Have you ever been on a train that stopped suddenly between stations? Perhaps one of the cars had a hot box. Here is how it happened:

Car axles must be kept well greased if they are going to move smoothly. They are fixed so that each end of the axle turns in a bed of oily stringy stuff called waste. The container that holds this bed of oily waste is the journal box, and there’s one for every wheel on a car.

Inspectors always check journal boxes carefully, but it sometimes happens that the oil gets used up while the car is moving. The unoiled axle grows hotter and hotter until the waste begins to smoke and burn. Then the car has a hot box, which railroaders also call a stinker. Hot boxes can be dangerous. If an axle goes too long without grease, it may break off and cause a bad accident.

When the train goes around a curve, the engineer or the fireman looks back for smoking journal boxes. The brakeman in the caboose keeps an eye out for them, too. On many new height trains the conductor or the brakeman can call immediately by radio telephone and tell the engineer to stop for a stinker. But on older trains, the conductor can only pull the emergency air-brake, which stops the whole train fast.

Although a hot box is dangerous, it’s easy to remedy. The box only needs to be re-packed with fresh oil-soaked waste.

Everybody who works on a railroad watches for smoking journal boxes. Suppose a freight train has stopped on a siding to let a fast passenger train go by. The head freight brakeman stands beside the track. If he sees a hot box on the fast train—or any loose, dragging part—he signals to the passenger engineer.

When railroad workers give a good look at a running train, they say that they’ve made a running inspection. Telegraph operators and station agents come out on the platform and make running inspections whenever trains go by.

The newest, fastest cars on both passenger and freight trains get fewer hot boxes than old ones. Their axles have roller bearings to help them turn smoothly, and the oil in their journal boxes is supposed to last for a long time. Still, an inspector may forget to check the oil, or it may leak out.

There’s no waste packed around roller bearings. So, how is anyone going to tell when one of the new cars gets a hot box? Some railroads have solved the problem with bombs! Into every journal box go two little gadgets that explode when an unoiled axle begins to heat up. One bomb lets out a big puff of smoke that can easily be seen. The other spills a nasty smelling gas that is sure to make passengers complain, in case the conductor doesn’t notice it himself.