split threads in mercury thermometers

Discussion in 'Science Technicians - General Discussion' started by JFKtech, Jul 15, 2019.

  1. JFKtech

    JFKtech and then there were two - now JFK Techs :)

    Hi All,

    I've got a sizeable stash of mercury thermometers, a large number of which have got splits in the column of mercury. With a spirit thermometer I would drop it repeatedly down a tube onto a bung until the split gets bounced back in to place, but I don't fancy the risk of breaking a mercury one !

    Can anyone advise how to repair them, or should I just give in and get rid ?

  2. We were told to get rid of all of ours as they are not safe for the kids in case they break them....
  3. Is there a difference between how accurate mercury and spirit thermometers?
  4. Tend to find that if you need higher temperatures at greater resolution Mercury ones are better than alcohol but largely that's about it
    Not sure why, CLEAPSS have it top of the "myths" document re: banned kit and experiments
    There as a Sigma Aldrich method I remember about putting dry ice in ethanol and then dipping the bulb - and only the bulb - into the solution until all the mercury retreats from the column, then swinging it around in circles to make sure it's all in the bulb
  5. JFKtech

    JFKtech and then there were two - now JFK Techs :)

    Sounds fun ! We'll be getting dry ice in at some point next term for cloud chambers, so I'll give it a go then - thanks !
  6. Got me curious so I went and found the original here
  7. Never tried with mercury thermometers, but for split spirit threads I put one into pop sock or one leg of a pair of tights, then spin it around my head for a bit! Works a treat. Remember to do it in a large space though!
  8. I heat a small volume of liquid (medicinal) paraffin over a low Bunsen flame, place the thermometer into the paraffin and watch carefully. The mercury will rise, recombining the split thread. As soon as it reaches the top in the small expansion chamber, remove it and leave to cool. Never had one break, cold stuff just seems to freeze the mercury in situ.
  9. PhysicsSimon

    PhysicsSimon COMMITTEE

    Glycerol works too, doesn't boil until 290 deg C (apparently) - works fine with alcohol thermometers & no reason why mercury would be any different - but only do one at a time! (have previously described what happened when I did 10 at once - too late taking one out, bulb burst, alcohol floated to the top where it instantly burst into flame....sigh)

    EDIT - re-reading the thermometer section on CLEAPSS (see below) reminded me that technically it's not alcohol in spirit type thermometers - it IS flammable tho'
    Last edited: Jul 30, 2019
  10. I'd probably get rid of them as they are more trouble than they are worth. If you do have Thermometers (whether they be Mercury, Alcohol or Kerosine) there is a way of repairing those with split levels. Simple place the Bulb of the Thermometer in boiling water for say 5-10 minutes until the levels rise then place in the freezer at a 45 degree angle for say 30 minutes. This will cause the contents of the Thermomer to recombine so that the level is no longer split.:)
  11. Precision thermometer-2.png Precision thermometer.png
    We have a super accurate Beckman Mercury Precision Thermometer which is 1 metre in length, though we have not used it in any of our current day practicals.:)
    Last edited: Jul 30, 2019
  12. PhysicsSimon

    PhysicsSimon COMMITTEE

    According to CLEAPSS, yes.....if you look at table 10.12 on p1055 of their lab handbook (section 10) they compare the deviance of 10 different thermometers straight out of the packaging (mercury, blue, red, green spirit type) at 2 different temps - the mercury seems significantly more accurate (worst reading was one of the spirit type: 104 deg C reading when at 100.5).

    One of the differences in everyday lab use is with mercury, more liquid is needed in the bulb so proportionally, less is in the column - so immersing to the correct depth is less important/critical (table 10.13 shows the effect of immersing to the wrong depth - one of the spirit type when at 130mm instead of the needed 76mm read 107 deg C when at 100.2....with mercury under the same conditions it read 100.5)

    Whilst I don't have a problem with us having mercury*, the only practical where we specify mercury thermometers is with Charles law - extrapolating the graph back to absolute zero needs the best temp readings you can achieve - and our air columns are sealed with mercury anyway rather than conc sulphuric (all fine with CLEAPSS & made according to their instructions in case anyone's wondering)

    *Back in the day of my own physics A level (nearly 40 years ago - eeek!) I made a barometer in class - seal the capillary, fill to the brim with mercury, stick finger over the end, invert then immerse in a beaker of mercury before releasing - worked pretty well too (tho' this exposure at a young age may explain one or two things;))
    Last edited: Jul 30, 2019
  13. PhysicsSimon

    PhysicsSimon COMMITTEE

    CLEAPPS mention this one too George: "The Beckmann thermometer has a very small scale range but provides great precision of temperature-difference measurement.
    This thermometer is used in procedures which require very small changes of temperature to be observed, eg, to find the depression of freezing point or elevation of boiling point when solutes are added to solvents. From these data, the molecular mass of the solute can be found, providing valuable evidence for the association and dissociation of solutes in solvents. Such investigations are now rarely carried out but could be a Y12 activity. With this thermometer, mercury from the main bulb can be added to or removed from a reservoir bulb at the top (by a suitable sequence of heating and cooling etc), thus allowing the temperature range covered by the scale to be varied."

    Aplogies for any formatting errors, c&p was a bit all over the place & I know there'll be more words per line as soon as I press 'Post Reply'...here goes anyway
    GeorgetheScienceTech likes this.
  14. You are, as always correct on all acounts Simon. However, as A-levels have been extensively watered down over the years todays students would not know anything about colligative properties.Happy holidays.:D
    PhysicsSimon likes this.
  15. is that total immersion?

    it's only accurate if you have an NPL certificate for it or calibrate it to one, I think they stopped doing mercury ones years ago, thankfully as I may have broken a few.