Alum is a chemical known as a flocculator which functions to agglomerate impurities in the water purification process. Alum is often used as a water purifier, because turbidity in water can be removed by adding a type of chemical called a coagulant. As for other uses of alum, it can absorb body odor, especially in the armpits, prevent excessive sweating in the armpits, so that the armpits don't smell easily, can prevent black armpits and can help stimulate the body's natural scent. Aluminum Sulfate