MIXING, TESTING, AND STORING
EQUIPMENT
The type of material, used for photographic
chemical mixing, solution testing, storing, as well as
film-handling equipment, must be considered before
mixing chemicals. Materials commonly used in the
construction of this equipment are Type 316 stainless
steel, polyethylene, and glass. Related equipment,
such as solution transfer lines, mixer shafts, impellers,
and machine parts, are also made of these same
materials.
Some metals are not suitable for use with photo
solutions. Serious chemical fog and developer changes
can be caused by tin, copper, brass, and bronze.
Aluminum, lead, nickel, zinc, galvanized iron, and
Monel, when used with developers and fixers, can be
harmful to films and papers. When these metals are
used, silver thiosulfate from the used fixer may stick to
them. Even when the utensils are washed after being in
the fixer, enough silver thiosulfate can be transferred to
the developer in the next processing or mixing run to
cause stain, fog, or changes to image tone.
Wooden paddles and other absorbent materials
must not be used with photographic solutions. Once
they have been used, it is almost impossible to wash
them clean of absorbed chemicals.
MIXING CONTAINERS
Chemicals should always be mixed in cylindrical
containers made of suitable materials, The size of the
mixing container should be suitable for the amount of
solution to be prepared. A small batch of solution
should not be mixed in a large vessel that uses
mechanical agitation because large amounts of air
may be introduced, and splashing may occur. So, the
mixing container, and for that matter, scales and
graduates, should be sized to the quantities and
volumes of solutions required.
GRADUATES
Graduates are used to measure liquids. Graduates
are made in various sizes, calibrations, and of various
materials. The units of measure of graduates are
calibrated in the U.S. liquid measurement system of
ounces, quarts, and gallons, and in the metric liquid
measurement system of cubic centimeters, milliliters,
and liters.
Glass is most commonly used for making graduates
because it is NOT affected by most chemicals. Glass
is also transparent and reasonably durable. Graduates
are also made from plastic and stainless steel. When
using graduates made of plastic, do not try to measure
strong acids, such as sulfuric acid, which could cause
severe damage. You must also be sure that the material
the graduate is made of does not react with any of your
photographic chemicals.
For accuracy in measuring liquids, graduates
should be proportional in size to the quantity of
solution being measured; for example, an 8-ounce
graduate should be used instead of a 32-ounce
graduate to measure 2 or 3 ounces.
When measuring a liquid in a glass graduate, hold
it at eye level and pour the solution into it until the
surface of the liquid reaches the correct mark. You will
notice a curved surface on the top of the solution. This
curved surface is called the "meniscus." The correct
amount is indicated by the lower of two visible lines
of the meniscus (fig. 9-1). These two lines can be seen
easily through the side of a glass graduate when it is
held correctly. With an opaque graduate, such as
stainless steel, the two lines can be seen by looking
down into the graduate from an angle. Stop pouring
the solution when the "lower line" of the liquid
reaches the calibration mark. Major divisions are
indicated by numbers on the graduate. Subdivisions
are shown by calibration lines only. You must
determine the value of the individual subdivisions; for
example, the marked or numbered lines may indicate
ounces and read in series of 10. When there is only
one calibration line between each graduation of 10,
then the value of the calibration line is 5.
THERMOMETERS
All chemical action takes place faster at high
temperatures than at low temperatures. In the
photographic process, when you mix or use a solution,
you must know its temperature.
Thermometers are used to measure the temperature
of the solution and may be made of glass or metal. The
average glass thermometer consists of a bulb, containing
either mercury or colored alcohol, attached to a capillary
tube. This tube may be calibrated or it may be secured
to a graduated scale. When you are reading a
9-2

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