When you open a container of yogurt, you'll often see liquid collected on top. What is it, and where does it come from?
Why is it okay to bleach cotton cloth, but not wool?
Things like coffee grounds and charcoal are called “physical deodorizers,” because they absorb tiny particles in the air that are causing the smell. The problem is, eventually they reach a state called “equilibrium,” in which the deodorizer has absorbed all it can.