Courtesy of Beckman Instruments, Inc.302.259XFigure 9-3.–pH meter.The ability of a pH meter to determine the pH valueof a solution accurately may be used for the followingpurposes:To verify that chemicals have been properlymixedTo test prepared chemicalsTo assure standardization of the processingsolutionsTo determine the exact replenishment rates forphotographic chemical solutionsTolerances in pH values must be established forindividual labs because of differences in procedures,types of equipment, impurities in water, and so forth. Onthe average, two readings from 10 different batches ofeach solution, mixed at different times, must be takenand recorded to establish these standards. These batchesshould be mixed as they would be for regular use butunder very close control to ensure that the solutions aremixed at the correct temperature, in the proper sequence,and so forth. This operation helps in determining thetolerance. This tolerance is the amount of variation ofthe pH that still produces high-quality results.9-5Courtesy of Kreonite, Inc.302.20XFigure 9-4.–Agitation mixers.The discussion of pH meters is intended as anintroduction only. Detailed step-by-step operatinginstructions for pH meters are not included in thischapter. Operating instructions in the form of technicalorders and manufacturer’s manuals for specific pHmeters will be available to you in your imaging facility.MIXERSIn the Navy, we use two methods of mixingchemicals: hand mixing and machine mixing. Handmixing is used when only small quantities of solutionsare needed or when machines are not available. Machinemixing is necessary to handle the large productionrequirements of most Navy imaging facilities.Agitation MixersProper agitation of the solution during mixingincreases the rate at which the chemicals are dissolvedand prevents undesirable side effects. For properagitation, an agitator type of mixer does not causeexcessive 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
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