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Author: Subject: Making a gas dispersion tube
White Yeti
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[*] posted on 6-11-2011 at 12:53
Making a gas dispersion tube


So here's the deal, I'd like to make some HCl by bubbling it through distilled water. But from previous experience, I need a gas dispersion tube to make this work well.

I've tried to make a gas dispersion tube in the past, but have failed every single time. I don't feel like buying one because it seems like something that can be made easily with a few common materials and tools.

Has anyone made a gas dispersion tube before?
Tips and advice are welcome.




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[*] posted on 6-11-2011 at 13:15


Just lead the HCl gas through a plastic tube, and press the tube on the bottom of the flask with water. This should disperse the gas well.
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Endimion17
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[*] posted on 6-11-2011 at 14:54


Aquarium airstones. They're usually resistant enough, but require somewhat higher pressure to work than regular sintered glass.
Real laboratory stuff is unbelieveably expensive. :(




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DJF90
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[*] posted on 7-11-2011 at 04:32


Use a disposable glass pasteur pipette. They fit nicely through a screwthread thermometer socket if you're using quickfit. You could even get fancy and seal one end, blow a small bulb, and then carefully blow small protrusions, which can be broken off to leave you lots of little holes. Probably trickier than it sounds, but I've seen it mentioned in a practical textbook somewhere. Alternatively, perhaps drawing the pipette out into a capillary would work.
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[*] posted on 7-11-2011 at 05:19


Hydrogen chloride is extremely and almost instantly soluble in water.
As soon as the gas touches the water, the water will be sucked back into your generator.
If you are using hot sulphuric acid and sodium chloride to make the gas there could be a very nasty incident.
A lot of accidents in meth labs occur when they are using hydrogen chloride to 'gas' out the meth.
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[*] posted on 7-11-2011 at 05:55


Instead of blowing the myriad of holes a small piece of stainless wire heated will easily pierce through, allowing you to make the said tube. I find using a graduated 10-50ml pipette the most functional as they are long thick walled and have an end suited to hosing. Simply seal the pointy end with a Bunsen, continue heating around a cm of the end, blow a small bulb, then prick with your wire, reheat to redness andlet to cool.



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[*] posted on 7-11-2011 at 08:36


Quote: Originally posted by ScienceSquirrel  
Hydrogen chloride is extremely and almost instantly soluble in water.
As soon as the gas touches the water, the water will be sucked back into your generator.
If you are using hot sulphuric acid and sodium chloride to make the gas there could be a very nasty incident.
A lot of accidents in meth labs occur when they are using hydrogen chloride to 'gas' out the meth.

? I doubt they "gas" an aqueous solution, though. The infamous suck back may of course still be a problem, but - apart from destroyed product - I don't think this is particularly dangerous. Personally, I never understood the appeal of the "gassing" method. No risk of hydrates?

Original poster should just stir and implement a safety washing bottle, evidently.
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ScienceSquirrel
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[*] posted on 7-11-2011 at 09:04


It would probably be best for the original poster to forget the use of a gas dispersion tube and use a funnel that is just touching the surface of the water.
I used this method at school decades ago and it works perfectly.
Hydrogen chloride is so soluble in water that a dispersion tube is not needed.
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[*] posted on 7-11-2011 at 10:24


Yes, that is the old school method of getting rid of gaseous HCl. Nowadays you just vent it in the fume hood.
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[*] posted on 7-11-2011 at 15:45


I'm aware that HCl is extremely soluble in water. I mentioned this project as an example where I will need a gas dispersion tube, and to give the thread some context.
However, I will also need a gas dispersion tube to make sulfites and bisulfites with SO2 gas, which is not nearly as soluble in water as HCl.

Thanks for all the tips!

@ScienceSquirrel, I was thinking about using an inverted container of some kind to capture any HCl gas that didn't get a chance to dissolve on the first pass. But as I said, I would like to have access to a gas dispersion tube to perform other syntheses as well, not just to make HCl.




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[*] posted on 7-11-2011 at 16:30


Aquarium wares are not likely to have chemical resistance. Experiments with sintering ground pyrex might go somewhere.



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[*] posted on 10-11-2011 at 05:18


Quote: Originally posted by S.C. Wack  
Aquarium wares are not likely to have chemical resistance. Experiments with sintering ground pyrex might go somewhere.

Never had any problems with those. I still don't know what are they made of.
I worked with ammonia, too. The inverted funnel works great to a certain point, after that the solution is too concentrated. Therefore I used an airstone and cooled the solution with ice water bath. Saturation FTW.




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[*] posted on 14-3-2023 at 19:48


Reviving this thread to point out a trick that I thought was common knowledge (until now!). Buy some glass wool (very cheap), then break off the end of a pasteur pipette so that you end up with a glass tube with a small amount of taper on one end. Then using a dowel or some other rod, pack the tapered end of the pipette with a centimeter or so of glass wool so that the wool just barely protrudes past the end of the tip.

These produce tiny bubbles, are chemically inert, and very easy to make. They work nearly as well as real fritted dispersion tubes.

[Edited on 15-3-2023 by CRUSTY]




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[*] posted on 15-3-2023 at 03:59


In a previous life I directed the induction tube to the bottom of the container and then put a layer of clean sand at the bottom of the container as well. The gas bubbling up through the sand, and if things get crazy the sand swirling around in the flask greatly breaks up bubbles/increases surface area.



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[*] posted on 15-3-2023 at 05:50


Quote: Originally posted by ScienceSquirrel  
It would probably be best for the original poster to forget the use of a gas dispersion tube and use a funnel that is just touching the surface of the water.
I used this method at school decades ago and it works perfectly.
Hydrogen chloride is so soluble in water that a dispersion tube is not needed.


Totally second that. No need for a 'dispersion tube' at all.




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[*] posted on 15-3-2023 at 07:47


I don't have a lot of gas bubbling experience,
but one thing I've learned is that
If the product of gassing is insoluble
the bubbler tends to clog up quite quickly.
(eg sulphite other than Na, K, NH4)

Strong (vortex) stirring helps gas/liquid mixing a lot.




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[*] posted on 16-3-2023 at 03:10


There is only one practical way (from my experience) to make HCl solution in something like water - to pass the gas over the solvent surface with efficient cooling (stirring).


[Edited on 16-3-2023 by teodor]
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[*] posted on 16-3-2023 at 09:48


I have a few various gas dispersion tubes with porous frits on the end if anyone wants a fancier one. They would be pretty cheap other than a few bucks for shipping. I have a few bigger/longer ones, and some short ones as well.
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[*] posted on 19-4-2023 at 07:07


if you have a blow torch and some spare glass tubes you could heat up and seal one of the ends and while still hot you could use a needle to poke holes in the glass near the sealed part and up the glass tube for 2-4 inches. make sure the holes are small enough that the gas gets dispersed better and also make sure that there are plenty of holes so that the force of the gas does not pop the tube off.
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