Today, one of my test tubes went bad: a small hole formed in its bottom. I thought for a while what to do, and designed this small custom Kipp
apparatus from the test tube and some common glassware.
The picture is attached and is pretty self-explanatory. It works like a proper Kipp generator: I've attached a valve to the exit tube, when I close
it, the pressure drives the liquid reagent from the test tube through the hole. However, the drawback of this apparatus is that it's very
pressure-sensitive: even small pressure halts its operation.
Hope this helps someone who has test tubes with bottom failures.
[Edited on 12-6-2016 by ave369]woelen - 12-6-2016 at 23:32
Very funny application of a broken test tube! Nice idea.
There is one issue which may cause problems and that is if the gas producing reagent falls through the hole into the erlenmeyer. That would lead to
pressure buildup and possibly the ejection of liquid from the outlet tube.
It would be nice to think over this design and see if the above issue can be solved.ave369 - 12-6-2016 at 23:52
This is a common hurdle with all Kipp designs. But here the problem is solved: if a particle of the solid reagent exits the test tube, the evolved gas
won't get to the test tube, it will end up in the erlenmeyer and will safely exit through the air exchange tube.
Addendum: the air exchange tube is very thin on my drawing. Please click on the drawing to see it. In the actual apparatus it's not even a tube but an
slit-like aperture in the bung cut with a knife. I've drawn a tube to make things clear, I couldn't imagine how to draw a cut bung in such a
primitivist 2D style.
Addendum 2: I think that making the apparatus without the air exchange tube will solve the problem of its pressure sensitivity, but will make it
unsafe in more than one way.
[Edited on 13-6-2016 by ave369]woelen - 13-6-2016 at 00:06
Ah, I see. I indeed did not click the image and missed the very thin air exchange tube directly into the erlenmeyer. That indeed solves the issue I
mentioned.
The air exchange tube indeed is a tradeoff between pressure sensitivity and safety. What you could try is removing the air exchange tube and adding
some synthetic cloth at the bottom of the test tube, through which liquids easily can pass, but through which solid particles do not move. The cloth
of course must not be attacked by the liquid, but many synthetic materials withstand aqueous acidic solutions quite well for quite some time.ave369 - 13-6-2016 at 00:20
This will solve the problem with escaping solid reagents, but won't solve the problem of unknown resistance of the apparatus to pressure inside. I
don't want bungs and test tubes being jettisonned into the ceiling when I close the valve.
Anyways, the bung was already cut, and I don't have another one of the same type.
[Edited on 13-6-2016 by ave369]woelen - 13-6-2016 at 09:43
You could make a little bit more advanced air exchange pipe, by having a valve in that as well. When the apparatus is used to produce gas, you close
the valve in the air exchange pipe and open the valve on the outlet. When the apparatus must be put aside, then you first open the valve of the air
exchange pipe and then close the valve on the outlet. The gas in the test tube will push the liquid downwards, the production of gas ceases, and any
pressure buildup in the erlenmeyer is taken care of by the air exchange pipe. You can put the apparatus aside with the valve in the air exchange pipe
left open or partially open until you want to use it again.ave369 - 13-6-2016 at 12:32
When I get another bung such as this one, and another valve, I'll give it a try.aga - 13-6-2016 at 12:38
