Sciencemadness Discussion Board

Water based barometer?

White Yeti - 15-3-2012 at 14:58

Hello everyone.

I've always wanted to make a barometer but never got around to it because I didn't really feel like messing around with mercury.

A barometer can be made with any fluid, so long as the column is tall enough to contain all the fluid necessary to exert a pressure of 1atm.

So, if you were dedicated enough, you could make a barometer with water. In fact, a water based barometer would have 13x the resolution of a mercury barometer which would lead to more accurate readings.

But in order to make such a barometer, I'd need a 10m long glass tube...

I was wondering if part (or all) of such a tube can be substituted for polyethylene tubing, because I don't think there is a place on earth that sells such tubes to amateurs. Plastic tubing also works to my advantage, since I can twist the tube up through my basement window so it can reach up to a second story window.

I measured the distance from the bottom of my basement to a window on the second floor, and I can definately accomodate a 10m long plastic tube (although I don't know if other people will tolerate such an instalment:D).

There are a few problems I have to solve before setting off:

I realised that I might have problems with water freezing during the winter. I can add a solute that would decrease the freezing point, but the vapour pressure of the water would be different and calibration would be a nightmare.

Is there something I can add to water to significantly decrease freezing point but leave vapour pressure essentially unchanged?

Temperature would be an issue for calibration, but so long as I remember to set up a few thermometers to measure water temperature and the temperature of the air, I should be fine.

Speaking of calibration, how do you guys suggest I calibrate this 10m monstrosity?

Above all, I need to know if plastic tubing can be used for the whole barometer, or at least the bottom part, whereas the top would be fitted with a glass tube of some sort to take accurate readings (accounting for the meniscus and so forth).

Any thoughts?

[Edited on 3-16-2012 by White Yeti]

Endimion17 - 15-3-2012 at 16:32

Quote: Originally posted by White Yeti  
Hello everyone.


Hello. °-°

Quote:

So, if you were dedicated enough, you could make a barometer with water. In fact, a water based barometer would have 13x the resolution of a mercury barometer which would lead to more accurate readings.


Not really, because the vapor pressure of water is a lot higher than of mercury and changes a lot with the temperature changing. There wouldn't be near vacuum in the upper part. It would be a very crude, inefficient and incorrect barometer, but it would be a a nice baroscope.

Quote:

But in order to make such a barometer, I'd need a 10m long glass tube...I was wondering if part (or all) of such a tube can be substituted for polyethylene tubing, because I don't think there is a place on earth that sells such tubes to amateurs. Plastic tubing also works to my advantage, since I can twist the tube up through my basement window so it can reach up to a second story window.


Glass is unneccessary and such tube would snap under its own weight. It can be any tube that doesn't leech air, for example flexible plastic tubing for gardening. The part where the meniscus will go up and down through the week can be made out of glass because plastic tubing gets opaque as time goes by.

Quote:

I realised that I might have problems with water freezing during the winter. I can add a solute that would decrease the freezing point, but the vapour pressure of the water would be different and calibration would be a nightmare.


Calibration would be a nightmare even with regular water. Such device would require constant monitoring of air temperature and every measuring would take some hefty calculations to get the reading.

Dr.Bob - 15-3-2012 at 18:34

I don't think plasric would work, as most plastics are permeable to air, water vapor or other chemicals, so air would slowly leak into the tube. Also, once the water dropped to form a vacuum, the tubing would collapse unless fairly thick. A glass rod would be fine, but you would have to clamp it out to hold the weight. The best way is to put up pieces starting at the top, which is best sealed, and then keep joining on new pieces until you get to the bottom. Then pull a high vacuum on it, via some rubber tubing with a 3 way stopcock, and then turn the stopcock to allow water to flow into the tube. I would try it in the summer. It might be that with a solution of a heavy metal salt, you could increase the density enough to make it much shorter. I think that there are some tungstate salts with solution densities above 2.5. (just google LST, SPT or LMT). But other simpler salts might work fine as well. It is certainly a good example of empirical science to test.

Morgan - 15-3-2012 at 19:36

Some water in tubes tidbits, perhaps not perfect but points to ponder.

"But even the best vacuum pump can pull water up to a height of only 34 ft (10.4 m) or so. This is because a column of water that high exerts a pressure of ~15 lb/in2 (103 kilopascals, kPa) just counterbalanced by the pressure of the atmosphere. How can water be drawn to the top of a sequoia (the tallest is 370 feet [113meters] high)? Taking all factors into account, a pull of at least 270 lb/in2 (~1.9 x 103 kPa) is probably needed."
"The answer to the dilemma lies the cohesion of water molecules; that is the property of water molecules to cling to each through the hydrogen bonds they form."

