A Büchner funnel is a laboratory apparatus used for filtration. It consists of a circular, perforated plate that is typically made of porcelain or plastic, mounted on a stem. The funnel is designed to hold filter paper, allowing liquids to pass through while retaining solid particles. It is commonly used in chemistry and biology labs for separating solids from liquids in various experiments. The Büchner funnel is often used in conjunction with a vacuum source, such as a vacuum pump or water aspirator, to enhance the filtration process. This setup creates a pressure difference that speeds up the flow of liquid through the filter paper, making it an efficient tool for purifying substances or collecting precipitates.