7. Maintenance
90
Chrome is a heavy metal. Do not discard the used mixture or
rinsing solvent as wastewater. First, dilute the collected chromic
acid mixture down to 1% concentration, and then, reduce it.
After confirming no Cr6+ is contained in it, adjust its pH to 7.5 a
8.5. Filter the liquid, and store the precipitation.
For more details, refer to the corresponding documents regarding
how to dispose of heavy metals.
How to dry the inner burette and diaphragm
Dry it in a decompression dryer for more than 2 hours.
Below sketch shows an example of commercially sold drying under reduced pressure.
Diagram of Decompression dryer
Commercially available vacuum dryer
燥器
Dry the inner burette itself only after removed from the titration cell in order to
avoid possible breakage of inside ceramic diaphragm.
Use a hair dryer if a compression dryer is not available. With a hair dryer, dry
the inner burette well enough as long as for more than 10 minutes, especially
dry the diaphragm until it is really dried. Any residue of moisture will cause
high drift level.
Set the temperature of the constant temperature drying oven at
65°C or below.
When drying with a hair dryer, make sure not to overheat its cable
and connector.
Overheating may result in malfunction.
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