The lattices of crystals very often contain parts of the solvent. This has not much to do with fast or slow evaporation but with the nature of crystals and how they form. Many substances need the molecules of the solvent to crystallise (or co-crystallise) properly.MagikVenom said:Pure xtals must build there lattice structure SLOWLY or they will trap impurities in the lattice.
Infundibulum said:Dessicants absorb moisture e.g. water.