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78 <br />• 7. The pH measurement taken is only as good as the buffers <br />which are used for calibration. In some instances with tablet <br />buffers, the solution makes an excellent nutrient for bacteria <br />growth. Some of the buffers which are already in solution <br />have a. bacteriacide in them and are stable for long periods <br />of time. In that respect, the prepared solutions may be <br />worth the expense. <br />In summary, pH measurements take a high level of technical <br />• <br />expertise. There appears to be no substitute for careful <br />maintenance of the glass electrode and the pH meter. Save <br />the instruction manual on the meter and the information sheet <br />on the! electrode. They usually.contain suggestions to try <br />if the system is-operating poorly. _ <br />CONDUCTIVITY AND TEMPERATURE <br />In comparison to pH measurement, modern electronic <br />circuit designs have made the measurement of conductivity <br />quite easy. The portable meters have a dial readout which <br />enables readings to be accurately made from 100 umho/cm to <br />50,000 umho/cm. New conductivity cells which are encased in <br />plastic are rugged and durable. In addition, some cells <br />have temperature probes built into them so both readings <br />can be! made with the same meter. The maintenance procedures <br />which are suggested for the new cells are quite good. Only <br />once has a conductivity cell gone foul and that was because <br />it was being used in a solution which had an appreciable <br />amount. of sulfide ion in it. Otherwise, the cleaning <br />•