Film about the railroad industry. Shots of freight cars carrying iron ore and being emptied. Mail being carried and sorted on a freight train. Shot of industrial Pittsburgh (factories are seen from a distance). Brakes lined up in factory and tested. Radio device being tested which sends signals to the train. Man sits at control booth and watches car move slowly on track. Heat recording instrument is set up by the track. Measures the heat of the ‘journal box’ of each railroad car (if too hot, there will be a problem). Called a ‘hot box detective’. CU of hot box signal machine in control room.