Refinery cracking plant run No. 52 was a crude shale-oil viscosity-breaking operation conducted from August 25 to 29, 1952. Both Gas Combustion and N-T-U crude shale oils were processed. Operating conditions, controlled to supply lacking visbreaking data, were limited to 950 degrees F. heater outlet temperature at 120 and 300 p.s.i.g. heater outlet pressure.