Internal pressure was measured in two special quartz mercury arcs developed in previous investigations. Numerous curves present the data. Pressure is a function of cross-section, voltage gradient, and current only, and independent of arc length and the mode of cooling. Above two atmospheres pressure increases about 140 mm for unit change in voltage gradient, irrespective of other variables. In the constricted arc, 2 mm in diameter, where the cooler absorbing vapor shell is very thin, intensity at given current strength is quite closely proportional to pressure from a few millimeters up to five atmospheres.With the addition of thermocouple inlets at the mercury surfaces and calibrated measuring tubes, mercury transfer for equal electrode temperatures was measured in the 9 mm arc. The relations are little changed when the cathode is at least 20° to 40° hotter than the anode. Apparently zero at the lowest pressures and voltage gradients, it rises to five gram atoms per faraday from anode to cathode at 5 volts/c and remains nearly constant up to 25 volts/cm. Current strength is of secondary importance. These conclusions are amply demonstrated by curves. The relative importance of the electron current and the positive ion current under the various conditions studied is briefly discussed.
GEORGE SHANNON FORBES and PHILIP ALBERT LEIGHTON, "RELATIONS INVOLVING INTERNAL PRESSURE, INTENSITY, MERCURY TRANSFER, CROSSSECTION, AND ELECTRICAL CONDITIONS IN MERCURY VAPOR LAMPS," J. Opt. Soc. Am. 12, 53-63 (1926)