chemisch
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Mel-temp thermometer question
I need to acquire a thermometer for this Mel-temp. I've been looking around the internet specifically for thermometers for a mel-temp and its not
working out so well. I don't want to purchase a thermometer that doesn't work because mercury thermometers are pricey. Thanks
Mel-temp looks like this one
http://store.clarksonlab.com/images/products/detail/M4125100...
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DJF90
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As far as I recall, the thermometers are exactly the same. Get a 0-360*C one, with as many graduations as possible, e.g. 0.5*C x 360*C or 1*C x 360*C.
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Dr.Bob
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You will want to buy one with the correct immersion length, they have ones for partial immersion, which is what you want, and ones for total
immersion, which will give incorrect results for the Mel-temp. If you can go digital, that is even better, although they do drift more than mercury
thermometers, in my experience.
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chemrox
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I have an older model and it works with 76mm immersion Hg thermometers. You're not trying to use one of the Chinese cheapo alcohol filled, child-safe
jobs?
btw they seem awfully expensive can't you find a used one? all the companies going out of business in the Bush hangover economy??
Oh and I couldn't find that model at the web site...
[Edited on 21-11-2012 by chemrox]
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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DJF90
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76mm immersion is almost a standard when it comes to thermometers. Its also possible to use a total immersion thermometer and apply a "stem
correction" formula. Details of such I have seen somewhere but I don't recall the exact source. I could look if its required.
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smaerd
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at my old school lab we used digital thermometers with probes using a similar mel-temp apparatus. This was a very nice set-up because rather then
quickly reading a thermometer as soon as a sample began to melt a digital read-out was right there.
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Dr.Bob
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There was a company called "Stanford Research Systems", which made a few very simple computerized melting point devices, using a small heating block
with a temperature controller and then a small digital camera which looked for the optical changes upon melting. When the company first started, they
had one model under $1000, but they went up after that. We got one where I used to work, and it worked OK, especially for finding the rough MP, and
then we could go back and get a more accurate one much more quickly, especially since it did 3 at a time.
Given the smart people on here, someone could build a similar unit for not that much, if they used a separate computer and just created a simple USB
interface or something to control the heater and camera. That seems like a great science project, independent study or engineering project. If I
had the time I would love to build one, as I really hate taking routine MP's.
http://www.thinksrs.com/products/MPA100.htm
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watson.fawkes
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Quote: Originally posted by Dr.Bob  | | Given the smart people on here, someone could build a similar unit for not that much, if they used a separate computer and just created a simple USB
interface or something to control the heater and camera. |
I suggested something rather similar in this thread about Arduino. I agree, it wouldn't be all that much to make. About the only machining that would need to be done is on a drill press. A
suitable USB webcam can now be had for ~ USD 25, which is the biggest change in costs from a decade ago. Getting a decent optical train so you can
focus on the sample might be more money now, though I have to disclaim I don't know much how folks are doing amateur optics these days.
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DJF90
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If I'm not mistaken, determination of melting point is enhanced by having the sample between crossed polarising filters. Perhaps this could form the
basis for a simple automatic melting point machine, using a photodiode or LDR to measure the change in transmitted light.
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mr.crow
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eBay is a good bet for MelTemps
I scored one for $5 a while ago that had a broken mercury thermometer inside it! Hows that for safe shipping?
I think they come standard with thermocouple probes. The ones at school and google images all have the same yellow ones.
Double, double toil and trouble; Fire burn, and caldron bubble
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Swede
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If I were re-working a melting point apparatus, I'd go for the most accurate PT-100 digital temperature probe I could find, and failing that, a good
thermocouple. The latter will be a bit less accurate, but the huge benefit is that ALL of the temperature sensing takes place at the junction, the
weld of the two wires. Pack any void in the mel-temp device with thermal grease (like the pink stuff as used for CPU's) and jam the digital probe
sensor in there. Done!
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chemrox
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I like the older Mel-Temp. I can't guess how the newer ones work. Mine uses the standard thermometer which is nice in case one breaks. I also
prefer capillary tubes to microscope slide covers. If I find another Mel-temp for $5<25, I will drill out the capillary tube slot enough to get a
boiling pt tube into it. That way I can do the bps without resorting to mineral oil and bunsen burners.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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