TM 5-4610-218-12
Section II. OPERATION OF A U X I L I A R Y E Q U I P M E N T
tubes having a 26 mm (millimeter) depth and on the
Determination of pH Values.
basis of a 15 ml water sample and 0.75 ml of indi-
cator solution. The graduated mark on the sample
a. Description and Purpose. The chlorine re-
tube is at 15 ml. The graduated mark on the dropper
sidual value should be determined before the water
is at 0.75 ml. The discs supplied will measure 0.1 to
is filtered and should be within limits established
10.0 ppm (parts per million) chlorine residual and
by the Area Command Surgeon. Chlorine residual
3.0 to 11.0 pH (differences in the acidity or alka-
values may be determined calorimetrically. The per-
linity) range.
is designed to give convenient and accurate mea-
(2) Clean equipment. Before taking readi-
surements. The calorimetric method is based on the
ngs, be sure that the glass color standards in the
fact that when a chemical reagent known as ortho-
disc are clean.
tolidine indicator solution is added to a water sam-
(3) Color and turbidity. To eliminate errors
ple containing chlorine, a characteristic color is pro-
due to natural color and turbidity of the sample,
duced which is indicative of the amount of chlorine
make sure that water is added to the right-hand
present. With a calibrated set of color standards, the
tube before making color comparison.
value of the sample may be determined by com-
(4) Sunlight. Do not allow direct sunlight to
paring its color with those of the standards. Per-
fall on the samples being tested. Sunlight causes
manent glass color standards are employed in the
the color developed by the indicator solution to fade.
that the water sample is easily compared with the
(5) Cleanliness. When taking samples, ad-
standards. A prismatic eyepiece brings the sample
ding solutions and mixing solutions with water in
and standard side by side for accuate comparison.
the sample tube, be sure that the hands are free of
all traces of chemical so that the sample will not be
b. General Test Precautions. Because of the
small quantities being measured, the color tests are
will change the true residual.
delicate chemical tests and, to insure greatest accu-
racy, several precautions should be followed.
(6) Clean droppers. Care must be taken,
therefore, not to contaminate the indicator solution
(1) Color disc and indicator solutions. All
by the introduction of droppers that are not per-
color discs and solutions are adjusted for sample
fectly clean.
Figure 2-24. Chlorine comparator in case.
2-53