Sciencemadness Discussion Board

Help: Thermometer bizarrity

jgourlay - 19-2-2014 at 09:31

Sorry if this is a double post, but I think my prior attempted errored out.

I have a red ink/dye thermometer where the ink has seperated in the glass. THere is ink in the bulb, a 1 or 2" or so gap, and a line of ink for a few degrees, another gap, and then ink all the way to the small air reservoir in the top.

I've heated it, frozen it. Neither gets all the ink into a contiguous line. Can I fix this? How? Note that I'm assuming that there is no way to get a reading with it this way.

DJF90 - 19-2-2014 at 11:17

You cannot use the thermometer in its current state. There are several ways to fix this, but depends on what you have available.

The first is to cool it in a cryogenic mixture to get all the liquid into the bulb. This has worked for me before using dry ice-acetone.

The second is to heat the thermometer to get everything together. I've seen one "pop" when trying this, so be careful and probably use a heating bath set at a temperature that should just get the liquid level to rise to the top. I'd advise against using a heat gun unless you're very careful.

Some people have reported success by swinging the thermometer in an arc so that the liquid is forced towards the bulb by centripetal action. Be careful not to let go of it and be cautious of your surroundings.

DrAldehyde - 19-2-2014 at 11:46

The swinging method has worked for me. It takes a fair amount of pretty serious whipping motion to get it to work. Of course getting the proper motion going where you are swinging fast enough to cause fluid to move, without starting/stopping so fast that you break the glass is the real trick. Also, make sure you have plenty of clearance. I don't recommend heating, too easy too blow out the end.

jgourlay - 19-2-2014 at 16:32

Thanks all.

subsecret - 19-2-2014 at 18:18

When you swing the thermometer, it might be wise to tie it to a small cord (or use gaffers "Duct" tape as this hold more securely).

I've never used the cryogenic liquid method, but I have successfully removed gaps in the liquid column be heating (With a blowtorch :D). Not to worry, I was fully protected.

The cryogenic liquid approach sounds the most reasonable to me, if you have access to dry ice.

jgourlay - 19-2-2014 at 19:13

Thanks guys, worked well.

zig - 20-2-2014 at 18:17

My thermometer pulled the same stunt today. DrAldehyde isn't exaggerating- it takes some seriously violent whipping to clear things up!

What causes this to occur? My thermometer is Hg, so it doesn't seem liquid-type-dependent.

Artemus Gordon - 25-2-2014 at 15:52

If I were to try the whipping trick, I'd make a holder for the thermometer from half-inch PVC pipe and a couple of corks held in with duct tape. Or, if you want to get fancy, you can buy PVC end caps to fit the pipe and use plumber's PVC cement to glue on the bottom cap. This way you remove the risk of snapping the thermometer while whipping it, and you have a decent holder to store it in after you fix it.