Any diluted stannous chloride not used
the day it is made should be discarded.
The following procedure is used to make the test
1. Without disturbing any settled sludge, transfer
enough of the sample to the test tube to till it about half
2. Add 1/4 tsp of decolorizing carbon. Stopper the
tube and shake vigorously for about 1 minute. The
carbon absorbs the tannin so it can be filtered out.
3. Fold a filter paper and place it in the filter
funnel. Do not wet down the filter paper with water.
Filter the shaken sample, using a combination mixing
tube as a receiver. The carbon absorbs tannin, and the
tannin and sludge present are filtered out more rapidly.
Avoid jiggling the funnel, as unfiltered boiler water
may overflow the edge of the filter paper into the tube.
You have to support the funnel.
4. After 5 ml of the sample has filtered through, as
indicated by the level in the tube, discard it. Continue
filtering to bring the level in the test tube again up to the
5-ml mark. The sample should come through clear and
free, or nearly free, of any color from the tannin. If not
nearly free of tannin color. repeat the test, using 1/2 tsp
of carbon. adding it in two 1/4-tsp portions, shaking it
for 1 minute after each addition.
5. Add the comparator molybdate reagent to bring
the level up to the second mark ( 15 ml). Stopper and mix
by inverting the tube several times.
6. Add fresh diluted stannous chloride up to the
third mark (17.5 ml). Stopper and mix by inverting. If
phosphate is present, the solution in the mixing tube
7. Place the tube in the comparator block.
Compare the color of the solution in the tube with the
standard colors of the phosphate color block. Colors
between the two standard colors may be estimated.
Take the reading within 1 minute after adding the
stannous chloride, because the color fades quickly.
8. Record the results as LOW, if below 30 ppm;
HIGH, if above 60 ppm, or OK, if between 30 and 60
Test for Tannin
The purpose of the TANNIN TEST is to determine
the amount of tannin in the boiler water. Tannin holds
sludge in suspension. In treating boiler water with
tannin, control the dosage by the depth of brown
formed in the boiler water by the tannin. To estimate
the depth of the color, which is necessary in adjusting
tannin dosages, compare a sample of the boiler water
with a series of brown color standards of successively
increased depths of color. A tannin color comparator,
which is used for the comparison, has five glass color
standards: No. 1, very light; No. 2, light: No. 3,
medium; No. 4, dark; and No. 5, very dark.
The kit for the tannin test contains the following:
One tannin color comparator
Two square tubes, 13-mm viewing depth
One plain test tube, 22 mm by 175 mm
One filter funnel, 65 mm by 65 mm
One package of filter paper, 11 cm in diameter
making this test, you first fill a plain test tube
almost to the top with cool boiler water. Then place a
square test tube in the slot of the comparator, and insert
the filter funnel in it. Fold a filter paper and place it in
the funnel without wetting it down. Filter water from
the plain test tube into the square tube until the tube is
neatly full. Remove the square tube from the
comparator and hold it up to a good source of natural
light. Note the appearance of the filtered boiler water.
Is it free of suspended solids and sludge? If not, refilter
the sample, using the same funnel and filter paper.
Repeat, using a double filter paper if necessary, until
the sample does come through free of suspended solids
To complete the test, place the square tube of
filtered sample in the middle slot of the comparator.
Then compare the color of the sample with the five
standards, viewing it against a good source of natural
light. The color standard most closely matching the
color of the filtered sample gives the tannin
concentration of the boiler water. For a number of
boiler water conditions, the tannin dosage is usually
satisfactory if it maintains a medium (No. 3) tannin
color. If the tannin color is too high, blow down; if too
low, add tannin.
Test for Caustic Alkalinity (OH) without
The boiler water sample for this test is collected at
a temperature of 70°F or below.