Courtesy of Beckman Instruments, Inc.
Figure 9-3.pH meter.
The ability of a pH meter to determine the pH value
of a solution accurately may be used for the following
To verify that chemicals have been properly
To test prepared chemicals
To assure standardization of the processing
To determine the exact replenishment rates for
photographic chemical solutions
Tolerances in pH values must be established for
individual labs because of differences in procedures,
types of equipment, impurities in water, and so forth. On
the average, two readings from 10 different batches of
each solution, mixed at different times, must be taken
and recorded to establish these standards. These batches
should be mixed as they would be for regular use but
under very close control to ensure that the solutions are
mixed at the correct temperature, in the proper sequence,
and so forth. This operation helps in determining the
tolerance. This tolerance is the amount of variation of
the pH that still produces high-quality results.
Courtesy of Kreonite, Inc.
Figure 9-4.Agitation mixers.
The discussion of pH meters is intended as an
introduction only. Detailed step-by-step operating
instructions for pH meters are not included in this
chapter. Operating instructions in the form of technical
orders and manufacturers manuals for specific pH
meters will be available to you in your imaging facility.
In the Navy, we use two methods of mixing
chemicals: hand mixing and machine mixing. Hand
mixing is used when only small quantities of solutions
are needed or when machines are not available. Machine
mixing is necessary to handle the large production
requirements of most Navy imaging facilities.
Proper agitation of the solution during mixing
increases the rate at which the chemicals are dissolved
and prevents undesirable side effects. For proper
agitation, an agitator type of mixer does not cause
excessive amounts of air to enter into the solution
(fig. 9-4). Developers are quickly ruined by oxidation;
a few minutes of improper and violent agitation can