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Author: Subject: Oil bath
PlatinumCal99
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[*] posted on 18-11-2006 at 19:06
Oil bath


What does everyone here use as a container for their oil bath? A huge 5 L flask or some pyrex bowl from the grocery store?
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BromicAcid
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[*] posted on 18-11-2006 at 21:13


A metal dog food dish. They stand upright easily, don't tip over, and heat up uniformly without worries of thermal shock. For small projects though I use a pyrex beaker.



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[*] posted on 19-11-2006 at 01:00


8 quart aluminum pressure cooker, sans lid... it easily accomodates a 3 liter flask... not for sure but I bet it would do a 5L flask, a 6 would be kinda iffy though.

For oil, Wal-mart brand heavy mineral oil laxative.
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[*] posted on 20-11-2006 at 11:29


Metal has to be a safer bet than glass, and it conducts heat better.
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[*] posted on 21-11-2006 at 08:47


Spaghetti pot on kitchen stove, with triac in the house wiring for better heat control. :cool:

Have to replace the engine oil with veggie oil though, neighbours start to thing I've got a garage in the second floor flat. :P
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[*] posted on 21-11-2006 at 11:38


What would the neighbours think if they saw you buy a few pints of medicinal parafin?
Vegie oil is easier to get (relatively environmentally benign) and the safe working temperatures of various oils are well documented. IIRC peanut oil is good- but check it rather than taking my word for it.
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Baphomet
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[*] posted on 22-11-2006 at 18:07


Peanut oil in 2Lt beaker but the dog food bowl sounds like a better idea!
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[*] posted on 22-11-2006 at 21:25


Ever had to clean up sticky polymerized veggie oil?

I will never use that stuff again.
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[*] posted on 22-11-2006 at 22:47


Yes, It comes off reasonably well with caustic.
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Chris The Great
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[*] posted on 23-11-2006 at 04:34


Why not motor oil? It's meant for high temperatures and it's cheap.
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PlatinumCal99
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[*] posted on 23-11-2006 at 09:29


Most of the metal dog food bowls and kitchen pots are not perfectly flat on the bottom. Towards the center of the bottom part of the pot it comes up a little so there is no contact with whatever the pot is resting on. Have the rest of you been able to find pots with flatter bottoms, or do you use these ones regardless of the lower surface area? I've checked local grocery stores, Wal-Mart, pet stores, etc. I'm sure they would work, but I'm looking for something that would work better.
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[*] posted on 23-11-2006 at 17:58


I use a small copper pot. The bottom is very slightly concave, which is nice because my hotplate is slightly convex.



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[*] posted on 23-11-2006 at 18:53


I use Visions Cookware by Corning. Entirely glass, never had any problems with it. No longer made, got it off ebay. I can't use any larger than a 2L RBF though, they're not deep enough. Peanut oil for the bath itself, but when it gets a little old, it stinks the whole house up. Metal pots would be more convenient were it not for the magnetic stirring issues... that's what boiling stones are for, I s'pose.



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[*] posted on 27-11-2006 at 03:52


Follow up.. I've tried the metal bowl idea and it's good. I've noticed that water has an advantage if you are dealing with reactions that need to be kept at or near 100c.
A temp measurement of peanut oil yesterday gave 250c and an answer to why the reaction I was trying did not give the expected results.
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[*] posted on 19-1-2007 at 21:14


What sort of temperatures can you get veggie oil up to before it starts to boil? Alas, wikipedia was no help in answering this query. :(



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[*] posted on 19-1-2007 at 21:33


Quote:
Originally posted by microswitch
What sort of temperatures can you get veggie oil up to before it starts to boil? Alas, wikipedia was no help in answering this query. :(


This site gives the smoke point of most common vegetable oils.

http://missvickie.com/howto/spices/oils.html

Joe
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[*] posted on 19-1-2007 at 22:58


joeflsts has it right, it's the smoke point and then the flash point you want to worry about. Refined peanut, soy, and safflower oils are about the best out of the common cooking oils, but they do top out at about 220 C.
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[*] posted on 19-1-2007 at 23:12


A stainless steel dish or pot with dimensions entirely depending on the size of flask you are going to heat.

A stirring hotplate underneath, a thermocouple probe and a digital thermometer, a spinbar in the flask and maybe another in the bath. I have not quite figured out why commercial oil baths sell. Unless the lab's procurement clerk is on the take?

Mineral oil or one of the high temp silicone oils is best but, I have used a good grade of peanut oil with very good results. Just do your cleanup before it dries on your glassware.

A word of caution:

Hot plate manufacturers advise AGAINST using steel vessels most likely their concerns are with inductive coupling.

As I have so often violated their injection...maybe they are being overly cautious. Opinions?

GLYCERIN is an excellent heating medium, and was used to heat absinthe stills in 19th century so that local overheating from direct heating would not char the herbs. As the bp is quite high this would do in many instances...although perhaps not for heating nitrating mixtures, or permanganate oxidations, for obvious safety reasons.

[Edited on 20-1-2007 by Sauron]
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joeflsts
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[*] posted on 20-1-2007 at 06:39


Quote:
GLYCERIN is an excellent heating medium, and was used to heat absinthe stills in 19th century so that local overheating from direct heating would not char the herbs. As the bp is quite high this would do in many instances...although perhaps not for heating nitrating mixtures, or permanganate oxidations, for obvious safety reasons.

[Edited on 20-1-2007 by Sauron]


The MSDS for Glycerin indicates a flash point of 199C. I guess it is safe to say that most MSDS cautions err on the side of worst case.

This could cause alarm since Glycerin, when decomposing, produces Arcolein.

Joe
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[*] posted on 20-1-2007 at 15:56


I never had a problem with pyrex cookware. I forget what its called; pinkish stuff, heavy walled. For oil I use 3 dot break fluid-higher temps than most oils without decomposing. The nice thing about glass is I can sit the apparatus on a stirrer hot plate and stir through the vessel.
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[*] posted on 22-1-2007 at 16:23


Here's a list of bath fluids and they're boiling points:

http://www.hartscientific.com/products/bathfluid.htm
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[*] posted on 26-1-2007 at 12:31


Doesn't brake fluid readily absorb atmospheric moisture???? Hence, old, unchanged/exposed fluid boiling in the brake lines under panic braking? (yes, yes, I know you're keeping it hot) ;)



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[*] posted on 3-2-2007 at 16:56
oil bath


I use visionware too and a big heavy pyrex bowl from the thrift store. I use 3 dot brake fluid. Sand is another medium mentioned in lab manuals. The stainless dog dishes would keep the magnetic stirrer from working wouldn't they?
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[*] posted on 3-2-2007 at 19:45


I can tell you right now that extra heavy mineral oil laxative from walmart is good to 200ºC without very much smoking at all... and it should be able to take at least 225ºC with not much of any problem... best of all it doesn't polymerize!

All the brake fluids I've tried can't take those temps. Plus they emit toxic fumes when they get that hot!
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[*] posted on 3-6-2008 at 19:09


I've gone to Dot 4 brake fluid which is a silicon oil and the price reflects this. I keep it too hot to pick up water and otherwise covered. I use a commercial deep fat fryer my partner picked up at the thrift store. It's a pretty amazing little find. The controller maintains temperatures between 50-250 *C at +/- 0.5*C or less. Once a temperature is established the thermometer just doesn't show any change and it's not hard to pin down a temp. It loves to sit at 100*C for hours at a time. The fryer is gun metal gray with no extra stuff on it. We use a jack stand to handle it and we put some duct tape on the stand surface and when using a stirring motor we fix the bath in place with tie wire just to be extra safe.



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