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Buret, Borosilicate Glass, with PTFE Stopcock
A high-quality buret with a replaceable PTFE stopcock assembly. The delivery tip and
buret sections are separate from the stopcock portion for easy replacement.
See free video at flinnsci.com.
Catalog No. Capacity Subdivisions Price/Each Price/Case of 6
GP1089 25 mL 0.1 mL $106.82 $596.10
GP1090 50 mL 0.1 mL 87.00 485.40
Proper technique for mani p ulating a
buret stopcock:
Wrap thumb and forefinger around
handle to turn stopcock. If you are
right-handed, use your left hand.
Dispense buret contents dropwise
when nearing the endpoint.
Use a Buret
Gently swirl the flask while titrating.
Before placing liquid in
a buret, make sure the
stopcock is assembled
properly and in the
“Off” position.
White paper under
flask makes a subtle
color change more
visible.
During a titration, rinse the walls of the flask several times using a
wash bottle.
BURETS continued on next page.
Always clean a buret with a glass stopcock after each use. Invariably the reason for a frozen buret plug is that it was not flushed thoroughly after the last
use. Now you have a problem. Some suggested steps to free the plug:
• Immerse the entire barrel and plug in a glass or beaker of fresh soda pop. Allow the buret to soak until no more bubbles are seen. Frequently the gaseous
bubbles will work their way into the joint and free it. Be patient enough to try this several times.
• If soda pop does not work, try applying a modest amount of heat. This can be done by setting a very low flame in a Tirrill type burner (Flinn No. AP1019)
and slightly warming the barrel while trying to move the stopcock. Wear heat-resistant gloves and apply only a reasonable amount of pressure.
• If you still have no success, you may simply want to soak the buret in water for an extended period (several days).
• After soaking, try the soda pop process again; but if it fails again, it is fair to conclude that the ground glass surfaces of the plug and the barrel are fused
with a contaminant and the buret will have to be replaced.
Frozen Glass
Stopcock
Free Frozen Stopcock Plugs
Buret, Borosilicate Glass,
with PTFE Stopcock, 25 mL
GP1089
Buret, Flint Glass,
with PTFE Stopcock
GP1086, etc.
Buret, Flint Glass, with PTFE Stopcock
A student-quality buret with a PTFE stopcock. These are not Pyrex® glass burets but
rather flint glass. The PTFE stopcock plug is ideal in the hands of a student because
it is virtually freeze-proof.
See free video at flinnsci.com.
Catalog No. Description Size Price/Each Price/Case of 4
GP1086 Buret, Flint Glass,
with PTFE Stopcock
25 mL $68.07 $258.60
GP1087 50 mL 74.95 284.80
GP1088 100 mL 83.00 315.40
GP9188 Replacement Stopcock for Burets
GP1086, GP1087, GP1088
25.79 —
Buret, Borosilicate
Glass, with PTFE
Stopcock, 50 mL
GP1090
Burets, continued
Clean a Buret Tip
Stopcock grease often hardens, breaks off and falls into the
tip of the buret, clogging it up. There are two methods used
to unclog them:
• Insert a fine wire into the buret tip,
breaking up the plug. Be careful—
glass tips are especially fragile.
• Fill buret halfway with water—turn open stopcock while heating tip with
matches. The grease will melt and the water/air pressure will push it out.
This may require several matches.
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