The amount of indicator added is critical to the
accuracy of the test and should be measured as
carefully as possible.
The strength of the indicator solution should be
checked occasionally in the range normally being
The indicator solution
may be checked by running the test on a prepared
buffer solution of a known PH.
If the meter
reading is too high the indicator has become too
concentrated through evaporation of the solvent.
If meter reading is too low, the indicator has
deteriorated and should be replaced.
(a) Take a water sample by accurately filling a clean grad-
uated cylinder to the 25.0 ml mark.
Pour the sample into a clean, dry
(b) Add exactly 1.0 ml of wide range pH indicator solution
using the 1.0 ml transfer pipet and swirl to mix.
(c) Fill another sample cell with about 25 ml of original
water sample and place it into the cell holder.
Insert the pH, wide
range meter scale into the meter and adjust the wavelength dial to 520
Adjust the light control so the meter needle rests at the far
right end of the arc.
(d) Replace the blank sample (step (c)) with the prepared sam-
ple in the cell holder and read the pH value from the center or lower
scale, according to the developed color.
If the color does not
correspond to those indicated on the center or lower scales, and/or
the meter reading does not fall within the ranges indicated, proceed
with step (e).
(e) Adjust the wavelength dial to 615 nm and standardize the
instrument as described in step (c).
Place the prepared sample in the
cell holder and read the pH value on the upper scale.
g. Sulfate, Range:
0-150 mg/l, Turbidimetric Method (para 2-18
and figs. 2-11 and 2-12).
(1) Sulfate appears in natural waters in a wide range of concen-
Mine waters and industrial effluents frequently contain
large amounts of sulfate from pyrite oxidation and the use of sulfuric
(a) Public Health Service drinking water standards call for
not more than 250 mg/l of sulfate because of its cathartic action.
The taste threshold of magnesium sulfate is 400 to 600 mg/l and for
calcium sulfate is 250 to 800 mg/l.
Sulfate may be either beneficial
or detrimental in water used for manufacturing and domestic supply.