TM 5-6630-215-12
Figure 2-3.
Rubber Bulb Pipet Filter
2-5.
DROP COUNT METHOD.
When titrating by drop count, the most
accurate results will be obtained with the sample and titrating
solution at room temperature and with the solution dispensed from a
vertical dropper at the rate of 1 drop per second.
2-6.
REAGENT POWDER PILLOWS.
Dry powdered reagents are used wherever
possible to minimize the problems of leakage and deterioration.
For
greatest convenience, the powders are packaged in individual, pre-
measured,
polyethylene or saran “Powder Pillows.”
Each pillow
contains sufficient reagent for one test and is easily opened with
nail clippers or scissors.
2-7.
REAGENT BLANK-COLORIMETER TESTS.
The term “reagent blank”
refers to that effect wherein the reagent itself adds some color or
turbidity to the sample being tested, thus giving erroneously high
readings.
In several of the tests, the blank is of such magnitude
that compensation must be made each time the test is performed.
This
is done by zeroing the instrument on a blank sample, as in the case of
the ammonia nitrogen test, paragraph 2-18d(1)(d). In most cases,
however, the reagent blank is so very small that the instrument is
zeroed on either an untreated portion of the original water sample or
demineralized water.
This is done routinely without any significant
loss of accuracy, except where extremely small amounts of a consti-
tuent are sought.
In such a case,
it is best for the analyst to
determine the reagent blank by performing the test on a sample of
high-quality, turbidity-free demineralized water.
The result is
expressed as the milligrams per liter reagent blank and is subtracted
from the results of subsequent tests using that particular bottle of
reagent.
It is necessary to determine the reagent blank only when the
material is first used, and at intervals of several months, unless
subsequent contamination is suspected.
2-6
