The drift in potential of the quinhydrone electrode
1928
Baver, L.D.
A study was made of various factors that may influence the drift in potential of the quinhydrone electrode. The fluctuation in pH values measured with the saturated calomel, N/20 potassium acid phthalate, acid 0.01 N HCl plus 0.09 N KCl electrodes varied with the different soils. The calomel cell is preferred because of its stability. There were no significant differences in the results obtained with the platinum cone, platinum foil, platinum gauze, and gold foil electrodes. The platinum cone has the advantage of being more rigid and compact. Mechanical stirring reduced the deviations in tile pH values of these soils. The lower part of the soil suspensions tended to be more acid than the upper. Recrystallized quinhydrone did not materially affect the changes in pH when compared with a good c.p. commercial product. Passing CO2 - free air or hydrogen through the soil-suspension did not influence the deviations in pH. Allowing the soil-water mixture to stand over night did not reduce the fluctuations in the pH values. A definite technic is necessary for obtaining satisfactory, results with the quinhydrone electrode. The care of the metallic electrodes is of prime importance. A solution of definite pH or a control soil is used to check the accuracy of the electrodes. The first reading, made at least within one minute after electrodes are immersed in the soil suspension, is the more nearly correct reading.
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