Furch - 3-4-2007 at 09:12
Hello!
I've gotten my hands on a new vacuum pump, and ye olde standard nomograph[1] doesn't go low enough vacuum wise, which means stupid me is unable to
calculate the vacuum which my pump produces.
I do know this, however: a substance that boils at approximately 280 °C at atmospheric pressure boils at 45 °C with this pump.
Are there "extended nomographs", or is the some other way to calculate the vacuum? It is said that half the pressure reduces the boiling point by 10
°C, but this is hardly something to be taking litterary, IMHO... Only a very rough guideline.
I'm going to purchase a vacuum gauge sometime in the future, but for now I will have to do with calculating.
Anyone?
[1]http://www.sigmaaldrich.com/Area_of_Interest/Research_Essentials/Solvents/Key_Resources/nomograph.html
[Edited on 3-4-2007 by Furch]
unionised - 3-4-2007 at 10:22
Do you have the boiling point at any other pressure?
A plot of log p vs T is (badly) linear and can be used to extrapolate pressure temperature curves.
It's lousy but it's better than nothing and it's also better than the pressure doubles for every 10 C rule (which isn't as bad as you might expect
and, I think, is the basis for those nomograms).
bio2 - 3-4-2007 at 10:33
You can place a thermometer into a flask of water with
the vacuum running. When the temperature stops falling
take a reading then insert that into a nomograph for
water boiling point.