The Production of High Velocity Mercury Vapor Jets by Spark Discharge

Photographs of sparks of microsecond duration in hydrogen to a mercury electrode show high velocity jets from the mercury surface regardless of polarity. Spectroscopic examination shows that these jets are largely composed of mercury atoms which sweep away the hydrogen. Measurements of jet velocity demonstrate that it is independent of current and gas pressure over a wide range. While it decreases with distance from the source, the original velocity of the cathode jet is 1.9 (${10}^5$) cm/sec., and that of the anode jet is 1.5 (${10}^5$) cm/sec. The energy of the anode jet can be accounted for by positive mercury ions crossing the anode drop. It appears that the energy of the cathode jet cannot be accounted for unless it is assumed that, in addition to positive ions striking the cathode and rebounding as neutral atoms, many mercury atoms leave the cathode as negative ions.