Phun Physiology: How Cold Is It? Check Your Humoral Thermometers

Boys on bicycles in village of Cheremshanka, eastern Siberia, February 2002. Photo by Oleg Nikishin.

Randonneuring blogs this time of year have a certain fascination with and well-placed respect for temperature.

When one of our local riders, Jerry, noted that the sweat in the sleeves on his jacket was frozen at the conclusion of an early-January ride, it caused me to think about how cold it must have been.

His comment reminded me of the classic children’s story by Jack London, “To Start a Fire,” in which spittle froze before reaching the snow-covered ground.

As he turned to go on, he spat speculatively. There was a sharp, explosive crackle that startled him. He spat again. And again, in the air, before it could fall to the snow, the spittle crackled. He knew that at fifty below spittle crackled on the snow, but this spittle had crackled in the air. Undoubtedly it was colder than fifty below—how much colder he did not know.

The scenario hints at a well-known aspect of science: different solutions freeze at different temperatures. We all know, for example, that water freezes at 32° F, while antifreeze freezes at a much lower temperature.

We use this type of information instinctively when we see a frozen puddle of water alongside the road and surmise that the ambient temperature is probably 32°F or lower.

The temperatures at which many other solutions freeze, including body fluids called “humors,” have been cataloged. Some of this information might be interesting, if not useful, to a cyclist. The one exception might be blood, which freezes between -2 and -3 °C (28.4 and 26.6 °F), since it may be difficult to distinguish between freezing and coagulation, I’m not sure.

Before answering how cold it must have been in order for Jerry’s sweat to freeze in the sleeves on his jacket on that January-cold 200km bicycle ride, our customary science lesson is in order.

Returning to our previous example, we know that water in its purest form freezes at 32° Fahrenheit (F) or 0° Canadian, otherwise known as Celsius (C). But if water has other items dissolved in it, ions and/or non-water molecules, then the freezing point— of what’s now considered a water solution—is lowered directly in proportion to the amount of the dissolved items (solutes).

The lowering of the freezing point of a solution to which solutes have been added is referred to as “freezing point depression.” That salt water freezes at a lower temperature than pure water illustrates this principle.

Consequently, we might correctly predict that body fluids, which contain mostly water, freeze at temperatures below 32 °F, since they include ingredients in addition to water.

Applying our present understanding (thereby demonstrating we have true knowledge and making Socrates very happy), we know that for Jerry’s sweat to have frozen, the ambient temperature on his sleeve must have been below 32 °F. Luckily for inquiring minds, the temperature range at which sweat freezes is known. We would expect a temperature range, since the composition of sweat varies for an assortment of reasons.

That range, -0.08 °C to -1.00 °C (31.86 °F and 30.2 °F), is consistent with the temperatures on the day that Jerry rode. But remember that this only tells us the temperatures at which sweat freezes; it could have been much colder than that. And in this case, it was.

What about the freezing point of saliva? Well that, too, is known (0.07 to 0.34 °C, or 31.87 to 31.39 °F), although, unlike the Jack London short story, unless you are willing to venture to the top of Grandfather Mountain, for example, you probably will not get a chance to determine the “crackling point” temperature of saliva in mid-air.

If you should go to Grandfather Mountain where it is not only cold (record -32 °F) but clothes-flapping windy (record 107 mph), here is some good advice from Jim Croce on experimental design you might want to consider.

While we are at it, how cold must it be for urine to freeze? Well, believe it or not, this has also been worked out by scientists _ _ _ _ -ing away their time in the lab (the correct missing word is “whiling”). Urine freezes between -0.45 °C and -2.5 °C (31.19 °F and 27.5 °F), which is a few degrees below the freezing point of saliva, perhaps useful information to a cyclist.

What about frozen eyeballs? After all, isn’t there watery stuff in the eyes? Some time ago, I read something about eyeballs freezing during an outdoor motorcycle race on the ice in Siberia, although I can’t seem to lay my hands on the article now. Perhaps it was nothing more than figurative speech.

Aside from the drinks with the same name, by most accounts, frozen eyeballs are not something about which cyclists need to worry. The eyeball does have a watery fluid (aqueous humor) in its anterior (front) chamber just behind the front outer clear cornea on which you place your contact lens. But the eye, located in the eye socket, is surrounded and protected by warming tissues including an ample blood supply. If in doubt, one could don protective goggles.

Although not really a body fluid—unless of course you are a Russian who binges or an American who downs too many frozen eyeballs—vodka has a really low freezing point.

80 proof vodka will freeze at approximately -26.95 °C or -16.51 °F.

100 proof vodka will freeze at approximately -40.43 °C or -40.78 °F.

Pure ethanol, the active ingredient in vodka, freezes at −114.3 °C.

It goes without saying that if your vodka should freeze on a bike ride, you are in really big trouble.

He travels fastest who travels alone . . . but not after the frost has dropped below zero fifty degrees or more.—Yukon Code
From a literary perspective, should you wish to compose a Londonesque short story for children about the north woods, you should probably try using another body humor in reference to the cold, since saliva is no longer considered novel. And stylistically, you might substitute a suitable onomatopoeic word for “crackle,” now inextricably linked with saliva. You could choose a perfectly good children’s word.

In summary, here’s your cycling-survivalist’s cheat sheet, with body fluids listed in descending order according to freezing point.

Body Humors
and
Reference Points Freezing Point (°F)
Water/ 32
Saliva/ 31.9 — 31.4
Sweat/ 31.9 — 30.2
Urine/ 31.2 — 27.5
Blood/ 28.4 — 26.6
Vodka (80/100 proof) -16.5/-40.8

Oh, yeah, I almost forgot. One more piece of advice. When it gets really cold, try to remember not to lick your steel touring bike . . .

Let’s ride (in Florida)!