Non-messy heat bath?

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bcrowell
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I teach physics at a community college, and I do a lab in which the students measure the pressure of air at constant volume, extrapolating to determine absolute zero. To get the best results (and also to make the lab more fun), I've worked on getting the widest possible range of temperatures. Currently we're using mineral oil for the hottest temp (smoke point of about 150 C) and an acetone/dry ice slurry for the coldest (about -20 C). The mineral oil has some disadvantages, however. It's messy, it isn't reusable, and if we don't dry out the glassware before heating it, we get spattering. Sometimes students are inattentive about the temp and it starts to smoke. I've been trying to figure out of there is some other solution that would be more convenient.

What might be nice would be some kind of soft, sealed, reusable thermal pack. Some of these are sold for use with food, others for medical use. They seem to contain cross-linked polymers. Handling them would probably be safer than handling the mineral oil. I'm not sure, however, how hot you can get these things. One brand is advertised as being autoclavable at 120 C, which isn't that hot. I'm also not sure if you could really mold them around the Erlenmeyer flask holding the air sample.

Another idea that's occurred to me is simply to put some canola oil in a ziplock bag and heat it in a microwave. The smoke point of canola oil is 225 C, which is quite a bit higher than the 150 C that I'm shooting for. In the worst case where the bag inflated and popped open during heating, we'd just get a mess inside the microwave.

Any suggestions? Thanks in advance!

-Ben
 

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Ygggdrasil
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Is it possible to use a simple sand bath (http://en.wikipedia.org/wiki/Sand_bath)?

I'm not sure heating canola oil in a ziplock is the best solution. I'm not so sure the ziplock be able to withstand the high temperatures and be secure enough to prevent spilling hot oil on your students.
 
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bcrowell
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Aha! Thanks, Ygggdrasil, that's exactly the information I needed!

[EDIT] The only thing that occurs to me now is that I'm not sure how equalized the temperature of the sand would be. You probably can't stir it as well as you can stir a liquid.
 
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Heating mantle?
 
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bcrowell
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Use a thermocouple within the air volume. Simplest way is to buy a 1/16" dia. SS probe type TC (say from Omega) and use a swagelok or similar fitting to handle the pressure. Some method of stirring the air within would be best, say a modified magnetic stirrer?
 

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