Poggendorff compensation method

Measurement of E.M.F.—The principle generally employed in the measurement of the e.m.f. s of voltaic cells is that embodied in the Poggendorff compensation method it has the advantage of giving the E.M.F. of the cell on open circuit, i.e., when it is producing no current. It has been already mentioned that a cell can be expected to behave reversibly only when it is producing an infinitesimally small current, and hence the condition of open circuit is the ideal one for determining the reversible e.m.f. 

Measurement of the E.M.F. of a Cell—Outline of the Method.— The method usually employed for the determination of the e.m.f. of a cell is essentially that known as the Poggendorff compensation method. 

Poggendorff compensation circuit (principle, method) — The correct measurement of the potential... 

Poggendorff compensation circuit (principle, method) — The correct measurement of the potential of a cell or a half-cell can be performed if during the measurement there is practically no current flowing... 

Apart from the necessity of excluding interferences from any diffusion potential, normal potentiometry requires accurate determination of the emf, i.e., without any perceptible drawing off of current from the cell therefore, usually one uses the so-called Poggendorff method for exact compensation measurement the later application of high-resistance glass and other membrane electrodes has led to the modern commercial high-impedance pH and PI meters with high amplification in order to detect the emf null point in the balanced system. 

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