Lynne Wong's PhD thesis

Table 5.4. Water activity (a w ) of aqueous sulfuric acid solutions at selected
concentrations and temperatures (Rüegg, 1980).
Concentration of
Water activity a w
sulfuric acid
solution/% (m/m) 30 °C 45 °C 55 °C* 60 °C
5 0.9808 0.9812 0.9816 0.9818
10* 0.9746 0.9751 0.9760 0.9764
20 0.8814 0.8839 0.8868 0.8882
30 0.7549 0.7629 0.7684 0.7711
40 0.5711 0.5866 0.5948 0.5989
50 0.3574 0.3765 0.3879 0.3936
60 0.1677 0.0548 0.1937 0.1988
* The water activity values for all sulfuric acid concentrations at 55 °C and
for the 10% (m/m) sulfuric acid solution at all temperatures have been
interpolated from the other data.
Bulk solutions of 2 kg sulfuric acid reagent were prepared from BDH laboratory reagent
grade sulfuric acid of 96% purity and kept in winchesters ready for use. Since the purity of
the acid was only 96%, the mass of acid used per 2 kg solution was as indicated in Table
5.5.
Table 5.5. Masses of reagents required to prepare 2 kg sulfuric
acid solutions of various concentrations.
Concentration of
sulfuric acid
solution/% (m/m)
Mass of 96%
H 2 SO 4 /g
Mass of distilled
water/g
5 104.2 1895.8
10 208.3 1791.7
20 416.7 1583.3
30 625.0 1375.0
40 833.3 1166.7
50 1041.7 958.3
60 1250.0 750.0
5.6.2 Equipment
Instead of the flat silica dishes used by Kelly (1957) to spread sugar cane fibre before
exposure to a prepared atmosphere, alternative options were evaluated in this work to
avoid loss of sample and the risk of desorption of the adsorbed water from taking place.
Glass bottles of 60 mm diameter and 70 mm height with snap-on metallic caps were found
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