Sciencemadness Discussion Board - Melting point apparatus.

Melting point apparatus.

Tacho - 6-2-2004 at 05:36

I've built this melting point determination apparatus.
Nothing really new here, but some practical details might give ideas for those who would like to built one:

1- The unit is built with commom aluminium profiles held together by screws. Most of it is hollow to allow the heating unit insertion, but the part under the sample spot is made solid by joining many pieces of aluminium.
2- The heating unit is one from a 50w soldering iron. It has a tubular shape and fits inside the hollow unit.
3- The sample is held inside a "sandwish" made of microscope glass covers. They are cheap and therefore disposable. This sample "sandwish" is covered with a plate to assure an even temperature distribution. This plate has a hole (window) for visualization.
4- The thermometer's bulb is inserted in a hole in the body of the unit, right under the sample.

Picture attached.

Mpappar.jpg - 23kB

axehandle - 13-2-2004 at 10:37

Very nice..... could be useful and seems extremely cheap to build.

MP apparatus

cavgdad - 27-4-2004 at 09:27

would you be interested in building me one (sell me one)? I am not tech inclined.
please email me if so.

thx
cavgdad@yahoo.com

Tacho - 27-4-2004 at 11:03

Sorry, can't do that. For many reasons.

I'm sure you can find someone to built it for you.

MPA

cavgdad - 28-4-2004 at 08:07

I understand. can you please post detailed intructions so i can try to do it myself. i would greatly appreciate it

Tacho - 28-4-2004 at 11:11

Sure.

I'll put some instructions together and post them as soon as possible.

Here it goes:

Tacho - 29-4-2004 at 10:56

1- Sorry, but my webcam is developing mould inside the lens, so the picture is quite blurry.
2- I’ve built the device with what I had at hand, so feel free to change the project as you like.
3- I used two extruded aluminum profiles. One is 25mm (1”), the other is 16mm, both are 3,5mm thick. Cut them in the lenghts shown in the picture. They are easy to cut with a metal saw.
4- With a drill, make the holes to the screws. If you use a drill press (highly recommendable), you can drill the holes as you hold the pieces together.
5- Screw the pieces to each other using screws and nuts. Put the soldering iron heating element before screwing the top plate. In my design, the screws in the back prevent it from falling. I presume you are able to connect a plug to it. You can find those heating elements in an electronics shop. I think Radio Shack should have it, if you live in the US.
6- Notice that using the profiles as I used, a small gap is left as shown in the picture, I used pieces of al sheet, 16mmx30mm, to fill it.
7- make the hole to the thermometer bulb. The bulb must fit as tight as possible.
8- The heating should be slow due to the thermal lag of the thermometer bulb/aluminum interface.
9- Am I making any sense?

wish you luck.

Eliteforum - 29-4-2004 at 17:01

Quote:

Sorry, but my webcam is developing mould inside the lens

Where do you keep your camera?!

ummmm.......

Hermes_Trismegistus - 29-4-2004 at 23:45

Where does Tacho keep his camera?

I hate to hazard a guess, cuz I'm sometimes wrong, but my money is on Brazil.....

Tacho - 30-4-2004 at 03:02

Quote:

Originally posted by Eliteforum

Where do you keep your camera?!

Exposed to humidity, greasy fingers, coffee, chocolate cookie crumbs, sneeze debris and acid fumes.
And, yes, in Brazil. Easy money huh Hermes?

Huh?

Hermes_Trismegistus - 30-4-2004 at 12:20

Humid in Brazil???

thunderfvck - 30-4-2004 at 12:25

All this talk of building MP aparati seems pretty useless to me. What's wrong with just boiling up the appropriate liquid, with a themometer & cap. tube attached immersed in the liquid, when it melts, read the temp, and there's your melting point.

I've even read about it being done directly on the hot plate, there is a special way of doing it however. And you don't need cap. tubes or high boiling liquids (or low boiling, depending on what mp you're taking)...Anyways, it was in Vogel. I can write it out if anyone's interested...

Not so.

axehandle - 30-4-2004 at 13:39

Quote:

All this talk of building MP aparati seems pretty useless to me. What's wrong with just boiling up the appropriate liquid, with a themometer & cap. tube attached immersed in the liquid, when it melts, read the temp, and there's your melting point.

