toxin - 30-12-2005 at 17:44
Whats so special about lab filter paper used during a filtration, are there any good tangable substitues ?
The_Davster - 30-12-2005 at 18:38
Lab filter paper has a constant density of porousity which allows you to remove the precipitate from a solution(in a reasonable ammount of time).
Coffee filters can sometimes do a half decent job, but they often have pores big enough that you loose some precipitate through them. Using double
coffee filters is a realistic solution, but still not the best. Nothing beats good lab grade filter paper.
Magpie - 30-12-2005 at 19:50
A friend (not swinm!) gave me some fermentation product for analysis. It was cloudy although he said he had run it through coffee filters. I put it
through about 2-3mm of diatomaceous earth on top of Whatman #1 filter paper using a Buchner funnel. The filtrate was crystal clear. 
[Edited on 31-12-2005 by Magpie]
mick - 13-1-2006 at 13:13
Is there a post on the art of filtration.
Filter under vacuum, pressure or gravity? Grade of filter, glass wool, cotton wool, coffee filters, blotting paper, 40 mu filter?
How to construct a filter bed?
Aqueous or organic?
Type of pump, diaphragm pumps can kick back and trash the filter bed.
mick
toxin - 11-4-2006 at 13:24
When they make that paper, how do they manage to get those small pores into the paper, how come common paper we write on doesn't have them ?
Magpie - 11-4-2006 at 19:19
Paper is essentailly made of cellulose fibers with additives. Writing paper additives would include pigments (TiO2, kaolin clay, CaCO3, etc) and
sizing (starch, protein, etc). These additives reduce porosity. Filter paper is likely almost pure cellulose with very little additives.
[Edited on 12-4-2006 by Magpie]
lacrima97 - 12-4-2006 at 04:52
Alot of times I have wanted to keep the filtrate, and not the stuff in the filter. Using maybe 5 coffee filters would result in a cloudy filtrate,
but if i stuffed the filtering funnel full of cotton balls, (and give it about 2-3 hours to drain), it would come out very clear.
geezmeister - 12-4-2006 at 07:28
A surprisingly effective filter can be made from a piece of toilet tissue. One square, folded over itself a couple of times, then rolled up from one
end, can be gently pushed into the neck of a funnel. Once wetted with the filtrate, the flow rate can be adjusted by pressing it down into the neck.
In a tapered funnel this also compresses the paper, resulting in finer porosity. Adjusted to a drip rate of a few drops per second, the so called
"Charmin Plug" (named for a soft brand of US toilet tissue that seems to work particularly well for this appication) will give fine filtration in a
single pass for gravity filtration. Overlaying the plug with a coffee filter will help prevent clogging.
Filtering
MadHatter - 12-4-2006 at 19:06
I've used folded up white paper towels with good, clear results but the best OTC paper
I've ever used is cutup HEPA vacuum cleaner filters. They do a fantastic job ! I'm not that
impressed with filter paper that came with my Buchner funnels.
[Edited on 2006/4/13 by MadHatter]
praseodym - 13-4-2006 at 04:45
How about using glass wool or shredded asbestos? Wouldn't they be more effective?