1. Pipette 50 ml of the sample into a 6-inch white
porcelain evaporation dish.
2. Place the same quantity of distilled water into a
second dish for color comparison.
3. To both dishes, add 1 ml of potassium chromate.
Titrate the dish with the sample. Add standard silver
nitrate solution (2.4 grams per liter) from a burette, a
few drops at a time, with constant stirring until the first
permanent reddish coloration appears. (This can be
determined by comparison with the distilled water
blank.) Record the ml of silver nitrate used.
4. If more than 7 or 8 ml of silver nitrate solution is
required, the entire procedure should be repeated by
using a smaller sample diluted to 50 ml with distilled
CALCULATIONSWhen making calculations
for chloride, use the formula below.
ml of AgNo3 used - 0.2 × 500
Ppm chloride (C l) =
ml of sample
Three precautions to bear in mind are as follows:
1. If the sample is highly colored, it should be
decolorized by shaking with washed aluminum
hydroxide and filtering.
2. If the sample is highly acid, add 10 percent
sodium carbonate solution until it is slightly alkaline to
3. If the sample is highly alkaline, add diluted
sulfuric acid until it is just acid to phenolphthalein.
The Sulfate Test
The sulfate test determines whether sulfates are
present in sufficient quantities in water to cause
undesirable physiological effects because sulfates can
cause diarrhea in human beings. In the sulfate test, the
sulfate value is found by trial, as the test merely
determines approximate values. For this reason, you may
have to repeat the test several times. The test is begun by
testing for sulfates at 100 ppm as follows:
1. Fill a clean test bottle to the 100-ml mark with
the water sample.
2. Add 1 ml of barium chloride solution to the same
and use a barium chloride pipette. Shake intermittently for
3. Tear a piece of filter paper into small pieces and
place the pieces in the solution.
4. Shake the bottle for 5 minutes or until the paper
becomes fluffy and gelatinous.
5. Place a funnel and filter paper in a second bottle.
6. Filter about 25 ml of the sample into the second
bottle. Rinse the second bottle with this amount of filtrate,
and discard the filtrate. Replace the funnel and continue
filtration until 50 ml of filtrate is collected.
7. Add 1 ml of barium chloride solution to the filtrate
with the barium chloride pipette. Shake for 5 seconds, and
observe immediately for a precipitate or clear solution.
If a clear solution is obtained, record the sulfates as
less than 100 ppm. As an immediate precipitate or milky
solution indicates the sulfates are greater than 100 ppm, a
new sample must be tested for 200-ppm sulfate. For each
additional 100-ppm sulfate test required, add 1 ml of
barium chloride solution. Therefore, 3 ml of barium
chloride solution must be added to test for 300-ppm
sulfate. However, the 1 ml of barium chloride solution
added after filtration is not changed.
If a clear solution is obtained, the sulfates are less
than the ppm for which they were tested, and the value is
recorded as being between the values of the last
preceding tests. A precipitate or milky solution requires
that a new sample of the water be tested for the next
Color in water is due to various materials in solution,
although suspended turbidity occasionally adds an
apparent color to water that may add to or disguise the
true color. In water with low turbidity, the apparent color
corresponds closely to the true color. However, if
turbidity is high, the apparent color may be misleading.
To determine the true color, first filter the water through
clean white filter paper before it is compared with the
standards. Because the filter paper often removes some
true color from the first portion of the sample, discard the
first 100-ml which pass through the filter and use the next
portion for the color comparison. Make the color
determination by matching the sample color with color
standards in a color comparator.
TASTE, ODOR, AND THRESHOLD
Unless the water has a definite taste (sweet, sour,
salty, or bitter), the sensation produced upon the observer
is generally due to the presence of odor, rather than taste.
These two senses work in unison. Sulfur water, for
instance, apparently tastes terrible when it is really
only its rotten egg odor that is registering on our senses.