Mercury Thermometer

[Nehebkhau]

i had a mercury thermometer and it broke inside one of my beakers, a white crystal-like substance came out along with the mercury. What is the white stuff? Also, why do they still sell mercury thermometers? are they better than others?

[DBSP]

Was there anything inside the beaker when it broke?

[danmcl2002]

as far as your question regarding why they still sell mercury thermometers, it depends on your application.
1. mercury thermometers arent very useful for colder temperatures as the mercury can become a solid at temperatures below -38.9°C whereas as an ethyl alcohol thermometer is still useable at
-114°C
2. they are much more useful at temperatures over 100°C as alcohol boils at 78.4°C and a gas is no use in measuring temperature (in a thermometer anyway)

anything above 356.7°C and you will need to use a scope of some sort to get your temperature as mercury boils at this point.

i think that the white powder may be a dehydrating agent, so that if the thermometer goes above 100°C there is no steam produced which may rupture your thermometer releasing mercury, which would be bad.

hope this answers your question, im not sure about the white powder but that would be my best guess.

[Nehebkhau]

the thermometer broke in a beaker containing sulfuric acid, during the purifying process. thx for the info

[vulture]

Why would there be a dehydrating agent in it? It's filled with mercury, which isn't affected by water in anyway and the thermometer is vacuum sealed anyway!

[Sarevok]

Originally posted by Nehebkhau
the thermometer broke in a beaker containing sulfuric acid, during the purifying process.

Your white stuff is mercuric sulfate. Concentrated sulfuric acid reacts with mercury to form mercuric sulfate, which is a white salt.

PS: I think mercuric sulfate is toxic.

[frogfot]

I've seen alcohol (red liquid) thermometer that goes above 200*C.. well, had to share this with someone :rolleyes:

[Nehebkhau]

Originally posted by Sarevok
Your white stuff is mercuric sulphate.

what exactly is mercuric sulphate used for if anything....and why didn't all of the mercury combine with the sulfuric acid

[Sarevok]

Originally posted by Nehebkhau
what exactly is mercuric sulphate used for if anything....and why didn't all of the mercury combine with the sulfuric acid
Its used to manufacture mercuric chloride, which is used to amalgamate aluminum, which is used to make methamphetamines.

For all the mercury to react, you need to do a decent procedure (like the one in the end of this post), not just throw the mercury on the acid...

--

Measure 20g Hg and place in a 100mL conical flask. Do not use a round bottom flask, as all the mercury will not react. Add 60 ml concentrated H2SO4 (should be at least 94%) to the flask and fit a single hole stopper with a tube leading outside. This reaction produces lots of SO2 that will give you chemically induced asthma if breathed. Now slowly heat the flask. Bubbles of SO2 will rise from the acid/mercury interface. Maintain a vigorous bubbling of SO2 by adjusting the heat. A white crystalline deposit of HgSO4 will appear. The mercury should be completely reacted after about 30 minutes. Allow the reaction mixture to cool and pour off the acid. Pour the crystals/acid into 750 mL hot water and filter. Source (http://www.rhodium.ws/chemistry/mercurychloride.html)

[vulture]

Mercury is a noble metal, therefore it will only react slowly with acids.

Sarevok, subscript is <sub> instead of [sub].

[T_Pyro]

Originally posted by danmcl2002
a gas is no use in measuring temperature (in a thermometer anyway)


Not heard of a gas thermometer? They're undoubtedly the most accurate thermometers around, as far as reproducibility and resolution go. Click here (http://www.unidata.ucar.edu/staff/blynds/tmp.html) for more info.

Originally posted by frogfot
I've seen alcohol (red liquid) thermometer that goes above 200*C.. well, had to share this with someone


Now I haven't heard of that before! Is the alcohol under high pressure in the thermometer? If that's the case, then there'll be loss in accuracy at higher temperatures to to the alcohol vapours...

[Anthony]

Just because somebody made the scale go up to 200*C doesn't mean it necessarily works at it ;)

[frogfot]

But why can't alcohol be used?? It's still liquid under confinement.

[T_Pyro]

Ah yes! Forgive me, for I looked, but did not see! A thermometer beyond 200*C need not be a working thermometer!
Theoretically, an alcohol thermometer CAN be used beyond 200*C, provided you can fulfil the following prerequisites:
1. The glass wall of the thermometer should be strong enough to firstly withstand the temperature, and secondly, high pressures.
2. A sensitive microscope would have to be kept ready to take the readings. As the temperature reaches (and crosses) the boiling point of alcohol, alcohol vapour starts forming in the free space above the liquid, and exerts vapour pressure on the alcohol column. Due to this, the sensitivity of the thermometer would start decreasing exponentially with the rise in temperature. Hence, for example, at 200*C, there might be a 1mm rise for 1 *C, but at 400*C, there would be something like a 0.01mm rise for 1*C !
3. You should have a good scientific calculator (and a hell lot of patience!!) at hand to calculate the temperature, by applying gas laws, then the ideal gas correction...

[frogfot]

Accuracy may be not that bad..
From http://www.stao.org/safeart2.htm
...alcohol thermometers "have a lower usable range than do mercury thermometers, typically being accurate only below 300C"...

There doesn't have to be a big rise in pressure to elevate boiling point with 100-200* and bring vapor pressure to normal. And since capillary is very thin, walls can be made thick and compact enough to hold this pressure.

Though there are other liquids that can be used for this purpose, dunno how one can assume "red liquid" to be alcohol, lol.

[T_Pyro]

At the end of the day, the question that must be asked is: "Why use alcohol at all for high temperatures?"
Mercury thermometers are perfect for high temperatures, and if you want more accuracy, you could always go for electronic thermometers, so why bother using alcohol at all?

[Trinitrotoluene]

If your trying to measure the temperature that's above the boiling point of mercury, then mercury thermometer is consitured useless. I perfer mercury thermometer over an alcohol filled sprint thermometer, one reason mercury is more accerate, as mercury does not cling to the walls of the thermometer and alcohol does, making acceracy slightly off.

[senjoronie]

Just found this thread and thought I would comment. I don't think the alcohol in an 'alcohol' thermometer is really ethanol. I broke one once by accident, and the liquid seemed oily, more like a heavier alcohol or perhaps kerosene. That's what I thought they were filled with, kerosene or something like it.

[Mumble]

The liquid is some usually sort of glycol. Propylene Glycol is is probably the one in mine(-20 to 150). I'm sure there are other sorts of compounds that can be used, but glycols are cheap and fit the purpose.