Lippmann electrometer

A capillary electrometer is a historic instrument for measuring electric charge or electrical voltage. It is a special design of the electrometer, which exploits a physical property of the surface tension as a measuring principle.

Design and operation

The capillary electrometer consists of a column of mercury in a capillary tube, which is covered up with dilute sulfuric acid. To a voltage - to measure, or more specifically, the electric potential difference between two points, the two points are connected to the two electrodes of the capillary electrometer. An electrode in contact with the acid, the other with the mercury. The unit now takes advantage of the property that at the contact surface between mercury and dilute sulfuric acid, the surface tension of the mercury capillary tip is increased by the electromotive force of the galvanic polarization upon passage of an electric current. This means that the meniscus ( = curvature of the surface ) of mercury displaced. It can prevent small voltage changes from just 25 microvolts are measured.

The enlarged shadows of the meniscus in order to simplify the reading of the measurement result on the film is projected, and the profile then analyzed.

History

The capillary electrometer was developed in 1872 by Gabriel Lippmann in Heidelberg. The device of Lippmann consists of a 1 m high, 7 mm wide, vertical glass tube, which is drawn out into a 10 mm long, bent- up capillary tube below; the latter is immersed in a glass vessel open at the top, which contains dilute sulfuric acid and including mercury.

Application in cardiography

1876 ​​used the French physiologist Étienne -Jules Marey the apparatus to record the electrical activity of the heart. This was an important milestone in the history of electrocardiography. 1887 was the physiologist Augustus Desiré Waller first record cardiac currents using a capillary electrometer.