Why weight change when I put effervescence tablet ?

[Gh778]

Hi,

I measure weight of : column of water + water + effervescence tablet + cover (hermetic)

When I put effervescence tablet (give a lot of small bubbles) in water and close very quickly the cover, the weight decrease of 0.2g with a precision of 0.01g for the weight-balance. The weight decrease more and more until -0.2g. When I open the cover I can ear pshiiitttt, this could say no gas has move out. I tried with big column (1 liter) and others smaller. Could you explain where is my error when I do experimentation ?

 

[Simon Bridge]

You need to be more detailed about the setup and how you are determining that the weight has decreased.
Weight decrease could be due to bad calibration of the scales, systematic error due to shifting load (water sloshes around while the tablet is gassing), a slightly leaky seal... lots of possibilities. We do not imagine that matter is vanishing from a sealed container right?

Note: just because there is a "pshiiitttt" does not mean that zero gas escaped - just that some gas was trapped.

I imagine there is a sharp weight discrepancy at the start, then it slowly increases? Is that correct?

Did you try rigging something so the tablet drops after the cover is in place? i.e. stick to the underside of the cover with gum so it is held out of the water, then, with the cover in place, turn the whole flask upside down. Wait until the entire tablet has dissolved, then, carefully, place the flask on the scales. Don't weigh the flask while water is moving about.

 

[Gh778]

it's only home experimentation, I see weight decrease but maybe not 0.2g like I said before maybe 0.03g but I'm not sure maybe it's gas escape.

 

[Simon Bridge]

it's only home experimentation, I see weight decrease but maybe not 0.2g like I said before maybe 0.03g but I'm not sure maybe it's gas escape.

You've repeated the experiment several times with different volumes of water and you are not sure of the order of magnitude of the weight discrepancy? Did you not make a record of each attempt?

You need to check your data before reporting a problem.
Try it again.

 

[Gh778]

yeah, I do 17 measures, and each time the weight decrease about 0.03g (accuracy 0.01g), different volumes, different containers, different type of cover. Long time before weight and I'm waiting long time for watch if weight move.

Datas (g):

1/ Only 1 tablet

170.35 -> 170.32
690.55 -> 690.52
122.89 -> 122.87
440.81 -> 440.79
190.63 -> 190.60

682.76 -> 682.73
520.30 -> 520.28
135.96 -> 135.94
269.95 -> 269.92
220.30 -> 220.27

489.36 -> 489.33
190.80 -> 190.78
164.32 -> 164.30
612.58 -> 612.55
338.22 -> 338.19

266.32 -> 266.29
694.29 -> 694.26

2/ 2 tablets:

655.32 -> 655.25
298.56 -> 298.50

Weight decrease more and more with time after the tablet is in water. It's not a lost of weight when I manipulate. Maybe it's the gas escaping but with different covers it's always the same and even I let one hour column on the weight-balance, the weight don't move.

Even I press the plastic column (when it's plastic), the weight don't change after 15 minutes, this could say if it is an escape of gas my pressure will escape more gas, but not.

 

[Simon Bridge]

How long is "a long time"?
Is this the same time in each case?
Which measurements had which covers etc?

However - it looks to me like your covers are not airtight.
If you tip the container, with cover in place, upside down - does it leak?

Here's an experiment for you:
Pick a container and a cover -
part 1.
put water in container, put lid on, put tablet on the lid (i.e. NOT in the water), weigh the ensemble like that.
Make a note of the weight. This is M0

part 2.
remove from scales, lift lid, drop tablet while looking at a clock, quickly replace the cover, make a note of the time. This is T0. To be clever, wait until the clock reads an easy time before dropping the tablet.

Wait until you are sure the tablet is completely dissolved.
Make a note of the time. This is T1.

Carefully weigh the whole thing. This is M1.

Work out the interval T=T1-T0, and the mass discrepancy M=M0-M1 - write them down.

Repeat until you have at least 5 sets of data - be sure to use the same interval T each time - record the data in a table.

Compare the mass discrepancies M between results.

Repeat with different covers.

 

[Gh778]

long time => in one minute the weight decrease, but I let 15 minutes or more
Yes, the same each time
Plastic and glass container, cover plastic and steal with gasket

Yes with upside down, it's the same weight decrease,this would say there is no gas escape

I will test your experiments and give you result

 

[Simon Bridge]

It was the same each time but you cannot say if it was 15 mins or more than 15 mins?

