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Test for Tannin | Up
Utilitiesman Basic Volume 02 - Manual for electric, plumbing, water and other utilities | Next
Test for Sodium Sulfite |
The equipment required is as follows:
Two 8-in. droppers with bulbs
Two 250-ml glass-stoppered bottles or flasks
labeled causticity No. 1 and causticity No. 2
Four marked test tubes, 22 mm by 185 mm
Three plain test tubes, 22 mm by 175 mm
Three rubber stoppers, No. 2
One 14-in. test-tube brush
One test-tube clamp
Two 9-in. stirring rods
One 1-oz indicator dropping bottle for
phenolphthalein
One test-tube rack
The following reagents also are required:
One 24-oz bottle or flask causticity reagent No. 1
One 24-oz bottle or flask causticity reagent No. 2
One 4-oz bottle phenolphthalein indicator
The following are the steps to follow in conducting
a test for causticity when tannin is not used:
CAUTION
Avoid exposure of the sample to the air as
much as possible to reduce absorption of
the CO2.
1. Without disturbing the settled sludge, fill a
marked test tube exactly to the first mark (25 ml) with
some of the original boiler water sample.
2. Shake causticity reagent No. 1 (barium chloride
solution saturated with phenolphthalein) thoroughly and
add enough to the graduated tube to bring the level
exactly to the second, or long, mark (30 ml).
3. Stir the solution with the 9-inch stirring rod,
which must be kept clean and reserved for the causticity
test only. When the mixture remains colorless or does
not turn pink, the causticity in the boiler water is zero and
the test is finished. When the mixture turns pink,
causticity is present. (If the pink color is not deep,
intensify it by adding two drops of phenolphthalein
indicator to the mixture in the tube.) Add causticity
reagent No. 2 (standard one-thirtieth normal acid), using
the 8-inch dropper, thatch must be kept clean and
reserved for the causticity test only. Causticity reagent
No. 2 is sucked from the reagent bottle into the dropper
by its rubber bulb and added, drop by drop, to the test
tube. After each addition, stir the mixture with a
stirring rod. After sufficient reagent has been added,
the pink color disappears; the change point is usually
sharp. As soon as the pink color just fades out, stop
adding the reagent.
4. The amount of causticity reagent No. 2
required to make the pink color disappear shows the
concentration of hydroxide (OH) or causticity in the
boiler water. The amount of reagent used is shown by
the marks on the test tube above the long mark (30 ml).
The distance between any two marks on the test tube
equals 5 ml, and readings less than 5 ml can be
estimated. For example, when only three fifths of the
distance between the long mark and the next mark
above were filled, then 3 ml was added. When the
distance filled was past one mark plus three fifths of the
distance to the next, then 5 + 3 = 8 ml was used. To
obtain the actual ppm of hydroxide or causticity shown
by the test, multiply the number of ml by 23. This
constant number, 23, represents the amount of sodium
hydroxide in the boiler water by volume. Thus, for 8 ml
of causticity reagent No. 2, there are 8 x 23 = 184 ppm
hydroxide or causticity in the water.
5.
Record the results of the test in a boiler log or
chemical log and adjust the range to meet
requirements. When causticity is too high, blow down;
if too low, add sodium hydroxide (caustic soda).
Test for Caustic Alkalinity (OH)
with Tannin
For this test, start with a warm sample of about
160°F. It may be reheated by placing the
sample-collecting container in a stream of hot boiler
water drawn through the boiler water cooler
connection. In a test for causticity when tannin is
used, make sure you observe the same precautions as
carefully as when tannin is not used.
CAUTION
Avoid exposure of the sample to the air
as much as possible to reduce absorption
of the CO2.
The equipment and reagents required for this test
are the same as those listed in the preceding section
where tannin was not used.
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