I disagree wholeheartedly. Geniousness lies in doing things in a non-conventional way, and I believe Tacho has very successfully done so, while he at the same time probably had lots of fun building it.

Call me wrong and radical, but my firm belief is that, all other things being equal, if you can 1) buy it or 2) build it, you build it. Not only for the satisfaction of a job well done, but for the fun of it.

Every once in a while, it's also cheaper.

Tacho - 30-4-2004 at 16:00

Thanks axe, you know that’s exactly how I think, but I believe I can explain to Thunderfvck the more prosaic advantages of the device.

Thunderfvck,

Picture this:
It’s 1:00 a.m. You have to wake up early today. You just cleaned up the attic (or basement, or garage) while your reaction was refluxing. Everything is tidy and clean. You are sleepy. Look at the clock and it’s time to turn off the heat. You filter that precipitate. Dry a bit with a hair dryer. Is that what you expected? How to tell? Melting point! And now you choose:

1) Get the Tiele tube or a test tube. Pick up the silicon oil bottle, put some oil in the tube. Get a capillary tube (where the hell do you get capillary tubes? Do you have to make them? Do you have to close one end in the flame?). Fill carefully the damn thing. Rubberband it to the thermometer. Fix some structure to hold the test tube. Fix some structure to hold the thermometer and capillary inside the test tube (no, no, no, it can’t touch the walls!). Get the gas tank, the Bunsen burner (where the hell did I put those matches?). Is the Bunsen burner already connected to the gas? You are lucky. Heat until you find the melting point. Use a lens to see when the sample melts and band-aids to the burn in your nose when you put it in the flame trying to look in the lens. Remove the thermometer and the sample. But wait, that silicone oil is HOT!!! Careful! Wash the thermometer to remove the oil. Now wash the tube. It may take a while, because silicone oil is a bitch to remove from glass. Don’t forget the gas tube, the fixtures, the Bunsen burner.

or:

2) Get the apparatus described and the microscope glass covers box.. Toss a bit of the sample on the glass. Cover it with another glass. Put the top plate. Put the thermometer in the hole and plug the thing to the wall plug. When that white spot suddenly becomes transparent, read the temperature. Turn it off. Go to bed. Tomorrow you can put everything back to the cabinet.

Maybe not as precise, but, believe me, much more practical and quick.

Edit: Hey Hermes, what's the thing about humid? We have all weathers here. Look at the size of this place in the map!

Well, maybe not the very cold ones...

[Edited on 1-5-2004 by Tacho]

Geomancer - 30-4-2004 at 17:59

I remember using a device that consisted of a polished metal bar heated at one end. The sample was sandwiched between cover slips and slid until it crosed where the melting temperature was on the metal. The distance was measured using graduations on the device, and then some sort of correction using a calabration curve was done. Altogether, a very smooth procedure--fast, precise, and microscale. I thought of making one, but they seem hard to calibrate. Tacho's device has similar advantages, without the disadvantage of difficult calibration. A bit slower and less precise, perhaps. Can any owners comment on how what they take the precision to be, and why?

thunderfvck - 30-4-2004 at 22:23

Oh, I agree with it being much more efficient. But for the person who had asked for one to be built, I'm just saying that their are other ways in doing it. You don't HAVE to have one...but that's obvious, of course!

Hermes_Trismegistus - 30-4-2004 at 23:12

Quote:

Originally posted by Tacho
Edit: Hey Hermes, what's the thing about humid? We have all weathers here. Look at the size of this place in the map!
Well, maybe not the very cold ones...
[Edited on 1-5-2004 by Tacho]

Tsss......don't tell me about weather, About five days ago I noticed that the snow was almost completely melted off of my front lawn, then two days ago it goes and snows again!

I've been mulling over this melting point apparatus and I think it's a good one.

You probably already thought of this but, I think that in making one I will try to have the thermometer the same distance from the heat source as the sample "dish" and the reasoning is that the heat at the thermometer will be the same as that applied to the sample.

I never really gave much thought as to this apparatus, but it seems like a valuable peice of equipment.

I really like your design, I wonder if a dremel will cut the aluminum plate up or whether I'll have to put in some elbow grease.

(When I get a chance)

Since becoming enamoured with science; albeit late in life, I often feel like a two-headed dog trying to play fetch.