You tried it upside down?
Did any water leak when you did?
(It's a simple seal test for improvised seals.)
... what did you make your covers out of? What sort of plastic? How cut?
Are these specially manufactured to be airtight?
What sort of containers?

What did you do to make sure the seals were airtight?

If you are getting a mass loss while the covers are in place - then the seal is leaking gas.
When you lift the cover, you must get a substantial weight discrepancy since now you know that gas has escaped right?

You can use this to find out how much gas is produced by each tablet - then you can see if the small weight drop while the cover is on added to the big weight loss when the cover is removed, is the same as the weight of gas produced by the tablet.

 

[Gh778]

I done 5 measures with 2 tablets

difficult to measure alone and have good time especially at start but all measures are approx the same

T=2'40s with M=-0.06 g
T=2'50s with M=-0.05 g
T=2'35s with M=-0.06 g
T=2'45s with M=-0.05 / -0.06 g
T=2'30s with M=-0.05g (after T=10' => M=-0.06g)

Plastic bottle with plastic cover only, but with upside down like that I don't think gas escape, and if liquid escape the weight will decrease again and again (the last measure I'm waiting 10 minutes)

 

[Gh778]

What did you do to make sure the seals were airtight?

I'm not sure cover are perfect, but:

1/ upside is down, no water escape (and if water espace, it would be on balance because there is a curve)
2/ I press for add pressure for see if weight decrease and the weight is the same after 3'
3/ I use bottles of plastic and glass/steal/gasket, I think plastic bottle is good because when I open, the pressure is big enough for to be dangerous for eyes

I suppose a problem with my balance but if I take several weight and wait 1,3 or more time, the weight is always the same. The only thing I do careffuly is to wait when I'm approaching to the weight-balance because vibration change the weight due to the floor.

The mass of gas for a tablet is approx 0.28g

 

[Simon Bridge]

You using something like a PET bottle?
Like you get coke in?

So the plastic+gasket is the bottletop?

You realize that plastic bottles are not gas-tight right?
Gasses can diffuse through the plastic itself.

Have you tried using a metal flask?

 

[Simon Bridge]

If you get 0.28g gas per tablet
and you get a gradual weight drop of 0.06g (say) with the lid on.
and you get a further 0.22g loss after the lid is removed
then you have support for the idea that gas escapes the bottle even with the lid on.

What I mostly want to get across to you is control of variables, and careful record keeping - as well as careful reporting.

BTW: following my method for post #9, M should be positive - you have reported a weight-gain ;)
But do you see how that extra care made things much clearer?

Off that data - the stats are not great but:
You lost (54±3)mg

 

[Gh778]

yes, I have tried with metal flask, it's the same, with glass bottle, this don't change the weight...

But do you see how that extra care made things much clearer?

the care of manipulations ? even I take time and precautions the lost of weight is the same

following my method for post #9, M should be positive - you have reported a weight-gain

I give negative because weight is lost, but with your method, the weight is positive ok, this don't change the result

After a long time, there is no bubble in the water, but pressure is always there. Water must transmit pressure like gas...

Why 3 tablets => -0.09g

I tried with a small bottle with small volume for gas, the bottle is under great pressure, and it's the same with low pressure when there is big volume for gas

Edit: I added a sheet of aluminium around tablets for delay effect, and this increase time for weight to reduce, but at final it's the same loss

I changed the room for measures, after let a moment the balance for temperature. It's the same weight decrease.

Maybe someone else can test for compare results ? I hope someone can do this experimentation in a laboratory, it's very easy and fast.

 

[Simon Bridge]

yes, I have tried with metal flask, it's the same, with glass bottle, this don't change the weight...

What is the difference between the metal and the glass? Perhaps the glass is thick and the metal is thin?

Anyway - I suspect there is gas loss due to diffusion - it depends on the difference in pressure between the inside and outside of the bottle.

Note: bubbles displace water - so they cannot form unless there is someplace for the water to go.
This also means that there could be a gas-permiable seal on the cover - this will allow gas diffusion even when the container is upside down.

