I am looking for one of these lab-grade units, calibrated in Celsius.

The choices are many. I've had a few alcohol based ones but sometimes the pink stuff doesn't want to come all the way to the bottom, making it useless. (Had that happen in a 6" camping unit. It is a cheap Taiwan thing and I tried boiling it, freezing but the pink stuff is still not in one place, broken apart)

Are the older Mercury types any more accurate and reliable?

I do know they are pretty dangerous if broken, you may contaminate the whole room, inhaling dangerous fumes for years in worse case scenario.


I am looking at a few 12" ones ranging from -20 to 100C. Although I could get the hang-on-the-wall type if I could get the same range--- but they tend to be a lot shorter, harder to read due to smaller incremenets and usually in F. I want an increment for each degree.

 

Radio Shack has some electronic ones, get out of the stone age.

I made one out of some thermocouple wires and measured the inside of my fireplace. I think it was about 1200 degrees.

 

What is it you want to do with this thermometer (besides measure temperature)? Do you want to see how cold it is outside; how hot your Ford is running; if the swimming pool is just right? Mike W is right about the digital stuff. And don't worry about the mercury in a thermometer-not enough there to get excited about.

 

Aren't they trying to do away with the mercury ones?The t.v. station had a thermometer swap last fall for them.I guess they can be dangerous if they break.

 

I've taken care of the gaps in the mercury on thermometers by carefully heating the bulb with a cig lighter until the mercury goes all the way to the top. Do this slowly. There is always the risk that you could overheat it and ruin it but oh well, it's not doing you any good in the condition it's in now. Do this work over a trash can or something just in case you break it.

As for mercury vapors filling the room and subsequently needing the haz mat team repleat with the "bunny suits" to come to the house and all, that's just not true. Mercury is only a concern if you ingest it. There was a big fiasco about mercury in tuna fish many years ago, but in the end it all just went away. Mercury is simply a metal that happens to be in a liquid state at room temperature. Lead is semi plastic at room temp. Steel, copper, zinc, etc are solid.

If the above fix doesn't pan out, just go digital. Like most everything else these days, they're not to expensive.

 

I have a National Institute of Standards Traceable (NIST) lab grade thermometer at work, and it is mercury filled. Anything else is less accurate. Since I have a degree in electronics let me talk about digital. We have a metrology lab come in every six months to calibrate all our digital instrumentation and they use a digital thermometer unit but guess what it's calibrated against? You got it, a very expensive lab grade primary standard thermometer that is mercury filled. The reason they do this is that the calibration is built into the mercury thermometer when it is manufactured, and will be correct until it is broken, whereas a digital unit muxt be periodically calibrated against a known standard or you are just guessing at measurements.

 

I wasn't aware of the mercury concerns in tuna "just going away". In fact, I'm not sure the warnings don't include several species of fish we eat.

 

I haven't had problems with the mercury ones getting gaps, but rather the alcohol ones (pink stuff). I tried heating them, freezing them, boiling them, nothing works. Maybe the fact they are made in Taiwan is the cause of it.

I use it to measure air temperature outside.

I think I will get a Mercury one


P.S. re danger, I heard the opposite - that what killed you were fumes, not ingesting it. that's why many got sick when processing various metals like gold. Even if you break yours, doubt there are enough fumes from a few grams. Maybe over many years?

 

Geez- I must be dead then cause we used to make a big puddle of the stuff (mercury) as kids and play with it.

We did everything with it but drink it.

 

If you think that Mercury has to be ingested to be a hazard, I've got some bad news for you! Mercury vapor is nearly just as deadly. Shine an ultraviolet light (a blacklight will do) on an open container of Mercury, and the shadow will show how much vapor excapes. It is harmful to the brain and liver.

 

Mercury does not emit fumes at room temperature, but when heated it will produce very toxic vapors.

 

This still doesn't answer my question if there is any inherent accuracy with Mercury vs. alcohol. Can you make alcohol-based ones just as accurate? What exactly is the difference? I didn't know that alcohol expanded when heated.

 

Quit interrupting

 

Not knowing exactly what your application will be, I will still try to help....

If you're just looking for an accurate temperature measurement in the range of -20 to 100 C, either will do just fine. Mercury will be slower responding due to the mass.

You can easily verify the thermometer yourself using a 2 point check, that at freezing, and at the boiling point of water. Just crush up some ice, preferably made with distilled water, and add just enough water to make a slush. Insert your thermometer into this slush and you will be as close to zero C as you need to be to verify. I have used tap water and refrigerator ice and found you will probably not see a difference, and if so it will be negligible.

High end check is to get your water boiling, and again preference is distilled, but an absolute requirement. With this check you will need to determine what your boiling point is for your altitude. Care needs to be taken as to NOT over heat the thermometer beyond it's range, or you WILL blow the end out. Trust me, I know this from experience. Keep the bulb suspended in the boiling water, away from the heat source. Do not bring the water to a hard boil either, as the steam bubbles are at a higher temperature than the water itself.

Glass thermometers DO change over time, as the glass, believe it or not, is still somewhat liquid. IT will flow and the markings shift. With a 1 degree resolution thermometer you won't see it, but with some of the lab grades, I have rejected them as out of calibration in the past.

Hope this has helped some.....

 

I don't know where you live, but mercury thermometers will freeze if it gets cold enough. I think that point is somewhere around -40 F.


Whistler