Ammonia is a gas for which reliable analytical methods are available to determine concentration in other gases.  To measure flow in a 15 inch schedule 40 natural gas pipeline, pure ammonia gas is injected into the pipeline at a constant rate of 72.3 kg/min for 12 minutes.   Five miles downstream from the injection point, the steady-state ammonia concentration is found to be 0.382 weight percent.  The gas upstream from the point of ammonia injection contains no measurable ammonia.  If the gas is flowing at 45°C and 1.7 atm (gauge) how many kilograms of natural gas are flowing through the pipeline per hour?