For pt.i see Ibid., vol.5, no.12, 1706. The Durham spectrograph MARS has been used to study the electromagnetic interactions of cosmic ray muons in iron in the energy range 6-200 GeV. The interaction probabilities for producing single electrons and electron bursts of various sizes from the knock-on process, direct electron pair production and bremsstrahlung are investigated as a function of muon energy. Reasonable agreement between the measured probabilities and those predicted has been found and it is concluded that significant deviations from accepted theory are not likely.