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Whales and cows are kin, eggs have a tough side, boiling means bubbles

Q: Did cows evolve from whales? Noell, Circle, Montana

A: Cows didn’t evolve from whales but they both came from a common ancestor. Cows and hippos are "sisters" and both are "cousins" to the whale. They all evolved from a common "grandmother," (the wolf-sized Pakicetus) who had wicked teeth in a narrow pointed skull.

Breaching humpback whale and (below) his “Grandmother”: Pakicetus.

[Illustration by Carl Buell and taken from http://www.neoucom.edu/Depts/Anat/Pakicetid.html  Northeastern Ohio Universities]

Between 40 and 50 million years ago whales, dolphins, and porpoises (cetaceans) evolved from land to marine animal. They changed fast — in less than 8 million years, says Hans Thewisson, paleontologist at Northeastern Ohio Universities.

Further Surfing:

Northeastern Ohio Universities: Whale Origins by Hans Thewisson

Eggs have a tough side

Q: What side of an egg is stronger? Jon Bob, Dallas, Texas

A: As any chick knows, it’s the ends. The ends are stronger than any middle side. The hatching chick pecks her escape through the weaker shell middle, just below the blunt end.

Each end functions as a miniature dome, which distributes weight or pressure evenly over the entire egg. This minimizes stress and makes for a tough egg (if stressed end-to-end).

Spotted gull eggs, Cherni Island, Southwest Alaska [Budd Christman, NOAA]

Boiling means bubbles

Q: My 13 year-old daughter and I saw on MythBusters (Discovery Channel) an episode in which they stated that distilled water, in comparison with tap water, will not boil. Rather, it will have a slight violent reaction. We tried the experiment at home but cannot get the same reaction. If they were correct, can you tell us how and why this reaction takes place so we can try it at home?

Boiling water on Earth (top) and, by the way, in space (bottom) [NASA]

A: MythBusters is a neat program but unfortunately I didn’t watch that episode. If they said distilled water won’t boil, they are incorrect.

Craig Bohren, meteorology professor at Penn State University, puts it stronger: "I bet them $10,000 that I can get distilled water to boil the same way that tap water boils." Exactly what you observed.

Distilled water will boil but (with sufficient care) at a higher temperature than normal — that’s the trick. The delayed boiling can be explosively violent — not slightly violent. Downright dangerous.

I’ll describe a "thought" experiment to explain how Mythbusters got such a reaction. Why does it happen? Because we suppress bubble nuclei. So, when bubbles finally do form, they form in a hurry — explosively.

I’m not recommending we actually do this experiment. Scalding hot, exploding water makes me nervous. This is a thought experiment.

First, let’s be clear on what we mean by "boiling". Of course, water evaporates at the boiling point. But, more than that, "boiling means bubbles," says Bohren.

We set a pot of water on the stove and turn on the burner. As it heats, little bubbles form along the bottom and sides of the pot. Pretty soon they rise, get big, and make it to the surface where they burst. The pot’s boiling.

To pull off the trick of delaying the onset of roiling bubbles until the water reaches a higher temperature — we discourage bubble formation. It’s that simple, almost a matter of definition. We delay bubbling by minimizing the number of tiny bubbles in the pot when we start and reducing the air dissolved in the water.

Unfortunately for us bubble suppressors — a pot of water abounds in tiny bubbles. Pour tap (or distilled) water into a pot and, bingo, you’ve trapped all kinds of bubbles in the invisible cracks and pits of the pot’s inside surface.

Bubbles begin life as tiny air bubbles, but once they grow to visible sizes, they are almost entirely water vapor mixed with a little air. Water surrounding the tiny air bubbles evaporates into them, causing them to grow.

Agh! No wonder you had trouble with this experiment. So did I. In 1874, John Aiken was one of the first to succeed. "Water from which gasses have been expelled may be heated in polished metal vessels to a temperature far above its boiling point, and ... when boiling does take place under these circumstances, it does with a wonderful violence."

Aiken heated water to 244 degrees Fahrenheit (118 degrees Celsius) before it exploded.

How did he do it? Bohren gives a recipe: a vessel with smooth sides (a glass flask, for example), really clean water, and ridding as much dissolved air as possible.

"Preparing ultra clean water is a heroic task", says Bohren, who finds ordinary distilled water "intolerably filthy". Many years ago doing light-scattering experiments, he had to doubly distill the water and pass it through micropore filters before he could use it.

Those are essential ingredients to a successful boiling-at-high-temperatures explosion. Be careful.

For more on bubble growth in water, please read pages 83 through 90 in Craig Bohren’s wonderful book, What Light through Yonder Window Breaks?

Further Reading:

Bohren, Craig F., What Light through Yonder Window Breaks? (John Wiley & Sons, Inc. 1991).

(Answered Mar. 12, 2004)