Method of Soil PH Measurement – Glass Electrode PH Meter

Method of Soil PH Measurement – Glass Electrode PH Meter

The glass electrode generally used for the PH measurement employes a glass membrane of special, chemically pure, soft glass paired with a calomel reference electrode are used for measuring the soil PH.

Composition of corning glass electrode: 72 % SiO2, 6.0 % CaO and 22.0% NazO.
1. Vacuum tube volt meter
2. Hg.Hg2Cl2 Half cell
3. Saturated KCL.
4. Glass membrane
5. KCL crystals
6. HCL
7. Test solution

Hg. Hg2-Cl2, KCL saturated H+ (a1) KCL. Hg2cl2 H.
Glass electrode system for measurement of PH.

Across the glass membrane develops an electrical potential that is proportional to the difference in PH, between the two slide in accord with concentration cell in which the glass membrane and liquid junction. A systematical potential E develops across the glass membrane even, when solution of the same H+ ion activity is on the two sides. For this reason the meter must be calibrated with the standards buffer solution.

Advantages of the Glass Electrode PH Meter:

1. It does not expel dissolved gases such as CO2 from the system under measurement.

2. It is adaptable to thick fluid, paste and coloured solution.

3. It is not affected by oxidizing and reducing solution in contrast to quinhydrone or hydrogen electrode.

4. It does not require H2 gas or catalytic surface required by H electrode.

5. It has relatively low salt error.

6. After standardization give accuracy within 0.1 PH unit with care within 0.02 PH unit.

7. Rapid convenient in expansive and adaptable for long term recording.

Precaution in the Use of Glass Electrode:

1. Electrode is not allowed to remain in the test solution or suspension longer than necessary especially if more alkaline than PH 9.0.
      
2. Immediately after testing, the electrode is washed off with a strong stream of distilled water from a wash bottle. If the system was alkaline, the electrode should be dipped for a few second in the acid PH buffer or dilute HCL to remove the film of CaCO3 that some time forms.

3. For storage after cleaning the electrode is suspended in distilled water and the system is protected from to evaporation. Drying out of the electrode is avoided.

4. Failure of the glass electrode PH meter is indicated, when , after standardization it gives slow response to large PH changes.