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