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Sale on Nitrogen, This Weekend Only!!!

August 17, 2007

I'm a chemist. And, as a chemist, I know things. I know things like all matter has mass. I know that an atom is the smallest bit of a substance you can have and still retain the properties of that substance. I know things like which elements are electronegative, and what a pi-bond is, and the octet rule.

I also, thanks to extensive work done by guys like Boyle, Charles, and Guy-Lussac, that gasses behave a certain way.

You can imagine my...confusion...last night when I was listening to/watching the news whilst working on editing my book, and an officer from the Garner police was talking about filling the tires on his cars with nitrogen, because, you see, nitrogen is not affected by changes in temperature.

Uh. Hmmm.

Officer, I'd like to introduce you to my friend, the Ideal Gas Law.

Ideal Gas Law, officer dumbass.

Now, it should be said that we here at the sprawling A Crown of Thistles home office have nothing but respect for the boys in blue. My uncle was a cop, my aunt is a county dispatcher, my cousin was a jailor, my other cousin is also a dispatcher, and I believe my uncle served as a dispatcher, as well, after retiring from the force. So, you can see, my family likes cops. Sure, sometimes they can be dickish, but for the most part, they're there to help.

It's just a frustrating thing when you hear someone touting the benefits of some new piece of technology, and yet, they are off base.

For the Garner police officer (and anyone else who hasn't spent their life dedicated to this thing), the Ideal Gas law is pV=nRT, which basically states that the pressure (p) and volume (V) of a certain amount of gas (n) is related to the temperature (T). That basically says that, as you heat a gas, it expands. If the vessel is closed, the pressure goes up, too. So, nitrogen, being a gas, would adhere to this.

Another thing the good officer failed to realize is that in every breath he takes, 70% of it is nitrogen. When he exhales, 70% of that is nitrogen. When he inhales, the air is cool. When he exhales, the air is warm. What this means is that nitrogen does, in fact, get affected by changes in heat.

Now, the Garner police department is using nitrogen to fill up the tires on their cruisers in an attempt to lower gas consumption. It's supposed to increase your gas mileage by up to ten miles per gallon. I'm guessing that there is no neat trick to having nitrogen, as opposed to regular air, in your tires. My best guess is that, since it's pure nitrogen, you're not getting partial pressures of all the mixtures of gasses that comprise "air". One thing about the Ideal Gas Law is that you're assuming the gas is pure, which "air" is not. It's a mixture of nitrogen, oxygen, argon, carbon dioxide, water vapor (I haven't yet seen a dessicator line on an air pump at the gas station), and a host of other gasses that comprise the last 1.3% or whatever it is.

There is another law that would cover this mixture is the Law of Partial Pressures, which basically states that the ratio of the gasses inside a vessel exerts a ratio of the pressure on the vessel, so nitrogen would exert 70% of the pressure inside of your tire if it is filled with air. Now, each of the other gasses on the inside of your tire would adhere to the Ideal Gas Law separately, and therein might lie the problem. Different gasses expand and contract different volumes when heated at the same temperature (that's basically what the n is for in the Ideal Gas Law). Also, I think the big key is that 23% of the air inside your tire is oxygen.

Oxygen is a nasty, nasty gas if you don't know how to use it. Your body basically has to repair itself constantly from oxygen's nastiness. Singlet oxygen (and Dr. Creary forgive me if I've switched the two) is the more reactive form of oxygen, which can do deleterious things to the inside of your tire. Also, water vapor on the insides of tires is probably not a good thing (and as I mentioned earlier, I've yet to see a gas station attendant changing the drierite on the air pump outside his station) and can cause some issues. Nitrogen, however, is damned inert and happy to remain as such.

Now, the kicker that really astounded me wasn't even the cop claiming that nitrogen is not affected by the changes in temperature. No, at the end of the report, the reporter told of a garage that will fill your car's tires with nitrogen...for $50!!! I'm not sure if that's per tire or the whole deal. But, fifty freaking dollars for nitrogen, the most abundant gas on earth? Well, hell, that's like paying $5 a bottle for water, the most Oh wait.

I need to come up with a good idea for people to throw money at me. Maybe I should start touting how helium in your tires will make your car lighter and therefore more fuel-efficient.

Hey wait...that just might work. I'll talk to you later. I think I just heard the unmistakable sounds of suckers being born this past minute.


Will Shannon said...

Gosh, when someone speaks wrongly on chemistry that even I remember, it's really bad.

I can hear the spirit of Fr. Kramer (if he is indeed dead, if not, then voice I guess) laughing at this goofball.

Not to mention the very much living faces of Robb Pfaff and Brian DiPaolo...

Anonymous said...

You are correct and the Cop has it wrong. However Nitrogen does not seep out as fast as air. About 80% slower. So the tire will be properly inflated longer. You lose 1 mpg per 2 pis under inflated. Maybe $300.00 a year at $3.00 a gal. The idea is sound. You can save the money by checking your tires weekly. However know one does. So it becomes a good investment. 40,000 people are injured a year from blowouts from under inflated tires. Bottom line check your tires weekly. Or you can use nitrogen and the pressure will stay safe until your next service (oil change)when it is checked. If you buy the nitrogen from the place you get service you have no more worries about tire pressure you will save some money on gas and your tires will last longer because they had the correct pressure. People making clams of more are just wrong.

the iNDefatigable mjenks said...

Thanks, Anon. I was going to add that to the end of my post, but I forgot about it and had to go turn on the LC/MS or something like that.

Thanks, too, for the numbers to go along with the underinflation of tires. I'm no physicist, but I do know that having tires properly inflated means that there is less rubber "dragging" on the ground and thusly less resistance to your car moving forward, so keeping tires inflated is the true trick in lowering gas consumption and increasing mileage.

the iNDefatigable mjenks said...

Oh, and as anon says...check your tire pressure. It not only could save you some scratch (do the kids still say that?), but it could also keep you from getting injured in an unfortunate blowout mishap.

Will Shannon said...

Perhaps we could use Babu's machine to confirm all of this?