Page 201 - Gas Adsorption Equilibria

4. Volumetric – Gravimetric Measurements 187

(1) Calibration measurement of the empty balance parameters as for
example the so-called “asymmetry of beams” in a two beam balance
or the mass of the permanent magnet and auxiliary equipment
inside a magnetic suspension balance:
(2) Measurement of the loaded balance in vacuum to determine the mass
of sorbent material:
(3) Measurement of the empty balance in an inert gas to determine the
buoyancy of the inner parts like beams, buckets etc. of the
balance:
(4) Measurement of the loaded balance in the sorptive gas atmosphere:

From these four measurements as defined in Eq. (4.4) can be calculated as,
cp. Chap. 3:

In physical terms gives the total mass adsorbed, i. e. the sum of the
masses of both components minus the buoyancy correction term
caused by the volume of both the sorbent (s) and the adsorbate phase (a),
cp. Eq. (4.4).

In Eq. (4.6) the volume of tubes and of the dead space of the gas circulator
has been added. This quantity is assumed to be known from inert gas
calibration experiments. It normally is small compared to the volumes of the
vessels but in principle should be taken into account.

Equations (4.1-4.4) provide four algebraic relations from which the four
unknown masses i = 1, 2) can be determined. Indeed, by adding
Eqs. (4.1) and introducing the microbalance equation (4.4) we get the relation

with