Processing kodak motion picture films, module 3 analytical procedures

water droplets adhere to the inside walls of the
glassware after one minute of draining, it is not
sufficiently clean. Only an unbroken film of water
should remain. Burets and pipets should drain in a
vertical position. Volumetric flasks are inverted with
the bottom at a slight angle from the horizontal, so that
drops on the bottom will drain away. If burets and
pipets are clean, they generally do not have to be dried
before being used with standard solutions. The slight
amount of water which remains after rinsing and
draining is removed by rinsing two or three times with
small amounts of the solution to be used, allowing the
buret or pipet to drain completely between rinses. If it
is necessary to have volumetric vessels dry, a gentle
stream of clean air can be used. Acetone should not be
used as a drying agent because of the likelihood of
trace amounts left in glassware causing unwanted
absorption in ultraviolet methods of analysis.
Use of Volumetric Glassware
1. General Instructions
a. Effects of Temperature on Glassware and
Solutions:
Glassware—The temperature at which
volumetric vessels are calibrated is 20°C (68°F).
For the greatest precision and accuracy, all
measurements should be made at this
temperature. Since this condition may not be
practicable, it is important to consider the
magnitude of the errors introduced into
volumetric procedures by using standard
solutions at temperatures other than 20°C
(68°F). The change in capacity of glass
volumetric apparatus with temperature is, at the
most, only 1 part in 10,000 for each 5°C change
in temperature in the region of 20°C. This source
of error generally may be disregarded.
Solutions—Whereas the change in capacity of
glassware with temperature generally may be
disregarded, it is not to be confused with the
change in volume of a solution with
temperature. The effect of temperature on
volume is shown in Table 2. To attain accuracy
of approximately 0.1 percent it is necessary that
the solution be at 20 ± 2°C (68 ± 3.6°F) when
measured.
The change in concentration of standard
solutions is also affected by temperature. It may
become of such magnitude as to introduce
appreciable errors. In general, the more
concentrated the solution the more serious the
change. The coefficient of expansion of dilute
aqueous solutions of different electrolytes is
practically the same for similar concentrations
and hence, the values given in Table 2 serve as a
general index of their behavior.
b. Meniscus
In the use of graduated cylinders, pipets, burets,
and flasks, the lowest point of the meniscus
should be taken as the reading. See Figures 1
and 2. Opaque solutions, however, must be
measured by reading at the top of the meniscus.
Another special case is the determination of
specific gravity. The top of the meniscus is read
because the hydrometer is calibrated on that
basis.
Figure 1
Reading the Meniscus on a Pipet or Volumetric Flask
F002_0901AC
Figure 2 Reading the Meniscus on a Buret
F002_0900AC
Correct Line
of Vision
Excessive
Volume
2 Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03
Deficient
Volume
Low
Reading
Correct Line
of Volume
High
Reading