Everything You Never Wanted to Know about Freezing Pee

Chemical composition of urea
Urea: CH4N2O

Last week I wrote that the kid had asked me how cold it has to be before your pee freezes in mid-air.

There’s an ongoing legend (you can’t call it an urban legend here because it’s just not urban, not by a long shot) in these and many parts of the northern US that if it’s cold enough your pee will freeze before it hits the ground. I think it’s perpetuated mostly by the Boy Scouts who want to impress their friends after their winter camping trips.

Anne asked what I gave the kid for an answer. For the record I told him, “I’m not sure of the exact freezing temperature of pee.” But what if there were a way to really know the answer to the kid’s question? This may be a question better left to the brilliant Faraday sisters, I’m going to take a shot at it.

For starters, let’s consider the ordinary freezing point of pee. Freezing point depends on the chemical makeup of a liquid, which, in the case of pee, can vary from one person to the next. It so happens that when they were sending astronauts into space for the moon missions, NASA commissioned a detailed study on pee back in 1971.

I’m not going to presume that you’re interested in reading the whole thing, so let’s just cut right to the chase. According to the summary on Wikipedia:

Urine is an aqueous solution of greater than 95% water, with the remaining constituents, in order of decreasing concentration urea 9.3 g/L, chloride 1.87 g/L, sodium 1.17 g/L, potassium 0.750 g/L, creatinine 0.670 g/L and other dissolved ions, inorganic and organic compounds.

Pee is mostly just water with a little urea, a trace of salt and even smaller traces of other stuff. Both urea and salt cause the freezing point of water to be depressed. Since most of the 5% of pee that’s not water is urea, let’s assume (hey, I’m was a physics major, we make assumptions. You’ve heard the one about the square chicken, right?) the urea concentration is a little less than 4%. Or, better yet, since we can find an actual experimental result for it here, let’s say a molar concentration (formular weight of solute per 1000 grams of solution) of 3.389. At that concentration, the freezing point compared to pure water is depressed by 5.594°C.

So the ordinary freezing point of pee is around -5.6°C (21ºF).

This makes sense. If you put pee in your freezer next to the bottle of vodka (I’m not recommending that you actually try this at home, just that you could) it freezes way before your vodka does.

21º isn’t all that cold of course, but to freeze in mid-air, it would have to be a lot colder. For one thing, your body temperature is 98.6°F (37°C), which means your pee needs to cool by 76.6ºF (42.6ºC) in a very short time.

Let’s assume that you’re out with your Boy Scout troop at winter camp. Let’s say you and your friends decide to try mid-air pee freezing and you can manage to pee upward high enough to give your pee a generous 1.5 seconds from “exit” to ground. The cooling rate would need to be 28.4ºC/sec.

Newton’s Law of cooling tells us that:

T(t) = Ts + (To - Ts)*e^{(-k*t)}


t is the time in the preferred units (seconds, minutes, hours, etc.)
T(t) is the temperature of the object at time t
Ts is the surrounding constant temperature
To is the initial temperature of the object
k is a cooling constant for whatever substance is involved.

In our case, we know that:

t = 1.5 seconds,
T(t) = 22ºF,
To = 98.6ºF

We want to find Ts (the surrounding constant temperature). The problem is that we have no idea what the cooling constant k is. The cooling constant for water (or any object) varies, depending on it’s mass, surface area chemical make up, etc. So the only way to figure it out is to get an actual reading on the temperature of a stream of pee after a known time at some other known ambient temperature. Unfortunately, I’m not finding on almighty Google where anyone has reported (admitted?) actually doing that.

So, in the absence of any actual data, let’s make a few more assumptions, shall we? (Is that an unfortunate pun?)

First, let’s assume, since pee is mostly water, that we’re basically talking about freezing water.

Second, I found a report by Laura Lowe from an experiment she did as a student at the University of Georgia where she found the cooling constant for some water (we don’t know it’s volume or surface area) was 0.0293. Now, that was probably for a beaker of water sitting in a lab. A stream of pee would have much less mass and much more surface area. So, let’s say that alters the constant by a factor of about 10. So we can assume a constant for moving pee at around 0.3.

With an assumed k = 0.3, we can solve Newton’s law of cooling equation for Ts, and we get -112ºF (-80ºC).

