Heating Element for DIY Melting Point Apparatus

Hi Everyone, this is my first post on this site!  I am seeking advice to help me construct a home-made melting point apparatus (M.P.A).  A melting point apparatus allows it's operator to determine the melting point of a chemical sample by heating it in a controlled fashion and noting the temperature when the sample melts.  I have most of the design made up in my head, but I'm not sure as to how I can obtain the proper heating element.  The heating element I am seeking is an emulation of the M.P.A.s heating elements in my school's chemistry lab, which look like this: a metal block (about 3cm tall by 2cm deep by 3 cm wide) with vertical holes bored into the face with a pane of glass pressed against said holes so a glass capillary tube (containing the sample) can be slid into the bored hole and viewed through the glass pane as the sample is heated by the metal.  Another hole is bored into the metal, adjacent to the sample hole, for a thermometer.  So again, my question is do you have any suggestions as to where I could by a heating element like this?  Or, any suggestions on how to build one?  I have a jewelry shop at my disposal so I can probably bore any holes myself.  

Any suggestions will be appreciated, thanks!

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Das Horse (author) 5 years ago
At this time, I have decided to use the Soldering tip method. I chose this because out of all of the heating cartridges I found, the lowest, maximum temperature was 900 degrees fahrenheit. I only need to achieve a maximum of 660 degrees fahrenheit (about 350 degrees celsius, this temp is really close to the max temp of my 25w soldering iron). I'm now waiting for a 25w, 6 Ohm rheostat to arrive in the mail. I plan to use the rheostat for the temperature control for the heating element.

Thank you all so much for your input and suggestions. I will keep you all up to date on my progress via this thread, please keep the suggestions coming.
Goodhart5 years ago
If these "substances" have a much lower phase equillibrium @ 1 atm of air pressure than metals, then maybe an element from a small electric soup pot would do?
Kiteman5 years ago
The tip of a soldering iron would probably make a suitable heating element.

If you can, I would recommend obtaining a block of aluminium in which to drill your holes, since it is a good conductor of heat, so making it more likely that the temperature of the block will be the same around the hole in which you insert the tube, and the the hole in which you insert the thermometer.
Jayefuu Kiteman5 years ago
A cartridge heater would be a better solution. They're available on RS and Farnell. For best results ream not just drill the hole, you'll get a better contact.
Kiteman Jayefuu5 years ago
I was thinking about easy-to-obtain options.
Das Horse (author)  Jayefuu5 years ago
My only question about a cartridge heater is, do they heat up too fast? When determining Melting Point, its best if the temperature raises slowly enough that the system (the aluminum, the thermometer, and sample tube) heats up relatively evenly. Now, I plan to install a rheostat in between the heating element (heating cartrage or soldering iron tip) and the power source, so that SHOULD be able to control the temperature of the aluminum block, right?
Das Horse (author)  Kiteman5 years ago
Hmm, I really like that. How would you suggest connecting the soldering iron to the aluminum block? Maybe drill another hole up in the underside of the block? How about drilling two equally spaced holes for two soldering iron tips? Also, I have never fabricated any electronics before, I don't expect it to be too hard, but what do you think? I do want to have a dial that has some kind of control of temperature.
Drilling sounds good (make sure it's a very snug fit, to get maximum transfer of heat).

If you're willing to pay a bit more, you can get soldering irons with a temperature control built in to the base, saving you any fabrication.
Honus5 years ago
Some time ago I saw a PID controlled hot plate that I thought was really neat. It basically uses a cartridge heating element placed inside a aluminum block. A few people have made them and they seem to work really well. It may be just what you're looking for and it's pretty simple to make.

http://www.neufeld.newton.ks.us/electronics/?p=537