Cathode Energy of the Iron Arc

The available energy at the cathode of the iron arc for welding in air, and the disbursement of this available energy to the cathode processes, are set up in balance-sheet form for purposes of study. Since many of the constants involved are not accurately known the results obtained are approximate only and indicate the probable order of magnitude of the quantities involved rather than the exact quantities themselves. The paper thus represents a preliminary survey. The energy as heat at the cathode includes that from: (1) Ionic bombardment, (2) Ohmic resistance of cathode tip, (3) Radiation from the anode, (4) Combustion. The sum of the first three items should approximate one-half of the total energy input to the arc, (since the division of total arc energy between anode and cathode is nearly an equal one). Item (1) is by far the largest heat source. But using values of f = 0.625 (fraction of current at cathode which is carried by electrons) as determined by Compton and by Gÿnther-Schulze, and taking the cathode voltage drop Vc = 9.0 volts which is higher than V1 the ionizing potential, (= 7.83 volts, Mohler) this quantity, together with the smaller items (2), (3), and (4), is still too small to account for the observed rate of melting of the cathode. Possibly ¿¿+, the heat of condensation of incoming ions, is not zero for this arc as Compton has shown for the tungsten arc.