Hach Digesdahl 23130-20, Instrument Manual, Page: 76 / 101

67
DIGESTION PROCEDURE FOR SOLIDS
1.
Transfer 0.50 g or
less of sample into a
100-mL Digesdahl
digestion flask; see
Sample and Analysis
Volume Tables for
Solids following
this procedure.
Note: Be sure you have a
homogenous sample. Solid
sample should be finely
ground or chopped and
mixed well.
2.
Add 4 mL
concentrated sulfuric
acid (spec. gravity 1.84)
to the digestion flask.
Note: Use only Hach
Digesdahl digestion flasks.
Volumetric flasks with
concave bottom should not
be used.
Note: Safety glasses and a
safety shield placed
between the operator and
the Digesdahl are required.
3.
Turn the temperature
dial to a heat setting of
440
°
C (825
°
F). When
the proper temperature is
reached, turn on the
water to the aspirator
and make sure there is
suction to the
fractionating column.
Note: Wait for the proper
temperature to be reached
before sample is placed on
the heater.
4.
Place the flask weight
followed by the
fractionating column
with funnel on the flask.
Place the flask on the
heater and boil 4
minutes. Do not boil to
dryness! If sulfuric acid
is not present in the
flask after the boiling
period, do not proceed
to Step 5! Discard the
sample and use more
sulfuric acid for the
digestion procedure in
Step 2. Or choose a
smaller amount from the
Sample and Analysis
Volume Tables for
Solids.
Note: If sample foams up
into the neck of the flask,
lower temperature to
335
°
C (635
°
F). Continue
heating at lower
temperature until all
water is evaporated. Then
return to original
digestion temperature.
Note: White acid vapors
accompanied with a reflux
line indicate that the
sulfuric acid is boiling
Note: Some organic
samples may need more
than 5 minutes for
complete digestion.
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