"The rattan vine may climb as high as 150 ft (45.7 m) on the trees of the tropical rain forest in northeastern Australia to get its foliage into the sun. When the base of a vine is severed while immersed in a basin of water, water continues to be taken up. A vine less than 1 inch (2.5 cm) in diameter will "drink" water indefinitely at a rate of up to 12 ml/minute.
If forced to take water from a sealed container, the vine does so without any decrease in rate, even though the resulting vacuum becomes so great that the remaining water begins to boil spontaneously."
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xyl...

http://www.youtube.com/watch?v=sz9eddGw8vg

"The tube I used was 6.5mil strong nylon, the type used in the brewery trade."
http://www.bio.net/bionet/mm/ag-forst/2000-March/015058.html

"To maintain a continuous column, the water molecules must also have a strong affinity for one other. This idea is called the cohesion theory. Water does, in fact, exhibit tremendous cohesive strength. Theoretically, this cohesion is estimated to be as much as 15,000 atmospheres (atm). Experimentally, though, it appears to be much less at only 25 to 30 atm. Assuming atmospheric pressure at ground level, nine atm is more than enough to "hang" a water column in a narrow tube (tracheids or vessels) from the top of a 100 meter tree. But a greater force is needed to overcome the resistance to flow and the resistance to uptake by the roots. Even so, many researchers have demonstrated that the cohesive force of water is more than sufficient to do so, "
http://www.scientificamerican.com/article.cfm?id=how-do-larg...


[Edited on 16-3-2012 by Morgan]

bquirky - 15-3-2012 at 23:30

this may be of interest


http://en.wikipedia.org/wiki/Bert_Bolle_Barometer

The Bert Bolle Barometer is a large water barometer. At over 12.5 metres tall, it is recognized as the largest barometer in the world by The International Guinness Book of Records.[1] The instrument was created in 1985 in the Netherlands, in 2007 it was reinstalled in the new Visitor Centre of Denmark, Western Australia and was removed from there in 2011.


Endimion17 - 16-3-2012 at 08:33

Plastic tubing such as this one and this one most certainly wouldn't collapse. It's PVC and it's thick. The only problem is that is gets opaque after few months of tap water contact. That's why the part with the meniscus is should be extended with glass tubing.

Regarding the very slow air leeching process, oh well. It's inevitable.

[Edited on 16-3-2012 by Endimion17]

Morgan - 16-3-2012 at 09:20

I wonder if you used a somewhat narrow, thick plastic tube about 5mm inside diameter or so and some unusual material that would have a like cohesive force equal to the affinity that water has to itself, if you could hold the height of water to a greater degree than ~33 feet? That is, at the very top of your tube have a material that "bonds" to water as strongly as water adheres to itself, if such a material exists.

"The reason a loop of tubing succeeds where a single tube fails is because the cohesive bond of water molecules is far stronger than the adhesive qualities of water observed in Galileo's lift-pump problem. Using a loop of tubing enables water molecules to bond to each other in an unbroken chain."
http://www.bio.net/bionet/mm/ag-forst/2000-March/015058.html

watson.fawkes - 16-3-2012 at 10:32

You can get rid of the bulk of air infiltration by using PEX-Al-PEX tubing. PEX is cross-linked polyethylene, and this tubing has an internal layer of aluminum foil. This product is manufactured for closed-loop hydronic heating systems, where air entrainment would have all sorts of problems.

If you do this, you'll want a transparent section. The bulk of borosilicate glass produced is either 4 feet or 1.5 m, which should be adequate for most atmospheric variation.

White Yeti - 16-3-2012 at 13:38

Thanks for the feedback.

For filling up the tube, I was considering sealing the bottom shut and then pouring water through the top end, filling from bottom to top. Using a vacuum pump is just silly.

One thing I was considering was if the air dissolved in the water were to come out of solution (as it always does) it would form an air bubble at the top, filling whatever vacuum (albeit partial) I could have gotten from constructing such a barometer. With this in mind, talking about air leeching through plastic tubes is really quite silly in the grand scheme of things.

I understand that water has a vapour pressure, so does mercury. As long as its vapour pressure is not ignored, the pressure can be calculated accordingly to account for it.

The purpose of this post was to open discussion on how to make barometers. Sure you can buy one, but making one is probably much more fulfilling. I also know I can throw one together in 3 seconds and it will give me an estimate if air pressure, but what about making a barometer so sensitive that it can show whether the pressure in increasing or decreasing in real time?

Morgan - 16-3-2012 at 15:40

Here's a very crude device as is but perhaps with a modification or an extension, one could adapt the shape in a clever way. Just some left field stuff.

"If you keep the temperature constant, the water level will measure the air pressure. Keep the air pressure contant, and you'll measure temperature."
http://www.kleinbottle.com/barometer.htm

Various glass Klein bottle shapes ...
https://www.google.com/search?q=klein+bottle+flickr&hl=e...

