GB277739A - Improved luminous electric discharge tubes - Google Patents

Abstract

277,739. Demoulin, J. June 18, 1926. Vacuum tubes.-Luminous electric discharge tubes filled with rare gas are provided at one or at each end with a plurality of substantially identical electrodes connected in parallel, each electrode comprising a spirally wound plate of metal of high melting point such as tungsten or molybdenum. At each end the discharge occurs at one electrode at a time and passes rapidly from one electrode to another; slight differences in the resistance of the electrodes due to lack of atomical homogeneousness of the metal cause the discharge to occur at the most conductive electrode first, the discharge then heating the electrode and increasing its resistance and passing to another electrode until the original electrode cools and again takes the discharge. Heating of the electrodes and absorption of the gas filling are thus minimized. At one or each end of the tube, electrodes 1, 2, Fig. 3, spirally wound to reduce their volume and to allow them to expand on heating without straining their glass supporting cups 4, are mounted in branches c. d of the luminous tube a and connected in parallel by leads 5. The electrodes are freed from occluded gases prior to mounting in the luminous tube by passing a discharge between them in a separate tube 7, Fig. 4, filled with nitrogen, the current being supplied and regulated by a transformer 8 and an adjustable inductance 9 with a movable core. Repeated fillings of nitrogen are introduced through a tube 10 and withdrawn through a tube 12 leading to a vacuum pump until spectrum analysis of the nitrogen shows that the electrodes no longer liberate gases. Potassium is placed at 11 to absorb gases such as ammonia and nitrogen peroxide formed by action between the nitrogen and gases liberated from the electrodes. After mounting the electrodes in the branches c, d and sealing these to the tube a, the tube is purified. by filling with nitrogen and producing a discharge. Oxygen and hydrogen are absorbed by an auxiliary electrode comprising a plate of palladium heated by the, current and mounted in a part subsequently sealed off from the tube. 'The tube is evacuated, nitrogen is eliminated by a glowing tungsten filament, and neon or helium, purified by a glowing tungsten filament in the supply pipe, are then introduced. The branches c, d may be cleaned in nitric acid before fusing to the tube a, traces of the acid subsequently decomposing to supply some nitrogen.