller et al, 1992). The manometric experiment provides a total amount adsorbed n°a = n° + n%, whereas the gravimetric experiment provides the total mass adsorbed m t=m° + m. Since n°Mx = m and n M1 = m we have two unknowns, n° and n, and two equations. From these we can obtain, for instance  

On practical grounds, some difficulties stem from the large volume of adsorption balances to measure pressure changes due to adsorption accurately, one must usually place a considerable amount of the adsorbent outside the balance pan (because of the limited loading capacity of the balance) yet close enough to be at the same temperature. 

Other techniques that have been introduced recently in association with adsorption manometry include the use of a magnetic suspension balance (Dreisbach et al., 1996) and a rotational pendulum (Keller, 1995). 

Most experiments described in Section 3.2.1 (with the exception of adsorption gravimetry) rely on the use of a calibrated volume. The basic calibration can be carried out in two ways directly or indirectly. Direct calibration implies that this part of the equipment can be isolated, removed and weighed (either evacuated or filled with dry air), filled with an outgassed liquid of known density and then weighed again. 

A practical limitation comes from the loading capacity of modem analytical balances. It is difficult to find a balance with a sensitivity of 0.1 mg and a loading capacity of more than c. 300 g. This means that the stainless steel gas storage vessels 

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