From: peter@tsto.co.uk   
      
   On 07/06/16 04:41, Charles wrote:   
   > How do you figure hotplates are more temperature uniform?   
      
      
   A good hotplate is made of eg thick aluminium, which conducts heat   
   laterally. The surface temperature doesn't vary much over the surface.   
      
   A heating bath does much the same thing.   
      
   A mantle does not conduct heat laterally, and can get hot in parts while   
   remaining cool in other parts.   
      
   This is especially important if the mantle is partly in contact with   
   glass which is in contact with liquid, and partly in contact with glass   
   which is not in contact with liquid.   
      
   This can lead to hot spots (or more usually rings in round vessels) on   
   the glass, which can cause unwanted decomposition etc.   
      
      
   -- Peter Fairbrother   
      
   ps I just thought of another possible reason for using round flasks - it   
   is easier to add side-joints to a round flask than to a conical flask.   
      
      
   >   
   > On Tue, 7 Jun 2016 01:43:56 +0100, Peter Fairbrother   
   >  wrote:   
   >   
   >> Round-bottomed flasks are usually used when boiling, refluxing or   
   >> distilling - but why?   
   >>   
   >> A mantle is more expensive and less temperature uniform than a hotplate   
   >> or oilbath of similar cost (or even half the cost). So, why do people   
   >> use them?   
   >>   
   >> The only reason I can find on the 'net is that round bottoms are more   
   >> compatible with Bunsen burners' flames.   
   >>   
   >> Plus I suppose if you were doing vacuum distillation a round flask would   
   >> resist the vacuum better - but is this significant in normal lab sizes,   
   >> eg up to a litre or two?   
   >>   
   >> I have a 2-litre conical Buchner flask which isn't terribly thick, but   
   >> which takes vacuum OK. Don't know how low it goes in normal filtering   
   >> use though ..   
   >>   
   >> Is there any other reason?   
   >>   
   >>   
   >>   
   >> thanks,   
   >>   
   >> -- Peter F   
      
   --- SoupGate-Win32 v1.05   
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