involves the use of only one reagent - orthotolidine. The blank consists only of the water
sample. To the indicator tube is added a dropper full of orthotolidine. Five minutes after
the orthotolidine is added, the TAC is read as described in figure 2-4. The difference
between the TAC and the FAC is CAC.
NOTE: CAC can be determined by using DPD Tablet No. 3.
(2) N, N-diethyl-p-Phenyl-enediamine method. The procedure for TAC
involves the same basic procedure. Substitute one total available chlorine tablet (DPD
tablet No.4) for the free residual chlorine tablet.
2-11. DETERMINING pH WITH THE COLOR COMPARATOR.
The determination of pH with the color comparator is essentially the same as the
total available chlorine test (see para 2-10d), except that time is not critical. The same
precautions--chemical cleanliness and exact measurements--should be observed as in
tests for residual chlorine. In addition, it is important that the pH range of the
comparator disk agrees with that of the indicator solution (printed on the bottle).
Figure 2-5 (A through D) illustrates the procedure in conducting a pH test with the color
comparator. The blank tube compensates for the natural color of the water.
A. Fill both tubes with water being
B. Squirt with force one dropper
tested and place in comparator.
full of pH indicator solution into
tube on left.