Filtering (Liquid not light)

Flotsam · Sep 8, 2005

After mixing powdered solutions, I like to filter out those last several grains that wouldn't dissolve if I mixed for a hundred years. I've been using the classic plug of cotton in a regular kitchen funnel. It always works fine but it can get kind of slow, especially as it starts to get clogged. Not much filtering surface area.

I'm wondering what solutions others have come up with

L Gebhardt · Sep 8, 2005

paper towels or coffee filters. Just keep moving them if they get clogged a bit.

Bruce Osgood · Sep 8, 2005

I use a metal screen coffee filter with a paper filter inside and a funnel.

The problem I try to overcome is the paper filter sticks to the side of the funnel and/or collapses slowing the process. So I put the paper filter inside the metal filter and use a close pin (3 actually) to hold it in place. The liquid does not back up or squish the paper around.

Flotsam · Sep 8, 2005

Bruce (Camclicker) said:
I use a metal screen coffee filter with a paper filter inside and a funnel.

That is a good idea. Do you need the paper filter or would one of those gold screen coffee filters work by itself?

I've thought of using a brass pipe screen. Are those still sold in tobacco stores these days? The last one I bought was back in the seventies in a head shop called the Om. I needed it for... well never mind.

jim appleyard · Sep 8, 2005

Coleman, the camping lantern and stove company, makes/used to make small aluminum filter-funnels for pouring Coleman fuel (white gasoline) thru and into your stove/lantern. The filters had a metal ring asround them and could be easily removed for cleaning. Try Wal-Mart, sporting goods places. They should still be pretty inexpensive.

Jordan · Sep 8, 2005

The classic way to speed up filtration by providing maximum surface area is by using a fluted round filter paper in a funnel. See here:

http://www.chem.ubc.ca/courseware/235/danalabsess/flutedfilterpaper.html

Fluting takes a tiny bit of practice but you get used to it (I've done it hundreds or thousands of times now and you become very fast at it after a short while).

Bruce Osgood · Sep 8, 2005

Flotsam said:
That is a good idea. Do you need the paper filter or would one of those gold screen coffee filters work by itself?

I've thought of using a brass pipe screen. Are those still sold in tobacco stores these days? The last one I bought was back in the seventies in a head shop called the Om. I needed it for... well never mind.

I used the gold screen filter by itself but it didn't do the job with things like selenium toner. The paper adds a layer of filtration that seems to remove the really fine stuff but I'm not sure if the plated gold filter hasn't an affect on the chemistry passing through it. I don't know. But the gold will tarnish and what that means to the chemistry is beyond me.

OMMMM :rolleyes:

hortense · Sep 8, 2005

I second Jordan's suggestion. This is the best way. You can buy them at a Scientific Supply store on the internet.

fschifano · Sep 9, 2005

Why bother? The few remaining bits of undissolved solids do no harm.

Flotsam · Sep 9, 2005

fschifano said:
Why bother? The few remaining bits of undissolved solids do no harm.

With film, I worry about a grain getting embedded on that otherwise perfect, irreplacable frame.
For paper, I may be wrong but I feel that those loose grains form a basis for crystal growth. It just seems that when I filter there are a lot less crystals at the bottom of the jug.

fschifano · Sep 9, 2005

Interesting. I've never found either of those two things to be a problem. Even if there are a few solids in with he film, they don't stick unless you let them dry there. There shouldn't be any left after washing. Maybe the stuck on bits of grit you're experiencing are not from the chemistry, but rather from the wash water/final rinse?

Gerald Koch · Sep 9, 2005

Common, run-of-the-mill coffee filters are not very good. They catch the very large stuff but finer particles get through. The best coffee filters are the Chemex filters since they are made of laboratory grade filter paper. They are also very large so you can use a large funnel which should speed things up. Don't buy the square ones.

http://www.125west.com/Chemex_Kitchen_Coffeemakers_Chemex_Filters_coffee_maker.html

Filtering (Liquid not light)

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Bruce Osgood

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fschifano

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Filtering (Liquid not light)

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