Mercury separated in thermometer

[al olson]

Anyone,

I bought a mercury darkroom thermometer several weeks ago on ebay. I wanted to use it to calibrate my other thermometers. Unfortunately, the mercury column is separated with a space of about 15 degrees between the main column and a 4 degree piece.

Would anyone know how I can rejoin the separated piece back to the main column?

I tried placing it in the freezer, hoping to suck all the mercury into the bulb. That didn't work. I've tried shaking it like we used to do with the old medical thermometers. That did not help either.

I am considering putting the thermometer in a pan of hot water -- boiling perhaps? -- to see if the pressure will cause the mercury will rejoin, but I am afraid of creating too much pressure that it will blow out the end of the thermometer.

Is there anyone who has had experience with this problem?

Your help is appreciated. Thank you!

[Brian Ellis]

I had the same thing years ago. Put it in boiling water.

[Eric Woodbury]

I've done this two ways. One is to freeze the thermometer. Used freon 'dust off' when it was still freon. Don't know if the new stuff is cold enough. The other way to freeze is liquid nitrogen, if you have a source.

The second way to get the column together is the same way it got apart. Shake it down as best you can and then tap and vibrate it. It should go together.

[Kevin Crisp]

Put it in hot water and watch the column rise. When it comes back together pull it out. If it goes up to the very top and you don't time it right on taking it out of the heat, it will shatter. You want it to just touch the top if it needs to go all the way up there, usually it comes together sooner. This probably happened in shipping.

[John Cahill]

Put the bulb in a glass filled with cracked ice and salt. That often does it.
Anscojohn, Mount Vernon, Virginia, USA

[Bob Jones]

One source of extreme cold that is somewhat easier to come by than liquid nitrogen is dry ice in denatured alcohol.

I'd only consider boiling if the range of the thermometer includes 100C, for a darkroom thermometer it might not. Either way, since you will be dealing with temps at the extremes of the thermometer's range, make the changes gradual and avoid thermal shocks which can shatter the glass. For example, put the thermometer into the alcohol and then add the dry ice.

[Donald Qualls]

Worth noting that a mercury thermometer will freeze solid at -40 (either F or C, all same); no need for anything colder than dry ice, though the liquid I recall being recommended to go with that was acetone rather than ethanol (don't recall the freezing point of ethanol, but I'm pretty sure it's above -100 F, which is about where dry ice can take the liquid bath). Worth noting that my local grocery store sells dry ice, and acetone is easily obtained at home improvement stores as a solvent. Cracked water ice and salt can only go to, at a minimum, about 25 F, which is probably well above the minimum indication on a thermometer made for darkroom use.

In keeping with Bob's advice, you'd want to put the thermometer into room temperature liquid and then add the dry ice (carefully -- the dry ice can shatter from thermal shock, or spit pieces of water ice that have formed on it by sublimation from the air). And you'll want to keep ONLY the bulb in the acetone; does no good to freeze the slug of mercury in the column.

My experience is that freezing does a poor job of rejoining a separated thermometer column, but heating must be done very carefully; it's tempting to suggest contacting the vendor about a replacement (especially if you paid lab grade prices for the mercury thermometer). If they can't pack them to survive shipping in a usable state, perhaps they oughtn't to sell them over the Internet...

[Alan Davenport]

...don't recall the freezing point of ethanol, but I'm pretty sure it's above -100 F...

Actually, it's –114.1°C, so we're good to go here. For reasonably pure ethanol, a fifth of Everclear would suffice, and after it's rewarmed to a reasonable temperature -- use the thermometer -- you can always dispose of the evidence in an environmentally sound way...

[Donald Qualls]

For reasonably pure ethanol, a fifth of Everclear would suffice, and after it's rewarmed to a reasonable temperature -- use the thermometer -- you can always dispose of the evidence in an environmentally sound way...

It'd take me a long time to dispose of a fifth of Everclear, but at least the dry ice won't hurt it any -- just make sure all the dry ice is sublimated before you try to dispose of the Everclear...

[al olson]

Thanks all for your help.

Alan, why waste the Everclear on a project like this. Everclear is for hockey games when it's 40 below. Used to buy it by the pint and hide it in my buffalo coat because it was illegal to have it on campus. Never had a problem disposing of it.

Actually I solved the thermometer problem today. The thermometer scale goes up to 130 deg F, and there is about another 5 degrees left in the tube. I heated some water to 160 and placed the thermometer in the water, giving it time to reach the top.

Problem solved. I was able to work all afternoon in the darkroom, using it to check against my Jobo and to adjust a couple of mechanical thermometers as well.

Boiling point in these parts is kind of wimpy anyway, something like 196 degrees I am told. I am not used to the scalding temperature of coffee when I am at sea level and have the blisters to prove it.

Kevin, I believe you're right. My guess is that the problem was caused by rough handling by USPS.

Thanks again, next time I might try the dry ice.