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variations in the chemical composition. the chemicals to dissolve properly, generally about 30 sample bottle should not be shaken, and it should be allowed to stand for 10 minutes after the sample is large particles to settle or turbidity (caused by Ordinarily, determining the pH and the specific these tests are followed up with valid sensitometric tests. solution. The pH of a solution is the negative logarithm of the hydrogen ion concentration. The electrical potential between the glass electrode of a pH meter and the solution surrounding it indicates the hydrogen ion concentration. value, you must standardize the temperature. Generally, you make pH measurements at the same temperature that the photographic process is operated. A change of 10°F produces a pH change of approximately 0.10 in a processing solution at a pH of 13.0. Thus temperature control is more important at adjust the meter consult the instruction manual or the read several samples. Of course, the more samples Usually, you must determine the pH value of more than one sample. After four samples have been read, elapse between any pH meter standardization or cross-check. Check the average value against the standard pH for that solution. When the pH is within limits, enter the value in the appropriate location on the certification sheet. When the pH is not within limits, further investigation is necessary. actual dilution of a developer is obtained by comparing a fresh developer to a used one. Another application may be to compare a fresh fixing bath to a used one. Since the silver content of a fixer increases with use, it is logical to assume that a experience, you will be able to establish upper- and lower-control limits for specific gravity of the various solutions needing such a check. recommended by the manufacturer, because temperature affects the specific gravity of a solution. Specific gravity standards for black-and-white processing solutions are set at 70°F, because many of these solutions are used in 70°F surroundings. simply indicate a change. So, further testing is required. When a developer is being replenished properly, specific gravity remains constant. If the flow of replenisher stops, a change of specific gravity will become evident. Replenisher flowmeters should indicate such a problem, but a backup check of specific gravity and pH, along with control strips, are recommended as well. gravity measurements of the developer are within tolerance, this test can certainly validate the activity of the developer. Advanced Photography Course |
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