Lab Thermometer

Just a quick b* note:

I was having trouble figuring out how two different mercury thermometers could be off by 2-3 degrees... for months now I just was assuming that my NON-lab thermometer was incorrect. I have been using this thermometer for brewing for the last 18 years.

I just noticed last night that a little glob of mercury (exactly 2 degrees) in my lab thermometer has "broken away" from the rest of the mercury and is at the very top of the thermometer. So, when the temp goes up the air pressure pushes the small glob up away from the main mercury and the opposite when the temp goes back down. So, I never get a correct reading from my lab thermometer.

I am thinking about ditching it all together expect for periodic calibrations. The thought of breaking it and mercury going all other the place freaks me out - I seem to have bad luck breaking hydrometers. Does anyone remember when hydrometers were like $40 bucks?

There are several things you can try to your seperated thermometer (usually one of them will work):

Drop it vertically onto a soft cloth or padded surface, you may have to do it several times.

A magnet.

Put it in the freezer over night, when you remove it stand it upright.

Putting it in the freezer works. I had this happen all of the time when I was working in the lab.

atarlecky said:

I am thinking about ditching it all together expect for periodic calibrations. The thought of breaking it and mercury going all other the place freaks me out - I seem to have bad luck breaking hydrometers. Does anyone remember when hydrometers were like $40 bucks?

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Ding, ding, ding! This is what I would do. You can get a decent digital thermometer for easily less than $20 probably closer to $10. No need to risk exposing you or your family to mercury.

Thanks for all of your responses. I think I will use the freezer thing... I just bought a digital thermometer from Target and I'll use the lab thermometer just for periodic adjustments.

Here's how we roll in the ghettos of Encino, thermometer-wise...behold, my Meat-Tun! I like my mash medium-rare.

I checked it against my electronic thermometer throughout the mashing range, and it's pretty accurate.

BlindLemonLars said:

Here's how we roll in the ghettos of Encino, thermometer-wise...behold, my Meat-Tun! I like my mash medium-rare.

I checked it against my electronic thermometer throughout the mashing range, and it's pretty accurate.

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That's funny...

Remember that "lab thermometers" are not necessarily more accuracy than non-lab thermometers. In fact, lab thermometers are usually calibrated every 4-6 months to ensure proper operation... and will often be inaccurate without frequent recalibration.

Jack said:

Remember that "lab thermometers" are not necessarily more accuracy than non-lab thermometers. In fact, lab thermometers are usually calibrated every 4-6 months to ensure proper operation... and will often be inaccurate without frequent recalibration.

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How is that possible? It's a closed mercury thermometer. As far as I know - I can't calibrate it.

In any case... I tried the freezer thing and it didn't work, so what I did was immediately stick it into boiling water. This forced the mercury glob to the top empty bulb where it appears to have started dissipating back into the rest of the mercury.

Lab thermos are more accurate than dial or electric thermos because they are closed systems that operate on the physical properties of expansion. As long as you are using it at a constant elevation, the readings will be constant and accurate.