Problem being the dog has one head on each end.

Tacho - 1-5-2004 at 01:49

By the way, the general idea is not mine, Zubrick's describes the Fisher-Johns apparatus in the chapter 12 of 4th edition. Mine is a DIY, quick and dirty version of it.

Vogel's third edition describes all sort of strange devices for mp determination. One of them uses an iron (the clothes one). He suggest drilling a hole for the thermometer on the iron's side.

I believe the device described by geomancer is there too.

[Edited on 1-5-2004 by Tacho]

If_6_was_9 - 1-5-2004 at 07:55

These doohickies are nice:

axehandle - 1-5-2004 at 08:46

Quote:

By the way, the general idea is not mine, Zubrick's describes the Fisher-Johns apparatus in the chapter 12 of 4th edition. Mine is a DIY, quick and dirty version of it.

As long as it works, what's the difference? (rhetorical question, the answer being "none"

Credit where credit is due! Huzzah!!!

Hermes_Trismegistus - 1-5-2004 at 16:32

Quote:

By the way, the general idea is not mine, Zubrick's describes the Fisher-Johns apparatus in the chapter 12 of 4th edition. Mine is a DIY, quick and dirty version of it.

Sorry Norseman

axehandle - 1-5-2004 at 16:41

Credit where credit is due? Perhaps. As a matter of honour. But as a Communist, I must say that all work should be on a hired basic. You shouldn't be able to profit from work you did 15 years ago.

Tacho - 2-5-2004 at 13:59

Quote:

Originally posted by Hermes_Trismegistus
(snip)
Sorry Norseman

Quote:

Credit where credit is due? Perhaps. As a matter of honour. But as a Communist, I must say that all work should be on a hired basic. You shouldn't be able to profit from work you did 15 years ago.

Sorry, but I don't get it.
Was there a dispute that I missed in some other thread?

If_6_were_9,

That's a beautiful piece of equipment, does it work well?

If_6_was_9 - 2-5-2004 at 15:59

Quote:

If_6_were_9,

That's a beautiful piece of equipment, does it work well?

It seems to be pretty accurate. Its in a hinged wooden box which is unusual for modern melting point apparatus. I bought it about 25 years ago from a head shop. Head shops are illegal now in the USA, but shops that look like head shops are around. They just can't sell paraphernalia.

nope.

Hermes_Trismegistus - 2-5-2004 at 16:22

just a convenient seque into politics

http://dictionary.reference.com/search?q=segue (for those who don't have english as a first language)

Utter confusion.

axehandle - 2-5-2004 at 21:40

No dispute, just me forgetting what thread I was in, confusing me into a sidetrack that had no relevance at all.

Interesting, the entry in the dictionary. "Vulgar latin".... I can't really picture vulgar latin. "Coitus"?

hate capillary tubes

Magpie - 2-5-2004 at 21:42

Filling capillary tubes with crystals has always been a real pain for me. Your other advantageous stated above are compelling also.

Do you have any data on the precision of your device? I'm just wondering how well a glass immersion thermometer works as a contact thermometer. Perhaps because you have essentially inserted it into a block of aluminum with a snug fit it is fairly precise. Let us know please.

Tacho - 3-5-2004 at 03:46

As you said, it's a thermometer inserted in a block of aluminum close to the sample, not much can go wrong here.

However, as stated by Murphy's law, there is a catch. If you heat too fast, and I usually do, when the sample melts and I turn off the power, the temperature in the thermometer keeps going up, showing the equilibrium between aluminum and mercury bulb was too slow for my heating.

Therefore, as any book on experimental chemistry should tell you, you must heat slowly when you get close to the mp temperature. A dimmer is necessary if you want precision.

Since the device has recently drawn so much attention, I will do some carefull controled tests with pure compounds to check it's precision.

Tacho - 3-5-2004 at 16:47

I did tests using resorcinol and vanillin. Resorcinol melted at 106-108 when Aldrich catalog says it’s mp is 110-113 and the Merck index says its 109-111. Vanillin melted at 79-80, Aldrich says 81-83, merck says “80-81 (81-83)” (sic!).

Just in case you are interested:
Starting at 40 degrees:

5minutes-83 degrees
7minutes-100 degrees
10-120
15-145
20-162
25-173
It stabilizes at 180 degrees in 30 minutes. I use a hotplate or blowtorch to reach higher temperatures.

close, but close enough?

