(4)
(5) Fill the eyedropper to the etched mark (approximately 0.75 ml) with the
pH indicator solution.
(6) Squirt the pH indicator solution from the eyedropper into the correct tube
on the right. The other tube is present to show the natural color of the untreated water.
(7)
Push both tubes down until the tips are flush with the top of the
(8) Match the color of the sample in the tube with the color on the disc. If
the color does not match any of the discs, then estimate pH as accurately as possible.
(9)
Record your results.
NOTE:
If other commercial test kits are used, be sure to follow the specific
instructions provided with the test kit.
1-21. TESTING FOR FREE AVAILABLE CHLORINE
a. The DPD Test. The test kit is the same kit used to test pH, FSN 6630-087-
1838. The most accurate way to test for free available chlorine is a method using DPD
(diethyl-p-phenylenediamine). Most Army kits now contain the materials for this test.
The specific items in a test kit may vary with the manufacturer but the principle
underlying the test remains the same. Like the pH test, the DPD test is based on the
ability of an indicator (a reagent tablet) to change color when placed in water containing
chlorine. The color is then compared with color standards. In addition to free available
chlorine the test can also be used to test for combined available chlorine (chloramines)
and total chlorine. However, as you are primarily interested in the amount of free
available chlorine, that test is described in this lesson.
b. Testing Technique.
(1)
Place about 1 ml of pool water in a test vial and add a reagent tablet.
(2)
Crush the tablet into a powder, using a glass rod.
(3)
Fill the test vial with pool water up to the mark.
(4)
Place a cap on the test vial and shake until the powder is dissolved.
(5) Insert the test vial in the colorimeter block and compare with the color
standards. Read the free residual chlorine directly in ppm.
(6)
Record your results.
MD0166
1-34