In domestic water systems, sulfates do not appear to cause any
increased corrosion on brass fittings but concentrations above 200 mg/l
do increase the amount of lead dissolved from lead pipes.
(b) The procedure for determining sulfate is a modification of
the Barium Sulfate Turbidimetric Method.
A single, dry powder reagent
called sulfate reagent will cause a milky precipitate to form if
sulfate is present.
The sulfate reagent also contains a stabilizing
agent to hold the precipitate in suspension for turbidimetric analy-
amount of turbidity formed is directly proportional to the
Sulfate Test Procedure.
Filtering (para 2-22j) is recommended for highly
colored and/or turbid water samples.
of color or turbidity will interfere and cause
The filtered water is then used
in steps (a) and (c).
The results will not be affected if the reagent
powder does not completely dissolve.
After each test the sample cells should be
cleaned with soap and a brush.
A white film will
deposit on the inside of the cells and lead to
errors in future determinations if this is not
done soon after each test.
Silica in excess of 500 mg/l will interfere.
To extend the range of the test, a sample dilution
is necessary (para 2-10a and table 2-1).
(a) Fill a clean graduated cylinder to the 25 ml mark, then
pour into a sample cell.
(b) Add the contents of one sulfate reagent powder pil-
low and swirl to mix.
A white turbidity will develop if sulfate
Allow the sample to stand 5 minutes but not more than 10
minutes before step (c) and (d).
(c) Fill another sample cell to the 25 ml mark with original
water sample and place it in the cell holder.
Insert the sulfate
meter scale into the meter and adjust the wavelength dial to 450 nm.
Adjust the light control for a meter reading of zero mg/l.
(d) Replace the blank sample (step (c)) with the prepared sam-
ple in the cell holder and read the mg/l (SO4).