A whole train made up of nothing but cars loaded with coal is called a black snake. Since rain and snow won’t hurt coal, it travels in cars without tops. One kind of coal car has sloping ends like the one on this page. It is called a hopper car. You load the coal in at the top, but you unload it by opening trapdoors in the bottom which let the coal drop into chutes. Coal also travels in gondolas, which are just square-ended bins on wheels. They have to be unloaded by hand or by a dumping machine. It is hard to believe how fast some of these machines work. First a switch engine pushes the car of coal onto a platform underneath a tower. Grippers hold the car tight while it is jerked up, tilted over on its side, dumped, then let down again empty. The whole job takes only a minute or a minute and a half. The empty car rolls away downhill while a full one is being switched into place. [Illustration] Another kind of dumper, the one you can see in the picture, looks rather like a barrel that can roll from side to side. It, too, tips the car over on its side so the coal can run out into a chute. Then the machine swings back and lets the car drift downhill. Locomotives and shops use almost a fourth of all the coal the railroads haul. It takes much less coal now to run an engine than it used to take, because engineers and scientists have thought up ways to make locomotives better and better. They figure things so closely they can even tell how much it costs to blow an engine’s whistle--three toots for a penny. Other things besides coal are often carried in hoppers and gondolas. Ore travels from mines to mills in hoppers. Gondolas haul lumber. [Illustration] Things such as sugar and chemicals are sometimes carried in covered hopper cars. Of course, these hoppers have tight lids and special linings, and they’re kept very clean, so you won’t find coal dust mixed with your candy. [Illustration] GRAIN CARS Early every summer the railroads put a lot of boxcars in the bank. That means they switch the cars off onto sidings all through the wheat-growing part of the country. Then, when the wheat is harvested and ready to be shipped to market, the cars can be drawn out of the bank, filled up with grain, and hauled away. The wheat gets ripe in the south first. When harvest is finished there, the cars move along. All through the summer the grain cars work their way farther north. Special grain doors have to be fitted in tight, just behind the regular sliding doors of the boxcars, to keep the wheat from leaking out. The grain doors go almost all the way to the top, but not quite. In a minute you’ll see why. After the farmers thresh their wheat, they take it to an elevator, which is an enormous storage tower close to the railroad tracks. Then, a chute from the elevator loads the wheat into the cars through the space at the top of the grain doors.