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Glass Pipettes: Tube Drawn to a Tip, Graduated by Weighing Water
A pipette is a straight glass tube drawn to a narrow tip: dip it in, close the top with a finger, and let out just the volume you want. Drawn and left plain it is a simple transfer pipette; marked along its length it is a graduated pipette, and a Mohr pipette starts its marks well above the tip and is read as it drains.
The picture: our diagram of a plain and a graduated (Mohr) pipette.
Intermediate
Half an hour per pipette
Instructions
1
1
Draw the tip
Draw the tip
Heat a band of straight, even tube while turning, take it out and pull a short taper, as for a capillary. Cut it at the taper to leave a tip about 1 mm across.
Materials for this step:
Glass Tubing Kit1 pieceTools needed:
Bench Glassblowing Torch
Diamond Scriber
Safety Glasses
Heat-Resistant Gloves2
2
Finish both ends
Finish both ends
Fire-polish the tip lightly without closing it, and fire-polish the top so a finger seals it well.
Tools needed:
Bench Glassblowing Torch
Files (Hand File)3
3
Graduate it (Mohr)
Graduate it (Mohr)
Fill above the top mark, let it drain into a weighed beaker on the balance, stopping each few grams and scratching a line at the level. Keep the first mark well above the tip.
Materials for this step:
Water0.2 literTools needed:
Balance Scale
Glass BeakerDiamond Scriber
Ruler4
4
Mark spacing
Mark spacing
Loading Jupyter Notebook...
5
5
Use
Use
Hold it upright, tip in the liquid but off the bottom; draw liquid up with a bulb (never by mouth), close the top with your forefinger and let it down to the mark.
Tools Required
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