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(4) seasonally influenced carbon dioxide content; (5) amount of grinding <br /> given the soil; and (6) electrode junction potential (Jackson, 1958; Peach, <br /> 1965). <br /> Care must be taken to insure electrode life and accurate pH measurements: <br /> (1) Electrode should not remain in the sample longer than necessary for <br /> a reading, especially if more alkaline than pH 9.0. (2) Electrode should <br /> be washed with a jet of distilled Water from a crash bottle after every <br /> measurement (sample or buffer solution). (3) Electrode should be dipped <br /> 3-n dilute (1 part acid to 3 parts water) Iyrdrochloric acid for a few seconds <br /> and washed with distilled Water to remove any calcium carbonate film which <br /> may form, especially from alkaline samples. (4) Drying out of the electrode <br /> should be avoided. Electrode is cleaned and suspended in distilled water <br /> (which is protected from evaporation) for storage. (6) Place pH meter in <br /> standby position When electrode is not in a solution (Jackson, 1958; Peech, <br /> 1965). <br /> The pH meter and electrode should be standardized with buffers differing by <br /> 3 or 4 pH units, such as 4.0 and 7.0, before beginning a series of <br /> measurements. After every tenth measurement, recheck the standardization <br /> with both buffers. Care should be taken not to contaminate one buffer <br /> with the other buffer or with the test solution. Never return used <br /> JO standard buffers to their stock bottles. The procedure describes the <br /> technique for measuring pH with a glass electrode and meter. If pH is <br /> taken in the field using color paper strips or indicator solutions, <br /> modification will have to be made by qualified personnel to the procedure. <br /> 3.2.2.3 Chemicals-- <br /> 1. Standard buffer solutions, pH 4.00 and pH 7.00. <br /> 2. Distilled water (H20). <br /> 3.2.2.4 Materials-- <br /> 1. pH meter (Corning model 12 or equivalent) equipped with combination <br /> electrode. <br /> 2. Paper cups, 30 ml (1 oz) capacity. <br /> 3. Plastic cups. <br /> 4. Stirring rod. <br /> 5. Wash bottle containing distilled water. <br /> 6. Balance, can be read to 0.1 g. <br /> 3.2.2.5 --Procedure- <br /> 1. <br /> .2.2.5 __Procedure---1. Turn on, adjust temperature setting, and "zero" pH meter per <br /> instruction manual. <br /> 46 <br />