chemicals, turn off electric fans for chemicals may be blown about the room and
contaminate the loading bench, screens, or other equipment. Hands that are wet with
chemicals should never be used for handling films, screens, or other accessories.
3-15. WATER SOURCE AND TEMPERATURE
Since water is the solvent for all processing solutions, same care should be
exercised in choosing its source. Most city water supplies are suitable, but they should
be checked for high concentrations of various salts before use. In general, any water
that is good to drink should be satisfactory.
a. Pure Water. Distilled water, since it does not contain dissolved chemicals, is
pure and therefore ideal for mixing purposes. Rainwater and water melted from clean
snow are good substitutes.
b. Water Impurities. The chief kinds of impurities usually found in water are as
(1) Suspended material consisting of decayed animal or vegetable matter,
mud, rust, or sulfur. Filtration will remove the majority of these substances.
(2) Some solid chemicals found freely in nature are often dissolved by
water. These chemicals cause hardness of the water and are composed of calcium and
magnesium salts in the form of bicarbonates, chlorides, and sulfates. These salts are
not injurious to the image but may produce a scum on the surfaces of the film that
reduces its transparency. It must and can be removed before drying by squeegeeing
the faces of the radiograph with cotton or a photographic sponge. Circulating the water
through a water softener may eliminate the hardness of the water. In general, most
metropolitan areas use water containing some minerals, but experience few, if any,
(3) Coloring matter of vegetable or animal origin, usually yellow or brown, is
sometimes found. Such water may stain the film and should be avoided.
c. Mixing Temperature. The temperature of the water in which chemicals are
to be dissolved should be as recommended on the label of the package.
3-16. MIXING UTENSILS
The containers for mixing chemicals should be of corrosion-resistant materials,
such as types 316 and 317 stainless steel. Vessels containing tin, copper, zinc,
aluminum, or galvanized iron should never be used because small quantities of these
metals in the solutions will fog film during the development period. Separate stainless
steel, hard rubber, or plastic mixing paddles should be used for the developer and the
fixer, after which they should be washed with clear, warm water and hung up to dry.