Sodium sulphate, data, equilibria

Figure 5.35. If RH over a saturated solution of sodium sulphate decahy-drate (A-B) is reduced, the solution is dehydrated and solid decahydrate is formed. When below a certain RH value, decahydrate emits the chemically bound hydrate water and is transformed into anhydrite (B-D). The boundary curve denotes RH over a decabydrate-anbydrite salt pair in thermodynamic equilibrium. The curve B D corresponds to this expression (b) measurement values denote the experimental data, cf. Timmermanns.

These studies were undertaken using a pressure-jump apparatus over the time range 10-10 sec. incorporating a rapid data capture and analysis system. The polymer, polyvinylpyrrolidone, PVP, (Aldrich) was used without further purification. Sodium dodecyl sulphate, SDS, (Henkel) was chosen as the surfactant system, since a considerable wealth of equilibrium data were already available involving this surfactant. SDS was purified by repeated recrystallisation from two solvents until the relaxation time at the CMC agreed with literature values. 

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