The potential fall between striæ in electrical discharges through rarefied hydrogen
✍ Scribed by John Zeleny
- Publisher
- Elsevier Science
- Year
- 1930
- Tongue
- English
- Weight
- 718 KB
- Volume
- 209
- Category
- Article
- ISSN
- 0016-0032
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✦ Synopsis
A study was made of the variation with gas pressure of the potential fall between striae in the positive column of a discharge through hydrogen because in this gas the distances between the striae change with pressure in an anomalous manner first noted by Willows. With decrease of pressure the stria distances at first increase, pass through a maximum value and then through a rather sharp minimum value at a pressure between I mm. and 2 an1. The color of the striae was found to be bluish in the pressure region of minimum separation and reddish at other pressures.
The potential fall between the striae was measured without the use of probes with hydrogen flowing through a tube 1.2 ca. in diameter. The potential fall was found to increase steadily with increase of pressure from 12 volts at 0.25 mm. pressure to 32.6 volts at 3.15 am. pressure, the current being 6 m.a. Similar values obtained with the gas stationary were between I and 2 volts lower. No anomalous change in the potential fall was found in passing through the pressure region of the closely packed bluish striae. Corrections to the above values were made for the losses of energy suffered by electrons in elastic collisions with molecules while passing between two striae. These were found to be negligible for pressures below 0. 5 mm. and to amount to 7-5 volts at 3.15 am. The average energies acquired by electrons between striae at the two pressures are therefore far from equal.
By a special procedure the narrow bluish and the wide reddish striae were made to co-exist in different parts of the same tube and the energy acquired by electrons between two striae under these conditions was found to be 13. 5 volts for the blue striae and 19. 4 volts for the red ones, the gas pressure being 1.43 am. and the current 7 m.a.
It does not seem probable that the purity of the gas was different in the different portions of the tube, although some authors maintain that blue striae are a sign of the presence of inlpurities in the gas.
It is shown that blue light can only arise fronl an excited state of the molecule having an energy of at least I4.5 volt-electrons above the ground level. Where the electrons between striae acquire less than this amount of energy directly from the field it is necessary to suppose that they obtain the addition, needed for raising molecules to the required level, from collisions of the second kind with molecules of impurities having much lower excitation levels than those possessed by hydrogen.
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