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Author: Subject: Melting point apparatus.
Magpie
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[*] posted on 19-4-2012 at 15:54


Quote: Originally posted by RonPaul2012  
How accurate is a thiele tube anyways ?


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.




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RonPaul2012
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[*] posted on 19-4-2012 at 17:32


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 :D
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arsphenamine
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[*] posted on 19-4-2012 at 22:24


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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[*] posted on 3-6-2013 at 15:37


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.



ZBch5-FOOh8jywbsxoAZGijfyD9Jy2mNGEAutUpZprg.jpg - 105kB

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.

Vanillin-9.jpg - 36kB Vanillin-4.jpg - 36kB Vanillin-13.jpg - 36kB Vanillin-18.jpg - 36kB
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[*] posted on 3-6-2013 at 17:54


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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[*] posted on 26-1-2014 at 13:44


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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[*] posted on 26-1-2014 at 14:50


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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[*] posted on 26-1-2014 at 15:03


Quote: Originally posted by Mush  
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


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.




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Mush
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[*] posted on 4-2-2014 at 14:47


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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