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# How can I measure the pressure inside a bottle of soda? Answered

I'm wanting to know the internal pressure of an unopened bottle of soda.

I'm thinking that I can cover it with an empty balloon and seal it off, then slowly open the bottle letting the balloon expand. Then by approximating the volume of CO2 in the balloon and bottle I'll be able to calculate the pressure of the soda that was in the bottle.

Would this work and any other ideas for this would be appreciated!

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## Discussions

I might not be a rocket scientist but I
still know that you can not measure pressure inside a sealed container
without actually opening or puncturing it somehow.

The only way I can think of doing what you ask is by using a saddle valve as used for water and gas installations.

But you would have to make a custom clap to cater for the bottle.

And
it might be a good idea to let some silicone cure on the bottle cap
first so they initial leaking when tapping into the cap is reduced.

Instead of a pipe you connect a pressure tester on the outlet.

I've seen saddle valves around before but I didn't understand how they worked till now. This might be the easiest thing to do! I would just need to figure out how to attach it to my bottle and attach a gauge to it to measure the pressure.

Thanks for the idea!

They come with two parts, the one with the valve and the other plate to hold it in place from the back.

If the bottle is not too thick you can use longer screws and a flat plate at the bottom.

Otherwise make a wooden or metal frame for the bottle with screw holes to fit the actual valve part.

You
can get those valves in pluming stores and they came in varoius sizes
for different types of water pipes, the big ones are hard to find.

For
quick checks on a lot of bottles it might be worth to think about a car
jack with a mount for the valve and a fixed frame for the bottle.

I only mentioned them as IMHO it is the best way to connect a gauge and not to loose too much pressure while trying to get inside.
So accuracy is basically down to the gauge, the volume lost in the valve system and gauge and (if any) leaking gas during the screw in.

This is what I came up with. Thanks for the idea, it worked out splendidly!

I'll be publishing my instructable that deals with this sometime in August. Sorry I'll take so long. I have to go to another country to finish it.

Dear tomatoskins,

Have you made an instructable on this?

Har.

It is not spam, but a member trying to make you aware of a neat solution to measuring pressure with a piezoelectric device.

They don't use a lot of bottles anymore, now it's mostly cans and plastic bottles.

Since this would be a critical factor in the engineering of the container they probably already have all kinds of charts and graphs of the pressures otherwise the container design would just be trial and error.

Contact someone who works quality control for a bottler and ask them how they do it. I would guess that they have an altered bottle with sensors in it and holes drilled for the wires or a wireless unite the size of a capsule that they can just drop in the bottle, somewhat like what Iceng has come up with. I think his would be the best solution, a sensor coupled with a sealed battery and a wireless transmitter would give you a constant readout of the pressure under varying conditions including being frozen, shaken, or opened and left to sit. A good quality control process would involve randomly dropping a sensor into a random bottle as it proceeds through the line in order to check the functioning of the machinery. So most likely the mechanism for checking this has already been perfected.

Buy a cheap tyre-pressure gauge, and connect it through a spare soda bottle lid.

Chill the soda bottle as cold as you can without breaking it.

Quickly switch the lids.

Let the bottle's temperature re-normalise.

---------------------

I did a crude experiment with a class many years ago to measure the volume of CO2 dissolved in lemonade. If I recall correctly, it was about 14 litres of CO2 in a two-litre bottle of cheap lemonade.

I though of another idea that might be more simple, (but still more complicated than just mating a bottle cap to a pressure gauge or electronic pressure transducer).

This other idea requires a way to place a known, downward force, against the top of the bottle. The upward force on the bottle cap, or some other flat thing in place of the bottle cap, should be just (Psoda-Pambient) times the area A inside the neck of the bottle.

I'm guessing you could get a pretty good esitmate of A as pi*r^2, just from measuring the inside radius of the neck of the bottle.

The way I imagine this measurement would work, is by: Piling on a large amount of weight, more than that needed. Then waiting for the bottle containing soda to reach its new equilibrium pressure. (How long does that take?) Then, slowly unpiling the weights, one by one, until the seal starts hissing.

OK If you scuba dive take a bottle down and at various depths open it to see if bubbles are released, keep doing this until no bubbles are released then calculate the pressure local to you at that time.

If your not a scuba diver then do this in a pressure vessel Not too hard to make.

http://hypertextbook.com/facts/2000/SeemaMeraj.sht...

It looks like in a can your looking at around 55 PSI. This changes with prodiuct and temperature so there is no fixed value.

Dumb question:

If I put an empty balloon over the top of a soda bottle, AND I seal the balloon to the top of the bottle tightly, AND then allow the balloon to fill with gas produced by the soda...

Will the soda-bottle-balloon system reach a new equilibrium? I.e. the balloon will expand to some positive volume, and then stop expanding.

Or will the soda bottle fill the balloon with gas, increasing the volume of the balloon, until BLAM - the balloon breaks?!

