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Page Title:
Schulze - Tiemann method cont'd |
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|  MIL-C-48868E (AR)
Quantitatively transfer 0.8 - 1.0 g (weighed to 0.1 mg) of the
dry sample into a 250 ml Kjeldahl flask, add 50 ml deionized
water and a few glass beads to prevent bumping. Attach the
addition funnel/check valve assembly to the freshly greased
joint of the Kjeldahl flask. Attach spring clamps or rubber
bands to the ears of the flask and addition funnel. Adjust the
gas evolution assembly so that the exit tube is gently resting
on the bottom of the NaOH bath. Place the lead band round the
exit tube opening.
Open the addition funnel stopcock and turn
on the heating
mantle. Following the purging of the Kjeldahl
flask, close the
addition funnel stopcock and purge the rest of
the tubing for
5-10 minutes. The system is thoroughly purged
when no more
bubbles escape into the bath.
Remove the heating mantle from the Kjedahl flask and observe
the drawing of the NaOH solution into the exit tubing and the
closing of the check valve. Remove the audiometer tube from the
rubber stopper. Place it over the open end of the exit tube.
Rest the bottom of the audiometer tube on the lead band and
secure the audiometer. Refill the leveling bulb to 90% of its
volume, stopper the bulb and place it back into its ring.
Place 25 ml of
solution into the addition funnel.
to flow
Open the stopcock slowly and allow most of the
into the flask. Retain a few drops in the stopcock to preclude
the flow of air into the system.
If air is allowed into the
system, the analysis is invalid and must be repeated. Place
25 ml of concentrated HCl to the addition funnel and add it to
the Kjeldahl flask. Add 10 ml deionized water in a similar
fashion. Following the last addition, fill the addition funnel
with 30 ml deionized water and tighten the stopcock nut. Place
the heating mantle around Kjeldahl flask and heat, for 20-30
minutes or until bubbling has stopped. Remove the heating
mantle and check to see that the valve closes. Loosen the
stopcock nut on the addition funnel, allow the water to drip
into the Kjeldahl, then increase the flow to effectively rinse
the walls of the flask, close stopcock before air enters and
tighten the nut. Attach the heating mantle, tap the check valve
lightly until it opens and continue for 510 more minutes.
Following the completion of the reaction, remove the heating
mantle and observe the closing of the check valve. Carefully
move the audiometer tube from its present position back to the
rubber stopper and secure it. Slowly release the vacuum inside
the Kjeldahl flask by allowing water and air to enter the flask
through the stopcock.
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