Laboratory Glass Funnels

Use a separating funnel for liquid-liquid extraction. Use a filter funnel for gravity filtration through filter paper. Use a powder funnel for transferring dry solids into narrow-neck vessels. Use a dropping funnel to add liquid reagents at a slow, controlled rate for exothermic reactions.

PTFE stopcocks are self-lubricating, require no grease, and are resistant to nearly all laboratory solvents and acids — they are the preferred choice for modern laboratory use. Glass stopcocks require stopcock grease which can dissolve in organic solvents like chlorinated solvents, potentially causing seizing or leaking.

For separating funnels, select roughly twice the total volume of both liquid phases to allow headspace for shaking. Common sizes are 100 ml, 250 ml, and 500 ml. For filter funnels, match diameter to your filter paper size. For dropping funnels, choose a volume that holds your full reagent charge with some headspace, typically 50 to 250 ml.

Use fast-flow coarse-pore paper (Grade 1 or 4) for large crystalline precipitates where speed matters. Use medium-grade paper for general gravimetric work. Use fine-pore paper (Grade 42) when retaining very fine particles for quantitative analysis. Always wet the filter paper before use to seat it in the funnel cone.

A separating funnel holds two immiscible liquid layers that are separated by draining the lower phase through the stopcock. A dropping funnel is designed to dispense a liquid reagent into a reaction flask at a controlled rate via a ground-glass joint while the reaction is actively running.

Fast-flow papers (Grade 1, 4) suit large crystalline precipitates. Medium-grade papers suit general gravimetric work. Fine-grade papers (Grade 42) retain the finest particles for quantitative analysis. Always wet the paper with solvent first to seat it and prevent liquid bypassing at the edges.

Borosilicate glass is chemically resistant to most organic solvents, but the stopcock grease can dissolve in chlorinated solvents like dichloromethane, causing seizing or leaking. For organic solvent work, a PTFE stopcock is strongly preferred as it needs no grease and resists virtually all laboratory solvents.

A powder funnel has a wide, short stem that allows dry solids to pass without bridging. It is used to transfer powdered or granular reagents into narrow-neck flasks or bottles, charge reaction vessels with solid catalysts, and fill chromatography columns without spillage.

After each use, remove and clean the stopcock plug and barrel with solvent. Apply a thin layer of stopcock grease, reseat, and rotate until uniform. Never leave in place for extended periods. If seized, soak in warm water. Switching to a PTFE stopcock funnel eliminates these maintenance concerns.