Mercury thermometer recommendation?

Kino · May 23, 2023

This is by no means a dismissal of Mercury's toxicity, but as kids a few of my friends and myself used to bike back to an certain oil field vent line near a prominent hill in our vicinity to collect same to sell to our Grade School Science Teacher. He paid us $5 a pop bottle full, which we raked out of the vent pipes with sticks. We averaged 2 bottles every few weeks and, yes, we did play with it a bit, but we knew at least to wash our hands and not to get it near our mouth or eyes.

Don't think I would do that again, but it did happen in a less informed time...

Cholentpot · May 23, 2023

During peak lockdown I needed an accurate thermometer. The forehead scanners were no good, my oral had run out of batteries. I realized it would be good to have a backup that didn't need electricity. It was then I learned you can't buy one anymore and the replacement blue stuff ones are really not very good.

I'd like to find an old accurate mercury oral thermometer.

Radost · May 23, 2023

Cholentpot said:
During peak lockdown I needed an accurate thermometer. The forehead scanners were no good, my oral had run out of batteries. I realized it would be good to have a backup that didn't need electricity. It was then I learned you can't buy one anymore and the replacement blue stuff ones are really not very good.

I'd like to find an old accurate mercury oral thermometer.

Bunch of kodaks on EBay.
Just got 2

Radost · May 23, 2023

Kino said:
This is by no means a dismissal of Mercury's toxicity, but as kids a few of my friends and myself used to bike back to an certain oil field vent line near a prominent hill in our vicinity to collect same to sell to our Grade School Science Teacher. He paid us $5 a pop bottle full, which we raked out of the vent pipes with sticks. We averaged 2 bottles every few weeks and, yes, we did play with it a bit, but we knew at least to wash our hands and not to get it near our mouth or eyes.

Don't think I would do that again, but it did happen in a less informed time...

USA has huge amount of lead pipes to this day…
So many environmental disasters. Pollution from cars and industry.

Radost · May 23, 2023

Cholentpot said:
During peak lockdown I needed an accurate thermometer. The forehead scanners were no good, my oral had run out of batteries. I realized it would be good to have a backup that didn't need electricity. It was then I learned you can't buy one anymore and the replacement blue stuff ones are really not very good.

I'd like to find an old accurate mercury oral thermometer.

If a mercury thermometer is manufactured right and tested it should be 100% accurate.
I doubt Kodak “or any other mercury thermometer manufacturers” were salling faulty thermometers.

Cholentpot · May 23, 2023

Radost said:
Bunch of kodaks on EBay.
Just got 2

Should have thought of that.

I grew up with them things. Never done me nothing wrong those didn't.

Agulliver · May 24, 2023

Brendan Quirk said:
Mercury thermometers can vary in accuracy by several degrees, although precision (reproducibility) is good. I used to calibrate our lab mercury thermometers against special traceble (NIST) thermometers, so we would know what to add or subtract to get an accurate reading. Therefore, do not assume a mercury thermometer is accurate, but it probably is reproducible.

I was coming here to say something very similar. Mercury thermometers have a very long lifetime as long as you don't drop them or heat them beyond their intended range. Decades. But the accuracy must first be determined by calibrating. If you're able to do this (eg, try a range of temperatures across the operating range and compare to a known accurate thermometer) then you're good to go with mercury.

The more modern spirit (alcohol) thermometers are, these days, pretty much as accurate but are more prone to split strands of liquid. This is usually recoverable but a hassle. Digital thermometers, generally you get what you pay for. They too can need calibrating against a known thermometer.

Got to say, the longest lasting, accurate thermometers I use in lab work are mercury. But we've switched mostly over to spirit thermometers just from a toxicity point of view. However, do note that one broken mercury thermometer isn't going to do you any harm even if you did decide to be silly and drink the contents. In my line of work, students typically break several thermometers every year and I have to keep a special vessel for their disposal.

Besk · May 24, 2023

Sirius Glass said:
If the Mercury separates, shake it down and/or heat it up to get the parts together.

Just be careful heating it up - too much and the expanding mercury will break the glass.

I store my Kodak upright.

guangong · May 24, 2023

Another use of Kodak thermometer. Can’t remember how many decades ago that I bought it. Still store it in original cardboard tube.

xkaes · May 24, 2023

Consistency is more important in a thermometer than accuracy -- just like everything else we do in processing.

Donald Qualls · May 24, 2023

The preferred alternative for above-freezing measurements where a liquid metal thermometer is preferred for some reason is galinstan -- this is an alloy of gallium, indium, and tin with a melting point of -19C. The metal is FAR less toxic than mercury, meaning almost all current manufacture liquid metal thermometers use this in the core now instead of mercury. Only if you need to measure temperatures between -19 and -40 C and still need a metal thermometer would you need mercury.

Radost · May 24, 2023

Agulliver said:
I was coming here to say something very similar. Mercury thermometers have a very long lifetime as long as you don't drop them or heat them beyond their intended range. Decades. But the accuracy must first be determined by calibrating. If you're able to do this (eg, try a range of temperatures across the operating range and compare to a known accurate thermometer) then you're good to go with mercury.

The more modern spirit (alcohol) thermometers are, these days, pretty much as accurate but are more prone to split strands of liquid. This is usually recoverable but a hassle. Digital thermometers, generally you get what you pay for. They too can need calibrating against a known thermometer.

Got to say, the longest lasting, accurate thermometers I use in lab work are mercury. But we've switched mostly over to spirit thermometers just from a toxicity point of view. However, do note that one broken mercury thermometer isn't going to do you any harm even if you did decide to be silly and drink the contents. In my line of work, students typically break several thermometers every year and I have to keep a special vessel for their disposal.

