The method of filling Neon lamps and the factors affecting their lifespan.
| Identifier | ExFiles\Box 79\1\ scan0259 | |
| Date | 19th February 1920 | |
| - 3 - unsymmetrical to the discharge, allowing it to pass much more easily in the direction indicated in the figure than in the opposite, hence it effectually stops the "reverse" current from the secondary of the coil. Other important results depending on the length of the filament will be discussed later, it should roughly be one hundred times the length of the spark the coil is capable of giving in air when running on the tuning-fork break. It is hardly necessary to state that the shape into which the filament is wound is not in the least essential and could be varied to any extent in lamps for special purposes. METHOD OF FILLING LAMPS. As Neon, like the other gases of the helium group, has the remarkable property of liberating gas from aluminium electrodes which have been completely run in for other gases, the operation of filling necessitates the contamination of a comparatively large volume of Neon, so that this can only be done economically and conveniently where liquid air is available for re-purifying. So far all the lamps have been filled on the author's Neon fractionation apparatus at the Cavendish Laboratory.X The gas for filling is contained in charcoal cooled in liquid air. A quantity is admitted to the exhausted lamp which is then sparked at a pressure of 1 to 3 mm. with a small coil for a time. The dirty gas is then pumped off with a Toepler mercury pump, a fresh supply of pure gas admitted and the tube run again. These operations are repeated until spectroscopic and other observations show the desired conditions of purity have been reached and are not altered seriously by prolonged running. The full charge of 5 to 10 mm. of gas is now let in and the lamp sealed off. The whole operation takes about 3 hours, three lamps being filled at once. The pressure, purity and time of running in are all matters of some nicety as will be seen from consideration of the life of the lamp. LIFE OF THE LAMPS. Apart from accident the lamps are serviceable until the pressure of gas within them becomes too low for the spark to light them adequately. Their life appears to consist of two distinct periods, the first during which chemically active impurities derived from the electrodes and walls of the tube are being slowly and completely eliminated (at least as far as a spectroscopic observation goes) and the second during which sputtering of the cathode takes place and the inactive Neon itself slowly disappears until the pressure gets too low for use. During the first period the luminosity steadily improves, remaining almost constant afterwards till near the end of the second period when it rapidly decreases. X v. {VIENNA} Lindemann and Aston, Phil Mag. XXXVII, May 1919, p. 527. | ||
From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).