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Author Topic: Vacuum Pumps and Glass Equipment  (Read 4936 times)

Offline beta0x64

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Vacuum Pumps and Glass Equipment
« on: 24/04/2010 23:03:09 »
I was planning on performing some basic distillation experiments using a Florence flask, Liebig condenser, and filter flask. I was going to use the filter flask to collect the distillate and to bring the pressure of the system down to about 0.5 atm for more efficient distillation. (I plan on using a cold trap of ethanol and dry ice between the filter flask and the pump, too.)

My question is 2-part: What is the threshold before I should be scared of shattering/imploding glass? I have seen experiments go to nearly a total vacuum without anything breaking, but that doesn't mean I'm not scared!

Also, should I be worried about liquid oxygen with ethanol and dry ice? I know it's a hazard with liquid nitrogen, but I feel like I should ask anyway.

Thank you for your no doubt finite time!


 

Offline Bored chemist

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Vacuum Pumps and Glass Equipment
« Reply #1 on: 25/04/2010 09:26:45 »
Well, the second question is easy, there's no way you will get liquid oxygen if the cooling agent is dry ice.

Most lab glassware will stand being evacuated, but the only way to be sure is to try it.
 Set up the glassware with nothing in it and cover it with a few layers of heavy cloth (towels are sort of traditional). Then evacuate it to the limit of your pump.

If it stands up to this it will probably be OK.
In any event, you should never run a vacuum distillation without a safety screen of some sort.
The other thing you need to consider is that, if it breaks, you might have lots of hot flammable liquid running into the heater.
At that point you will almost certainly have a fire.
Think very hard about where you are going to do this.
 

Offline daveshorts

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Vacuum Pumps and Glass Equipment
« Reply #2 on: 25/04/2010 09:59:57 »
Yes glass doesn't have a critical pressure at which it breaks, glass objects have a critical pressure, it all depends on how it is designed and how it has been treated during its life. Invisible cracks can make glass immensely weaker so just because it worked last time doesn't mean it will this time.
 

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Vacuum Pumps and Glass Equipment
« Reply #2 on: 25/04/2010 09:59:57 »

 

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