Oh, those sludgy squdgy valves.

Shell says in its recent batch of television commercials, that the petroleum titan is adding nitrogen to its gasoline to clean gunk off of valves and other moving parts.

Those who understand how an automobile engine works should immediately recognize the colossal blunder in the ad.

Meanwhile, the atmosphere is already almost 80 percent nitrogen by volume, so there's already loads of the inert gas entering the cylinder. After the gasoline burns, the catalytic converter quickly breaks the nitrogen oxides created at high temperatures, into nitrogen gas and water.

So, what is it Shell is adding? Nitrogen is present in protein, and countless other compounds. But it is most often associated with explosives, (the nitro in nitroglycerin), ammonia, hydrazine rocket fuel, ammonium nitrate, and all sorts of nasty stuff. Of course, so is oxygen, carbon, and every other element, other than xenon, helium, and stuff like that.

Did you figure out the blockhead mistake in the ad yet? The ad shows gasoline showering down on a cylinder valve, cleaning away accumulated sludge. That would mean gasoline in the rocker panels and on the cam shafts. Gasoline never gets into cam shaft territory and certainly does not stream onto the tops of cylinder valves.

The only gasoline that hits the top of a valve would be a gas-air mixture, vapor really, from an ancient device called a carburetor, which cars don't use these days.

That makes the add doubly mysterious. Companies put all sorts of compounds into gasoline to maintain the engine, such as nitrogen-containing detergents, petroleum distillates, and who knows what else. But nitrogen?

And someone should have pointed out that if gasoline reaches the external tops of the valves, something is seriously wrong with the engine, like it's in the middle of a horrendous crash and is disintegrating.

To clean the tops of the valves, put some cleaning goop in the oil. Gasoline goes into the cylinders via the valves, and the valves are lubricated and cleaned, or not, by oil that circulates through the engine.

T0 clean the underside of the valves, where the high temperature gas-burning takes place, add something to the gasoline.

Don't expect that nitrogen-laced gasoline is going to make your engine last 500,000 miles.

Mommy, can I please get this toy bull pup assault rifle?

Why are children, especially boys, drawn to guns?

Many parents avoid buying toy guns, do not expose their babies to violent TV shows or games, and yet, the youngsters want squirt guns, Nerf guns, or will fashion substitutes.

More than one baby has bitten a piece of toast into the shape of a pistol, horrifying and puzzling his parents.

While babies seem to be born with an innate fear of heights, darkness, snakes, and a few other things, gun lust is unlikely to be genetic. Aggression may be in our genes, but not the preference for a particular weapon.

Children must acquire a knowledge of guns from their environment. Television shows have greatly reduced explicit gun violence. Twenty or thirty years ago the Lone Ranger, Eliot Ness, Ben Cartwright and other characters routinely shot and killed people. The victims, not displaying any injury or blood, instantly dropped dead.

How does a child shielded from CSI, Grand Theft Auto, Metal Gear Solid, Mortal Kombat, and restricted to family-friendly Disney movies, learn about guns?

Possibly because of what's happening in the world.

Most children won't go near a newspaper, but the wars in Iraq and Afghanistan leak in through discussion, and television news. Columbine and other notorious school shootings are over-covered by 24-hour news channels, and are apt to be overheard.

Perhaps the knowledge comes through their friends: "I'll be Osama bin Laden and you be the 10th Mountain Division. I'll take the AK-47 and you get the M-16."

Maybe a gun, even a toy one, gives children a feeling of safety in a post 9/11 world with a scary former vice-president predicting Armageddon, flag-draped coffins being unloaded from Air Force cargo planes, neighbors being shot, and stray rounds crashing through bedroom walls.

Can you really blame a kid for wanting to protect him or herself, even symbolically?

People, pellets and public health

Almost everyone is mixed up about air guns.

Let's briefly put aside the issue of taking an air gun to school and shooting a fellow student.

That obviously is wrong and requires disciplinary action. The 9-year-old Celentano School student who shot an airsoft gun at a another boy on a bus probably now appreciates that carrying a weapon of any sort, even something as innocuous as an airsoft gun, poses more risk than safety.

"Air gun" encompasses many different types of weapons, ranging from toys to rifles capable of killing small game.

Airsoft guns were introduced in Japan in the 1980s for teens fascinated with real guns, which are illegal and difficult to find there. Participants played a "combat" game like paintball with these plastic guns, which were considered toys.

Air soft guns employ bright orange barrels to indicate that they only fire plastic pellets, but it is a simple matter to paint the barrel or cut it off.

They were considered toys because they fire small (6 mm) plastic pellets at a slow velocity. Since kinetic energy equals the mass of the pellet times the velocity multiplied by itself, and all of that divided by two, it is clear that the only way to seriously injure someone with an airsoft gun is to use it like a club.

The one exception is that eyes are delicate and unprotected, so goggles had to be worn, along with plastic "armor."

Then there is the BB gun. BB guns were devised to fire BB-sized bird shot. Most BBs are made of steel or copper. The .177 caliber spheres can travel at 300 to 400 feet a second, and could conceivably cause serious injury. These are not toys.

The next step up the air gun line is air rifles. Some use a built-in pump to compress air. More powerful air guns compress air using a large, powerful spring. The highest quality air rifles are made in Germany and cost more than conventional firearms.

Spring loaded air rifles can fire a .177-cal. pellet at up to about 1,000 feet a second. The speed of sound is about 1,100 feet a second, and supersonic pellets make a loud "crack," which is self-defeating. Europeans (mostly) use these weapons to eliminate rats, and keep rabbits, starlings and other unwelcome small animals away from farm lands.

The most powerful air rifles propel .22-cal pellets at 800 to 900 feet per second.

Many of these rifles are used for target shooting in lieu of conventional rifles, because air rifles are the same size, but are relatively quiet, use inexpensive ammunition, and do not require a permit.

All air rifles should be treated as "real" guns, should be equipped with trigger locks, locked in a cabinet, and pellets should be locked in another container. As with firearms, you always act as if the rifle is cocked and loaded, never point it at anything you do not intend to shoot, and consider what is behind the target, because it is in the line of fire.

Hardly any robber uses an air rifle because the arms are large (45 inches long), heavy and unwieldy. Moreover, a conventional pistol has a higher muzzle velocity and much heavier projectiles, and can readily inflict lethal wounds.

Consequently, many criminals use use real-looking airsoft guns, or pellet-firing pistols to commit crimes. Perhaps they think that using an air weapon will aide their legal defense when caught, but it doesn't.

But air soft gunfs are cheap and easy to acquire and are sufficiently gun-like to scare potential victims. The least we can do is make realistic toy guns illegal.

If kids want to play games -- and they seem to be genetically programmed to fight mock battles -- they can use Nerf guns that are fancifully shaped and shoot light foam cylinders at low velocity. No one could confuse a Nerf gun with the real thing.

Ultimately, here's what needs to happen: toy manufacturers must stop producing realistic-looking weapons; air rifle ownership should be regulated, and only people with a demonstrable need should be allowed to own real firearms.

Unfortunately the Second Amendment is ambiguous and grammatically obscure, so gun fanciers and the firearms lobby will continue to ensure that gun ownership if widespread.

The question is, would the National Rifle Association consider a ban on air soft guns to be an assault on our Constitutional rights?