What is typically used to filter liquid drugs after heating them?

The use of a cotton ball to filter liquid drugs after heating is grounded in its ability to effectively trap particulate matter while allowing the liquid to pass through. When a solution is heated, it may contain undissolved substances or impurities that could affect the safety and efficacy of the medication. The cotton ball acts as a simple yet effective filtration medium, as its fibrous structure captures these unwanted particles without letting the liquid escape.

In contrast, other items like a pencil or a strainer may not be designed for this specific purpose. A strainer could be too coarse or may allow smaller particles to pass through, while a pencil serves no functional role in the filtering process. A paper towel might absorb some liquid, potentially wasting medication, and may not filter effectively for finer particles compared to the cotton ball. Thus, the cotton ball remains the most suitable choice for this task.