Lippmann electrometer

Fig. 20.4 Lippmann electrometer for studying the variation of the excess charge on mercury with variation in potential difference at the mercury solution interface...

Electrocapillary curves obtained with the Lippmann electrometer are not usually parabolic. For a few electrolytes, such as potassium nitrate (and even then within a limited concentration range) parabolic curves are found but more usually the curves show varying degrees of distortion. Such behaviour is always found with cations and anions which are specifically adsorbed. 

In the case of a solution with a previously known aH+ (see below), we could determine 2°H+-.H2(iatm)> provided that a reference electrode of zero potential is available however, experiments, especially with the capillary electrometer of Lippmann, did not yield the required confirmation about the realization of such a zero reference electrode16. Later attempts to determine a single electrode potential on the basis of a thermodynamic treatment also were not successful17. For this reason, the original and most practical proposal by Nernst of assigning to the standard 1 atm hydrogen potential a value of zero at any temperature has been adopted. Thus, for F2H+ H2(iatm) we can write... 

G. Lippmann introduced the capillary electrometer to measure the surface tension of mercury (Fig. 4.10). A slightly conical capillary filled with mercury under pressure from a mercury column (or from a pressurized gas) is immersed in a vessel containing the test solution. The weight of the mercury column of height h is compensated by the surface tension according to the Laplace equation... 

Lippmann Ann. v. 494, 1875), independently made the same observation as a result of his study of the capillary electrometer. 

Gabriel Lippmann, 1845-1921. Professor of mathematical physics at the University of Paris. Inventor of the capillary electrometer and of a process of direct color photography. The phenomenon of piezo-electricity in crystals predicted by Professor Lippmann was first demonstrated experimentally by Pierre and Jacques Curie. 

Lippmann was the first to record an accurate study of the relation between electrical potential and surface tension, in the classical memoir1 in which the capillary electrometer is described. 

See also -> adhesion, -> Dupre equation, -> Lippmann equation, -> Lippmann capillary electrometer, -> point of zero charge, -> Young equation. 

See also - electrocapillarity, - electrocapillary curve, -r Gibbs-Lippmann equation, - Wilhelmy plate (slide) method, - ring method, - Lippmann capillary electrometer. 

Electrocapillarity — (a) as a branch of science, this term covers all phenomena related to the thermodynamics of charged - interfaces, esp. of metal-solution interfaces. The term is practically synonymous with -> capillarity, but emphasizes the electric aspects, (b) The term electrocapillarity is often used in a restricted sense to mean the study of the equilibrium properties of metal solution interfaces, such as the - interfacial tension of mercury solution interfaces, the height of a mercury column (in the case of the - Lippmann capillary electrometer), or the -> drop time (in the case of the - dropping mercury electrode). More generally, however, the equilibrium properties of many other interfaces fall... 

Mar. 22,1874 Semily, then Austro-Hungarian Empire -Apr. 16, 1921, Prague, Czechoslovakia) Since 1912, Professor of experimental physics at Charles University, Prague. Kucera introduced the measurement of surface tension of polarized mercury by applying the dropping mercury electrode [i] rather than the Lippmann capillary electrometer, and he inspired thereby -> Heyrovsky, J. to introduce - polarography. 

Lippmann capillary electrometer — Figure 1. Lippmann capillary electrometer [ii]. For explanation see text... 

Lippmann capillary electrometer — Figure 2. (a), (b), (c) from left to right Lippmann capillary electrometers. (Reproduced (a) from [iii], and (b) and (c) from [iv]). For explanation see text and sources... 

This equation was first derived by Lippmann in the course of his studies that led him to develop the Lippmann capillary electrometer [i]. 

Ring method — Method to determine the - interfacial tension in liquid-gas systems introduced by Lecomte du Noiiy [i]. It is based on measuring the force to detach a ring or loop of a wire from the surface of a liquid. The method is similar to the -> Wilhelmyplate method when used in the detachment mode [ii]. See also -> electrocapillarity, -r electrocapillary curve, -> Gibbs-Lippmann equation, - Wilhelmy plate (slide) method, - drop weight method, - Lippmann capillary electrometer. 

Gibbs-Lippmann equation, drop weight method, -> ring method, Lippmann capillary electrometer, -> Wilhelmy. 

Figure 3.47. Sketch of a Lippmann-type capillary electrometer. The mercury-solution interface resides in the slightly conical capillary A. in which a certain height h is chosen at which the measurements are carried out. The potential is externally applied R is the reference electrode (in Llppmann s experiments it was a calomel electrode, connected to the solution S via a salt bridge). The interfacial tension between mercury and solution is obtained from the height h, defined in the sketch...

For practical reasons the capillary rise technique is rarely used for the measurement of interfacial (rather than surface) tensions large amounts of the two liquids are needed and there are suitable and convenient alternatives. An exception to this is the measurement of the Interfacial tension between mercury and (mostly) aqueous solutions at various potential differences applied across the liquid-liquid interface. Such measurements are done in a so-called Lippmann capillary electrometer, already described in the chapter on electric double layers (fig. 11.3.47). 

The capillary electrometer method first used by Lippmann [4] is based on the capillary rise principle. The interface between the liquid Hg electrode and the solution is established in a fine capillary, the position of the interface being determined by the interfacial tension (see fig. 8.2). More specifically, y is given by... 

It is not obvious why (13.1.31) is called an electrocapillary equation. The name is a historic artifact derived from the early application of this equation to the interpretation of measurements of surface tension at mercury-electrolyte interfaces (1-4, 6-8). The earliest measurements of this sort were carried out by Lippmann, who invented a device called a capillary electrometer for the purpose (9). Its principle involves null balance. The downward pressure created by a mercury column is controlled so that the mercury-solution interface, which is confined to a capillary, does not move. In this balanced condition, the upward force exerted by the surface tension exactly equals the downward mechanical force. Because the method relies on null detection, it is capable of great precision. Elaborated approaches are still used. These instruments yield electrocapillary curves, which are simply plots of surface tension versus potential. 

G. J. LIPPMANN (1845-1921) introduces the capillary electrometer that bears his name Ann Phys 225 546... 

CT = (7q - CV y where gq is the maximum value for the uncharged surface. Hence the c, V curve is a parabola. This was confirmed by Konig. Lippmann found that a current flows in the circuit if the size of the mercury surface in the capillary electrometer is altered by mechanical means this should cease when the mercury is uncharged and Pellat found that this happens when an electromotive force of 0 97 volt acts against the natural potential difference, agreeing with Lippmann s value of about i volt for the maximum of surface tension. Ostwald found that in different acids the surface tensions could differ by a ratio of more than i to 3. He emphasised that it is the charge on the mercury, and not (as Lippmann thought) the potential difference, which determines the surface tension. 

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