Lewis-Sargent equation

The solution is given for the case of a smeared-out boundary and linear spatial distributions of concentrations. Generally, Henderson and Planck equations yield similar results however, for junctions with a pronounced difference in ion mobilities (like HCl-LiCl), the deviation can reach about 10 mV. A specific feature of the Planck equation is the existence of two solutions, the firstbeing close to that of Henderson, and the second one being independent of the solution concentration and of no physical meaning [iv]. Two particular types of liquid junctions are (a) two solutions of the same electrolyte at different concentrations and (b) two solutions at the same concentration with different electrolytes having an ion in common. For type (b) junctions, the simplification of the Henderson model results in the Lewis-Sargent equation ... 

When the concentration of the two electrolytes is the same the more simple Lewis-Sargent equation may be used ... 

Table 9.6 Liquid Junction Potentials Estimated from Cell (9.7.44) and from the Lewis-Sargent Equation (9.7.33)...

Solution 1 Solution 2 1 Experiment A2(t)/mV Lewis-Sargent Equation... 

Electrolyte junction — A liquid junction is the region of contact of two different -> electrolyte solutions kept apart by a porous -> diaphragm, such as sintered glass or ceramic. At the contact a -> Galvani potential difference appears, which is called -> liquid junction potential (Ej). In the case of two solutions of the same electrolyte, but with different concentrations (c(a) and c(/S)), the potential Ej is defined by the equation Ej = (t+-t-) ln ry, where t+ and t are - transport numbers of the cation and anion, respectively. If the concentration of one of the ions is the same in both solutions, but the other ion differs (e.g., NaCl and KC1), the potential Ej is given by the Henderson equation, which is reduced to the Lewis-Sargent relation for a 1 1 electrolyte Ej = ln, where A (/3) and A (a) are molar conductivities of the electrolytes in the com-... 

Table III. Liquid Junction Potentials, El, Calculated by the Lewis and Sargent Equation and Compared with Measured Values...

Equation (3.9) is also known as the Lewis-Sargent formula [31]. This formula operates with equivalent conductivities of solutions A, not of the ions. The paper [31] published 1 year after Henderson s papers played a historical role. The cells of the same geometry as were used in [31] are still utilized for emf measurements. These cells with free diffusion boundary are sometimes called Lewis-Sargent cells. Another important note in ref. [31] concerns the search of conductivity values. 

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