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Glass Retort: a Blown Bulb with a Long Neck Bent Down
A retort is the old distilling vessel: a round glass bulb whose long neck bends down to a receiver, so the neck itself condenses the vapour. Alchemists used it, and so did Lavoisier and Berzelius before condensers. Blow a bulb on a long tube, bend the tube down in a wide flame, and add a corked filling hole on top.
The picture: a mid-19th-century glass retort with a stoppered filling hole (Wellcome Collection).
Advanced
Two hours, plus annealing
Instructions
1
1
Blow the bulb on a long tube
Blow the bulb on a long tube
Close one end of a long tube, gather glass and blow a round bulb, as for a flask. Keep the rest of the tube full length for the neck.
Materials for this step:
Glass Tubing Kit1 pieceTools needed:
Bench Glassblowing Torch
Safety Glasses
Heat-Resistant Gloves2
2
Bend the neck down
Bend the neck down
Warm a long stretch of the tube just past the bulb in a wide, soft flame, turning it, until it bends under its own weight. Bend it smoothly so the neck slopes down at a sharp angle, without kinking.
Tools needed:
Bench Glassblowing TorchHeat-Resistant Gloves3
3
Filling hole
Filling hole
Heat a spot on the top of the bulb, blow it out into a small bubble, break it off and open it into a short collar with the jacks for a cork.
Tools needed:
Bench Glassblowing Torch
Jacks
Corks4
4
Cut and anneal
Cut and anneal
Cut the neck end square, fire-polish it, and anneal the retort in the kiln, cooling slowly.
Tools needed:
Diamond ScriberBench Glassblowing Torch
Kiln5
5
Neck length for cooling
Neck length for cooling
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Materials
1- 1 piecePlaceholder
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