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BÜCHI Distillation Unit K-314 6 Bedienung
5.11 Carrying out the Kjeldahl distillation
• Switch the unit on and preheat,
• Wear goggles!
• Insert the digestion tube containing the specimen diluted
in water
Dilution with water prevents too violent a reaction when
subsequently adding the hydroxide solution.
The specimen must be diluted in a ratio of approximatly
1 part of acid to 2 parts of water.
• Prepare a conical flask or a similar receptacle (250 ml)
as the receiving vessel, dilute with 60 ml boric acid
(2%) and 2-3 drops of Sher indicator (Item No. 03512).
Alternative: Choose a suitable indicator for the back
titration.
• Add sodium hydroxide solution:
Recommeded alkali concentration: 32%
Add alkali to the specimen in a ratio of about 1 part
acid to 3 parts sodium hydroxide solution. The volume
of the added sodium hydroxide solution is measured
on the scale (behind the distillation glass).
The added volume selected must produce a clear shift
in color to brown or blue.
• Distillation
Steam tap to ON
A distillation time of approximately 3 minutes is required
to get a volume of 100 ml.
• After the completion of the distillation turn the steam
tap back to OFF.
5.12 Cleaning the unit
Clean the unit by distilling 100 ml distilled water for a period
of 2 minutes.
Fig. 13: K-314 in operation
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