The spectra of crystals grown under the conditions similar to the crystallisation in the flow cell exhibited less temperature-dependent behaviour. The feature at 1.2 THz was slightly more intense at low temperatures, while the peak at 1.7 THz was consistently observable in the whole temperature range. The latter shifted to 1.6 THz upon heating to room temperature, though as a single feature rather than a double one at temperatures above 80 K. The high similarity between the terahertz spectra of heptahydrate and grown crystals, especially at 294 K, confirmed that the crystals grown in the crystallisation cell were indeed MgSO 4