GB503112A - Improvements in high-pressure mercury-vapour electric discharge devices - Google Patents

Abstract

503,112. Discharge lamps. GENERAL ELECTRIC CO., Ltd. (Patent-Treuhand-Ges. f³r Elektrische Gl³hlampen) Jan. 4, 1938, No. 205. [Class 39 (i)] In a high-pressure mercury-vapour discharge device of the type in which (1) each electrode that acts as a cathode during the discharge is thermionic and heated in operation by the discharge only (2) the inter-electrode distance exceeds the greatest diameter of the envelope at a plane midway between the electrodes and (3) the vapour pressure of the mercury in full operation exceeds 5 atmospheres, each such electrode is in close contact with the end wall of the envelope so that transference of heat between electrode and wall is substantially independent of the presence of liquid mercury, arid the amount of mercury within the envelope is so small that it is all evaporated in full operation. The electrode may be a perforated tungsten canister or closed tungsten helix filled with alkaline earth, mounted in close contact with or sunk into the end wall of the envelope and having a very narrow gap between it and the side walls of the envelope. Alternatively, it may comprise two helices 5, Fig. 3, enclosing the alkaline earth 6 and held in a molybdenum cup 8<1> tightly fitting the end of the envelope. The discharge chamber of the device may be narrower than the part holding the electrode and may be cooled. The electrode chambers may be protected from the cooling medium by a coating or by quartz sleeves 11, Fig. 7. In manufacture the electrodes 3 are first welded to the leads 4 sealed into the quartz rods 9; the discharge chamber 2, which is not less than 5 mm. in internal diameter, is then sealed to the two rods, and the sleeves 11 to shoulders 12 formed on the outside of the envelope. The device is adapted to operate at 80 atmospheres pressure, and may contain other gases besides mercury.