Railroaders call a tank car a can. It really is an enormous can with different kinds of lining for hauling different liquids. Milk tanks have glass or steel linings. Tanks for certain chemicals are lined with rubber or aluminum or lead.

Altogether there are more than two hundred types of tank car, and here are some of the things that travel in them: fuel oil, gasoline, and asphalt; molasses and sugar syrup; turpentine and alcohol; lard, corn oil and fish oil for vitamins.

Some tank cars have heating coils that warm up lard or molasses and keep it from getting too stiff to flow out easily. Most tank cars have a dome on top. If they didn’t, they might burst open at the seams when the liquid inside them begins to expand in hot weather. Instead, the liquid bulges up into the dome, and no harm is done.

Wine tank cars have four compartments for carrying different kinds of wine.

Milk tank cars are built with two compartments that tip slightly toward the center so that every bit of milk will flow out. Each compartment is rather like a thermos bottle, with special wrapping around it to keep the milk from getting warm and sour. And the tanks are always filled brim full so the milk won’t slosh around and churn up a batch of butter on the road. Can you guess why milk tanks don’t need domes? Remember the milk must stay cool. Even when the sun is hot outside, the cool milk doesn’t expand, so no dome is needed to keep the tank from bursting.