For reasons best left unexplored (why yes, alcohol was involved, you’re all so clever!) I found myself peeing into an empty plastic three liter soda bottle a couple of times a few nights ago. The bottle ended up about 25% full of urine, with some small residue (well under .25 oz I’m sure) of Mountain Dew-like soda. The bottle was kept capped at room temperature and normal atmospheric pressure. The bottle when being filled maintained its usual contours. Within 24 hours of being peed into (yes, it sat for a while, shut up) the sides of the bottle started curving inward. I don’t have any tools useful for measuring the curvature, but it’s not tremendous. Four shallow indentations, roughly equal in size, equidistant around the circumference of the bottle, having the net effect of making the formerly cyllindrical bottle a rough rectangular. So what could be going on inside the bottle that would cause it to indent?
The pee cooled off and caused the air in the bottle to contract? I saw a guy totally collapse a paint thinner can by heating/sealing/cooling it.
My WAG is that the urine was warm when it exited your body and warmed the air in the bottle. After some time, everything cooled down and therefore contracted.
Hot air expands, cool air contracts.
The liquid was at internal body temperature when it was put into the container. It cooled to room temperature and in a tightly sealed container that lowered the interior pressure by reducing the volume of the liquid.
Rio by Duran Duran
Water vapor is a more important factor here. When you peed directly into a bottle, a lot of water evaporated from the warm stream + pool of urine. If the bottle was sealed immediately, the water vapor stayed inside the bottle. As it cooled down, the vapor condensed into water, which lowered the pressure inside.
Could it have anything to do with bacterial growth? I know urine is supposed to be sterile, but the inside of the bottle wasn’t.
No, if anything that would increase the pressure in the bottle. It really is just that it was nice and warm when it went in and then cooled off. You can duplicate the phenomenon yourself with clean water heated to 100°F if you’d rather not have a bottle of stale pee lying around.
(Not that there’s anything wrong with that – I have one beside my desk right now.)
I, for one, will not rest until we hear the gory details.
I’ve noticed that too (my excuse is I live in a house with four people and one bathroom). I always assumed it was a bacterial thing but let’s test the temperature theory. PV=nRT. So V=(nR/P)xT. Let’s assume nR/P is a constant here. Assuming the 2L container is 1/4 full of liquid and 3/4 air that gives us V1=1.5L. Let’s be generous and assume the air starts out due to the influence of the urine at body temperature - 37°C or rounded to 310°K. nR/P= 1.5L/310°K=4.83x10E-3L/°K. Let’s call the final temperature T2 room temperature or about 295°K. so the final volume V2=(4.83E-3L/°K) X 295°K = 1.43L. So we lost about .07L or 4.7% of the volume.
It seems to me that in real life 1) the volume changes more drastically and 2) the initial temperature of the air is not going to warmed up that much by the urine. Does the urine itself undergo a drastic change in volume do to the temperature differential? Are we sure there isn’t a biological process involved? Stuff definitely starts growing after awhile.
This site shows that the urine, assuming it’s mostly water, will change volume by a little over 1%. However, I would think that bacteria growing would probably result in some sort of gas being evolved and increase the pressure.
The thing is, I don’t think it takes much of a pressure differential to bow in the sides of a platic container.
The ferocious corrosiveness of your urine is collapsing the walls of the container.
Where you have gone wrong is that you are using the ideal gas equation when the system we are talking about isn’t restricted to the gas phase. Bravo for doing the equations, but they are totally inapplicable to the system described.
In reality what we are discussing is the change in vapour pressure over a liquid. This process involves a phase change, not simply a change in temperature. As a result you simply can not use the ideal gas equation.
In simple terms, warm water has a much higher vapour pressure. When you pee into a bottle the air inside the bottle becomes saturated with water at a vapour pressure appropriate for 37oC. As the air cools the water condenses out as liquid. However you put the lid on, so the gas volume lost in that phase change isn’t replaced by gas from the atmosphere. Instead it is simply lost from the system altogether. As a result you can not assume that assume n in the gas phase is a is a constant. n in this system varies WRT to the gas phase. At high temperatures there are literally more water molecules in the gas phase.