Did you check to see if the total weight lost is equal to the total weight of gas released by the tablets?

 

[Gh778]

If you get 0.28g gas per tablet

I'm not sure of that, it's not write on the paper, it's just the lost of weight I suppose it has...I done what I lost + what I lost after and I suppose it's the weight of gas.

The tickness of glass is 3 mm and the thickness of metal is 1 mm. With a big volume (1,5 l) the pressure is only a pshiiit like you move a bottle with CO2 inside.

No the total lost is not the all gas give by tablet, I lost 0.06g but if I open the bottle I lost 0.2 g more.

With 2'40 it's not possible to incriminate temperature but maybe balance or diffusion or ...

Edit: I tested with another balance today, it's the same result approx, the weight is not the same, I use glass+steel cover. And I have add oil to gasket.

 

[berkeman]

Hi,

I measure weight of : column of water + water + effervescence tablet + cover (hermetic)

When I put effervescence tablet (give a lot of small bubbles) in water and close very quickly the cover, the weight decrease of 0.2g with a precision of 0.01g for the weight-balance. The weight decrease more and more until -0.2g. When I open the cover I can ear pshiiitttt, this could say no gas has move out. I tried with big column (1 liter) and others smaller. Could you explain where is my error when I do experimentation ?

Do not edit your posts after you have received help here at the PF. We have restored your original post.

 

[Gh778]

Do not edit your posts after you have received help here at the PF.

sorry, but when I edited, I don't have a reply.

 

[berkeman]

sorry, but when I edited, I don't have a reply.

Interesting. The reply was maybe being composed as you edited, because it sure looked like he understood your question. Okay, thanks for the clarification.

 

[Simon Bridge]

Oh OK - so the tablet provides 80mg of gas to the air normally without the top being screwed on - leaving bubbly water behind?

Note: 1mm is very thick for a metal flask - what kind of flask are you using?

That's rather annoying actually - you could wait for the water to go flat, plotting weight against time at equal intervals to see what figure it tends to.

It would take quite a while for me to duplicate the experiment.
My experiment is certain to be different from yours anyway, since you have not given a complete writeup.

Since the gas is probably CO2 - I suppose you could immerse the bottle in lime-water?
I'm not sure if such small quantities would show up though.

 

[Gh778]

I use a flask for food, the precise thickness for cover is 0.8 mm due to a 0.2 mm of plastic (not gasket).

I'm waiting a long time (1 hour) and the weight never moved after 4', lost 0.07g maybe one time 0.08g. With plastic or glass it's the same.

What you need for duplicate experiment ? Great if you can do this type of experimentation :)

Yes, gas is CO2 and true I can use lime-water for what ?

Edit:

1/ with bottle opened I lost 0.17g (with 1 tablet)
2/ with bottle closed I lost 0.04g, and after if I open the bottle the total lost is 0.17g

When I measure: with or without bubbles (on the walls) the weight move very few, so each time I shake the botlle a little for escape bubbles on the walls.

 

[256bits]

Simon, one thing I thought is that he has a bouyancy effect due to the container expanding due to the pressure and affecting the weight recorded, but I don't see a discrepancy between containers ( plastic, glass, metal ) as the op says it is always 0.02 g per tablet, or multiples therof per tablet, which seems odd.

 

[Gh778]

For take Archimede's law in account: Density of air is 0.0013 g/cm3, so the volume is 0.03/0.0013 = 69 cm3. For 0.03 g lost, with a 78 cm² for surface's cover, the deformation of steal cover must be like 0.88 cm. And for 0.09 g the deformation must be like 2.64 cm. I'm right ?

 

[Gh778]

Maybe I found: when bubbles move up in water, they have gas in it (CO2), this gas move up with a speed, so there is a quantity of movement, the weight losses is the sum of mass of bubbles multiply by speed. Like quantity of movement is conserved, the weight don't change after the loss of 0.03 g/tablet. What do think about that ?

 

[jbriggs444]

Maybe I found: when bubbles move up in water, they have gas in it (CO2), this gas move up with a speed, so there is a quantity of movement, the weight losses is the sum of mass of bubbles multiply by speed. Like quantity of movement is conserved, the weight don't change after the loss of 0.03 g/tablet. What do think about that ?

