Sulaiman
International Hazard
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Registered: 8-2-2015
Location: 3rd rock from the sun
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melting point kit availability?
I have recently bought a set of ex-soviet short-scale thermometers that I wish to calibrate.
(eight thermometers covering -35C to +360C in 0.5C graduations)
Question 1
Calibration certificates only a couple of decades old ... do mercury thermometers really need re-calibration?
I have on order a PT100 sensor which may help
but since one of the main uses of these thermometers will be melting point determinations
i would like to calibrate them using reference melting point chemicals
I've read USP and WHO standards
but the cost of suitable reagents is too high.
Question 2
Can anyone point me to an affordable kit of melting point reference substances?
P.S. as general interest, in the WHO document that I have
samples of 'reference' materials were sent to 15 different (presumably competent) laboratories for testing,
results varied by standard deviations of 0.4 to 1.4 Celcius
nice to know that things aren't 'perfect' even for major laboratories.
[Edited on 7-7-2015 by Sulaiman]
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Dr.Bob
International Hazard
Posts: 2689
Registered: 26-1-2011
Location: USA - NC
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Melting Points are an observed phenomena, so that brings a lot of variation into the measurement, and they are observed as a singularity, a single
sample melts at a certain temperature, within a few seconds. For a BP, you often have a large sample, so you can get a more "averaged" signal over
minutes, not seconds. I have taken many mps, and the error is due to quickly ramping the temperature, the size of the sample (it takes more time
and heat input to melt a larger sample, thus the temperature range will be larger by simple logic), and the humidity can affect samples if they absorb
water from the air and form hydrates. Good mp standards are stable, non-hazardous, non hygroscopic, crystalline solids like benzoic acid, Caffeine,
Naphthalene, acetominiphen, Cetylacetic acid, benzophenone, and several other OTC drugs.
Details on mp variation:
http://www.thinksrs.com/downloads/PDFs/ApplicationNotes/MP_C...
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