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Fery
National Hazard
Posts: 990
Registered: 27-8-2019
Location: Czechoslovakia
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Hi Fyndium, when distilling out fuming nitric acid from a mixture of azeotropic HNO3 + H2SO4 the glass aspirator should be resistant against HNO3 acid
vapor and NOx. Also suitable plastic material should withstand such corrosive attack. I'm not sure with metals, maybe everything corrosive would be
diluted and washed out quickly?
I wanted to have some backup equipment if my plastic aspirator would be not working properly. It is very old piece from a long time ago closed down
biochemistry lab which I got for free, yellow color changes clearly visible on formerly white plastic. I tested it some time ago when not yet having
any device for measuring vacuum level. I evacuated a flask, submersed the flask into water bath, opened the flask so water entered the flask, compared
the difference between the volume of water filling the evacuated flask and water filling full flask. This experiment showed that 3/4 of the volume was
filled with water. I expected more, like 9/10. The water was colder than 10 C.
[Edited on 14-3-2021 by Fery]
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zed
International Hazard
Posts: 2277
Registered: 6-9-2008
Location: Great State of Jefferson, City of Portland
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Mood: Semi-repentant Sith Lord
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No way of measuring vacuum level? A thermometer will do! There are extensive tables for the boiling point of water at various pressures. Pull your
hardest vacuum on a flask partially filled with water. Warm the flask, until the water starts to boil. Note the temperature. Reference it on the
table. Ummm. Let me see if such tables are available on-line. I'll be back!
OK, not the table I wanted. But, workable.
https://www.engineersedge.com/h2o_boil_pressure.htm
[Edited on 14-3-2021 by zed]
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Fery
National Hazard
Posts: 990
Registered: 27-8-2019
Location: Czechoslovakia
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It was some time ago... I already have 2-stage oil rotary vacuum pump and manometer. But that time I haven't so I tried to check how much water enters
evacuated flask. It was 3/4 of its volume. Not too much. That water aspirator is really old one. I still have it as it remembers me the old lab where
it served. The lab is not there anymore and the building serves for different purposes. I saved few items from the lab. Heating plate with stirrer
etc. Valuable items were sold in an auction. Many low value items were condemned to be thrown into waste or at best into recycling (glass/plastic)
when I asked for their intended destiny they were given to me for free.
Using water boiling point depression is also very clever idea to check the vacuum capabilities.
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Fery
National Hazard
Posts: 990
Registered: 27-8-2019
Location: Czechoslovakia
Member Is Offline
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So I checked the old water aspirator with a manometer and it is much more powerful than the evacuated flask filled with water showed. The value on
manometer is -92 kPa. So strange that the flask was not evacuated to 92%, the difference between an evacuated flask consequently filled with water and
flask full of water should be only 8%. I do not suggest to measure the vacuum power using an evacuated flask inverted in water which is then filled
with water after opening its neck.
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