A dropping funnel, also known as an addition funnel, is a type of laboratory glassware used to transfer liquids. It is equipped with a stopcock that allows precise control over the flow. Here are some key points about dropping funnels:

1. Slow Addition of Reagents: Dropping funnels are particularly useful for adding reagents slowly, drop by drop. This controlled addition is desirable when rapid addition could lead to side reactions or if the reaction is too vigorous.

2. Ground Glass Joint: Dropping funnels typically have a ground glass joint at the bottom, allowing them to fit snugly onto a round-bottom flask. This joint ensures a secure connection without the need for separate clamping.

3. Pressure-Equalizing Dropping Funnels: Some dropping funnels include an additional narrow-bore glass tube from the bulb of the funnel to the ground glass joint around the stem. These are called pressure-equalizing dropping funnels. They serve a crucial purpose when handling air-sensitive reagents in a sealed, inert-gas environment. The narrow tube equalizes the pressure between the sealed receiving flask and the funnel bulb, preventing the flow of fluid from coming to a halt.

4. Separatory Funnels: While similar in shape and design, separatory funnels can also be used as dropping funnels. However, they may not always have the ground glass joint at the stem and instead feature a narrow tube suitable for insertion into a rubber stopper.