This should have about forty drops of nitric acid to the quart.

Grind well, and after letting the mortar stand two minutes, pour into a third.

After remaining undisturbed eight minutes, finally pour off into a fourth to settle.

Rinse back the sediment in the second and third, and grind over with a new batch.
Repeat the operation till you have all in the fourth vessel.

Let this stand several hours, and pour off the water very carefully.