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Author: Subject: thermometers: two different types needed
chemrox
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[*] posted on 28-3-2007 at 22:47
thermometers: two different types needed


I have a Claisen adapter that takes a thermometer equipped with ST joint. I don't know what this type of thermometer is called and haven't found one in a catalog.

I also am looking for a shallow emersion thermometer I can use with an aluminum block I had machined for melting points. It has a shallow well drilled in one corner for oil and the thermometer.
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not_important
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[*] posted on 28-3-2007 at 23:21


like this?

http://www.sigmaaldrich.com/catalog/search/ProductDetail/ALD...


Older model melting point usually drilled a horizontal hole almost through the block. Some just had close fit to the thermometer, some had a small expansion chamber and were oil filled and stoppered.

A digital thermometer might do the job for you, some have short active regions at their probe tips.

An alternative is a thermocouple like these
http://www.omega.com/ppt/pptsc.asp?ref=5TC&Nav=tema02
and a measurement unit.
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Tacho
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[*] posted on 29-3-2007 at 03:51


I describe a simple, cheap, DIY digital thermometer here:

http://www.tecnotacho.com/projeto1.htm

Hope it helps.




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chemrox
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[*] posted on 2-4-2007 at 20:53


Exactlty as not_important posted for the one with the st. I also was looking for a bulb-only immersion callibrated one but might have to go electronic or thermocouple.... what I need is something reliable enough for melting points that I can use with my block.

http://www.omega.com/ppt/pptsc.asp?ref=5TC&Nav=tema02

how does one use these? callibrate them?

BTW- I should have mentioned I only looked in the catalog my vendor has and my local sources .. I used to a lot of business with Aldrich then moved to Spectrum .. they both have their virtues..

[Edited on 2-4-2007 by chemrox]

[Edited on 2-4-2007 by chemrox]
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not_important
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[*] posted on 2-4-2007 at 22:54


Use them -

You can buy one of the compatible meters from the vendor

For work is to build your own interface, analog to be read with a voltmeter or digital to be read by a computer.

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3149

If you don't need temperatures high than 140 to 150 C, you can use a digital sensor in place of a thermocouple and read it with a computer.

http://www.national.com/pf/LM/LM92.html

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3497

Calibration is done using standard reference materials and taking their melting points. You make a plot of the melting point reading vs the stated melting point. When testing an unknown you use the plot to interpolat the actual melting point of the unknown.

The reference standards must be decently pure, there's a book on purification of lab chemicals in the library area.

Some standards that are fairly common or easy to prepare are

ice 0 C MP
gallium 29.7646
p=dichlorobenzene 53
naphthalene 80
vanillin 83
p-nitrophenol 113
acetanilide 115.5
iodoform 119
benzoic acid 122
urea 133
phenacetin 136
citric acid 153
indium 156.5985
salicylic acid 159
benzanilide 165
sulfanilamide 166
hydroquinone 169
aniline chloride 198
silver nitrate 212
tin 231.928
caffeine 237
sodium chlorate 248
phenolphthalein 263
sulfanilic acid 288
sodium acetate (anhydrous) 324
lead 327.3
potassium chlorate 368
potassium dichromate 398

The metals need to be really pure and take special and apparatus to get that high accuracy.



[Edited on 3-4-2007 by not_important]
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