A device for controlling a secondary or controlled electric circuit by means of a primary or controlling electric circuit

932,458. Mercury switches. TECHNIKUM PO ELEKTROTECHNIKA S. M. KIROV. July 28, 1960, No. 26250/60. Class 38 (5). A switch comprises a glass tube A containing an electrolyte 5 and a mercury drop 6, the electrolyte 5 being connected through electrodes 1,2, to a D.C. primary circuit, closure of which causes the drop 6 to move towards the negative electrode 1 and bridge electrodes 3, 4, so closing a secondary circuit. Opening of the primary circuit allows the drop 6 to be restored to its original position by gravity. In a modification, Fig. 2, the drop 6 coheres to the roughened surface of electrode 2 so that upon passage of primary current the drop elongates to bridge electrodes 3, 4, restoration being effected by the surface tension of the drop 6 with or without the aid of gravity depending on the position of the tube A. In another modification, Fig. 3 (not shown) the tube has a pair of secondary electrodes at each end, each pair facing a recess in the flat, horizontal base of the tube, so that a mercury drop bridges either pair according to the direction of primary current, and remains in the corresponding recess until the primary current is reversed. The electrolyte may comprise diluted sulphuric acid, organic salts dissolved in water, ether or alcohol, or a solution of acid, base or salt in a suitable solvent. Instead of an electrolyte, a semi-conducting mixture, a gas or a vapour may be used. A plurality of mercury drops may be used, in which case the tube has partitions to prevent the drops coalescing.