Lewis - 18-10-2008 at 13:10
I've been in the market for a heating mantle for quite some time now. A unit that stirred as well would be ideal, but those gems seem to go for a lot
of money.
Anyway, I'm scrutinizing two particular models via eBay, both which could be probably got for about 100 bucks (80USD), and both offered by a Canadian
supplier, which is a plus. Should I go for:
Mantle (a)- The correct size for my largest and most used flasks (500mL). This one looks to be in slightly better condition of the two, and is tested.
The downside is I'd need to hack apart the power cord and attach a dimmer switch for temperature control.
Mantle (b)- Larger unit for the same price (2000mL). This one has a built in knob for varying the heat, as well.
I have heard that using too large of a heating mantle for a flask isn't a great idea, and I'm not thrilled about the untested nature of the second one
(although they did say they would take a return minus shipping if it didn't work).
So I'm trying to make a somewhat hard decision here. I could also obviously buy neither, and keep looking. 
crazyboy - 18-10-2008 at 14:13
I spent awhile on eBay looking for a good mantle I finally found one. I chose this model because it had a heat knob built in and it was 500ml. I
suggest waiting and getting a 500ml mine cost me about 75 dollars (90 with shipping.)
Good luck.
Sauron - 18-10-2008 at 17:21
I have a 1000 ml of same type, it's all right, but I bought it new.
Mostly I prefer Glas-Col mantles. When buying used ones, always make sure the correct power cord is included, some take a two prong ungrounded cord
and some a grounded two prong plus center post cord. If missing you will have to order from Glas-Col.
Do not use a larger or smaller flask than the stated size round bottom flask (borosilicate glass) for your mantle.
The seperate controller design allows you to upgrade to a controller that will accept input from a thermocouple probe in order to control reaction
temperature. Otherwise you are committed to sitting there and adjusting manually. In the course of a long reaction or distillation this is a huge
plus.
Lewis - 18-10-2008 at 18:18
Interesting. So larger mantles cannot be used for microscale operations with tiny flasks? It would seem to me a little less efficient, but doable if
the temp did not need to be insanely high.
Would I be more likely to find a surplus mantle with a mag stirrer, or would it be more worth my time, effort, and cost, to simply find an overhead
stirrer when I will inevitably need it?
Sauron - 18-10-2008 at 19:16
Mantles and their built in thermocouples (that wire hanging off on fabric mantles) work properly when in contact with a flask of correct size and
shape. You can't operate a mantle with a smaller flask inside any more than you can an emptry mantle, not without damaging the mantle.
If you want a one size and shape fits all heating device you want a bath not a mantle. There are water baths, oil baths, fused metal baths, sand
baths. They all have pros, cons, limitations. Water baths rather obviously are limited to 100 C and really work best at 60-70 C beyond which you get
low efficiency due to evaporative losses. Oil baths can be messy. Shield against spaltters. Choose the "oil" carefully. Glycerine is a good choice,
but for example, don't use it to heat mixed acid nitrations., (DUH!)
Steam baths used to be a lab fixture but few now have a steam line.
For mantles, you need a range of them to fit your flask sizes and shapes. I have mantles from 250 ml to 72 L, by no means every stop in between.
Mostly I use 250, 1000, and 5000 ml. I never work in microscale.
Oh, there are also such things as air baths such as the flask oven of a Kugelrohr. These are t/c controlled baths where air is the medium and they run
up to a bit more than 200 C and handle flasks from 25 ml to 2000 ml and for older models 4000 ml. They are used horizontally and the flasks rotate,
and are evacuated. So they are really a specialized sort of rotary evaporator good for sensitive distillations and sublimations. Receiver flasks
(bulbs) are interposed between the oven flask and vacuum takeoff/motor and can be cooled.
You can build your own air bath easily enough, but the rotary function and inline vacuum takeoff are trickier. The point of rotation is to increase
effective surface area and thus boilup rate. The point of vacuum is to reduce bp. Without these the air bath loses a lot of its capability and
versatility.
Heat guns, which are essentially heavy duty hair dryers, and infrared lamps deserve a mention.
[Edited on 19-10-2008 by Sauron]