Applications of magnesium sulfate monohydrate MgSO4 · H2O
Magnesium sulfate is frequently used in the laboratory, especially after aqueous work-up.
Aqueous work-up is a common technique in the lab to get rid of residual impurities after completion of a reaction.
For this the organic solution of the reaction is cooled to room temperature and mixed with water. Specific impurities will then diffuse into the aqueous phase and can be separated with a separatory funnel. 
Unfortunately some residual water will stay in the organic phase and this can have negative impact for following characterization of the compound.
Therefore magnesium sulfate is added, which is able to catch the residual water in its crystal lattice. After filtration of the solid magnesium sulfate, the water is reduced to a non-significant amount and the compound ready for further investigation.