QUESTION: Why is four-fifths of the air made up of nitrogen? And why does no one seem to care?

ANSWER: It's about time we started getting really worried about nitrogen.We're already worried about garbage, deforestation, water depletion, soil erosion, ozone destruction and the Greenhouse Effect. But did you know that 78 percent of the atmosphere is nitrogen? Does that strike you as safe? You know they used to say that cocaine was harmless, too. You start with nitrogen and the next thing you know you're hooked on the hard stuff. Yeah. Uranium.

Volcanoes are to blame for the nitrogen in the air. When the Earth was in its adolescence it had a severe complexion disorder, with volcanoes everywhere spewing stuff into the atmosphere. The emissions included lots of water vapor, and oxygen, and carbon dioxide, and hydrogen, and helium, and so on. The question we should ask is why the nitrogen stuck around in huge quantities but not the other gases.

The key thing to understand is that words like "nitrogen" and "oxygen" have a slightly lyrical quality that makes us imagine that these substances are radically different, that one is perhaps a cloudy green substance while the other is, say, clear and bluish. In fact, there's hardly a dime's worth of difference between the two. A nitrogen is seven protons and seven neutrons and a little cloud of electrons. Oxygen has an extra proton and neutron, and that's about it.

The biggest difference is that, for complex reasons (our standard phrase when we don't totally understand something), oxygen is extremely reactive to other elements. Oxygen is always hopping around, sticking to things, causing fires, getting in your blood. A nitrogen atom is also somewhat reactive, but when it hits another nitrogen atom it forms a nitrogen "molecule," which is virtually inert. It just hangs there in the sky, killing time. (A little bit will get in your blood when you breathe it, but this is only a problem when you scuba dive and the increased air pressure gives you a big nitrogen fix; if you come up too quickly to the surface the nitrogen bubbles, which is very bad.)

Anyway, you got this early atmosphere filled with gases. Water vapor condenses and forms oceans. Carbon dioxide gets sucked up by plants through photosynthesis. The light elements, like hydrogen and helium, float off into space. Oxygen is dissolved in sea water and is breathed by animals. The only reason we still have so much oxygen - about 20 percent of the atmosphere - is that there are so many plants that exhale the stuff. There are also traces of gases like neon, iodine and krypton, but mostly the only thing left is nitrogen.

Surely the government should appoint a commission to study the nitrogen problem. And come to think of it, we're a little uneasy about the iodine and krypton, too.

QUESTION: Why are some rulers in the Arab world called emirs, while others are called kings, and still others are called sultans?

ANSWER: Jordan, Morocco and Saudi Arabia are kingdoms. Kuwait, Qatar and Bahrain are emirates, as are five tiny states that make up the United Arab Emirates. The only sultanate left is Oman. Frankly, we'd be sultans if we had the choice. We'd wear insanely baggy silk pants and play with sharp sabers. The title "king" seems pompous by contrast, too stuffy, inhibiting, and you'd probably have to wear a really embarrassing crown. An "emir" sounds like some kind of horned deer-like creature that roams the Serengeti Plain.

Fortunately we dug up an experienced Middle East foreign service officer who understood the distinctions. A king is almost the same thing as a sultan, and both have more power than an emir.

There are real kings and fake kings. Fake kings are like the ones in England, who are rubber stamps for the real government, the parliament. Saudi Arabia has a real king. That's why the country is called Saudi Arabia, because it is run by the Saud family. King Fahd is picked by the family and has virtually absolute power. He gets to appoint everyone in the government. He's the final court of appeal. He doesn't mess around with democracy. But we Americans still love the guy, because he's got so much oil.

The Sultan of Oman is also an absolute monarch. The only distinction is that, when Oman was part of the Ottoman Empire - named after the cushioned seat, of course - there were many sultans ruling different lands, all answerable to the supreme leader who controlled the empire and was so incredibly powerful he didn't really have a title, folks just called him by his name.

An emir is hamstrung by contrast. Emirs rule by the consent of the aristocracy. Being the ruler is more of a job than a hereditary privilege.

What about "sheik?" That's a fairly generic title for an aristocrat in one of these emirates or sultanates or kingdoms. Sheik means "prince." Our pronunciation advice is to treat it as a homonym of the word that means fashionable, rather than the word that means a frozen milk-based beverage that comes with burgers and fries.

THE MAILBAG:

A question you've heard a million times and which we get in the mail about every three hours: "Why don't we put all the criminals on an island somewhere?" For example, a "concerned citizen" in Lansing, Mich., has just sent a letter saying, "If a criminal has a second or third offense, put them on an island. They could murder, rape or whatever to survive to the best of their ability. If they don't make it, they won't be multiplying."

Dear concerned citizen: Go look at a map. Where is this island? You want to be the one to ask Bermuda if it will house all our psychopaths? Do you think maybe Manhattan has a few vacancies? The only time this experiment worked was a couple of hundred years ago when the British sent their prisoners to Australia. The result was, eventually, Mel Gibson and Crocodile Dundee.

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