moved by filtering,the solution will remain weak. Redis-
solve the precipitate by warming the solution. Do not boil it.
(4) The solubility of hydroquinone decreases rapidly at low tem-
peratures. It usually crystallizes in long fine needles when
developers are chilled or stored at temperatures below 40
F. Ethyl, isopropyl, or butyl alcohol may be added to de-
veloper up to 10 percent of developer volume to prevent
hydroquinone crystallization.
b. Development Using Cold Solutions. At 55 F. or lower, D-72
developer can be used full strength to reduce developing time. How-
ever, processing at low temperatures is not recommended because of
the length of time required and the hardship imposed on laboratory
personnel. All solutions should be warmed to about 68 F.
c. Fixing. The rate of penetration and the reaction time of fixers
decrease at low temperatures. At temperatures below 68 F., double
the fixing time for every 18 F. decrease.
d. Washing. Washing time must be increased at low temperatures
because of the reduced penetration rate and the slower diffusion of
chemicals. If prints are washed at 50 F., twice the normal washing
time is necessary. At 35 F., four times the normal washing time is
required. Prints may be washed for immediate use by immersion,
with agitation, for about 2 minutes in each of three or four changes
of water at 65 F., but they should be rewashed thoroughly before
being stored in permanent files.
e. Finishing Prints. When prints are made under cold or extremely
dry conditions, the fixing bath hardener may be reduced to one-half,
and sometimes to one-fourth, of the standard concentration.
34. Tropic and Desert Areas
a. If it is necessary to store the printer outdoors in very high tem-
peratures, cover it with a shelter cloth to protect it from dust.
b. Before using the equipment in desert regions, use a soft bristle
brush to clean any sand or dust from the projection-head window and
the plate glass on the projection stage. Open the door on the left side
of the printer and brush dirt and sand from the bottom of the Fresnel
condenser lens, the rear surface mirror, and the condenser lens. Open
the rear door of the printer and the lamphouse door, and brush dust
and dirt from the reflector, the projection lamp, and the rear surface
of the condenser lens.
c. Under conditions of high humidity, inspect the equipment for
traces of fungus, mold, and metallic corrosion. Remove all traces
immediately. Refer to TB SIG 149 for further information on this
subject.
37
TAGO 4738B
