The Electrodeless Discharge in certain Vapors

Appearance and Spectrum of Electrodeless Discharge in Various Vapors.—The discharge was produced by electromagnetic induction, the bulbs containing the vapors being placed within a Tesla coil through which passed a high-frequency condenser discharge. The effect was found to vary with vapor pressure, controlled by the temperature, and with electromotive force, controlled by a spark gap. In general, for a certain range of pressure, an intense ring discharge was obtained which weakened to a faint luminosity for higher pressures. Potassium at temperatures of 250-300° C., gave a bright ring with a spectrum including seven or more members of each sub-ordinate series. The bright yellow discharge in sodium above 300° C. showed the D-lines, four members of the diffuse series and three members of the sharp series. With lithium up to 500° C. only a feeble discharge due to impurities was obtained. In the case of mercury, the work of Kowalski was confirmed and extended. A dazzling white ring discharge appeared from 70 to 110° C. or higher depending on the spark gap; then became fainter, while a greenish glow whose spectrum showed a few lines superposed on a continuous band extending from the violet to the yellow, appeared for 110 to 115° C., irrespective of the spark gap. It is suggested that the glow may be associated with polyatomic molecules formed at the higher vapor pressures. In the case of iodine, the only diatomic vapor studied, at temperatures from — 5° to 5° C. a pale yellow ring showing a band spectrum changed to a green, pink-bordered ring with a line spectrum when the spark gap was increased; the higher the pressure, the greater the spark length necessary to excite the line spectrum. The change probably accompanies dissociation of the molecules into atoms.

Electrodeless Discharge as a Source of Sharp Lines should be of value in measuring wave-lengths and in analyzing, with an instrument of high dispersion, lines with components due to isotopes.