Book 30, Question 102
How does a plant make dirt stick together so it can be removed?
Muddy water holds tiny particles that are too light to sink on their own.
Workers add a chemical called a coagulant, such as alum, which has an electric charge that attracts the particles. Gentle stirring then helps them join into fluffy clumps called floc. The clumps are heavy enough to sink, leaving clearer water above. This is called coagulation and flocculation.