That actually sounds about right. When we used to play around with the liquid nitrogen in the physics lab in college, we froze lots of water-based things in less than a second, but the temperature of a liquid nitrogen bath is about -320ºF. Freezing a little bit of water in a second and a half could be done without going to that kind of extreme.

Still, -112°F is colder weather than I care to go out and pee in. And it’s colder than most Boy Scouts go winter camping in. I’m not saying it’s never happened. The other day it was -110 (counting wind chill) on the top of Whiteface Mountain, 7 miles from here. But that’s counting wind chill. Maybe it happened to Ernest Shackleton when he went to the South Pole. The record low temperature there is -116.

Other than that, though, it seems as if the kid’s hopes of experiencing mid-air pee freeze are going to be disappointed.

What can I say, it’s a tough life sometimes.

Eggs Benedict Arnold

Eggs Benedict Arnold
The Kid’s Eggs Benedict Arnold

A month ago now, we were watching Worst Cooks in America one evening on the Food Network. On that episode, contestants were given the assignment to make eggs Benedict for their coaches.

The kid watched this with rapt attention. Eggs Benedict (or Eggs Benedict Arnold, as he called them when he was smaller — and I’ve called them that ever since, even though he’s stopped) are one of his favorite meals, breakfast or otherwise.

After the show, he said, “We should have eggs Benedict.”

“We agree,” we said right away. “And if those worst cooks in America can make them, so can you. And yours would probably be even better.”

“Ok,” he said.

So the next Saturday, I coached him. I just gave him step by step instructions and tips along the way. He did the whole thing. And he did it. The whole thing: poached eggs, hollandaise (“holiday”) sauce, Canadian bacon, toasted English muffin. It was delicious.

And, he liked it so much himself that he made it again the next Saturday morning, too!

But just when we were getting used to having eggs Benedict Arnold every Saturday morning, he went on a sleepover at a friend’s house last Friday night.

We pointed out that we’d missed his cooking on Saturday afternoon when he got home. He promised to make them again this Saturday.

Life is good.

Post Schedule

Last year I wrote a blog post every day. Not on this blog, but I did.

This year, I thought I’d back off a bit. Take a little more time on things. I didn’t set any particular post schedule. But that’s maybe turned out to be a little too lax. I get out of the habit of writing, and nothing gets posted for weeks.

So I’m going to try to post here on Tuesdays and Thursdays, and the occasional Saturday. At least for a while.

Do me a favor. If I miss, drop me a line and remind me.


What Winter Break Does to You

Day 4 of winter break.

He wants to go see the Spongebob movie.

Crazy thing is, I kinda want to see the Spongebob movie, too.

There I admitted it.

Also, it’s been cold. Very cold. This morning was the 15th straight day I’ve let the dog out in the morning and read a below zero temperature.

So the other day, the kid asks me, “How cold does it have to be so when you pee in the air it freezes before it hits the ground?”

That’s my boy.

Winter Break

School is out this week across New York State.

For the last eight years, Brooke has taken teenagers from across the state to New York City, to the UN for a three-day leadership seminar. Most years, the kid and I go with her just to tag along and mess about in the big city. This year, for a variety of last-minute reasons, we’re staying home.

We’ve tried to do some fun things. Last night we had movie night in. This morning we had brunch out.

I’ve tried to make it clear that I have to block out some time to do some work, and that he could do whatever creative activity he felt up to. So far, that’s working. He spent the afternoon making various superhero accessories out of cardboard. He finds the templates online, prints them out and puts them together.

Except one project didn’t quite work out. The instructions called for foam board and a glue gun. We don’t have either of those things around the house, so he did the best he could with cardboard and a glue stick. It didn’t hold up.

He was a little upset about it, but in the end decided that the failure was ok because he learned a lot about how materials work together (and sometimes don’t). Now he’s on to something else.

I’m waiting for the day when the creative process for superhero accessories will start moving in the opposite direction. He’ll start making his own templates and posting them online. Surely, that day is coming soon. We’ve already started talking about his putting his comic stories online. He has several story lines going. Most of them are done in pencil sketches. Pencil sketches on their way to becoming graphic novels.

Not a bad way to spend winter break when it’s way to cold to go outside to play.