The Speed of Smell

We all remember Hippolyte Fizeau's famous 1849 speed-of-light experiment from sixth-grade science lessons. Through some byzantine combination of a mirror, a cigarette lighter, and a zoetrope he calculated that light must travel at 313,000 kilometers per second, remarkably close to the accepted measurement of 299,792.458 kmps. William Derham calculated the speed of sound in the early 1700's using a shotgun and a stopwatch (343 meters per second). But smells seem to be difficult measurement subjects. Children's television host Bill Nye attempts to explain:

The speed with which a smell travels depends on how fast the molecules are going, how massive they are, the relative temperature of the molecules making the smell, and how many molecules there are in a given volume, their density. We express all this mathematically as a gas's temperature and pressure.

Not good enough, Mr. Nye! I want numbers! PSI's vs. FPS's PDQ! Over at Yahoo Answers we find a more convincing explanation:

Smells are just chemicals. The speed that chemicals diffuse in the air is predicted by Graham's Law when you compare two gases.

Use oxygen as your standard gas.

The ratio of the speed of diffusion on the smell compared to oxygen is equal to the square root of the inverse of the mass of the oxygen molecule divided by the mass of the molecule of the smell.

The molecule of sulfur has 8 atoms of sulfur in each molecule, oxygen has two atoms per molecule. The mass of sulfur is 32 and oxygen is 16. The mass of their respective molecules are 8x32 and 2x16 or 256 and 32. Take the ratio of the two, oxygen over sulfur is 32/ 256 or 2^5/2^8 or 1/8. Take the square root of 1/8 is 0.354.
smell is about 1/3rd of the average speed of the molecules of oxygen in the air.
the speed of smell is smell is about 1/3rd of the average speed of the molecules of oxygen in the air.

YES! I'm generally willing to hedge my bets on the reliability of Yahoo Answers, typos and all, but what is the average speed of oxygen molecules in the air? I traipsed over to http://www.newton.dep.anl.gov to investigate:

There's a really neat mathematical equation based on a theorem called the "equipartition theorem" which states that the energy of a gas system (equal to 1/2*mv^2) is equal to the temperature of the gas (equal to 3/2*kT). If we rewrite this equation to solve for velocity we get:

sqrt(3*T*k/m) = v

where T is the temperature in Kelvin, k is the Boltzman constant = 1.3805*10^-23 J/K and m is the mass of the gas particle.

If we assume that the average mass of air (since it is a mixture of different gases) is 28.9 g/mol (or each gas particle is around 4.799*10^-26), and room-temperature is 27C or 300K, we find that the average velocity of a single air particle is around 500 m/s or 1100 miles per hour!

So, if we take a 27° C room (a balmy 80.6° Fahrenheit), with air molecules moving at 500 m/s, the smell of a rotten egg travels at 166.66 meters a second! Is that FAST or WHAT!

Apples to Apples

Hey Everybody,

As you may or may not know, I recently moved to New York City, and I have some exciting news to report: New York City smells great - all the time! Whether you are strutting down Avenue A, hopping on the Fung Wah in Chinatown, or just plain hiding behind a garbage can ogling sunbathing girls in Central Park, an offensive smell is nowhere to be found. Clear to the horizon, no foul odor, as far as the nose can smell. It's really incredible!

nope, still good!

PS. Do you ever think about how at any given time, the smells you smell represent a rough chemical approximation of the sphere of air around you, about how your nose sucks up all these tiny particles of everything and like, nostril-licks them to see what they smell like, and then sends off the lab results to your brain?

Smells vs. Tastes

Many readers have asked me about the relationship between smell and taste. It's true that a connection can be drawn between the two, which I have illustrated in the following graph:


I hope this clears things up.

Outdated science

When I told my friend Tyler that I had been keeping a blog about smells, he pointed to an African talking drum sitting in the corner of his living room and said, "You should smell that drum." These drums have a compelling history: because one is able to alter the pitch with ease, a range of tones is available to the player. Speech-like tones and phrases can mimic those used in some African languages, and in certain cases, a drum can communicate language nearly as well as a human! Here's a snippet from a 1942 article on the subject:

The Bulu dialect of the African Bantu language can be drummed almost as well as spoken. Reason: it is even more a language of tones than official Chinese. Where the Chinese use four tones, the Bulus have five—two high, two low and one in the middle. So distinct are the pitches and rhythms of the language that sometimes a couple of people "too far apart to hear actual words call back and forth using only the syllables kiki in the tones of the words they would employ in ordinary conversation."

Whoa! Here's another:

A hungry man returning from a hunt may stop at a village four miles from home, send a message to his wife to come in from her garden in the jungle and feed him. Message in drum code: "She is better than the daughter of other tribes, she who stands there. Oyono must not join the fighting, I don't want Oyono to die. Come walk quickly, quickly, I feel hunger not small." Dinner will be waiting when he gets home.

All pretty neat stuff, except the drum smelled awful! Talk about old milk on your telephone mouthpiece!

In all fairness, the drum is partially carcass. I needed to know more about this nasty skinflap, so I read an article called "How to Buy a Goat Skin for your D'jembe." I was wary at first, as the title seemed to be the result of a "how to buy a ___ for your ____" Mad Lib. It was the real deal, however. Turns out that "Skins from Africa tend to smell, especially male skins." So there you have it, Tyler, stick to those X chromosomes the next time you are in the market for a new D'jembe skin.

Note to Consumers! pt. 2

Relief has finally arrived for all of us who would like to cash in on the much-regarded benefits of Omega-3 fish oil, but recoil at the thought of a dead herring crawling back up the rathole ten minutes later. Target Brand Origins Omega-3 Odorless Fish Oil Capsules will deliver the same dose of Docosahexaenoic acid without the unpleasantness! For those not in the know, Docosahexaenoic acid (DHA) is the active ingredient in fish oil, which may as well be snake oil for the ailments it claims to cure: it supposedly reduces the effects of Alzheimer's, shrinks cancerous tumors, and it "has recently gained attention as a supplement for pregnant women, ... [with] improved attention and visual acuity" in infants.

Target knows they have a potential goldmine with this one, as is clear from the catchphrase in the cartoon bubble usually reserved for the "TNT" on a box of Roman Candles:

NOTE: Snake oil is also an actual Chinese remedy for joint pain.

the Sleeping Bag Challenge

I used to challenge my friends to the Sleeping Bag Challenge. The object was to enter the sleeping bag headfirst, then, when you reach the bottom, to turn around inside and make it back out headfirst. First one to fresh air was the winner. I remember thrashing around at the bottom of the sack, claustrophobic as hell, the air and skin becoming hot and moist with the creeping fear of getting stuck, which, as I grew older became a real threat*.

We've been in the middle of a two-week-long heat wave, or, in Austin, "May." It's 95 degrees outside (but it feels like 97). Last night, a sulfuric smell drifted down our street. I thought at first a sewer line had burst, but it was a bit too "eggy" and it didn't smell inside of the house. The night was breezy and the stink kept drifting in from the east. The cause is yet unsolved.

*The Sleeping Bag Challenge is not intended for mummy-style bags.

Note to Consumers!

Watch out for OFF! brand "Smooth & Dry Feels Comfortable Powder Dry Formula" bug repellent! Upon application, this stuff creates a dense sphere of extra-potent rubbing alcohol vapor. You might as well keep an open canister of tear gas in your breast pocket.


It smells pretty good when it dries, though.