[Edited on 17-3-2012 by Morgan]

dann2 - 16-3-2012 at 19:29


There will be air coming out of the water for ages. You would want to store the water under a vacuum (or and boil it) to get rid of dissolved air.
Consider using oil (vacuum oil if you can get it) as it will have a lower vapour pressure.

Dann2

johansen - 16-3-2012 at 21:11

a few inches of oil on top of the water column may be sufficient to prevent sudden changes in water vapor pressure due to temperature changes from affecting the barometer, however it will not prevent any dissolved gasses from exiting the water.

btw, you don't need 31 feet of water to watch the pressure change.
simply take a bottle and put an air lock on it. (the kind used for brewing)

Morgan - 3-3-2020 at 18:15

Quote: Originally posted by Morgan  
Some water in tubes tidbits, perhaps not perfect but points to ponder.

"But even the best vacuum pump can pull water up to a height of only 34 ft (10.4 m) or so. This is because a column of water that high exerts a pressure of ~15 lb/in2 (103 kilopascals, kPa) just counterbalanced by the pressure of the atmosphere. How can water be drawn to the top of a sequoia (the tallest is 370 feet [113meters] high)? Taking all factors into account, a pull of at least 270 lb/in2 (~1.9 x 103 kPa) is probably needed."
"The answer to the dilemma lies the cohesion of water molecules; that is the property of water molecules to cling to each through the hydrogen bonds they form."

"The rattan vine may climb as high as 150 ft (45.7 m) on the trees of the tropical rain forest in northeastern Australia to get its foliage into the sun. When the base of a vine is severed while immersed in a basin of water, water continues to be taken up. A vine less than 1 inch (2.5 cm) in diameter will "drink" water indefinitely at a rate of up to 12 ml/minute.
If forced to take water from a sealed container, the vine does so without any decrease in rate, even though the resulting vacuum becomes so great that the remaining water begins to boil spontaneously."
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xyl...

http://www.youtube.com/watch?v=sz9eddGw8vg

"The tube I used was 6.5mil strong nylon, the type used in the brewery trade."
http://www.bio.net/bionet/mm/ag-forst/2000-March/015058.html

"To maintain a continuous column, the water molecules must also have a strong affinity for one other. This idea is called the cohesion theory. Water does, in fact, exhibit tremendous cohesive strength. Theoretically, this cohesion is estimated to be as much as 15,000 atmospheres (atm). Experimentally, though, it appears to be much less at only 25 to 30 atm. Assuming atmospheric pressure at ground level, nine atm is more than enough to "hang" a water column in a narrow tube (tracheids or vessels) from the top of a 100 meter tree. But a greater force is needed to overcome the resistance to flow and the resistance to uptake by the roots. Even so, many researchers have demonstrated that the cohesive force of water is more than sufficient to do so, "
http://www.scientificamerican.com/article.cfm?id=how-do-larg...


[Edited on 16-3-2012 by Morgan]


Thoughts on negative pressures and preventing cavitation, maybe of interest.

Capillary-driven desalination in a synthetic mangrove
https://advances.sciencemag.org/content/6/8/eaax5253

B(a)P - 3-3-2020 at 23:57

I actually own a very crude one, but it is a good indicator of rising and falling pressure.

[Edited on 4-3-2020 by B(a)P]

IMG_20200304_185807.jpg - 3.4MBIMG_20200304_185804.jpg - 3.8MB

Sulaiman - 4-3-2020 at 01:02

I have a diy Hg u-tube manometer made from two 1.5m long 9mm id borosilicate tubes that can be used as a barometer,
but I bought two used domestic aneroid barometers for a few pounds (inc. p&p) each via eBay.

Unless you are doing something extremely sensitive to atmospheric pressure,
domestic aneroid barometers are accurate enough for common corrections such as b.p. of liquids.

Calibrating your aneroid barometer to read absolute pressure at your lattitude and altitude needs a little effort.
(one of my barometers was corrected for true/absolute atmospheric pressure,
one shows the weather forecast pressure)
(I chose a nice model for the absolute pressure indicator, adjusted it, used it for about a month, then dropped it onto a concrete floor)

I had considered a vacuum pump oil based manometer/barometer but the height is impractical.
(except maybe as a low pressure manometer vs. vacuum)

Along with the relatively high vapour pressure and thermal expansion of water,
another problem is ... water freezes
Here in Malaysia not a problem,
in UK etc. antifreeze may be required - modifying the vapour pressure and density.
doable ... but why ?

macckone - 4-3-2020 at 11:30

If you really want a liquid barometer, there are gallium liquid metal mixes that are commercially available.
Then you can make a barometer of reasonable size, 60 inches or so. (less than 2M).
One example is below (overpriced). You can get even lower MP with a Ga-In-Sn-Zn mix.

https://www.bonanza.com/listings/20-Grams-Liquid-Metal-Alloy...