Aqueous magnesium sulfate solutions were prepared to various defined concentrations from commercial MgSO 4 •7H 2 O (Sigma-Aldrich, Gillingham, UK). The experimental setup was described in detail in and consisted of a liquid cell inserted into a hollow metal sample holder. The temperature was controlled by a recirculating water bath. The setup could be used either under stagnant conditions, i.e. the solution was inserted at the beginning of the measurement and the liquid cell was sealed, or in the continuous flow conformation, i.e. the solution was initially kept in a heated syringe that was fixed to a syringe pump, and was slowly injected into the cell.