Heat Dissipation at the Electrodes of a Short Electric Arc

H I S paper is an account of direct calorimetric measurements of the energy dissipated at positive and negative electrodes when they are brought together to discharge a condenser. T h e experiments are called for by the fact t h a t the erosion at the closure of electrical contacts is due to arcing, 1 and understanding how the energy of a closure arc is distributed between the electrodes is likely to help in developing a comprehensive theory of this arc which in turn may aid in the control of contact erosion. T h e experimental method is an adaptation to the present problem of a procedure 2 used earlier in which crossed wires are separated and brought together 60 times per second by means of a magnetic loudspeaker unit, each closure discharging a condenser which is recharged after the wires have been separated. For the present experiments the two wires are made of platinum and are rather heavy, and the flow of heat in each of them is measured by a pair of thermocouples. There is a known length of wire between the two thermocouples of each pair which are connected in series to oppose each other, so that a galvanometer in either circuit will give a deflection proportional to the difference in temperature across the wire.11 The flow of heat along each wire is calculated from this temperature difference and the thermal conductivity and dimensions of the wire. After making some corrections this gives the amount of energy dissipated upon the electrode at each discharge of the condenser.