Steady-state movement does not change apparent weight. You've indicated that you waited for one hour.

This theory is perilously close to the classic story of the man banging on the sides of a truck full of chickens to reduce the scale reading at the weigh station.

 

[Simon Bridge]

@256bits:
I had thought of the buoyancy effect too ...
Considering the different materials involved, I don't think the volume expansion was big enough but it's easy to check - simplifying the 1l of water is a cube 10cm on each side that weights 1kg. Water is nice like that. How much would the volume have to increase to cause a weight decrease of the order of 50mg? Ergo: how much do the sides increase? Would you notice?

The fact that there is no measureable difference in weight-loss for the other materials is problematic, but there is not a good enough control available to see if it is real. The trouble with home experiments is that you seldom get the kind of rigor needed to draw decent conclusions.

@Gh778:
As the bubbles rise, an equal volume of water must fall...

It's a bit like the sealed container of birds sitting on a sensitive electronic balance - and all the birds start flying around. What happens to the reading on the balance?

Another imagining: you sit in a sealed container with a cylinder of helium and a stack of balloons. You inflate the balloons and let them float up to hit the top of the container.

Note:
... lime water (a saturated solution of calcium hydroxide) turns cloudy when carbon dioxide bubbles through it.

There's all sorts of problems concerning the quantities over the time involved.
You could do the experiment under water to see if bubbles form around the seals and over the surface of the container. Presence of bubbles confirms gas is escaping. Lack of bubbles is no information because the escaping gas is so small and slow that it could be dissolving into the water instead of forming bubbles. Similarly, doing the experiment under lime water - the concentration of CO2 may be too low for any clouding to be visible.

You could ramp up the experiment with an insane number of tablets so outgassing will be significant... but that does not confirm outgassing for the low-pressure case unless you are very careful.

There is probably something else I'm forgetting.
It's really not that difficult though:

Things that cause scales to read low are:
1. reducing the amount of matter present on the scales (outgassing suspected)
2. adding an extra gravity-opposing force from outside (buoyancy)
3. faulty scales - perhaps the scales lose 50-60mg over that time anyway?
4. acceleration of gravity changes

 

[Simon Bridge]

I still favor outgassing as most likely.
See: de Segovia, J. L. Physics of Outgassing p99 s2 "Permeation of gasses through matter"
... The vacuum systems de Segovia is talking about only need to oppose ~100 kPa @ ~300K.

You seem to think that the pressure in a can of soda ("pshhhht") is low. People like Pepsi and Coca-Cola bottlers pressurize the cans to 40PSI gauge @294K ... that's about 276kPa over atmospheric. Soda goes flat in the bottles if left for too long even if the bottles are unopened... PET iirc Coca Cola Co bottles go flat in 3-4 months, and cans in 6-9 months.

Of course it depends on what you are comparing it to.
40psi is a reasonable pressure to inflate car tyres to - is that "low"? It's probably higher than many people would imagine inside a soda can. OTOH: My LPG bottle is about 300psi (3mm steel-plate walls with a weld around the middle) and hospital O2 often comes like 2000psi or so.

Listening is not a good way to tell pressure anyway - you have to measure it.

 

[Simon Bridge]

@256bits:
I had thought of the buoyancy effect too ...
Considering the different materials involved, I don't think the volume expansion was big enough but it's easy to check - simplifying the 1l of water is a cube 10cm on each side that weights 1kg. Water is nice like that. How much would the volume have to increase to cause a weight decrease of the order of 50mg? Ergo: how much do the sides increase? Would you notice?

... crunching the numbers back-of-envelope ... the change in volume needed is about 0.5ml ... or half a cubic centimeter. Gives a change in dimensions of 0.002cm on each side ... about 1/50th of a millimeter.
So no.. you wouldn't notice.

Buoyancy is a contender!

 

[Simon Bridge]

Steady-state movement does not change apparent weight.

No, but the transitions could - when the momentum changes. If you drop stones onto the pan of a balance (which subsequently bounce off the pan) you get a weight reading.

So - in principle, a bubble forming on the wall of the container and detaching would require a change in momentum that could, in principle, affect the scale reading.

The trouble here is that the system is presumed to be closed.

You've indicated that you waited for one hour.

