CAUTION
TM 5-6630-215-12
No air should be introduced with the reagents.
Reagents are added by allowing the drops to fall
onto the test sample.
Because of the greater
density of the reagents, they will quickly des-
cend into the sample.
After each addition of
reagent or reagents, the bottle is carefully
capped for mixing, making sure that no air bubbles
are formed.
(2) Dissolved Oxygen Test.
Thoroughly rinse the sample bottle
with the water to be tested and replace the cap.
Completely submerge
the capped sample bottle in an upright position under the surface of
the water source.
Remove the cap and allow the water to enter the
bottle.
With the bottle still submerged, gently squeeze or tap the
sides to eliminate any trapped air bubbles and replace the cap prior
to removing the bottle from the water.
After bringing the bottle to
the surface,
inspect it to be certain that no air bubbles have been
trapped inside.
(a)
To the sample, using the plastic dropper-pipet, add 8
drops of manganese sulfate solution, rinse the pipet and add 8 drops
of alkaline potassium iodide solution.
Rinse the pipet, carefully
cap the bottle, mix by gently inverting,
then allowing the precipitate
to settle below the shoulder of the bottle.
(b) Using the 0.5 ml dropper pipet, add one measure (0.5 ml)
of sulfuric acid, cap the bottle and mix until the precipitate is
completely dissolved.
NOTE
Following the completion of step (b), the contact
of water sample with air will not affect the final
reading.
Samples collected in the field can be
“fixed” by carrying out steps (a) and (b) on
locations and the actual titration step (c) can be
completed at a later time.
(c) Fill the titration flask to the 50 ml line with the pre-
pared water sample.
(d) Fill the micro burette with standard sodium thiosulfate
solution in the manner described in paragraph 2-11.
(e) Titrate with standard sodium thiosulfate solution until
the brown iodine color has nearly disappeared.
Remove the micro
burette and cap and using the plastic dropper pipet add 8 drops of
starch solution.
The test sample will turn blue.
Titration is
continued with the standard sodium thiosulfate until the blue color
just disappears.
If the test solution contains little or no brown
iodine color, the starch solution can be added at the very beginning
2-28
