The electric arc in vapors and gases at reduced pressures: W. A. Darrah. (Metallurgical and Chemical Engineering, vol. xiii, No. 15, December 1, 19I5.)
- Publisher
- Elsevier Science
- Year
- 1916
- Tongue
- English
- Weight
- 65 KB
- Volume
- 181
- Category
- Article
- ISSN
- 0016-0032
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✦ Synopsis
Some very promising experiments in the development of a design of an arc lamp in which the large factors in the cost of operation of trimmingand cleaning are eliminated have been described in a paper read before a joint meeting of the American Electrochemical Society and the Illuminating Engineering Society. These experiments had for their object the design of a lamp in which the supply of material for the arc did not come from the electrodes, but from a surrounding gas or vapor, and if, in passing through the arc, the vapor were not destroyed, to construct a lamp that would require no trimming or materially more attention than an incandescent lamp.
The lamp consists essentially of a glass bulb arc chamber, at the centre of which the arc is drawn between two tungsten electrodes about 3/16 inch in diameter. The electrodes are partly surrounded with a refractory insulator designed to prevent the arc from movir~g far from the ends of the electrodes, as this allows the magnetic blow of the arc to continue to extend it and ultimately rupture the arc. The refractory insulator also assists in maintaining the electrodes at a high temperature, thus increasing the efficiency of the lamp and the stability of the arc. The upper electrode is fastened by means of a tungsten rod to an iron core, which is surrounded by a glass shell to protect the iron from corrosion, as the vapors used readily attack nearly all metals, except tungsten, platinum, gold, and a few other inert materials. A flexible tungsten spiral serves to conduct the current from the upper movable electrode to the upper seal.
The appearance of the arc is quite different from other commercial arc lamps. It is usually very stable, about ~ inch in diameter, tubular in form, and varies from 2 to 5 inches in length with 11o volts direct current applied, the variations being due to differences in pressure, nature of the gases supplied, etc.
Regarding the efficiency secured, it is to be expected that this will vary widely with the nature and the condition of the vapors used, and actual results range from t watt per mean spherical candlepower to less than one-quarter of this value. This performance may be secured with a white light which closely resembles afternoon north-ray daylight. The vapor of titanium bromo-chloride is recorded as giving a high luminosity white light and a very stable arc.