After a long time I'd expect the rate bubbles form to taper off and some weight-loss (by that mechanism) to be recovered. That has not been reported... which counts against the proposed mechanism being significant to the observed readings.


I see this sort of discussion a lot.
The answers are not very obscure - only the details of the process.
Because of this, when we say "well it must be due to effect A", the experimenter responds "but it couldn't be because I have done x and y and z to account for it"... which just shows that their r efforts have just been in vain. They are mistaken about having accounted for effect A. We end up trying to say why effect A is still plausible ... especially with the Holmes precept[*]. But this is seldom convincing and the experimenter insists that we have to repeat the experiment.

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

[*] Doyle, A.C. (1890) The Sign of Four ch6. (Doubleday p111)

 

[Gh778]

I'm just wake up, so I need time to read all messages...

As the bubbles rise, an equal volume of water must fall...

I'm agree, water give a mass*velocity, idem for gas. But when water move down and gas move up, nothing happens, it's only when gas has reached the surface it can give extra velocity to gas in the bottle. If velocity of gas is conserved, the speed is around 1cm/s, the velocity of CO2 at 20°C is 427 m/s, so the difference of temperature is around 427²-427.01² => 2.9°C.

I'm freezing the bottle with water (-12°C) and the weight come back near to normal: +0.03g. Another problem to understand. Like one tablet give sometimes -0.04g (I saw -0.05g after one hour) maybe it's not good enough to tell something (and it's only one bottle, and the external temperature where is the balance has changed). Maybe this come from the junction liquid/solid. In a solid, there is no vapor pressure like in liquid, the vapor pressure can take less molecule to the solid than it can do with a liquid. When a molecule is ripped away an extra force is added to up due to the rip away, it's just an idea. In the contrary, the pressure of gas don't change result, I test with small volume for gas and this don't change the result: -0.03 g (but this confirm there is no escape for gas). But vapor pressure change a lot with the external pressure or not ?

And for one bottle I pasted with glue (special glue) the cover and it's the same -0.03g and magnet is used for move down the tablet with external system, I waited 2 hours before to move down tablet.

... crunching the numbers back-of-envelope ... the change in volume needed is about 0.5ml ... or half a cubic centimeter. Gives a change in dimensions of 0.002cm on each side ... about 1/50th of a millimeter.
So no.. you wouldn't notice.

Buoyancy is a contender!

Are you sure, for me lost -0.03g with Archimede's law need more. Air is 0.0013 g/cm3, for lost 0.03g you need: 0.03/0.0013 = 23 cm3 and for 0.09g you need to expanse 69 cm3, no ?

 

[Simon Bridge]

I'm freezing the bottle with water (-12°C) and the weight come back near to normal

... don't know what this means - you cooled it in a water bath?

for buoyancy - I just did the proportionality and compared volumes - I may have missed a constant.

 

[Gh778]

I put the bottle in my freezer (home) and I don't forget to wipe the bottle. With second bottle freeze (water => ice), the weight increase too: +0.04g but like I'm waiting more than one hour maybe it's something from balance. And if I heat bottle for have water the height decrease -0.03g. Third and forth bottle no, the weight is always the same with ice. So it's not enough for say something.

PET iirc Coca Cola Co bottles go flat in 3-4 months, and cans in 6-9 months.

ok, but the measure is done in 2 minutes. And the glue ? and the upside down ? and the same lost with different containers ? and proportionnal to the number of tablets ? and with different volumes for gas ? And with glass containers and steel covers ?

It's possible to use the formula of Newton: force=2mv; if top speed is 0.25 m/s the weight losses is 2*0.6/1000*0.25/10 = 0.03 g with 0.6 g of CO2 (it's what I can read on internet about Efferalgan tablet), image show speed that I found on Internet. If it's that, the weight must change with a ball full of air (ping-pong ball) in water. But the CO2 in a tablet is very powerfull, 0.3g give 0.187 liter of CO2, even the ball move faster the volume is not great in a bottle. The ball must be down before close the container. And the gas must relax when the ball reached surface. There is a big difference between gas and a solid. In space, if I accelerate in one direction gas in a chamber, the gas keep the velocity even the walls are heavy, in the contrary it would be possible to move centre of mass. If I replace gas by small solid in each bubble in water, it's not the same case, solid move up from the surface a little and after move down and the momentum is not conserved due to gravity. Under gravity, gas keep momentum until temperature is conserved I think.

