DavidJR
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Why don't drying tubes have two joints?
Here's something i've never been able to figure out:
Why do drying tubes commonly have only one ground glass joint, with the expectation that you'll use a rubber bung at the other end?
I've seen pictures of ones with two joints but haven't been able to find where I can buy one (24/29).
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j_sum1
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I asked much the same question recently.
I don't know that we got a complete answer but zed gave some details of the history of the device.
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UC235
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I only use them to provide an inlet/outlet for pressure without allowing moisture in.
If you need to dry a gas stream, get a gas drying tower or make one from an empty hempel column with a wad of cotton or glass wool at the bottom. Fill
the column with dessicant, plug at top if desired.
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wg48
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Quote: Originally posted by UC235  | I only use them to provide an inlet/outlet for pressure without allowing moisture in.
If you need to dry a gas stream, get a gas drying tower or make one from an empty hempel column with a wad of cotton or glass wool at the bottom. Fill
the column with dessicant, plug at top if desired. |
0r a Chromatography Reservoir
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DavidJR
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Hmm, a chromatography reservoir would be a bit bulky for my liking.
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LearnedAmateur
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The only times I’ve seen them used are during moisture sensitive reflux/distillation where they’re placed at the top of the condenser or the
receiving end respectively, hence no need for a second ground joint (or from my personal experience, no joint at all, just a narrow tube to slot into
a holed bung). The bung/cotton wool is placed at the end to keep the desiccant in the tube, especially when you have a bent design to save vertical
space since a reflux arrangement can be pretty tall.
Like a lot of glassware, having extra bits like a second joint is just to increase versatility - following along the same lines, it would be like a
single jointed condenser versus a double jointed one, where the latter can be more easily configured into other QuickFit arrangements and is better
suited for a wider variety of applications, especially when you’re dealing with vapours that will corrode rubber. The reason you’re having trouble
finding a double jointed drying tubes is because there isn’t really the need or demand for one outside of niche applications, and because other
glassware does the job.
IMO, half the fun of glassware is coming up with ingenious applications for pieces that typically have unrelated uses. For example, a Liebig or air
condenser, usually with two joints, can be used as a drying tube if packed with a desiccant between cotton or glass wool. Saves the issue of buying a
specialised drying tube and you have some extra length if you need to dry a large amount of gas or to ensure that it is absolutely dry.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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Sulaiman
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I have found fractionating columns / air condensers to be very useful;
Fractionating column
- rare and fragile glass spirals are required for loose column packing, but internal operation can be observed
Air condenser
really useful for products with b.p. higher than water
either as the main condenser
or as a pre-condenser to put less thermal stress on a following water/glass condenser.
I've not done any anhydrous chemistry yet but as above, an air condenser would make an excellend air-drier.
OR if you are likely to venture into chromatography
then a column with a glass fritt would also make an excellent air drier - I assume.
CAUTION : Hobby Chemist, not Professional or even Amateur
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LearnedAmateur
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| Quote: Originally posted by Sulaiman |
I've not done any anhydrous chemistry yet but as above, an air condenser would make an excellend air-drier.
OR if you are likely to venture into chromatography
then a column with a glass fritt would also make an excellent air drier - I assume. |
Nor have I to be honest, pretty much every single reaction I’ve done involves water to some degree, the one exception being the synthesis of aspirin
using acetic anhydride under reflux (obviously water needs to be kept away to prevent hydrolysis but it doesn’t require absolute atmospheric
dryness). I think an even better option would be a chromatography column like you said or even an addition funnel, a bonus of this could be that a gas
line can be easily slipped over the exit tube and the stopcock can be used to regulate gas flow if required, something which a simple tube lacks. The
glass frit should be fine for most drying applications also, with the exception of a few gases (namely HF if a brave amateur wished to dry it) which
can corrode glass, rendering it useless for any future applications.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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unionised
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That's not the expectation.
It's also a very bad idea.
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LearnedAmateur
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You can use an intubated bung to keep the air flowing, it’s what I, and I assume DavidJR, were referring to.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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DavidJR
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Yes that's exactly what I meant.
Anyway thanks for the suggestions, I'll probably buy an air condenser which could double as a drying tube.
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