Magpie - 3-5-2004 at 18:00

Thanks Tacho for all your work. I don't have enough experience to comment on these results. Perhaps someone else does.

It would be valuable to compare those results to what you would get with a Thiele tube or one of the modern commercial devices. But I'm not asking for you to do more work (while I just sit and come up with more questions).

Is experience neccessary?

Hermes_Trismegistus - 3-5-2004 at 19:27

Slow heating, accurate results.

Good job! :cool:

Tacho - 4-5-2004 at 03:24

Quote:

Originally posted by Magpie
Thanks Tacho for all your work. I don't have enough experience to comment on these results. Perhaps someone else does.

It would be valuable to compare those results to what you would get with a Thiele tube or one of the modern commercial devices. But I'm not asking for you to do more work (while I just sit and come up with more questions).

It depends, Magpie. If you are testing something for PURITY, you have to count on precision. Even then, notice that two respectable books give different mp for very common compounds. This happens a lot.

Sometimes the problem is “did the expected reaction happen or not?”. If I the starting compound has a mp of 180ºC, and I am trying to get a compound that has a mp of 90ºC and my resulting compound has the right color and a mp of 80ºC, it’s very likely that I did something right. Recrystallise in the proper solvent and mp goes to 85ºC: very, very likely that I did something right.

Usually, impurities bring the mp down, but if you quote me on this, I’ll deny it and call you a lier. Unless I’m right.

Thought... or lack thereof....

axehandle - 4-5-2004 at 08:11

Hmmm. Thinking that perhaps replacing the Al with Ag, and using a Pt thermocouple... hmm. No, that will have to wait.

Brilliant work, Tacho! Me, I'm going to play with sand now.

MP apparatus

cavgdad - 4-5-2004 at 12:18

Wow... didnt expect to fuel such a discussion. Thanks tacho for the hard work. I really appreciate it. now to work building one.

good discussion

Magpie - 4-5-2004 at 19:27

In my background (academic) I was testing for purity - so precision was important. But I see your point about differences among the experts in the references.

I like axehandle's idea about trying a thermocouple.

I believe you are right about contaminants lowering the melting point. Remember "freezing point depression." It is quite sensitive to this.

axehandle - 5-5-2004 at 17:17

Actually my mentioning of both silver and platinum was a hard-to-catch joke referring to my metal fetishism. But there are some valid points as well: 1) Silver has a higher thermal conductivity than Al. 2) A Pt resistivity metre is more accurate. However, there "improvements" would rise the cost of the device by at least a factor of 10, and they would only (guesstimate) lead to a resolution improvement of 2C. I think Tacho's device is fine as it is. Which is proven by the fact that's it's efficient, cheap, and accurate, as well as easy to build.

metal fetish

Magpie - 5-5-2004 at 20:04

Axehandle: at least you did not suggest the use of Rheingold. That would have increased the cost factor infinitely!

axehandle - 6-5-2004 at 10:07

Quote:

Axehandle: at least you did not suggest the use of Rheingold. That would have increased the cost factor infinitely!

No, no, no, no, no! We all know that Pt has better thermal conductivity than Au! Platinum is clearly the way to go. Or... perhaps iridium, but I'm not sure about that one.

mycoguy - 17-2-2005 at 02:35

an ex buddy of mine had one of those wooden hot boxes. He would use it to check purity of substances he was aquiring. How many dealers do you know that go through that much trouble?

Anyways. I just came up on an adjustable radioshack soldering station. Unfortunately, the thing goes up to something like 700F.

I'm planning on making one of these MP apparatii out of it, however, I just need to figure out how to drop the temp a bit more, in order to put it in a more controllable range. It even has a built-in digital thermometer. Pretty cool stuff.

mick - 17-2-2005 at 13:10

The benefits of a good quality melting point set up must be to check what you have through the mixed melting point method and it will also to to give you a good idea as to how pure the compound is. The closer the shrink temp. is to the melting point range (and the shorter the melting point range) the purer the compound is.
mick

Melting Point Controller

armo - 21-9-2005 at 07:35

Hi Tacho,

Nice piece of equipment. However I would use a electronic variac to control the rise of temperature. This kind of controller can be buyed in electronic supply house or built in a DIY basis. I have several circuits that I´ve built in the past. I use then mostly to control my iron solder temperature.

