61-22
CYANIDE, continued
Distillation Procedure
The following steps describe the distillation process using apparatus
offered by Hach:
a) Set up the distillation apparatus for cyanide recovery, leaving off the
thistle tube. Refer to the Hach Distillation Apparatus Manual. Turn on
the water and make certain it is flowing steadily through the condenser.
b) Fill the distillation apparatus cylinder to the 50-mL mark with 0.25 N
Sodium Hydroxide Standard Solution.
c) Fill a clean 250-mL graduated cylinder to the 250-mL mark with
sample and pour it into the distillation flask. Place a stirring bar into the
flask and attach the thistle tube.
d) Arrange the vacuum system as shown in the Hach Distillation
Apparatus Manual, but do not connect the vacuum tubing to the gas
bubbler. Turn on the water to the aspirator to full flow and adjust the
flow meter to 0.5 SCFH.
e) Connect the vacuum tubing to the gas bubbler, making certain that air
flow is maintained (check the flow meter) and that air is bubbling from
the thistle tube and the gas bubbler.
f) Turn the power switch on and set the stir control to 5. Using a 50-mL
graduated cylinder, pour 50 mL of 19.2 N Sulfuric Acid Standard
Solution through the thistle tube and into the distillation flask.
g) Using a water bottle, rinse the thistle tube with a small amount of
demineralized water.
h) Allow the solution to mix for 3 minutes; then add 20 mL of
Magnesium Chloride Reagent through the thistle tube and rinse again.
Allow the solution to mix for 3 more minutes.
i) Verify that there is a constant flow of water through the condenser.
j) Turn the heat control to 10.
k) It is very important to monitor the distillation flask at this point in
the procedure. Once the sample begins to boil, slowly lower the air flow
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