I am guessing the balloon has some sort of pressure-volume characteristic. P as function of V, or V as a function of P, where a measurement of one infers the other. I am guessing stretching a balloon, by inflating it, is somewhat analogous to stretching a spring, only for that the graph would look like force F versus displacement x. Continuing the analogy, there is some maximum force, Fmax, above which the spring breaks, and some maximum pressure, Pmax, above which the balloon breaks.

I mean, that's really what I'm asking about regarding the question of whether or not the bubbling soda breaks the balloon. Just wondering if P inside the soda bottle can climb to values greater than Pmax of the balloon.

By the way, the P vs V characteristic for a latex balloon, is not something obvious. I think it is going to depend mostly on how "stretchy" the latex is.

*Breaks out a Dictionary, :P

Hopefully a standard party balloon won't break. Otherwise, it would look cool; Take a Video !

Yeah, the balloon idea wouldn't be anything super accurate and I'd need to find a big balloon that wouldn't break.

Glass is a flexible material.

Simply measure mechanical pressure and deflection compared to a database of internal pressure.

Always press on the same diametrically opposing areas in relation to the glass seam recording the external pressure and deflection at a room fixed reference temperature. Look up the internal pressure in a deflection data table constructed at a previous time.

There will probably be a variation in the physical properties in the glass.

I doubt anyone here has the equippment to measure the pressure this way.
Even if glass bottles would expand under pressure to a degree than can be measured I see no way of getting any results from it.

Glass bottles are produced automatically and no bottle is the same in terms of accurate wall thickness everywhere.

Even checking by the push out of the cap under pressure is no way reliable for similar reasons, including the fill level of the bottle.
Without something like a saddle valve I see no option to get any results just from outside measurements.

Maybe internal pressure affects the refractive index of the primary gas CO2 in a measurable way just as sugar concentration is detected in solution against a glass plate by refractive index changes.

After all anyone can buy a laser for a dollar and explore CO2 refractometry...

LOL, I love the approach!

But don't you think that is like using a rocket to shoot at pidgeons? ;)

And I don't want to think about compensating for the glass, differences in the glass surface and so on...

But maybe you can use idea for a new type of sensor to use optics within a closed system, like pipes, in an Instructable?

Maybe as a sealed unit with wireless data upload/reading?

Just kiddin´ ;)

I do get a lot of laughs, but I'm still on it.

Calibrate by measuring the soda glass angle of reflectance for glass characteristics, fluid / glass is not affected by bottle pressure....

THEN measure the CO2 gas glass reflectance which is proportional to the gas == bottle pressure.

Regarding latex balloons. I think a latex balloon might work well as an indicator of small pressure difference. That is to say if your laboratory, or garage has a chamber, set up so you can control, and measure, the pressure inside this chamber, then the balloon could sort of act as an indicator of pressure difference, if the balloon were somehow placed in between the chamber, and the soda bottle.

My idea here is to pump up the chamber, until the balloon goes completely flat-limp. Then when that occurs, the pressure in the chamber is equal to the pressure in the soda bottle.

I drew some pictures of this, as I sort of imagine it might work. None of the apparatus needed for pressurizing, or measuring pressure of, the exterior chamber is show. The actual equipment might involve a bicycle pump, a pressure gauge, plumbing fittings, etc. I have abstracted all that into a symbol called P-control; i.e. a pressure source controlled by the experimenter. The blue thing is the balloon. The little red squares symbolize squishy gaskets, needed for to make a gas-tight seal.

Note that if you actually build this thing, I think it has to be made out of something transparent, for to see inside and observe how the balloon is changing shape. If you build it out of glass, then please remember to wear your safety glasses, for protection in case it goes explode-y on you.

I really like this idea a lot! The only issue that I see is finding a sealed container that I can pressurize with a visible window.

Well... How accurate does it need to be? Just out of your Curiosity, or you need Specifics?

I would slip a balloon over the top similar to what you and Jack suggested, but slide the balloon down far enough so you can twist off the top and trap %100 of the gas in it.

for a more accurate reading... Put it in a sealed container with a pressure gauge and open it then :)

**Plz Note**

Boyle's law will screw with your Results! The warmer (More Energy stored) the substance the more pressure will be exerted.

AND Temperature will also effect how quickly the Disolved CO^2 is released from the liquid (Henry's Law?)

So keep a constant temp for each set of tests! http://en.wikipedia.org/wiki/Boyle%27s_law

http://en.wikipedia.org/wiki/Henry%27s_law

Can anyone confirm this for me? It's been a while since High-school Chem >.<

Sorry, I was a little un-clear before. I have revised my question to specify that I want the pressure of an un-opened bottle.

Err. You are still unclear - the situation you are setting up REQUIRES the bottle to be opened to fill the volume !!

It would be easy to make a device that can seal against the cap, pierce the cap, and measure the pressure using a gauge.