It’s been too long since I studied phys chem for me to be able to do these partial pressure equations, but rest assure the phase change of the water is where the greatest pressure change is coming from, not the temperature change of the gas. Liquid water is simply so much denser than air.
Depending on how much alcohol was consumed there may be a significant amount of alcohol involved as well. Being more volatile than water alchol potentially has even more influence.
Once again though, that site only refers to water in one phase. While jack has disregarded the liquid phase you appear to have disregarded the gas phase altogether.
I attempted to use the first graph on that page to get some rough idea of the pressure change associated with the vapour pressure, but I can’t even understand the graph. It seems to be saying that the log of 0oC in K is 2.17. My calculator says the log of 274 is 2.44. 
Given that only about 2% of consumed alcohol is excreted in urine, it seems doubtful that it accounts for more of the pressure differential than the water – the solution simply isn’t that alcoholic.
(Unless you didn’t mean proportionate to the water, but rather than if the solution was entirely aqueous, of course.)
Goddamn if this board doesn’t turn our attention in the most peculiar directions from time to time.
You didn’t get rid of the pee yet, did you? Leave it for longer, if you can. I’m interested to see what a plastic bottle of pee and mountain dew will breed. Maybe leave it in the sun, if you can, to encourage it.
37.8oC = 0.9492 psi = 6.5 kpa = 0.06atm
20oC = 0.3389 = 2.3 kpa = 0.02
So the change in vapour pressure will result in a volume change of about 4% of the initial gas volume. That’s less than I would have guessed, but still not insignificant. And when we add this 4% loss with a 5% loss due to changes in temperature of the gas we get a total loss of 9% of the gas volume. That’s pretty significant, and more than enough to cause the bottle to buckle inwards.
I’m not sure what you mean. I just meant that because the vapour pressure of alcohol is so much higher than that of water that it would contribute disproportionately to the pressure change.
Let’s assume that urine contains 2% ethanol. Let’s also assume that ethanol and water is an ideal mix (which it isn’t, but it deviates in such a way that this will be a serious underestimate).
Looking at the link I gave above
@ 37.8oC ethanol will contribute 0.32kPa to total vapour pressure. Water will contribute 6.37kPA. That gives a total pressure of 6.9kPa.
At 20oC etoh contributes 0.116kPa and water 2.254 = 2.37.
Due to the presence of etoh we get a pressure change of 4.5% rather than just 4%. And overall a change of 10%.
In reality an etoh water mix will deviate from an ideal mix and the result will be even higher, but I have no way of calculating how much. I suspect we may get as much as 7 or 8% change due to vapour pressure changes alone.
Sometimes?
OTOH it has prompted me to use knowledge I haven’t touched for 15 years. Amazingly I still remember most of it.
In my defense I wasn’t trying to solve the problem but merely to pin down how much the volume of the water changed with temperature.
I considered the problem posed by the OP, i.e. “What happened?” as being solved. The temperature change reduced the pressure inside. Whether it was air, water. water vapor or all three is an interesting detail and proves the answer but I didn’t need rigorous proof. 
Fair enough.
Agreed, then – but what I meant is that the amount of alcohol in the urine is likely so small as to make this a fairly fine point.
Is that a good assumption? We’re assuming then that Otto drank as much ethanol as can be found in a litre-and-a-half of scotch, his bladder was totally empty when he started, and that the ethanol he drank was mixed with less than three-quarters of a litre of water?
You don’t have to be that out of it to pee in a bottle. 
Betas me. I was just assumin’. I am lazy and had no real intention of actually working out what the alcohol content was. So I simply extrapolated from your 2% figure. On re-reading (and thinking for moment) I see that this was totally incorrect and pretty dumb.
Whatever. The main point isthat we know that temperature changes will produce ~9% decrease in volume of the bottle. That explains the decpmpression without needing to invoke microbial effects.
When you;re that out of it peeing into anyhting as small as the neck of a bottle is out of the question. Not peeing on your own foot is the challenge.