Of the forms and varieties of railroad passenger coaches there are many, and these will be described when we come to consider in a later chapter the luxury of modern railroad travel. But the variety of passenger equipment quite pales before that of the freight service. Flat-cars, coal-cars, box-cars, grain-cars, live-stock cars--the list runs on into catalogue form. There are refrigerator cars that are kept filled with salt and ice or ice alone, precooled cars that are merely kept air-tight, and ventilator cars employing a distinct reverse of that method; and up in northern climates there are heater-cars which are kept warm by lamps or by stoves and which are used for the transportation of fresh fruit and vegetables in winter just as the refrigerator-cars and the precooled cars are used for that same purpose in summer. Almost all the safety devices that have been added to the running-gear of the passenger equipment have been added to the freight equipment also, to the great safety and peace of mind of the railroad employee. The car itself remains the simple essential of the very beginnings of the railroad. Its change has been a change in size, in weight, and in strength. The first freight cars of the very old railroad at Mauch Chunk weighed 1,600 pounds each, and were permitted to carry a weight or "burden" of only 3,200 pounds. When the Boston & Albany first began using freight cars 30 feet long, it was so confused that it gave each end of the car a separate number for convenience in billing and designating consignments. Nowadays 40 tons is the right load for an efficient car, although they go as high as 55 and 60 tons' capacity; the car itself may weigh approximately half that figure. Freight cars by hundreds of thousands go bumping all over the different railroads of the land, and all the while they are getting bumped and broken in accidents--large and small. In such cases they are hauled to the nearest shop of the railroad upon which they are travelling and there repaired at the cost of the road that owns them. In earlier days, the job of master mechanic was no sinecure, for each road built its cars upon its own plans and no two of these plans were alike. A simple broken part necessitated the manufacture of a new part. It was a matter of great confusion and expensive to every line.