Arc Discharge not Obtained in Pure Argon Gas

Between very pure iron electrodes in an argon atmosphere of fairly good purity, the low-voltage arc was easily maintained. When the argon was rigorously purified the arc could not be struck even with moderate potentials. Although the present theories do not require it, the normal arc discharge does appear to depend upon the presence of chemically active atoms or molecules, either in the gas or on the electrodes. Various hypotheses are presented.