What is a whale's spout made of? One theory: the spout is condensed vapor from the whale's moist breath. But in the tropics, where breath does not condense, the whale's spout is just as visible as in arctic cold. In Britain's Nature, Dr. F. C. Fraser and P. E. Purves tackle the old controversy again.
The Fraser-Purves theory: the spout is foam (mucus, gas and globules of emulsified oil) that forms in the whale's lungs. When the whale surfaces after a dive and empties its lungs, the foam expelled is the visible spout.
When a human diver descends to great depths, the nitrogen...
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