Sciencemadness Discussion Board

"Broken" thermometre

sumatra - 23-10-2018 at 09:50

So I had a lab incident recently, I didn't have any mineral oil on hand so I used cooking oil for an oil bath. However it caught fire, I managed to get everything under control and after I cleaned my glassware I noticed that my alcohol thermometre (-10 C/200 C) has little gaps in the alcohol column (see image below). It does not appear to be broken anywhere and upon heating and cooling the gaps do not dissapear. I haven't tried heating untill everythimg reaches the bulb at the top yet.
Is this fixable and will the thermometre be accurate afterwards?

IMG_20181023_204948.jpg - 800kB

unionised - 23-10-2018 at 10:50

I'd try cooling until everything is in the bulb at the bottom before I tried heating it.
It might be OK afterwards- the only way to know is to test it.
Testing in ice, and in boiling water will give you a pretty good idea if it is right.

happyfooddance - 23-10-2018 at 13:16

Sometimes those gaps can be gotten rid of by condensing everything into the bulb with dry ice, or this and a combination of careful warming on the rest of the thermometer. It's also very easy to break a thermometer attempting this so proceed at your own risk.

DrP - 24-10-2018 at 03:00

I'd say gently tapping might release it - but I don't want to risk breakage. What about vigorous shaking? Will that dislodge it?

Sulaiman - 24-10-2018 at 04:23

My score so far: two fixed and one exploded.

The length of stem between 0 and the bulb indicates that a very low temperature will be required to force all of the liquid into the bulb,
maybe even colder than dry ice.
I did not have a low enough temperature source to try with mine.

I have 'repaired' a mercury thermometer by CAREFULLY heating the bulb until the gap entered the small bubble at the end of the stem.
The liquid then forms a continuous thread on cooling ... one fixed thermometer :)

This is also how I 'exploded' a different mercury thermometer :(

The thermometer in the photograph has so many breaks in the thread that I suspect that neither cooling nor heating will easily fix it.

I agree with DrP that tapping may work,
I'd hold the thermometer vertically above a piece of wood (or hard plastic) and release it and catch it after the bounce,
start about 1cm above the wood and repeat and increase height until the thermometer is either repaired or broken :P

I think that the bulb should hit the wood with the stem as vertical as practical for even stress on the bulb..

DrP - 24-10-2018 at 04:48

Quote: Originally posted by Sulaiman  


I'd hold the thermometer vertically above a piece of wood (or hard plastic) and release it and catch it after the bounce,
start about 1cm above the wood and repeat and increase height until the thermometer is either repaired or broken :P

I think that the bulb should hit the wood with the stem as vertical as practical for even stress on the bulb..


I re-agree - this is what I'd try - as long as you are aware that breakage is a real and likely event.... I'll guess the results will be similar to what you have tried already with 2 fixes to every 1 breakage or so. Good luck! :D

vmelkon - 26-10-2018 at 03:50

Instead of heating the bulb to make the alcohol rise to the top, couldn't you heat the upper part of the thermometer to vaporize that little section of alcohol?

I guess this will increase the pressure inside and might cause breakage. You probably should not overheat. You don't want to reach the boiling point of the alcohol.

phlogiston - 26-10-2018 at 04:43

How about centrifuging?
I'd try putting it in a (plastic) test tube attached to a rope and swing it around.
If you can generate enough g-force, it might pull the alcohol down towards the bulb.

Ubya - 26-10-2018 at 05:10

Quote: Originally posted by phlogiston  
How about centrifuging?
I'd try putting it in a (plastic) test tube attached to a rope and swing it around.
If you can generate enough g-force, it might pull the alcohol down towards the bulb.



The alcohol expands due to thermal expansion, making it to contract centrifuging it wouldn't work. Try compressing water by just spinning it... Same idea

Metacelsus - 26-10-2018 at 10:48

I think Phlostigon intends for centrifugation to move the separated part down towards the rest of the alcohol, not actually compress the alcohol. This might work but I would be careful since thermometers are fragile.

phlogiston - 26-10-2018 at 11:48

Yes, exactly.
And now that we talk about this, it seems to me that the -gas bubbles- will be able to compress a little due to the increased force of the alcohol above them. If they get small enough, that may also aid in allowing the separated alcohol to get past the air bubbles and join the larger mass.

As with all the above methods, you risk cracking it.
Perhaps supporting the thermometer in a tube filled with sand as you centrifuge it may help it survive.

j_sum1 - 26-10-2018 at 19:57

Put the end in a hot flame and seal the glass.
It is always useful to have another stirring rod. :P

Ubya - 27-10-2018 at 12:28

Quote: Originally posted by j_sum1  
Put the end in a hot flame and seal the glass.
It is always useful to have another stirring rod. :P

maybe this only if it breaks;)