 

[Simon Bridge]

I'm afraid your reporting of events is unclear. List what you did and what the result was each time.
Remember, we don't speak each other's native language, so we need to be careful.

The mass-reading goes down by 0.06g = 60mg during the reaction, but increases by 0.04g=40mg after freezing? If you heat the bottle after that, the mass goes down again. But you only see this up-and-down shift for some of your tests not all of them?

How accurate are your scales? What is the smallest unit of mass it can measure?
Have you tried weighing a lump of metal and seeing if the reading is consistent over time, and with subsequent measurements?

Wiping the bottle after freezing is good - but the quantities we are talking about are very small ... how much condensation would 40mg be and how long would it take to form?

Water expands when it freezes - which, in your case, would increase the pressure on the gas at the top. Soe would re-dissolve. There would certainly be less activity so you may have a case for considering it.

The gas bubble in the liquid accelerates, as you have observed, because it is acted on by an unbalanced force. An equal volume of water, then, goes downwards with the same acceleration as the bubble. This water has a greater mass, so it's momentum will be higher. So more momentum gets transferred down than gets transferred up - so how is it that this gives rise to a decrease in force to the scales?

Newtons law for force is F=Δp/Δt which simplifies to F=ma.
"Specific Impulse" is Δp and Δp=2mv in the kind of collision where the object rebounds with the same momentum as it struck. You have to understand the equation before you apply it.

ok, but the measure is done in 2 minutes. And the glue ? and the upside down ? and the same lost with different containers ? and proportionnal to the number of tablets ? and with different volumes for gas ? And with glass containers and steel covers ?

In order:
. You are losing a lot less mass over 2mins than the coke does over 3months - and your bottles have already been used more than once - probably worn, certainly not factory-new.
. Glue, upside down... makes no difference to the diffusion through the walls of the container.
. Diffusion is proportional to the pressure - which is proportional to the number of tablets, so this supports the proposition.
. Pressure also depends on the volume of gas... but you have provided no data on this part.
. The type of cover does not matter - the diffusion is through the walls. Gasses can diffuse through steel too (did you not read the reference I gave you?) That you get the same reading for different materials is problematic but you also have no controls so I cannot tell if the readings are significant: maybe the variation with materials is too small for your scales to measure?

Keep investigating - what is the pressure inside the bottle after the tablet has dissolved?
You'll need to measure it.

Inflate an empty bottle with compressed gas to about that pressure and see if you get significant weight loss afterwards. That'll removing outgassing from the list at least.

 

[Gh778]

Ok for take care about language english, where do you come from ?

For the volume of the gas, I take with same bottle: 5 cl to 1.45 liter (for large as I can, some bottle the max is 0.45, others max is 0.95 and others 1.45) but the result is always the same, for example with a bottle of 1.5l I have tested with volume of gas of: 5cl, 25 cl, 50cl, 75cl, 100cl, 125cl, 145cl.

The mass-reading goes down by 0.06g = 60mg during the reaction, but increases by 0.04g=40mg after freezing?

yes for 2 bottles, I don't have same result for 2 another bottles

How accurate are your scales?

0.01 g. I measure in real time. I read the 0 after too, for watch if it's always to 0.

Gasses can diffuse through steel too (did you not read the reference I gave you?)

Yes I read it yesterday. But with different diameters of cover this don't change the result. And I tested with glass container and glass cover and the result is the same, ok there is a 2mm thickness of gasket but it is compressed and the thickness is around 1mm.

You'll need to measure it.

I will do today

Inflate an empty bottle with compressed gas to about that pressure and see if you get significant weight loss afterwards. That'll removing outgassing from the list at least.

I don't think it's possible with materials I have, it's not easy to do.

how much condensation would 40mg be and how long would it take to form?

I can't measure it

You are losing a lot less mass over 2mins than the coke does over 3months

Are you sure ? if I lost 0.03g in 2 min, after 3 months I would lost 0.03*30*24*30*3 = 2 kg

so how is it that this gives rise to a decrease in force to the scales?

for me the gas inside bubble has a velocity, this velocity is conserved when the gas is mix to another. Sum of force is always 0, because there is always gravity in account and when I put down the tablet, I put down the gas (with its momentum). But after, I close the cover and measure the weight. .

