Celite is often used as filtration medium. Because of its high porosity due to the small and hollow particles it is composed, celite is used to filtrate very fine particles that will pass through normal filter paper.
Solid impurities such as silver iodide will remain in the Hirsch funnel. Organic fractions containing the crude product S2 will go through celite and be collected. The organic fractions will be concentrated in the next step.