P RACTICAL   T ASK   P3.
T HERMOMETER
Outline
This   checks   the   accuracy   of   a   standard   thermometer   at   the   freezing   point   of   water,   0
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C.
It   is   sometimes   used   in   conjunction   with   a   check   at   the   boiling   point   of   water,   100
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C.
Bulb   thermometers   cannot,   of   course,   be   adjusted   if   they   are   inaccurate.
Laboratory   uses   of   thermometers   vary   in   terms   of   the   accuracy   required,   so   a   thermometer   that   is   reading   1
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low   may   not   be   suitable   for   a   purpose   where   greater   accuracy   is   required,   but   would   be   fine   in   a   drying   oven.
Some   laboratories   would   simply   discard   any   thermometers   that   fail   a   check,   to   avoid   the   possibility
of   a   lower   accuracy   one   being   used   in   the   wrong   situation.
Procedure
1.
Obtain   a  ‐ 10   to   110
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C   thermometer   and   place   it   in   the   laboratory   refrigerator   for   10   minutes.
2.
Obtain   a   Styrofoam   cup   and   fill   with   crushed   ice.
3.
Add   a   small   amount   of   water   –   the   mixture   should   not   be   too   runny,   but   loose   enough   for   the   thermometer   to   slide   in   easily.
4.
Put   a   watchglass   over   the   top   and   leave   for   5   minutes.
5.
Remove   the   watchglass   and   insert   the   thermometer   until   it   touches   the   bottom   of   the   cup.
Lift   it   up   about   1   cm   or   until   the   0   point   of   the   scale   is   visible.
6.
Allow   the   thermometer   to   equilibrate   and   read   the   temperature.
Reporting   Requirements
Use   the   standard   Performance   Check   reporting   sheet.
Acceptable   error   range:  ‐ 1   to   +1
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C