A type-A vacuum arc on copper electrodes was subjected to an axial magnetic field up to a strength of 0.35 T. The arc current was about 500 A, with an arcing time of about 30-35 ms. A study of the dissipation of the extra energy input caused by the magnetic field was carried out, and the mass change of both electrodes at different field strengths was measured. The energy input to both electrodes increased with the magnetic field strength, and the input to the anode was a factor 1.7-1.9 greater than the energy collected by the cathode. At high field strengths the anode surface suffered gross melting due to anode spot formation. Probably, energetic ions are emitted from the anode surface, resulting in additional heating of the cathode.