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Separating Funnel: Glass Stopcock with a Screw-On Plastic Stem (Demers, US 5,580,528)
Charlie

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Charlie

9. November 2026DE
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Separating Funnel: Glass Stopcock with a Screw-On Plastic Stem (Demers, US 5,580,528)

A separating funnel holds two liquids that do not mix, so the lower layer can be run off through a tap at the bottom. J. P. Demers (US 5,580,528, 1996) fuses a bought glass stopcock to the bottom of a pear-shaped glass vessel and screws a flexible plastic stem onto it, because the usual glass stem breaks just below the stopcock. The glass stopcock body stays clear, so you can watch the boundary between the two liquids as it reaches the tap. Source: J. P. Demers, US Patent 5,580,528 (filed 1995, granted 1996). Picture: its Figs. 1-3.
Advanced
Unknown

Instructions

1

Read Demers

"The stresses resulting from such impacts usually fracture the glass just below the stopcock, or else chip off the end of the stem ... When the fracture is close to the stopcock, repair is impossible without replacing the stopcock".
2

Blow the vessel

Blow a glass vessel, pear-shaped (or spherical or cylindrical), with a neck at the top for pouring in the liquids and an opening at the bottom. Glass, size and how it is blown are not given; the patent leaves this to a scientific glassblower.

Materials for this step:

Unknown GlassUnknown Glass1 vessel

Tools needed:

Bench Glassblowing TorchBench Glassblowing Torch
Unknown Forming MethodUnknown Forming Method
Unknown DimensionsUnknown Dimensions
3

Fuse on the stopcock

Take a glass-bodied stopcock (bought: the patent calls them articles of commerce, with a glass or PTFE plug) and fuse its upper stem to the bottom of the vessel so the vessel opens straight into the stem. Form a male thread on the end of its lower stem (how is not given).

Materials for this step:

Glass StopcockGlass Stopcock1 plug of glass or PTFE

Tools needed:

Bench Glassblowing TorchBench Glassblowing Torch
Unknown Forming MethodUnknown Forming Method
4

Make the plastic stem

Make a stem of moderately flexible plastic tube with a female thread in its upper end and an inner shoulder where the end of the glass thread meets it. Lay an O-ring on the shoulder when the funnel will hold reactive or toxic liquids or work under pressure or vacuum. Cut the lower end at about 45 degrees as a drip tip. The plastic is not given.

Materials for this step:

Unknown MaterialUnknown Material1 flexible plastic stem
O-RingO-Ring1 piece

Tools needed:

Unknown Forming MethodUnknown Forming Method
Unknown DimensionsUnknown Dimensions
5

Assemble and use

Screw the plastic stem onto the glass thread. Close the stopcock, pour the two liquids in at the neck, shake and let them separate, then turn the plug to line its bore up with the stems and run the lower layer off, watching the boundary through the glass stopcock. Unscrew the stem to clear a blocked stopcock.

Materials

4

Tools Required

3

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