You have to understand the equation before you apply it.

I try to calculate the difference of force due to the gas, the increase temperature would be like +2.9° but after I don't know how to apply for have the force if I consider 0.5g of CO2 for example. Do you know ?

For Archimede's law application, have you good result ? Because it can be the solution

The best is to repeat this experience with laboratory materials. But I don't have.

 

[Gh778]

I try new test:

1/ I put water in small glass/steel container with a tablet in it, upside down, oil on gasket, closed
2/ I place this container in a bigger glass/steel container, oil on gasket, upside down, water inside

The tablet is in water when I return the big container, not before. I close the big container before return it and put in balance like that I have the exact weight. I can see if gas move in big container because this give bubbles (I tested this point).

I measure the weight of all.

The weight decrease of the same value in 2 minutes (like before). Here like the big container don't have a lot of additional pressure because the small container is closed (I don't ear pchiiitttt when I open the big container), I'm not sure it's possible to incriminate the diffusion.

 

[Simon Bridge]

That doesn't look like you are losing mass then.
That leaves one of the other three.

 

[Gh778]

That leaves one of the other three.

could you explain ? It's not possible it's Archimedes effect too.

That doesn't look like you are losing mass then.

not mass, weight

A friend of a friend who works in a Lab for analysis has tested with 2 balances of 0.001 g (Kern PEJ and PBJ, I don't know if it's good but it's pro balances), with a small glass/metal in a big glass/metal like I described before. He has near the same result. The weight decrease 0.0273 g (mean) in 2 minutes. He done 4 measures. At least, I can say it's not my balances, I think it's better to have another measures with different balance. I don't tell to him my results so he don't knew that I'm waiting 0.03 g. He don't use exactly the same effervescent tablet but I think it must be CO2 in it too. If someone has a balance precise enough he can do the tests, because I prefer to have a lot of measures and say that don't come from a problem with balance. If you do the test, don't forget to put all thing in container, like that Archimedes law don't interact more after than before.

Image: red is small glass/steel container, black is big glass/steel container, I use support for don't shock the glass. Tablet is block like that it is in water only when I return all the system. I think like that it's not possible to incriminate Archimedes and diffusion.

I added sensor (mountain watch) for measure the pressure in big container and it's never change with big values (only +1.3% max of pressure). Like that I'm sure it's not diffusion of gas.

What do you think I need to add for understand where the problem come from ? I measure weight while 2 minutes, not only for limited escape of gas.

 

[Buckleymanor]

Hi,

I measure weight of : column of water + water + effervescence tablet + cover (hermetic)

When I put effervescence tablet (give a lot of small bubbles) in water and close very quickly the cover, the weight decrease of 0.2g with a precision of 0.01g for the weight-balance. The weight decrease more and more until -0.2g. When I open the cover I can ear pshiiitttt, this could say no gas has move out. I tried with big column (1 liter) and others smaller. Could you explain where is my error when I do experimentation ?

The weight decreases because of bouyancy. The production off a lot of small bubbles causes a decrease in density this results in an increase in bouyancy.The mass remains the same but the atmosphere does not support the extra gas supply from the effervesence tablet in the same way.
Because the experiment is closed the effect of the tablet is like attaching a helium balloon inside the column resulting in a weight decrease.

 

[Simon Bridge]

OK - things that can lead to a lowered weight reading on a balance:

1. there is less mass sitting on the balance
2. there is an additional force acting on the system being weighed
3. it is an artifact of the weighing process
4. the acceleration of gravity has changed

If you rule out #1, then it must be one of the other three.

One thing that springs to mind is when the object being weighed has some sideways vibration, the weight reading can be lowered. I see this in experiments from people who think they have discovered antigravity using rotating widgets. The wobble from the machine throws the weight off - especially for electronic balances - making it look like the machine's weight is reduced.

I usually overcome the effect by making the machine do some work - like lifting a smaller weight over a pulley (compared with machine switched off). Accounting for any very small vibrations caused by the chemical reaction and bubbles would be difficult... but it would work in well with your observations.

You could mount a mirror on the scale surface and bounce a laser off it to put the spot on a wall some meters away to see if there is much vibration present compared with the initial setup?

