Arcing Voltages in Mercury Vapor as a Function of the Temperature of the Cathode

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Abstract
Low Voltage Arcs in Mercury Vapor.—One of the objects of this work was to study the production of the low-voltage arcs in a more uniform mercury-vapor atmosphere than had been used before. As a result of improved apparatus much more consistent results have been obtained. It has been shown that there is a linear relation between the striking voltage and the current through the cathode for the larger currents. This in turn has been shown, in the case of platinum coated with lime, to mean that the striking voltage forms a linear relation with the temperature of the cathode. The results further suggest that the difference between the potential at which ionization takes place and the accepted ionization potential is directly proportional to the absolute temperature. Results with Tungsten Cathodes.—In line with the above it has been shown that tungsten cathodes produce lower arcs than lime-coated platinum cathodes. A striking voltage as low as 3.2 volts was obtained, the lowest for platinum coated with CaO having been in the vicinity of 4.9 volts. Effect of Thickness of Oxide Deposit on the Cathode.—It has been shown that the thickness has an effect on the value of the striking voltage. A thinly coated platinum cathode produced an arc at a potential as low as 6.0 volts whereas a thickly coated one produced an arc as low as 4.9 volts. Effect of Hot Anode.—A hot anode used with a thinly coated platinum cathode has been found to produce a lower arc than when the anode was not heated. Discussion of Results.—The results are briefly discussed but no definite theory is offered to explain them.

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