UFC 3-240-13FN
25 May 2005
Table 6-5. Relationship Between Causticity and pH
Hydroxyl Alkalinity (ppm)
pH
as CaCO3
as OH
9.0
0.5
0.17
9.5
1.6
0.54
10.0
5
1.70
10.2
8
2.72
10.5
16
5.44
10.6
20
6.80
10.7
25
8.50
10.8
33
11.2
10.9
40
13.6
11.0
50
17.0
11.1
63
21.4
11.2
79
26.9
11.3
100
34.0
11.4
126
42.8
11.5
158
53.7
11.6
199
67.7
11.7
250
85.0
11.8
315
107
11.9
397
135
12.0
500
170
6-6.3
Conductivity and TDS. Each of these water quality parameters is a
measure of the amount of soluble minerals present in the water. Conductivity is
measured with an electronic instrument based on the flow of an electrical current
through the water sample. The measurement of TDS requires evaporation of a fixed
amount of water to determine the weight of the remaining minerals (i.e., the TDS in the
water). The conductivity instrument may report the mineral content as micromohs or as
dissolved solids. In neutral or alkaline waters, there is no consistent relationship
between conductivity and TDS since each ion has its own specific conductivity. The
hydroxyl ion has the highest conductivity of all the common ions found in boiler water. If
alkaline boiler water is acidified to the phenolphthalein end-point with an organic acid,
such as gallic acid, which neutralizes causticity but does not contribute to conductivity,
the TDS is approximately equal to two-thirds of the neutralized conductivity in
micromhos. This is known as "neutralized conductivity." In boiler water, a factor of 0.7
can be used for water treated with synthetic polymers as a sludge dispersant, and from
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