Does a phase shift occur in an AC arc?
  This is a translation of a classic paper in German showing that the apparent power in an AC arc is larger than the active power although no phase shift exists between the voltage and the current, indicating that the reactive power vanishes. The phenomenon studied in this paper gave rise to a variety of mutually conflicting "power triangle" models relating the active, reactive, and apparent powers P, Q, and S whose merits are still under debate today. 
Charles Proteus Steinmetz (author), Gerald Kaiser (translator)
physics.hist-ph physics.class-ph