bfesser
Resident Wikipedian
Posts: 2114
Registered: 29-1-2008
Member Is Offline
Mood: No Mood
|
|
Vacuum Desiccation vs. Atmospheric Desiccation
Vacuum desiccation is better than ambient pressure dessication for drying products and samples, provided the compounds have low enough vapor
pressures, right?
But what about for preserving bottled reagents? I have 25 g of ACS reagent grade silver nitrate from Sigma-Aldrich still manufacturer sealed in a
small amber glass bottle. The bottle is labeled "Desiccate." That's all it says about the subject.
Currently I have the bottle in an unevacuated vacuum desiccator over Drierite. Would it be better to store the bottle <em>in vacuo</em>?
What if I store other bottles that I actually have opened and will use regularly in the same evacuated desiccator? When the pressure is reduced in
the desiccator, over time the gas in the AgNO<sub>3</sub> bottle will slowly bleed out to equillibrium, right? Then when I break the
vacuum to remove another bottle or dry a sample/product, the pressure outside the bottle is increased while the inside of the bottle is still at
reduced pressure, and the atmosphere will slowly bleed back in. If this cycle continues, won't this lead to my currently very dry
AgNO<sub>3</sub> absorbing atmospheric moisture?
My overall question is this: <strong>Is it better to desiccate previously dried reagents at reduced or atmospheric pressure (for long-term
storage)?</strong>
[Edited on 10/1/08 by bfesser]
|
|
|
Klute
International Hazard
Posts: 1378
Registered: 18-10-2006
Location: France
Member Is Offline
Mood: No Mood
|
|
I would go for atmospheric dessicators, one where you put your containers that you don't use much. Better then weigh out a little amount, and place it
in the "common" dessicator to be used.
The pressure differences will surely do exactly as you said, as your product is already dry, I don't think there si any point in applying vacuum. If a
good dessicant is used, the humidity will be very low any way, and there will not be any water to come and increase the water vapor pressure.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
|
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