What happens to mercury after decades?

xkaes · May 24, 2023

It drifts.

Radost · May 24, 2023

xkaes said:
It drifts.

Please explain.

Kino · May 24, 2023

xkaes said:
It drifts.

I have more faith in mercury than cheap digital circuits.

To each their own...

xkaes · May 24, 2023

titrisol said:
Mercury thermometers drift over time, and need maintenance (and can break)

Radost said:
Please explain.

You'll have to ask titrisol -- but perhaps he has drifted away with the mercury.

BobUK · May 24, 2023

titrisol said:
In this day and age a digital thermometer is a better investment.
Mercury thermometers drift over time, and need maintenance (and can break)

I buy type K thermocouples from Omega and have a Fluke 51 reader that is calibrated easily.

I was given an expensive digital thermometer by a lab chemist. The instruction leaflet said it would be guaranteed accurate for two years. After around eighteen months it was way out, useless, even with new batteries.

So how do you know your mercury is faulty and it is not the digital?

What do you test it on, and how?

The only spirit thermometer that I use is small five inch one kept in the corner of the print developer dish.
Spirit is good enough for my printing.

An interesting short article link to darkroom thermometers.

Radost · May 24, 2023

I only have former communist high school chemistry knowledge but i am sure that nothing changes the structure of mercury.

Radost · May 24, 2023

BobUK said:
I was given an expensive digital thermometer by a lab chemist. The instruction leaflet said it would be guaranteed accurate for two years. After around eighteen months it was way out, useless, even with new batteries.

So how do you know your mercury is faulty and it is not the digital?

What do you test it on, and how?

The only spirit thermometer that I use is small five inch one kept in the corner of the print developer dish.
Spirit is good enough for my printing.

An interesting short article link to darkroom thermometers.

The video does not apply to c41. The only reason for a very accurate thermometer os for c41 development.

titrisol · May 24, 2023

xkaes said:
You'll have to ask titrisol -- but perhaps he has drifted away with the mercury.

Mercury in Glass (MiG) thermometers are fine as long as you don;t move, they are treated carefully and you make sure there are no air bubbles.

They have been the workhorse for a long time and they are fun to play with.
In industry MiG thermometer calibration was a big deal; in the 80s and 90s we had to take them to the university to be recertified every year; FDA and USDA requirements were in the same line. That meant 2-3 days of shutdown as the thermometers had to be carefully taken out of their cages, packed and driven there... where we had to wait until they were done.
I kept one or two carefully which I could use as reference afterwards and compared them to the recertified thermometers from time to time. However, after moving several times I found MiG thermometers problematic, in my last move from Europe to the US I wasn't allowed to bring them with me anymore.

In the early 2000s industry moved to electronic sensors (thermocouples and RTDs) which are as sensitive, easier to calibrate and drift a lot less so I moved on as well.
Thermocouples are more sensitive, have less mass (thermal Inertia) and are sturdier
I like type K or J which are great for the 0-100C temp range; and have Fluke meters.
Calibrate the meters every 2-3 years with an ice bath (triple point cell) and good to go (mine are still good since 2009)

xkaes · May 24, 2023

Radost said:
The video does not apply to c41. The only reason for a very accurate thermometer os for c41 development.

A thermometer does not need to be accurate for B&W or COLOR work. It just needs to be consistent.

Just because a developer recommends 95° doesn't mean that the chemicals have to be absolutely at 95.00000°. Is 94.5° OK? How about 94.9°?

You can use 93° if you want. The important thing is to run a test first -- and then always be consistent -- regardless if your thermometer is reading 95.00000° as 94° or 96°.

DREW WILEY · May 24, 2023

Get the real deal and be done with it : a Kodak Process Thermometer. These were individually certified, just like all true scientific lab thermometers. Even if you use cheaper thermometers or even an electronic one, you should have one of these on hand as a reference. But it's the only option I now use. Electronic ones proved to be a headache. The problem with lax mentalities is that little errors tend to add up and compound each other, and then you end up not knowing which stage of the overall process to blame when something goes wrong. But in this case, thermometer consistency per se, session to session, is the most important factor.

BobUK · May 24, 2023

A few of my mercury thermometers have engraved on the back "76mm immersion" etc.
One reads "total immersion"

Apart from me, does anyone take any notice of these instructions.

Radost · May 24, 2023

xkaes said:
A thermometer does not need to be accurate for B&W or COLOR work. It just needs to be consistent.

Just because a developer recommends 95° doesn't mean that the chemicals have to be absolutely at 95.00000°. Is 94.5° OK? How about 94.9°?

You can use 93° if you want. The important thing is to run a test first -- and then always be consistent -- regardless if your thermometer is reading 95.00000° as 94° or 96°.

Not really. From what I have researched C41 is designed to work at 38 ± 0.15°C (100.5 ± 0.25°F).
I have gotten strange color shifts being .5 .7C off. Also when it starts at 100F and ends at 98F.

DREW WILEY · May 24, 2023

Depends on what you mean by color photography. Making consistently matched color separations via black and white film might ideally demand tolerances within plus or minus 1/10th F. I actually have a thermoregulator capable of that kind of accuracy. But I rarely need it. And it in turn needs to be calibrated using a truly trustworthy, accurate thermometer, not some cheap toy thing.

Ordinary RA4 processing, just like Cibachrome of the past, can easily tolerate plus or minus 3 degrees, though I have always kept it tighter than that. With routine black and white film developing, I just use one of those Zone VI compensating developing timers with its water jacket probe. As long as I start out a little above 20C, any drift down in water temp seems to be correctly factored in.

Mercury thermometer recommendation?

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