Use an appropriate grade of filter paper for the solution
you are filtering. A coarse grade will allow for faster filtration,
but small solid particles may go through its pores. A fine grade
of paper catches small solid particles, but its pores may become
clogged easily. The paper should just fit onto the flat surface
of the Buchner funnel without folding up along the sides, but
it should be big enough to cover all the holes in the funnel.
This piece of filter paper is too small for the funnel... (Note the uncovered holes)
while this piece is too large. (Note the curling edges.)
