I’m sure that’s true. It just means that the partial pressure of the CO2 inside is at most 1 atm. So there is a lower limit to how flat it gets, though it’s much less than when fresh. That’s in contrast to an unsqueezed bottle that has (say) 1 L of headspace but zero partial pressure. At least 1 L of CO2 has to leave the liquid to repressurize to the same level, but it probably won’t get there because there isn’t enough gas left.
Ran some experiments. Wanted to actually measure the pressure inside the bottle and came up with this:
It’s pretty simple. Basically squeezes the bottle in a predictable way. I squeeze a specific distance and measure the applied force. This doesn’t tell me the pressure directly, but it gives me a number I can compare in relative terms. Double the force means double the pressure (roughly).
At 21 C (room temp here), the scale measured 3.2 kg at a specific distance (actually a 1.5 degree angle, but same diff). I used two 1 L bottles of seltzer. Both measured the same.
Chilled to 2 C. Pressure went down: measured 2.65 kg. Seems reasonable; the CO2 capacity went up and the remaining gas exerted less force (PV=nRT).
Drained 250 ml from each bottle. Bottle 1 was squeezed before closing to remove any headspace. Bottle 2 was closed without any special attention (didn’t try to specifically fill it with air or anything).
24 hrs later, bottle 1 measures 1.2 kg pressure, and bottle 2 1.8 kg. Note that bottle 1 has expanded back to the original shape and feels fairly tight. However, the pressure is definitely less.
48 hrs, bottle 1 measures 1.1 kg pressure and bottle 2 1.8 kg. Basically the same (the device is probably only precise within ~10%).
Removed from fridge, back up to 21 C. 72 hrs later. Bottle 1 is at 2.1 kg, and bottle 2 2.5 kg. So bottle 2 remains at a higher pressure, but both increased significantly when they warmed.
That’s all the data for now. My conclusion is that the headspace removal doesn’t do much. Bottle 2 was consistently at a higher pressure, but it also contained the normal air, and my pressure test measured both. It seems like the partial CO2 pressure is likely about the same in both cases, which means the liquid lost the same amount of gas.
I haven’t checked the fizziness since I haven’t figured out a good way to do that scientifically. Just eyeballing it, they look similar. And on the timescale of ~1 day, I don’t think the rate of CO2 coming out of solution matters at all. It gets to equilibrium in under 24 hrs.
Very impressive, Doctor, but I’m puzzled by your mechanism. Can you explain how it works, and how it squeezes the bottle? I can’t figure it out from the picture.
IIRC, one method of measuring how much CO2 is in a liquid is to put a balloon securely over the neck, and shake the bottle until the balloon stops inflating. Presumably heating might drive out CO2 dissolved in a liquid, instead of shaking, but you’d have to let the heated gas return to STP. And you might need a larger balloon more securely fastened to the bottle.
With either method you’d have to measure and the volume of air in the bottle before you started, and subtract it from the final volume, of course.
Just insert the bottle in the hole (it’s a close fit), attach the scale to the lever, and pull down until it reaches a particular position. The little tab to the side of the hole pushes on the side of the bottle, creating an indentation. Read the force from the scale.
Basically no different from pushing on the side with your thumb and judging how stiff it feels, just done in a more predictable manner.
D’oh! I didn’t realize that the black circle was a hole. I thought it was a solid rubber or plastic thing, and I couldn’t see where it would go or what it would do. The arc of darker copper at the bottom looked like a shadow, creating a 3D effect.
Very clever. Well done.
Ahh, yeah, I could see how it might look confusing on some screens, depending on how the colors come out. The scorch marks from the laser cutter don’t help.
I was brainstorming lots of ideas, up to and including building a tiny wireless pressure sensor that goes inside the bottle… but all them were complicated. While handling the bottle I noticed myself squeezing it to judge the pressure, so I had the bright idea of just replicating that.
I might try the balloon suggestion. Just need to get my hands on some balloons first.
I’m quite surprised your squeezed bottles return to shape when capped. When I squeeze the standard two liter bottle to remove air, it generally keeps that shape once half the liquid (or so) is gone. As I mentioned before, I would have to blow into the bottle to return it to shape. This was done because sometimes the deposit refund scanners couldn’t read the bar code on a squeezed bottle.
Note that I only removed 25% of the liquid, and there was only a single bottle opening. I might try another round of testing with 50% removed to see how that behaves. And it would be worse over multiple depressurization rounds.
Making the background a woodgrain surface sure made it obvious for me. Although I am looking at the pic on a ~8x10" tablet, not a phone.
There are probes
to measure dissolved CO2…
I’m not the most educated or smartest on this board, but I am an AP Chem teacher, and it’s almost axiomatic that gases have higher solubility in cold liquids. They bounce around and find each other to make bubbles LESS in cold liquids. Also, we all know that the way to make a huge mess is to leave a full soda bottle in a closed car in the 110F desert heat, making the dissolved CO2 come out as a gas. Chilling it to 40F is the opposite of that.
Good idea. I’m going to try this out and run tests again. I may need to get something better than my old fish scale though.
I’m also considering if the reported effect was not based on simply chilled soda, but bottles of soda chilled, then removed and left out for a while as it is consumed, like at a party, and then returned to the fridge. It will lose a lot more CO2 in that time it’s out of the fridge, getting warmer, and open multiple times. Not much attention paid to it while it’s out, but the difference in fizziness between the first use and after it has been chilled again will be noticeable.