[schaadrak]

For a faster response time, couldn't you hook up a small air pump to pull air from inside the checker and into the water in such a way that it bubbles back into the checker?

I'm not sure if the diffusion times for CO2 from water to air would be enhanced enough to warrant going through the trouble, but I thought I'd just throw it out there.

 

[schaadrak]

Try using a heat gun (like a hair dryer, but hotter) to weld PET plastic. That way if it gets too hot you can just back off a little.

Also maybe try using two different bottles of different diameters. Use the bottom off of the smaller one and flare it out where it meets the top of the larger. That way you get more surface to surface contact which means a stronger weld.

 

[schaadrak]

Tyvek (the stuff they wrap houses with before they add the siding) is a gas permeable membrane that is pretty much available anywhere. I've only seen it sold in the big rolls, but if there's any new houses being built around, your sure to find scraps of it.

I remember I worked for a place that sold raincoats made out of Tyvek. The company gave us a display that was a clear cylinder with a sheet of it in the middle dividing it in two. Water was poured into the top chamber and an air pump was connected to the bottom chamber which forced air through the Tyvek and up through the water. Even while the pump was off there was never any water in the bottom chamber.

 

[schaadrak]

Now that is a creative burst of inspiration!! I should be able to find some scraps of Tyvek, and I had forgotten completely that it is a semipermeable membrane, and a very rugged one at that. If I can find some scraps at Home Depot, for example, I will try to make a KH reference "condom" for my pH meter and see how it works. THANK YOU!! If you also post at Tom Barr's forum I suggest you post this there. If I don't see it in a day or two I will post the idea myself.

You're welcome and post away. I barely have time to post in this forum.

 

[schaadrak]

Just a thought, but if the membrane idea pans out, these could be made even easier by gluing a piece of membrane to the top of any small clear container filled with indicator solution.

Like this:

It wouldn't matter which way was up since water can't go through the membrane and you could use any small clear container you have lying around with virtually no modifications. Heck, you could just glue membrane to either side of a piece of air line tubing. Then if it starts going bad, toss it out and throw a new one in.

 

[schaadrak]

I am continuing to read up on gas permeable membranes, and I notice that silicone rubber is a good material for CO2 permeability, but I don't see where one could obtain thin sheet silicone rubber.

What about some thin, clear, silicon rubber tubing?

Some other avenues to explore are Gore-Tex and SympaTex, both relatively common fabrics. I think eVent is another brand, but I'm not sure.

 

[schaadrak]

Quick thought. I might not explain this right, but here goes:

Why not cut a large sirynge in half, and put some of the solution in the bottom half (the half with the plunger). Then attach the membrane to the opening and push the plunger in until the fluid is against the membrane. If the membrane is gas permeable, it will let the air out of the chamber , leaving just the solution.

Did I say that right?

 

[schaadrak]

As soon as I posted that I thought to myself, "How the Heck are you supposed to see the solution through the plunger?"

Oh well, I did come up with another suggestion. You could assemble it while submerged in the solution. Meaning put the container in a larger container that is filled with the indicator and then attach the membrane.

And also I came across these while in my garage:

There little containers of paint that you can get just about anywhere. They're small, transparent, water tight (maybe) and cheap. What I figure I'd do is cut off the bottom and glue a piece of an Tyvek envelope to it. Then fill the container with indicator solution and snap the lid on and *BLAMMO!* instant DIY drop checker. When the indicator solution goes south, flip open the lid and change solutions. Simple, eh?

The only problem I can think of is water and/or solution wicking between the lid and the top of the container. If the container is full of water and I squeeze it hard enough (probably harder than any pressures it will actually endure while in the tank) a small amount of water seeps out at the hinge. I'm not sure if the gap is there because of warping and flexing of the sides from me squeezing it or not so I'm currently performing an experiment. I've filled the container with water and red food coloring and put it in a bowl of plain water. Over the course of the next few days, I'll check to see if the food coloring has leeched into the plain water.

Here is the container floating in the "Test Chamber":

It's cap side down so that the entire cap-to-container junction is completely submerged. If it passes, the next test is to put some indicator solution in the container and submerge it in a water and vinegar solution and observe if there are any changes over the course of a week.

I'll try to post every evening over the next week as to the progress.

Tschuss,

Kent

 

[schaadrak]

banderbe- The way that I understand it, gas molecules in general are do not have the cohesive properties that liquid molecules do, so they are able to pass through the small holes of the membrane. Plus I think tannin molecules are just plain old too big.

Hoppy- I'll start testing to see what kind of attachment method works best. I don't think anything could fit in that between that lid and still shut properly

Also paint container update; its been almost twenty-four hours with no sign of leaking or wicking of the red dye. Things are looking good.

 

[schaadrak]

When you smell acids you are indeed smelling the acid that has evaporated into a gas. This means that there is a possiblity that some acids could cross the air gap and end up in the indicator solution, but that pecentage is probably too small to affect the results of what we're testing for, since the surface area in the air gap is small and the air gap is saturated with evaporated water. The membrane would not allow acids in gaseous form through since evaporation only occurs at the surface.

I think that's right.

 

[schaadrak]

Regular drop checkers staying green - maybe (I'm speculating here) there isn't enough water movement around it, or it's too close to the outlet of the CO2... if CO2 actually displaces air in the checker instead of equilibrating with it, you won't get it back out unless you remove the drop checker so that regular air is mixed in again (CO2 is heavier than air and could blanket the surface of the checker, but I would think it would go yellow if this happened).

Also - it isn't faster (or slower) than the open types, but it won't leak, even if flipped... and it's super easy to assemble (2mL LC sample vial, some of Hoppy's probe membrane, 4dKH purified DI, API pH indicator solution):

The red thing is the setting knob from my Visitherm Stealth heater. It's a tight fit, but that's a christmas mini-light suction cup holding the checker to the inside wall of my 46 (also w/ new pic today - see sig. link)

Where is the membrane located on that?

*Paint Container Update*- I can see a tinge of red in the water, so it looks like there is some wicking going on. Also that sample vial made me realize that my wife could get me something similar to those since she works in a DNA lab and they have to guard against cross contamination. I'll see if she can suggest anything that might be closer to the shape that Hoppy has.

 

[schaadrak]

I have a idea for anyone who has an electric pH meter; make a long tube out of some membrane a little longer than your probe and only a smidge wider, seal up the bottom and fill the tube with some 4GH water. Then put your probe in and seal the top (somehow, I don't know if they have attachments that would work or if you would have to seal it with silicone or something). That would give you a large amount of membrane surface area and a small volume of "solution"