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Magpie
lab constructor
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Mood: Chemistry: the subtle science.
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If you are patient and bring the temperature up slowly in the vicinity of the mp I believe it is quite accurate, and you can observe a melting point
range.
I picked up 3 Thieles in an eBay grab bag for not much. I've used machines at school that have microscopes etc. But I prefer the Thiele as it is
simple, a classic, and very satisfying to use.
The single most important condition for a successful synthesis is good mixing - Nicodem
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RonPaul2012
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I just did a MP test on a sample of sorbitol of unknown purity and I got a MP of 96-98 °C , my thermometer is resonably accurate (it shows 100 °C
at the BP of water and 0 °C at the MP of ice) .
Wow , I'm suprised my little test tube gave such a good result 
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arsphenamine
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Differential thermal analysis is yet another way to do it.
Poke thermocouples in your compound and a stable reference like washed sand, heat them up in the same thermal block, and plot the voltage vs.
temperature. The melting point shows up as the start of a trough.
Explanation with drawings: http://physicalchemistryresources.com/Book5_sections/TA_Diff...
Excellent DIY from physics lab class, shows how crude (seemingly) the thermocouples can be and still give useful results.
http://www.lehigh.edu/imi/docs_edu/DTA_AAPT_2011_10min.pdf
Word salad from Wikipedia:
http://en.wikipedia.org/wiki/Differential_thermal_analysis
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mayko
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Here is my MP apparatus. It's a volumetric flask filled with mineral oil on a hot plate, with a thermometer and the capillary tube clamped in place.
To better observe the sample, I've also clamped my USB microscope such that its focused on the capillary tube.
I ran a test using vanillin; my copy of Merck gives two melting point ranges, 80-81 and 81-83. Using this setup, I measured a melting point range of
80-82. There was a bit of temperature fluctuation which was annoying, but I was overall very satisfied with this setup.
   
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Finnnicus
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Not sure how original my idea is but it goes along the lines of:
Aluminum block 2x2x2 inches (Oh yay, imperial measurement), with two machined holes; one for thermometer, the other for the sample. For increased
chemical resistance the sample hope could be coated with enamel.
Also another hole could be drilled on the side for an soldering iron, otherwise the whole apparutus could be placed on a hotplate.
If I get time (I'm in maths class, so not now), I will draw something up.
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Mush
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Does anyone have experience with this type of melting point apparatus?
http://www.ebay.com/itm/MELTING-POINT-APPARATUS-MANUFACTURER-HEATING-ANALYTICAL-INSTRUMENTS-FOR-LAB-/161028976692?pt=LH_DefaultDomain_0&hash=item2
57e133034
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Paddywhacker
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How about focusing a webcam, or even a USB microscope on the thermometer and capillary tube and taking snapshots every second. No need to hold your
breath and squint, just look at the pics later. That way you could have a really slow temperature ramp for accuracy, and just go away and leave it do
its thing.
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DraconicAcid
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That type? Yes- that is the standard type that I've seen in most of the colleges and universities I've worked at. They work fine.
That particular brand? No.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Mush
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Quote: Originally posted by DraconicAcid  |
That type? Yes- that is the standard type that I've seen in most of the colleges and universities I've worked at. They work fine.
That particular brand? No. |
Thanx DraconicAcid! You helped me a lot.
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