Glauber's salt, common name for sodium sulfate decahydrate, Na2SO4·10H2O; it occurs as white or colorless monoclinic crystals. Upon exposure to fairly dry air it effloresces, forming powdery anhydrous sodium sulfate. Johann Glauber was the first to produce the salt (from Hungarian spring waters). The naturally occurring salt is called mirabilite. Glauber's salt is water soluble, has a salty, bitter taste, and is sometimes used in medicine as a mild laxative; it is also used in dyeing.