Dave Hinz wrote:
On Tue, 18 Apr 2006 22:36:21 +0000, Christopher Tidy wrote:

Dave Hinz wrote:

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.


Molten zinc or tin? Or molten iron, but it'll probably destroy your
discs. I can only think of molten metals which have a density that high.


I see that iron powder has a density of 7.9 which is right in the
middle.


Are these coins by any chance? If so, it might be worth looking at how
vending machines work. Some have rather novel ways of sorting coins.


Yup, pennies. Copper is way up, and bullion value of a penny is near 2
cents. The zinc ones would float on a vibratory bed of iron powder, the
copper ones will sink.

That's an interesting thought. I don't know if the vibration will
disturb the floating effect, but I suspect not. You'll need pretty fine
iron powder (maybe with a variety of different particle sizes) to get a
density above 7, otherwise the air spaces will take up too much room.

Chris