I'd like to sort a large quantity of disks by weight. They're 0.75" in diameter and the two type have a mass of either 3.1 grams, or 2.5 grams. Little to no deviation of those two values from sample to sample. I can think of a couple ways to do this in an automated fashion, but I'm interested to know how a problem like this has been solved previously.
Alternately, the disks in question have a different density - SG of one is around 9.0, SG of the other is around 7.0 - is there a reasonable substance with a SG of 8-ish, that I could use to differentiate them by which ones float? I'm thinking not, but...