Note the stopcock, glass tube at the left rear, and ground glass joint in this pressure-equalizing dropping funnel.

A dropping funnel is a type of laboratory glassware used to transfer fluids. They are fitted with a stopcock which allows the flow of to be controlled. Dropping funnels are useful for adding reagents slowly, i.e. drop-wise. This may be desirable when the quick addition of the reagent may result in side reactions, or if the reaction is too vigorous.

Dropping funnels are usually fitted with a ground glass joint which allows the funnel to fit snugly onto, e.g. a round bottom flask. This also means it need not be clamped separately.

Pressure-equalizing dropping funnels have an additional narrow-bore glass tube from the bulb of the funnel, to the ground glass joint around the stem. Without means to equalize the pressure between a sealed receiving flask and the bulb of the funnel, the flow of fluid will rapidly come to a halt.

See also

• Separatory funnels are similar in shape and design, and may be used as dropping funnels. They do not have the ground glass joint at the stem.