If you build it its going to cost less than US$ 5.00

armo :cool:

MP higher temp

armo - 21-9-2005 at 07:38

To reach higher temperatures you can use resistive elements for 100W welder.

armo :cool:

Melting Point again

armo - 21-9-2005 at 09:20

Hi, Tacho

Have you calibrated your thermometer? If you take 10 thermometers at the same temperature you will end up with 10 differents readings. Unless you use a precision thermometer all results are not true. You can not compare with literature...
armo

Tacho - 17-10-2005 at 01:30

Sorry armo, I haven't seen your posts before.

I have 1 thermometer that is very acurate. It reads 0°C in water-ice mix and 100°C in boiling water at sea level. My other thermometers have a piece of tape glued to them saying how many degrees I must add or subtract to find the right temperature.

If I were to build another device, I would make it out of plaster (gypsum) and only heat the small stage under the sample.

A dimmer is a good idea, but maybe just a diode, cutting the power in half, would be enough to ensure a slower temperature rise when needed.

cnidocyte - 27-12-2010 at 06:25

I'm glad I came across this thread. I was planning on clamping a boiling tube and thermometer into an oil bath but that would be useless for higher MP compounds. I'm definitely gonna build one of these.

DIY Melting point apparatus

Amy Winehouse - 18-4-2012 at 22:57

Im sorry if you opened this expecting me to present an amazing DIY melting point apparatus, but the purpose was more to hear about other's homemade melting point tester experiments.

Most melting point apparatuses(sp?) are non-garage chemist friendly i.e. expensive as f$#%. I know there are other cheaper ones like the Theile tube that require an open flame or w/e, but I was actually thinking of something more along the lines of completely homemade, even if it has a small margin of error. Beyond visual observation, I've been pretty blind as to the purity of my solids, has anyone successfully created one? Seems like some inert oil and a heat source is all you need, maybe im completely wrong.

What are some of your successes/experiments?

watson.fawkes - 19-4-2012 at 06:53

Quote: Originally posted by Amy Winehouse

Beyond visual observation, I've been pretty blind as to the purity of my solids, has anyone successfully created one?

I haven't made one myself, but I've been thinking about it. One points of the design I'd build is to dedicate a small webcam into the device. They are, relatively speaking, dirt cheap nowadays. With the help of a bit of software, detecting the visual changes could be completely automated. Furthermore, at the cost of some even-cheaper storage, the video record of the changes could be recorded.

With a second version of the control software, the system could cycle the temperature of the sample both up and down, and thereby also measure liquidus and solidus points, important for getting a handle on impure materials and assessing purity.

Dr.Bob - 19-4-2012 at 11:16

There was a company out of Cal. that advertised an automated system using a small camera for MP that was under $1000. Haven't seen them for a while, but the big instrument companies all have there versions for much more. Likely, the big companies bought the little one and closed them...

It would be pretty easy to do, and if you automated it, it would not matter if you only did a degree a minute, so you could ramp it very slowly and get good data, or even do multiple samples in parallel that way. The hardware is trivial, as shown above, and the video analysis just needs to look for a change in pixels at certain spots to detect a change, the operator should be able to look at the video and then confirm that is was a melting point. Or the system could get crude values, then ramp back near the MP on the 2nd run and have an operator watch it on a screen for confirmation.

S.C. Wack - 19-4-2012 at 14:14

Before going to extremes unless you're looking for a Project, I strongly suggest trying a thermocouple, candle and capillary, twine, oil, and test tube first. A heat gun or electric Bunsen for not-flame, live steam, spent fuel rods...

Duh...and a magnifying glass.

[Edited on 19-4-2012 by S.C. Wack]

RonPaul2012 - 19-4-2012 at 15:26

How accurate is a thiele tube anyways ?

I just tried using a test tube suspended over a hotplate , it seems to work ok but it is kind of a hassle to set up .

I really wouldn't want to build a MP apparatus though.

I just want to test the MP of my products in a tidy fashion.

Magpie - 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.

RonPaul2012 - 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

arsphenamine - 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

mayko - 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.

Finnnicus - 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.

Mush - 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

Paddywhacker - 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.

DraconicAcid - 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.

Mush - 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.