 

[Simon Bridge]

The weight decreases because of bouyancy. The production off a lot of small bubbles causes a decrease in density this results in an increase in bouyancy.The mass remains the same but the atmosphere does not support the extra gas supply from the effervesence tablet in the same way.
Because the experiment is closed the effect of the tablet is like attaching a helium balloon inside the column resulting in a weight decrease.

Which would also work - except I'd like to see the math.
The system is closed - so one would naively expect that this means the same mass is occupying the same volume before and after release even though CO2 locked into a solid is less dense than released as a gas.
Can you link to an example?

 

[Gh778]

You could mount a mirror on the scale surface and bounce a laser off it to put the spot on a wall some meters away to see if there is much vibration present compared with the initial setup?

I don't have a laser, but could you explain more ?

For vibration, ok when I walk I can see the weight changed, but this cancel if I don't move. At one time there is no bubble moving up in the water (or I can't see it). One "system" has waited the night and I don't watch movement in the water but the weight never change (-0.03g / tab).

If the acceleration of gravity has changed, 2 solids and 2 liquids I use like "references" (I test my balance with "references" before) must changed its weight, but not.

What is an artifact ?

 

[Simon Bridge]

An "artifact" is the name for an erroneous or false reading caused by the way the equipment works or is used ...
http://oxforddictionaries.com/definition/english/artefact
http://en.wikipedia.org/wiki/Artifact_(error )

Have you tried vigorously shaking the container before weighing for the second time?

Does the weight loss stop when new bubbles stop being made?

 

[Gh778]

Have you tried vigorously shaking the container before weighing for the second time?

yes

Does the weight loss stop when new bubbles stop being made?

Yes, but it's not so simple, because new bubbles coming after 2 min but very low number if I compare when the tablet is always there. I stop measuring after 2 min now but like yesterday I have my new system for measuring, I wait this night, and I can say this morning the weight don't change.

If it's an artifact, I would understand how does it works.

 

[Simon Bridge]

I have my new system for measuring, I wait this night, and I can say this morning the weight don't change.

... you need to be clear: do you mean that if you leave the container overnight, there is no weight lost?

 

[Gh778]

no, sorry for me bad english...yesterday I done a measure, the weight decrease -0.03g, I let all the night and the weight don't change in the night, it is always -0.03g in the morning.

 

[Simon Bridge]

No worries - I've had a go trying attract some people who may be able to help you with your quest.
Meantime - did you discover anything that recovered the lost weight? Freezing or something?

 

[Gh778]

did you discover anything that recovered the lost weight? Freezing or something?

I don't have time for this because I focused on Archimedes and diffusion problems. But tomorrow, I will test with new "water->ice->water" cycle and test weight each time. The problem of condensation will be always there. Even if I tested a "simple" bottle of water to see if I weight the good weight.

I appreciate if someone can test and measure weight for have an external point of view with physician knowledge, maybe I forget something in my test.

 

[dlgoff]

IMO gas is escaping. But I'm jumping in here, as safety could be an issue for other experimenters that may read this thread.

https://www.youtube.com/watch?v=nZHGK37jBp8

Need I say more?




Be Safe

 

[Gh778]

Need I say more?

yes, have you read message #36 and see the image ? Because I put tablet in small glass/steal container, and put it in another bigger glass/steel container, I measure the pressure in big container and maybe one or two percent is added. So this don't change the -0.03g I lost

 

[Simon Bridge]

Well you didn't fill the container completely full either.
Outgassing requires that gas escape both walls. But that may happen if the seals are not as good as you think.

Will you show us a video of your setup in progress?

 

[Gh778]

Will you show us a video of your setup in progress?

sure, tomorrow or wednesday

Well you didn't fill the container completely full either.
Outgassing requires that gas escape both walls. But that may happen if the seals are not as good as you think.

It's possible to have diffusion through wall of the first container, but like pressure in the second container is always the same than external pressure, the diffusion through the big container must be near 0.

Have you datas of the diffusion of CO2 through glass and metal function of time and thickness ? Because when I saw the value on internet I don't read big value and something that can gave 0.03g in 2 minutes with 1 g of CO2. And like I said before even there is diffusion, this is the same value with different containers ?